40395-1(Task 1).book

Technology Demonstration and Verification Research

Quarterly Technical Progress Report for the period April 1, 1998 - September 30, 1998 Dr. John Plodinec, Principal Investigator October 1998 Prepared for the U.S. Department of Energy Agreement No. DE-FT26-98FT40395 Diagnostic Instrumentation and Analysis Laboratory Mississippi State University 205 Research Boulevard Starkville, Mississippi 39759-9734 [email protected] www.msstate.edu/Dept/DIAL

Notice This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product or process disclosed or represents that its use would not infringe privately-owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or nay agency thereof. The views and opinions of authors expressed therein do not necessarily state or reflect those of the United States Government or any agency thereof.

Table of Contents

Abstract TASK 1

................................1

Verification Monitors for Thermal Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Subtask 1.1. Monitors for Thermal Processes . . . . . . . . . . . 3 Air Plasma Off-gas Emission Monitor (APO-GEM) . . . . . 4 Laser-induced Breakdown Spectroscopy . . . . . . . . . . . . . 14 Subtask 1.2. Mercury Absorber Technology . . . . . . . . . . . 18

TASK 2

Deactivation and Decommissioning Technology Support . . . . . . . . . . . . . . . . . . . . . 20 Subtask 2.1. Pipecleaning Technology . . . . . . . . . . . . . . . . 20 Subtask 2.2. Wall Removal Monitor . . . . . . . . . . . . . . . . . . 23

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Contents

TASK 3

Technical Data to Support Cleanup Decisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Subtask 3.1. Dioxins/Furans in Incinerator Burner . . . . . . 26 Dioxin Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Detection of Chlorinated Organics by Cavity Ring-down Spectroscopy . . . . . . . . . . . . . . . . 29 Subtask 3.2. Dissolution of Hanford Salt . . . . . . . . . . . . . . 32

TASK 4

Product Acceptance Support

. . . . . . . . . . . . . . 56

Subtask 4.1. Monitors for Idaho LAW Stream . . . . . . . . . . 56 Subtask 4.2. Pressure in Drums . . . . . . . . . . . . . . . . . . . . . 67 TASK 5

Advanced Cleanup Support: Robust Immobilization Devices

. . . . . . . . . . . . 71

Subtask 5.1. Hybrid Plasma Induction Cold Crucible Melter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Subtask 5.2. Hollow-electrode DC Arc Furnace for Mixed-waste Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 78

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List of Figures

FIGURE 1.

Schematic of APO-GEM continuous emission monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

FIGURE 2.

The effect of moisture on the emission of Mg in an air-plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

FIGURE 3.

ICP emission spectra obtained using the AOTF-echelle spectrometer, illustrating the resolution of the system . . 12

FIGURE 4.

LIBS signal (a) and background (b) as a function of laser energy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

FIGURE 5.

S/B as a function of laser energy . . . . . . . . . . . . . . . . . . 17

FIGURE 6.

Results for 1,4-dichlorobenzene . . . . . . . . . . . . . . . . . . . 31

FIGURE 7.

Block diagram of the solubility apparatus.

FIGURE 8.

KCl solubilities determined with the experimental apparatus and compared to literature data and ESP model results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

FIGURE 9.

Solubilities of Na3PO4

FIGURE 10.

Predicted solubility envelope for Na7F(PO4)2.19H2O . . 41

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. . . . . . . . . 38

. . . . . . . . . . . . . . . . . . . . . . . . 39

Figures

FIGURE 11.

Comparison of experimental and predicted results for nitrate anion concentration – Tank BY-106. . . . . . . . 44

FIGURE 12.

Comparison of experimental and simulation results for sulfate anion – Tank BY-106 (25°C) . . . . . . . 45

FIGURE 13.

Predicted solids mass in SY-101 during in situ dilution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

FIGURE 14.

Schematic of cavity-ringdown spectroscopy technique . 58

FIGURE 15.

Schematic of the laser-induced fluorescence spectrometry technique . . . . . . . . . . . . . . . . . . . . . . . . . . 59

FIGURE 16.

Schematic of isotopic energy shifts and the associated LIF spectrum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

FIGURE 17.

Cavity ringdown decay for air with mirrors optimized for 360-nm operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

FIGURE 18.

Cavity ringdown spectrum of atomic chromium absorption at 357.9 nm . . . . . . . . . . . . . . . . . . . . . . . . . . 62

FIGURE 19.

Schematic of hybrid plasma induction cold crucible melter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

FIGURE 20.

DC arc furnace at Montec Associates, Butte, MT . . . . . 79

FIGURE 21.

DC arc furnace at Montec Associates, Butte, MT, July 1998 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

FIGURE 22.

Feeder for the hollow-electrode DC arc heater experiment, Montec Associates, Butte, MT, July 1998. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

FIGURE 23.

Hollow-electrode dc arc heater at Montec Associates, Butte, MT, July 1998 . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

FIGURE 24.

Off-gas species concentration during bulk-solid addition, Montec Associates, Butte, MT, August 1998. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

FIGURE 25.

Dissolution of the refractory bricks . . . . . . . . . . . . . . . . 86

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List of Tables

TABLE 1.

Detection limits for the APO-GEM for various metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

TABLE 2.

Relative accuracy of DIAL Air-ICP data . . . . . . . . . . . . 10

TABLE 3.

Major anions present in select Hanford Tanks (in ppm). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

TABLE 4.

Comparison of solid phase species observed in simulation with core sample analysis of Person . . . . . 46

TABLE 5.

Solid phase species distribution - 2M NaOH addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

TABLE 6.

Additional simulation results for the 2M NaOH addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

TABLE 7.

Lessons learned (preliminary). . . . . . . . . . . . . . . . . . . . . 87

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Abstract

The Diagnostic Instrumentation and Analysis Laboratory (DIAL), an interdisciplinary research department in the College of Engineering at Mississippi State University (MSU), is under contract with the U. S. Department of Energy (DOE) to develop and apply advanced diagnostic instrumentation and analysis techniques to aid in solving DOE’s environmental management and nuclear waste problems. The program is a comprehensive effort which includes five focus areas: • • • • •

Verification monitors for thermal treatment; Deactivation and decommissioning technology support; Technical data to support cleanup decisions; Product acceptance support; Advanced cleanup support - robust immobilization devices.

As part of this program, diagnostic methods are developed and evaluated for characterization, monitoring and process control. The measured parameters are used to improve, optimize and control the operation of the overall treatment process. Moreover, on-site field measurements at various DOE facilities are carried out to aid in the rapid demonstration and implementation of modern fieldable diagnostic methods. Such efforts also provide a basis for technology transfer.

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Abstract

In addition to the diagnostic instrumentation development efforts, DIAL is engaged in the operation of plasma torch facilities. These facilities are used for both process development and instrumentation verification. Significant effort is also directed towards the improvement of plasma torches by extending electrode lifetimes.

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TASK 1

Verification Monitors for Thermal Treatment

Subtask 1.1. Monitors for Thermal Processes Thermal treatment processes (incinerators, melters) typically emit toxic metals (esp. mercury), volatile and semi-volatile organic materials (esp. dioxins and furans), and particulate matter during processing. While the levels from DOE facilities meet current regulatory limits, the EPA is in the process of promulgating new rules (the socalled “MACT” rules) with much lower limits. Based on limited test data, some of DOE’s thermal treatment facilities will require continuous emissions monitoring of process effluents in order to comply with this rule. Currently, several such monitors are under development, but, as yet, there are no accepted monitors for this use. During the first year of the Cooperative Agreement, DIAL will test monitors for toxic metal effluents in its combustion test facility. DIAL will contact users, developers, and other stakeholders, and with their assistance develop detailed test specifications for toxic metals monitors. Monitors will be brought to DIAL’s test beds for extended testing. At the completion of testing, a report will be drafted, reviewed by all parties, revised and issued. This report will detail the results of testing, and compare the performance of each of the monitors against the specifications.

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Task 1. Verification Monitors for Thermal Treatment

Personnel from the major thermal treatment process operators in the DOE complex (the TSCA incinerator at Oak Ridge, the CIF at Savannah River, the WERF at Idaho, and the DWPF at Savannah River) will assist in developing specifications for CEMs, and in reviewing test plans and test results. DIAL will utilize DOE’s Ad Hoc CEM group to guide testing and review test results, as well as the Mixed Waste Focus Area. DIAL will also test the ability of the CEMs to act as process monitors. The objective of this subtask is to determine, through testing, whether existing CEMs meet DOE user specifications.

Air Plasma Off-gas Emission Monitor (APO-GEM) George P. Miller

Introduction Project Significance Increasing regulatory demands requiring significant reductions in the emission of hazardous air pollutants have led to the need for techniques capable of providing real time monitoring, at the stack, of toxic metals in combustion gas streams. These waste streams range from coal-fired boilers and municipal waste combustors to plasma vitrification systems used for the remediation of low level radioactive waste. This lack of a fieldable continuous emission metal monitor (CEM) and process monitor (PM) has been recognized as a significant gap in the available technology. The system described below has been designed to fill this gap.

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Background Over the last twenty years, the use of argon ICP-AES for the measurement of trace elements in solution has matured into a standard analytical technique. However, unlike the laboratory ICP, it is essential for a CEM that the system be hardened sufficiently to handle the problems of a real world environment. These problems include the ability to readily tolerate the introduction of a variety of molecular gas matrices, significant variations in moisture and particle loading, as well as the thermal, vibrational and clogging problems found outside the laboratory. The system under development at DIAL has taken the advantages inherent in inductively-coupled plasma technology and incorporated them into the APO-GEM - a CEM capable of tolerating the real world environment while accurately measuring the real time concentration of metals in exhaust stacks. Although the APOGEM provides significant reduction in operating costs, the main advantages of the air plasma lie in its increased tolerance to molecular gases, particle loading and reduced susceptibility to moisture content (due to more efficient heat transfer from the air plasma to the sample). On the other hand, it requires higher rf powers, and the maximum available ionization energy is reduced from that available in an argon plasma. The introduction of exhaust gases into the air plasma results in a considerably more complex spectra from the line spectra seen in an argon plasma. The emission spectra includes numerous molecular bands (e.g., OH, CN, NO, N2+) in the wavelength regions of interest (200 - 350 nm). This increase in interferences places stringent requirements on both the resolution of the detection system and the software used to analysis the data. We are developing two separate approaches to address these problems: a unique chemometric software package to handle the analysis, and an ongoing collaboration with Ames National Laboratory to reduce the size of the detection system while increasing the resolution.

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The remaining hardware required to complete the system consists of an isokinetic sampling interface between the APO-GEM and the exhaust duct. The extractive sampling techniques used introduce the sample stream into a controlled environment where matrix effects are minimized and the plasma properties are stabilized. Calibration is handled by a unique system which mixes calibration standards with the combustion stream via the isokinetic sampling apparatus. This effectively compensates for any remaining matrix effects, options that are impossible for in-stack methods. Methodology The APO-GEM system incorporates a novel 3.5-kW solid-state 27.12-MHz rf generator with the load coil modified for air-plasma operation. This is coupled to a detection system with the off-gas sample being extracted from the duct and introduced into the air plasma via an isokinetic sampling system. Figure 1 is a schematic diagram of the APO-GEM continuous emission monitor.

DETECTOR

AIR-PLASMA

ISOKINETIC SAMPLER

rf POWER

NEBULIZER

CCD

CONTROLLER

AIR COMPRESSOR A R G O N COMPUTER

FIGURE 1.

Schematic of APO-GEM continuous emission monitor.

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The APO-GEM plasma is started using argon and progressively switched over to air. Calibration is performed using an ultrasonic nebulizer. The detection system uses a 1-m monochromator and a CCD detector. This remains the largest single component of the system. It has adequate resolution, but operates sequentially and is relatively large. It, nevertheless, provides the ideal platform for identifying and characterizing the spectral emissions and possible interferences arising from unidentified components making up exhaust gas emissions. (To provide simultaneous metal concentration measurements, this monochromator could be replaced by a polychromator.) In addition, we are evaluating a novel solid-state spectrometer developed for this project by Dr. David Baldwin, Ames National Laboratory. This instrument is compact, thermally and vibrationally stable. It uses a combination of an acousto-optic tunable filter and an echelle grating to provide the resolution of a 1.5-m monochromator into a 10-kg package. The successful combination of the solid-state APO-GEM and this spectrometer represents a large step forward in instrument development and will reduce the overall size and weight of the complete package substantially (from original ~1000 kg, present 250 kg, to ~150 kg) while improving the resolution and thereby the detection limits. Isokinetic sampling system. To correctly measure the concentration of metals present within an exhaust gas stream, it is necessary to introduce a sample from the exhaust gas stream into the ICP under isokinetic conditions. Therefore, a sampling system has been designed to extract such a sample from a gas stream and introduce it into the air plasma for analysis. The system operates by filling a loop with sample gas, then pushing this sample with air into the plasma. The robustness of the air plasma permits an optimum sample flow rate into the ICP of 1.14 sl/min, approximately three times more than tolerated by an argon plasma.

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Calibration. An important concern with any CEM is the question of calibration. In this instance, instrument calibration follows a modified standard ICP calibration procedure.1 An ultrasonic nebulizer is used to provide metal-containing aerosols at known concentration (µg/m3). This concentration is determined from C s uε C A = -----------, F

(EQ 1)

where CA is the aerosol concentration (x 103 µg/m3), Cs is the standard solution concentration (µg/gsolv), u is the solution uptake to the ultrasonic nebulizer, F is the air flow rate to the plasma, and ε is the nebulizer efficiency. The efficiency of the nebulizer was determined both in the laboratory and again on-site prior to the test. For the initial instrument calibration, the metal aerosol is mixed with ambient air. Instrument response was checked against standard calibration curves prepared previously. In the field, the presence of fly ash as well as variations in loading and exhaust gas composition allow the possibility of substantial matrix effects significantly impacting the results of any real world analysis. This variation in composition between laboratory air and the exhaust gas composition renders any direct comparison of the laboratory air calibrations to the instrument off-gas response highly suspect. To circumvent this problem, we have developed a novel technique whereby the calibration standards are mixed with the exhaust off-gas at the entrance to the sampling loop while maintaining isokinetic conditions. This ensures that the standard and off-gas samples are matrix-matched. This allows recalibration and QA checks to be performed on-line under actual operating conditions. To further improve the sensitivity of the instrument, a novel chemometric software package has been developed which by modeling background spectrum (at the spectra regions of interest) effectively reduces the background noise and thus improves the instrument sensitivity. To apply this method accurately, data from the spectral

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regions of interest was collected during the shakedown period prior to the test. In addition, as the instrument presently employs a sequential detection system, wavelength calibration is essential. A chemometricbased software package was developed to check and, if necessary, correct wavelength calibration. This software checks the wavelength position with respect to the pixel position on the CCD every time the wavelength setting is changed as well as periodically checking for instrument drift. Detection limits. The toxic metal species of concern to EPA and DOE include: As, Be, Cd, Cr, Hg, Sb, Pb. The present detection limits for a number of metals are given in Table 1. Further improvements in sensitivity are required to meet the expected emission limits.

TABLE 1. Detection

limits for the APO-GEM for various metals. Metal Instrument

Detection Limits (mg/sdcm)

As

47

Be

0.07

Cd

2.5

Co

0.6

Cr

0.25

Hg

20

Mg

0.05

Ni

0.4

Pb

0.9

Sb

55

Sr

0.003

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TABLE 2. Relative

accuracy of DIAL Air-ICP data. Be

Cd

Cr

Hg

Pb

RM 1 to 10

40%

26%

40%

13%

21%

RM 11 to 20

43%

46%

59%

67%

42%

Metal concentrations and relative accuracy. The

DOE/EPA demonstration at Raleigh was the first opportunity to check the accuracy and quality of the data provided by the APO-GEM. The relative errors with respect to EPA Method 29 are given in Table 2. Three of the five metals are within 30% for the high concentration level (75 µg/dscm). None are within that range at the low concentration level (15 µg/ dscm). These results are excellent considering the uncertainty present in the RM data at these low levels. Work Accomplished Results and Discussion The field trip late last year to participate in the DOE/EPA-sponsored demonstration at Raleigh, NC was the instrument’s first field trip and its first long test run. It amply demonstrated the technique’s potential as a CEM and as a process monitor both in terms of robustness and results. As was expected, the field trip served well as a shakedown. A number of possible improvements were noted and are being implemented. These improvements are relatively minor compared to the areas of research that remain to be addressed (see below). Research Progress Progress this quarter has been hampered with the move into the new building. In addition, the loss of Dr. Zhu (without replacement) has had a significant impact on progress. However, a certain amount of progress has been made. In particular:

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Air plasma parameters. A laboratory study characterizing the effects of moisture on the air plasma’s properties has been performed (see Figure 2), and a publication is in preparation. Chamber temperature effect on Mg II/Mg I 1

0.70

1.75

0.60

2.5

0.50

3.25 4

0.40

4.75

0.30

5.5 6.25

0.20

7

0.10

7.75 8.5

0.00 140

78

63

53

49

44

Chamber Temperature

9.25 10 10.75

Chamber temperature effect on Mg II/Mg I 1

0.70

1.75

0.60

2.5

0.50

3.25 4

0.40

4.75

0.30

5.5 6.25

0.20

7

0.10

7.75 8.5

0.00 140

78

63

53

49

44

Chamber Temperature

9.25 10 10.75

Chamber temperature effect on Mg II emission 12

1 1.75

10

2.5 3.25

8

4 4.75

6

5.5

4

6.25 7

2

7.75 8.5

0 140

78

63

53

Chamber Temperature

49

44

9.25 10 10.75

The effect of moisture on the emission of Mg in an air-plasma. (140 corresponds to dry, 49 to saturated flows). FIGURE 2.

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Sampling interface. Modifications to the isokinetic sampling system

are in progress An evaluation of high resolution AOTF-echelle spectrometer in collaboration with Ames National Laboratory. Detection System.

A week-long test of this instrument occurred at DIAL in August 1998. The result of these experiments indicated that significant progress has been achieved over the earlier AOTF-FP spectrometer, and a decision was made to use this instrument to eventually replace the 1-m monochromator. This will provide a substantial reduction in overall instrument size. A paper was presented at the ACS 215th national meeting, Dallas, March - April, 1998, entitled “High-resolution interferometric spectrometer for continuous emission monitoring” by D. P. Baldwin, D. S. Zamzow and G. P. Miller. Abstracts were submitted to both the FACSS and Gaseous Electronic Conferences which are scheduled for October 1998. a) Intensity (arb. units)

Intensity (arb. units)

b)

228.76

228.80 Wavelength (nm)

228.84

309.95

310.00

310.05

310.10

Wavelength (nm)

FIGURE 3. ICP emission spectra obtained using the AOTF-echelle spectrometer, illustrating the resolution of the system: (a) Cd (I) 228.802 and As (I) 228.812 nm emission-lines are nearly baseline-resolved; emission lines for Fe (I) at 309.990, 309.997, 310.030, and 310.067 nm are shown in (b).1

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Work Planned A 75% reduction in available manpower hours will continue to make a significant impact on progress as will delays due to the move into the new building (off-gas system inoperable). While progress has been made, considerable research remains. Areas to focus on include: Air Plasma Parameters A study of the following real world effects on the properties of the air plasma need to be understood and accounted for: •moisture - dry to saturated, •particle loading - size, •interferences.

Sampling Interface Further research on potential losses within the isokinetic system under sampling conditions ranging from dry (static) to saturated is essential. The impact of long term, real world effects (e.g., clogging, vibration, thermal effects) also remains to be studied. Calibration Our novel method of spiking the combustion stream as it is sampled has the potential of solving the CEM calibration problem. However, significant research remains to be done to validate this assumption. Experiments will be performed to measure the accuracy and repeatability of the technique. Detection System Monochromator-based system. The software package needs to be rewritten taking into account the lessons learned at the North Caro-

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lina test. Enhancements in the modeling package can be made to further improve signal-to-noise, i.e., detection limits. High resolution AOTF-echelle spectrometer. Significant progress has been achieved and the instrument is expected to eventually replace the 1-m monochromator. However, a number of improvements are required to harden the instrument to withstand a real world environment.

Reduced-pressure Air-ICP (Ames Laboratory) The milestone for this project involves testing the hardware on the DIAL test stand in August 1999. Preparations and modifications necessary for this test will be established during the next quarter. The other areas to be addressed in the next quarter will depend on both manpower limitations and availability of the off-gas test stand. Reference 1.

Baldwin, D.P., Miller, G. and Zamzow, D.S., November 1998. AOTFEchelle Spectrometer for Air-ICPAES Continuous Emission Monitoring of Heavy Metals and Actinides. Proceedings of the SPIE Technical Conference, 3534:59.

Laser-induced Breakdown Spectroscopy J. P. Singh, F. Y. Yueh and H. Zhang

Introduction Toxic metal emissions from various waste processing off-gas systems represent a significant health hazard. This technical task has been focused on the development and application of laser-induced

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breakdown spectroscopy (LIBS) to monitor RCRA metals from thermal treatment processing facilities. LIBS is a laser-based technique. It applies a high power laser beam to vaporize and excite the sample in situ in a single step.2,3 This is accomplished by focusing a pulsed laser beam at the test point to produce a laser-induced plasma. The plasma atomizes and electronically excites the various atomic species present in the test volume. The intensities of the atomic emission lines observed in the LIBS spectrum are used to infer the concentration of the atomic species. The capability of the LIBS system for real time metal monitoring was evaluated in various field tests.4-9 The field test results show the calibration technique of LIBS needs further improvement to provide accurate quantitative measurement in various test environments. During this work period, a study of laser energy to LIBS signal was performed. The results of this study is summarized. Work Accomplished LIBS has been evaluated as a near real time measurement technique for monitoring the concentration of metallic species in the offgases from waste processing facilities. To be accepted by EPA as a CEM, the quantitative figure of merit for LIBS needs to be improved. Due to the difficulty of injecting a known amount of sample into the practical gas stream, LIBS calibrations were all performed in the laboratory. How to transfer the LIBS calibration obtained in the laboratory to a practical environment is a great challenge for quantitative LIBS measurement. A series of studies to correlate LIBS background with the change in excitation condition was conducted. LIBS data were recorded with different detection windows and laser energies. Figure 4 shows the variation of the Pb LIBS signal and background at different laser energies. The background was found to increase as the laser energy increased. The Pb signal also increased with the laser energy. However, the Pb signal was almost unchanged after laser energy went above 180 mJ. This indicates the signal-to-background ratio (S/B) can be used in LIBS calibration but in limited laser energy ranges. Figure 5 shows S/B for Pb, Cr, Hg, Cd, and Be at different DIAL 40395-1

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laser energies and detection windows. These data are helpful to determine the best experimental setup for LIBS calibration. Since laser energy fluctuates from pulse to pulse, the laser energy which give an S/B change less than 20% in the laser energy fluctuation ranges should be used in the calibration to improve the precision and accuracy of the LIBS measurement.

LIBS signal (a) and background (b) as a function of laser energy. FIGURE 4.

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S/B as a function of laser energy. Data were taken at the gate delay/ gate width of (a) 20 µs/5 µs, (b) 25 µs/5 µs, (c)35 µs/5 µs, and (d) 45 µs/5 µs. FIGURE 5.

The study of LIBS calibration will continue. LIBS calibration data will be collected at different sample temperatures and ambient conditions. References 2.

Cremers, D.A. and Radziemski, L.J. 1987. “Laser Plasmas for Chemical Analysis” in Laser Spectroscopy and its Application, L.J. Radziemski, R.W. Solarz, J.A. Paisner, eds. New York: Marcel Dekker, Ch. 5, p. 351.

3.

Radziemski, L.J. and Cremers, D.A. “Spectrochemical Analysis Using Plasma Excitation” in Laser Induced Plasmas and Applications, L.J. Radziemski and D.A. Cremers, eds. New York: Marcel Dekker, Ch. 7, pp. 295-326.

4.

Singh, J.P., Yueh, F.Y. and Zhang H. 1997. Process Control and Quality, 10:247.

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5.

Singh, J.P., Zhang H., Yueh, F.Y. and Carney, K.P. 1996. Applied Spectroscopy, 50:764.

6.

Singh, J.P., Zhang, H. and Yueh, F.Y. February 1996. Transportable Vitrification System Shakedown Test, Westinghouse Savannah River Corporation and Diagnostic Instrumentation and Analysis Laboratory: Laser-induced Breakdown Spectroscopy Measurements. US DOE Contract No. DE-FG02-93CH-10575. DIAL 10575 Trip Report 96-1.3.

7.

Singh, J.P., Zhang, H. and Yueh, F.Y. April 1996. DOE and EPA Continuous Emission Monitoring Test at EPA National Risk Management Research Laboratory (NRMRL). US DOE Contract No. DE-FG02-93CH-10575. DIAL 10575 Trip Report 96-2.

8.

Singh, J.P., Zhang, H. and Yueh, F.Y. 1996. Plasma Arc Centrifugal Treatment PACT-6 Slip Stream Test Bed (SSTB) 100-hour Duration Controlled Emission Demonstration (CED) Test. DIAL Trip Report 96-3.

9.

Singh, J.P., Zhang, H. and Yueh, F.Y. September 1997. DOE and EPA Continuous Emission Monitoring Test at EPA National Risk Management Research Laboratory (NRMRL). DIAL Trip Report 97-1.

Subtask 1.2. Mercury Absorber Technology Many of DOE’s low-level wastes contain mercury. If the LLW is treated by thermal treatment processes such as incineration, the mercury will be emitted to the off-gas system and must be removed. While the levels from DOE facilities meet current regulatory limits, the EPA is in the process of promulgating new rules (the so-called “MACT” rules) with much lower limits. Based on limited test data, some of DOE’s thermal treatment facilities will be unable to comply with these rules without significant capital investment. A mercury removal technology, based on an innovative absorber, has been developed in Russia and deployed in room temperature applications there. DIAL will test this absorber because, if it proves

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to be effective, its use would require almost no changes to existing facilities. Key performance characteristics which will determine whether the absorber can be used in an off-gas system are the maximum temperature at which it is effective and its capacity. DIAL will utilize its test stand and off-gas systems to provide this data. The mercury absorber will be installed in the off-gas system. The temperature of the off-gas hitting the material will be varied and mercury removal will be monitored. Mercury-laden off-gas will be sent past the absorber until no further removal of mercury occurs. The maximum mercury loading will be determined, as well as the maximum temperature at which the material is effective. Representatives from the Idaho office of DOE, and from the developer of this innovative technology, will assist in developing test plans, will observe the tests, and will review test plans and test results. If initial testing is successful, stakeholders will be notified (through the Southern States Energy Board and the California EPA) and invited to participate in further performance testing. The objective of this subtask is to determine, through testing, the maximum temperature at which the mercury absorber is effective, and the maximum loading of the material. This project has been deferred.

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TASK 2

Deactivation and Decommissioning Technology Support

Subtask 2.1. Pipecleaning Technology R. Daniel Costley

Introduction One of the most difficult aspects of D/D of DOE’s existing facilities is dealing with pipes which have carried radioactive solutions. Current practice is to attempt to flush contamination out of the pipe, or fix the contamination in the pipe, and then to either leave the pipe in place or cut it out. Flushing tends to either create more waste, and generally leaves behind the radioactivity which is trapped in the oxide layer in the metal. Cutting contaminated pipe creates the potential for airborne activity. Leaving the pipe in place is sometimes justified, but in the case of DOE’s separations canyons is not likely to be successful because of the level of activity left behind. Researchers at Mississippi State University have developed a technique which uses repetitive high voltage acoustic shock waves in water to produce acoustic shock waves. Laboratory and field testing has shown these shock waves to be very effective in removing scale, silt, and other fluid saturated deposits from the interior walls of steam condenser and heat exchanger tubes. The debris removed from the

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Task 2. Deactivation and Decommissioning Technology Support

walls is then flushed away. This method is a noncontact, nonchemical method for removing these deposits. A version of this technique has been demonstrated on heat exchanger piping in an operating nuclear reactor. However, this was a once-through system which is not optimal from a waste generation standpoint. DIAL will develop a closed loop system. DIAL will test the system on pipes containing simulated contamination in many forms (e.g., scale, corrosion products, sedimentation). The ability of this technology to remove obstructions from process piping (e.g., WERF’s heat exchangers, or the HLW evaporator at SRS) will also be investigated. The system will then be demonstrated at Florida International University’s D/D testing facilities to see if it is feasible to use this system to unclog pipes. In the outyears, a radioactive demonstration using actual contaminated piping is anticipated. This most likely will be held at Savannah River. The objective for this task is complete development of pipecleaning technology, leading up to a radioactive demonstration. Work Accomplished A second tube cleaning system is being built at DIAL. The first was built at the High Voltage Lab at Mississippi State University. Parts have been procured. A closed loop circulation system is also being built. The laboratory space has been modified to accommodate the system. A presentation on this system was made at X’Change 97. A short video was made as part of this presentation. The video, along with other materials, has been circulated to several companies and agencies involved in D&D in an effort to market the technology and find a commercial partner. We have found a partner willing to collaborate on an SBIR type proposal.

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Conclusions The TCS has been successfully demonstrated at Sequoyah Nuclear Power Plant (TVA) and the Wabash River Coal Fired (Plant Public Service of Indiana) to clean scale and other deposits from 1 in. diameter heat-exchanger tubing. This previously developed and demonstrated technology provides an excellent basis for further developing a system that will decontaminate radiologically contaminated surfaces. This method appears suitable for cleaning and decontaminating tubes, pipes, and other cylindrical storage containers capable of containing fluids. There are several advantages of this technique over existing technologies. The primary advantage is that the exposure of workers to hazardous and radioactive materials is minimized. This is because the cable can be fed through a bushing into the pipe so that workers do not come into contact with the material within the pipe. Further, the generation of secondary waste is minimized, or avoided. The water in the pipes transports the scale out of the pipes. This same water can be reused to clean other pipes after the foreign matter has been separated from it using conventional means (filtration, centrifuge, settling). Since deposits are knocked off the surface of the pipe through its interaction with the acoustic wave, the use of brushes or chemicals is avoided, further reducing the generation of secondary wastes. Work Planned A new, improved pulsed acoustic pipe cleaner will be completed at DIAL. This new system will be more robust and have several improved features. We will also finish the assembly of the closed loop circulation system. Pipes with different types of fouling will be cleaned in this system in order to determine the effectiveness of the TCS for different applications. We will continue to seek an on-site demonstration at a DOE facility.

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References 10.

Costley, R.D., Mazzola, M.S., and Grothaus, M.G. December 1997. Pulsed Acoustical Technique for Decontamination of Piping and Containment Systems. Presented at X-Change’97: The Global D&D Marketplace, Miami, FL.

11.

Mazzola, M.S., Grothaus, M.G., Walch, M., and Jones-Meehan, J. July 1995. New Electrical Control Methods to Prevent Power Plant Fouling. Tenth IEEE Pulsed Power Conference, Albuquerque, NM.

Subtask 2.2. Wall Removal Monitor Mark Henderson and R. Daniel Costley

Introduction DOE will generally use private vendors to D/D its existing facilities. A key to the success of this privatization approach is finding a method capable of providing near real time feedback on the removal of contaminated material. This will allow the vendor to make decisions while crews are still deployed about the status of removal of contamination, and allow DOE to make informed decisions about payment of the vendor. DIAL has developed an approach based on Fourier transform profilometry which appears to at least partially fulfill this need. This technique uses the Fourier transform of an image of a surface to provide depth information. Thus, for removal of contaminated concrete from a wall, the technique can provide depth information for the entire wall relative to a starting point. DIAL will first automate the process of image capture and processing, so that it can be done in the field with minimal operator inter-

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vention. The automated operation of the equipment will then be demonstrated at DIAL. A demonstration of the system as part of a D/ D operation will be conducted at the D/D test bed which has been established by Florida International University. A radioactive demonstration of the technique will be sought at the Fernald site. The same technology potentially can also be deployed as part of the Hanford Canyon Initiative. The objective of this task is to develop and deploy a technique to monitor the rate and uniformity of removal of contaminated concrete walls. Work Accomplished An acoustic ceiling tile, which had random, dark flecks, was used as the test object (ceiling tile is easily modified with a knife). A rail, which sits on two tripods, was constructed to hold the camera and the projector. Tests were done on the “noisy” tile by gauging holes and sections from the tile using a knife and measuring the amount of material removed both by using FTP and a caliper (for reference see the DIAL technical memo on the Wall Removal Monitor which includes several images). The camera used in these tests was a commercial home video camera. The spatial resolution (the distance between points on the surface) depends on the area of the surface being imaged and the resolution of surface variation. As a result the finished profile map can be referenced to the original surface and only the things that are different show up in the report. A third enhancement to FTP has been developed to allow information to be collected at multiple resolving abilities concurrently. The technique uses two patterns that are projected onto the surface at the same time so that they overlap. This allows both the global picture to be seen along with the details, and prevents “forest-for-the-trees” problems that can occur.

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Conclusions A system has been demonstrated that can accurately measure large areas with a high degree of precision on “noisy” surfaces. The system has been constructed for fieldwork and uses commercial parts. All necessary field measurements are quick and easy to make, and processing is in near real time. FTP fits the role of wall removal monitor well, as it can measure a surface profile relative to the original surface. From the depth information gathered using FTP it is possible to calculate volume of material removed, average depth of material removed, and point-wise depth of removal. The system can be used at the job site potentially saving the contractor and the contracting agency time and money by preventing costly re-visits and ensuring quality. Work Planned A demonstration of this technology is scheduled for December 1998 at the test facility at HCET-FIU. Modifications will be made to the configuration so that floors, ceilings, and other surfaces can be monitored. A commercial partner will be sought to commercialize the technology for this application. Reference 12.

Henderson, M.E. and Costley, R.D. Wall Removal Monitor. DIAL Technical Memo WRM 1198.

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TASK 3

Technical Data to Support Cleanup Decisions

Subtask 3.1. Dioxins/Furans in Incinerator Burner Thermal treatment processes (incinerators, melters) typically emit toxic metals (esp. mercury), volatile and semi-volatile organic materials (esp. dioxins and furans), and particulate matter during processing. While the levels from DOE facilities meet current regulatory limits, the EPA is in the process of promulgating new rules (the socalled “MACT” rules) with much lower limits. As was discussed at the National Technical Working Group “pre-meeting” on November 4, 1997, preliminary data indicate that the Consolidated Incinerator Facility at SRS may not be able to meet the very stringent MACT rules for dioxin. Based on preliminary testing, Savannah River personnel suspect that the fuel oil burner used in the incinerator may be an important contributor to the problem. Installing additional control devices on the CIF would be expensive, and difficult to accomplish in a radioactive environment. As a result, SRS and the other DOE incinerator operators require additional testing to confirm that the incinerator’s burner is the source of the dioxins/furans. DIAL will expand the scope of testing to be performed for a commercial burner manufacturer to include determination of the concentration of dioxins/furans produced as a function of

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Task 3. Technical Data to Support Cleanup Decisions

burner operating conditions. DIAL will take its instrumentation to the burner manufacturer. Dioxin/furan contents in the effluents will be determined as a function of burner operating conditions. As a result, DIAL may be able to provide a window of burner operating conditions which could avoid the need for additional control devices. An engineer from DOE’s Consolidated Incinerator Facility will work with DIAL on this effort. He will assist by ensuring that testing adequately reflects conditions in the CIF, and by reviewing test plans and test reports. The objective of this task is to determine dioxin/furan production from a fuel oil burner.

Dioxin Tests John Etheridge

Introduction Because of the concern over dioxin production in mixed waste and municipal solid waste incinerators, there is a great need for more definitive data concerning the affects of incinerator operating conditions of on the production and destruction of dioxins and furans. Although there is a substantial quantity of data available, it is derived mostly from laboratory scale combustion systems that may be too small for the data to be meaningfully applied to full scale incinerators and from operating incinerators where precise control of the system parameters and repeatability of results are both problematic. DIAL’s combustion test stand is large enough to produce data that is applicable to full scale incinerators, is highly controlled, and is capable of producing very repeatable operating conditions.

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Work Accomplished A series of tests using DIAL’s combustion test stand have been designed to produce data that should provide insight into the conditions with produce dioxins. A sampling system which is both isokinetic and isothermal has been designed for sampling of both particulate bound and gas-phase dioxins. A test section which is eight feet in length has been designed for this series of tests. The test section will provide a nearly constant temperature for its entire length. The combustion test stand is being reconfigured to produce temperatures that can be varied from 300 to 700 F in the test section that was specifically designed for these tests. In order to provide this range of temperatures without changing the combustion conditions, retractable single loop water cooled heat exchangers will be used at several locations in the high temperature sections of the test stand in order to temper the gas stream. This technique for producing a range of lower temperatures should minimize the chance of produce dioxins in the heat exchanger due to local cooling of the gas stream to the temperature at which they are formed. At present the channel and the combustor section of the test stand are in place. Work Planned The air pollution control system and fuel tank will be moved to the new test facility at about mid-November. Installation of the control and monitoring system will begin at that time. The first tests should begin during the first half of December. The combustion test stand will be fired with natural gas for the first series of tests and then the series will be repeated with fuel oil No. 1.

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Testing planned is intended to add insight into the dependence of dioxin/furan concentrations on both temperature and metal content of the ash, off-gas chemistry, and SO2 concentrations in the off-gas.

Detection of Chlorinated Organics by Cavity Ring-down Spectroscopy Ram Vasudev and William Dunsford

Introduction The goal of this project is to develop a sensitive real time probe for chlorinated volatile/semi-volatile organic compounds (VOC/ SVOC). The need for such a detector is especially urgent in the case of SVOCs such as dioxin characterized as being among the most toxic man-made chemicals.13 We are exploring the technique of cavity ring-down spectroscopy (CRDS) for this purpose.14,15 Traditional laser techniques such as resonance-enhanced multiphoton ionization (REMPI) and laser-induced fluorescence (LIF) are not very suitable for chlorinated aromatics because of fast excited-state intersystem crossing (ISC) in these molecules.16 CRDS, by comparison, is not influenced by excited-state photophysics because it is solely absorption-based and is thus a perfectly general technique. It is also superior to conventional methods such as FTIR spectroscopy because it is more sensitive and optoacoustic spectroscopy because it can provide absolute absorption cross-section. It is thus a very promising universal toxic gas detector. The experimental setup for cavity ring-down spectroscopy has been described previously14,15 and will not be repeated here in detail. Briefly, the absorption pathlength of a pulsed laser through an absorbing sample is made very long by trapping the pulse between the mirrors of a high-finesse (low-loss) confocal/semi-confocal optical

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cavity containing the sample. The effective pathlength in suitable cases can be several kilometers, so very small concentrations of chemical species can be detected, being limited predominantly by scattering losses and cavity mirror reflectivity. The absorption coefficient of an absorber is obtained by analyzing the time-decay profile (the “ring-down” waveform) of the light transmitted by the cavity. Work Accomplished Considerable difficulties have been encountered because of lack of infrastructure in DIAL’s new building. In spite of the hardships, progress has been made in the detection of chlorinated VOCs. In these studies, we have exploited the accidental coincidence of the fourth harmonic (266 nm) of an Nd:YAG laser with a weak absorption feature of each VOC. Linear relationship is found between absorber concentration and CRDS signal, as shown in the example in Figure 6. The inferred detection limit (DL) is in the parts-per-million range. This can be improved considerably because the fixed wavelength (266 nm) used in these experiments overlaps with rather weak absorption features in the spectra of these molecules. In addition, the cavity mirrors used in these studies are rather cheap/substandard (with reflectivities, R, of ~ 0.980 - 0.997), and the cavity is somewhat short (23.8 cm). With improvements in these parameters, the sensitivity is expected to improve significantly, to the parts-per-billion range in suitable cases. However, we note that even the DL achieved here should be good enough for detecting VOCs at concentrations found in, for example, landfills.17 The most significant aspect of this work is the ease with which chlorinated VOCs can be detected by CRDS. In addition, the DL is unaffected by the extent and site of chlorination. In this respect CRDS is superior to methods such as LIF and REMPI that are influenced by excited-state nonradiative decay induced by the presence of chlorine.

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Results for 1,4-dichlorobenzene. Shown here is the inverse of cavity ring-down time τ (proportional to absorption) at 266 nm as a function of pressure of 1,4-dichlorobenzene. The error in pressure measurements is ~2-3 mTorr. FIGURE 6.

Work Planned Work will continue with a variety of chlorinated aromatics, especially those that are good surrogates for dioxin. It will include: •acquiring high-quality spectra for these molecules, and •improving the detection limits through improvements in the

experimental setup, as stated previously. References 13.

I.K. Puri (ed.) 1993. Environmental Implications of Combustion Processes. Boca Raton: CRC Press.

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14.

J.J. Scherer, J.B. Paul, A. O’Keefe and R.J. Saykally. 1997. Chem. Rev. 97:25 and references therein.

15.

R. Vasudev, et al. July 1998. Application of Modern Diagnostic Methods to Environmental Improvement. DIAL 10575, Final Report.

16.

E.C.Lim (ed.) 1974. Excited States, Vol. 1. New York: Academic Press; J.R. Birks. 1970. Photophysics of Aromatics Molecules. New York: WileyInterscience.

17.

B. Eklund, E.P. Anderson, B.L. Walker and D.B. Burrows. 1998. Environ. Sci. Technol. 32:2233.

Subtask 3.2. Dissolution of Hanford Salt J. S. Lindner and R. K. Toghiani

Introduction Project Significance The Tank Waste Remediation System (TWRS) is responsible for pretreating the legacy wastes contained in the double and single-shell tanks at Hanford and delivering these streams to the privatization contractor, British Nuclear Fuels Limited. The stored wastes contain three discernible constituents, high ionic strength liquid, sludge, and saltcake. Most of the experimental and theoretical modeling efforts to date have been concerned with the sludge and liquid fractions; however, a large portion of the waste, estimated to be 60% by mass in some tanks, exists as saltcake. Recognizing this deficiency, the Tank Focus Area (TFA) issued Technical Response 671:PBSTW05. The work described here is a result of a successful proposal funded by TFA with cost sharing from DIAL.

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Thermodynamic modeling of complex, multi-component electrolyte solutions at high ionic strengths and with proper consideration of solids formation is a formidable task. Workers evaluating the waste at Hanford have selected, based on initial comparisons between experimental results and an assessment of available software, the Environmental Simulation Program (ESP, OLI Inc.). The code has subsequently been used for modeling laboratory sludge leaching experiments and tank contents.18-20 To our knowledge, the work reported here is the first application of the model to saltcakes. The short time period in which ESP has been in use at Hanford suggests, however, that evaluation of the code for different applications is an evolving process. Thus, the work performed here is implicitly centered on model validation. All of the work connected with this subtask has been aimed at providing end-users at Hanford with additional information regarding the performance of the ESP code. A main goal of the work is to increase confidence in the predictive capability of the model. A proven, validated process engineering tool could result in considerable cost savings. For example, proper modeling of the pretreated waste will indicate the propensity of the waste to foul transfer lines; thereby eliminating the high costs of effecting repairs and slipped delivery schedules. In addition, analytical characterization of the large volume of waste at the site, (55 million gallons) along with the process streams that will be generated upon retrieval of the waste, is impractical. A tool is needed which can describe the waste and associated process streams with sufficient reliability such that costly characterization studies can be minimized. Background The previous work at Hanford has indicated some limitations in the application of ESP.18-20 Solid-liquid equilibrium (SLE) model calculations have been found to agree with laboratory results for aqueous solutions containing most of the pertinent single salts (NaCl,

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Na2C2O4, NaNO3, etc.). At elevated ionic strengths, however, the solubilities predicted by the model are less than experimental observations. Consequently, the code predicts higher solids loadings and this has potential ramifications on the privatization contract through the amounts and types of diluents used for pretreating the waste. Other questions regarding the code concern the quality of the data used in the integral software databases, Analytical results on the tank wastes at Hanford have indicated the presence of a number of double salts such as, Na-F-PO4, Na-F-SO4, and Na-SO4-CO3.21 Literature data on these systems are rare. What results are available indicate that various types of solids structures, crystals and gels, can result depending on composition. Natrophosphate, Na7F(PO4)2.19H2O, for example, has been observed to form gels.22,23 Sodium phosphate Na3PO4.XH2O can form different crystal structures depending on the extent of hydration. Accurate modeling of the partitioning of the solids and liquid phase constituents will only be as good as the fundamental data used in the model. Methodology Some identified options for validating the ESP code include: •comparisons to experimental data on actual tank samples; • determination of the SLE behavior for those systems which

are of direct importance to the end-users at Hanford and where literature results are fragmentary; •comparison of the results of the model to other thermodynamic models; and •examination of the thermodynamic data called by the code. Little is known about the pretreatment requirements of saltcakes and experimental studies on this portion of the waste are lacking. An evaluation of the predictive capabilities of the ESP model is possible by comparing code predictions with the results of experimental stud-

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ies. Other comparisons of the model to tank sample analysis include direct customer requests. Critical evaluation of the fundamental thermodynamic constants called by the model permit an assessment of the quality of the data used by OLI Inc. and can identify possible error sources. In many instances, especially with regard to the double salts systems cited above, sufficient data does not exist in the literature and any compilation will only consider the available information as estimates. Determination of the solubilities and associated phase diagrams for selected systems provides a means for ensuring the quality of the experimental data and a path for model sensitivity calculation. Different theoretical representations can be used to calculate the SLE behavior of aqueous systems. Comparison of the results from ESP with other thermodynamic models allows an independent check on the thermodynamic framework used and may also indicate deficiencies in the ESP model or associated database. Work Accomplished Results Progress made in the four project areas has previously been reported to TFA.22 Two letter reports on the application of ESP to dissolution of the crust present in Hanford tank 241-SY-101 have also been distributed.23,24 Highlights of these efforts are given below. Additional information on these studies is available in the cited references. The work scope of the last half of FY 98 concerned evaluation of the fundamental data in the ESP databases, validation, and use of an instrument capable of measuring solubilities, a comparison of ESP predictions with those from the SOLGASMIX model for natrophos-

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phate, modeling of saltcakes from three Hanford tanks, and extensive studies on SY-101. Fundamental data called by ESP. The prediction of solid-liquid equilibrium by ESP is only as accurate as the fundamental thermodynamic constants called by the software. To this end, the program contains, in specific application databases, extensive listings of the constants for many inorganic and organic constituents. The heterogeneity of the elemental constituents in the Hanford feed implies a considerable number of possibilities with regard to molecules that can be formed. Consequently, the quality of the data is critical with regard to properly describing the waste that will be encountered.

Evaluation of the data was centered on the comparison of the enthalpy of formation, Gibbs free energy of formation, standard state entropy at 298 K, and heat capacity. Sources for the data included the ESP public and private databases, NIST, CODATA and NES.25-27 The constants in the NIST and CODATA compilations have been critically reviewed. A majority of all of the results available is collected in the NEA listings. The data search engine (periodic table function) within ESP was used to select the molecules and ions for comparison. Elements that are present in large quantities in the waste at the site include H, Na, Al, N, O, N, S, P, and F. The inclusion of other systems containing Si and Cl are currently in progress. All of the data from the different sources were collected in a spreadsheet. The NIST and CODATA values were treated as confirmed, whereas, the constants given in the NEA database were subjected to a statistical calculation. If a particular value within the given NEA set was found to be outside of ± 2 standard deviations of the mean, that value was omitted and a new calculation performed. Tables of the fundamental constants and the relative errors of these values between the different data sources are collected in Ref.

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23. In summary, the data from all of the sources was very similar for the Gibbs free energy of formation and the enthalpy of formation. Ratios in ∆G˚F and ∆H˚F were calculated for all of the entries at 99.93 ± 1.8 and 99.72 ± 1.6 kJ/mol. Errors in the standard state entropy and heat capacity were larger for systems containing fluorine; AlFx, HF, and NaF. If these molecules and ions are omitted, the average difference between the ESP values and the other data bases for S0298 was calculated as 97.1 ± 19.9 J/mol K. Data for the heat capacities, where available, also exhibit considerable scatter. Although additional data comparisons are needed, especially with regard to the aluminosilicate system, it appears that a short-term examination of the fundamental constants called by ESP can be used to identify potential discrepancies with reported literature data. The apparent errors in the constants for fluoride containing systems, such as NaF, which is a common molecule observed in laboratory analysis of Hanford wastes, are also being addressed in the experimental studies of this project. Experimental solubility determinations. As

noted above, only limited results have been cited for many of the double salt systems present in the site holdings. Determination of solubilities at different solution conditions, pH, ionic strength and temperature, provides one method for direct comparison to the ESP model. Such measurements can be performed under isobaric (constant pressure) conditions, or by capitalizing on changes in the system refractive index, which occur at the SLE point.28,29 Experiments at constant pressure require considerable control during the lengthy duration’s needed to achieve equilibrium. Consequently, the initial choice in developing an experimental apparatus was to perform the measurements based on the refractive index or Tyndall effect.29 A block diagram of the instrument is given in Figure 7. The sample cell is a glass-jacketed reactor flask that is connected to a circulating water bath. The top of the cell was machined from poly(oxy-

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ethylene) and is equipped with ports for a calibrated thermocouple, pH electrode, and addition funnel. The top of the assembly is insulated and the entire cell rests on a magnetic bar stirring plate. A low power laser beam is passed through the solution and is detected using a silicon photodiode. The signal is amplified and viewed on an oscilloscope. ADDITION THERMOCOUPLE

pH

INSULATION

To Circulator

DETECTOR

LASER

DISPLAY

STIR BAR

From

GLASS JACKETED CELL

STIRRING PLATE

FIGURE 7.

Block diagram of the solubility apparatus.

The experimental apparatus was tested with KCl, Figure 8. Good agreement with the literature reports from a number of different laboratories was obtained.22 (For citations of the data given in Figures 8 and 9, the reader is referred to Ref. 22). The error bars associated with the data from this work arise from repetitive measurement of the temperature of the SLE point.

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7.25

Solubility [mol KCl/kgH2O]

6.75

Present Work Zhang Silcock ESP

6.25

5.75

5.25

4.75 300.0

310.0

320.0

330.0

340.0

350.0

360.0

Temperature K

KCl Solubilities determined with the experimental apparatus and compared to literature data and ESP model results.

mol Na3PO4/kg H2O

FIGURE 8.

3.5 3.0

Apfel

2.5

Kobe

2.0

Wendrow

1.5

ESP

1.0

Present Work

0.5 0.0 270.0

280.0

290.0

300.0

310.0

320.0

330.0

340.0

Temperature [K]

FIGURE 9.

Solubilities of Na3PO4.

The method is currently being applied for determination of the phase behavior of the double salts that have been identified in the Hanford inventory, Na7F(PO4)2.19H2O, Na3FSO4, and Na6(SO4)2CO3. Literature results on these system are scarce, however, recent work by Herting at Numatec Hanford Corporation, and by Weber and by Beahm et al. at Oak Ridge National Laboratory have been performed on Na7F(PO4)2.19H2O.30-32 Initial experimental studies on the Na-FPO4 system were begun to provide addition data. Determination of the phase diagram of a double salt requires the determination of the solubilities of the individual components, i.e., NaF, and Na3PO4 and then further observations with mixed solutions.

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Results for Na3PO4 are given in Figure 9 where ESP calculations and the results of previous work have been included. The plot illustrates some of the typical scatter observed in solubility data from different laboratories. The experimental results obtained in this work follow the available experimental data and the ESP calculations except in the small temperature range between 300 and 310 K where ESP predicts a gradual increase in solubility followed by a region of near constant solubility. ESP solid phase results predict that the octahydrate form of trisodium phosphate (Na3PO4.8H2O) comprises the bulk of the solids speciation at temperatures greater than 310 K. Another hydrate, Na3PO4.12H2O, is present at lower temperatures and both crystal structures may exist in the region of constant and slightly increasing solubility between 300 and 310 K. Further measurements are in progress to determine additional solubilities in the transition region and to examine whether the possible influence of kinetic effects. Following these experiments the solubility for NaF will be obtained and this will complete the arms of the phase diagram and also provide additional data for comparison to the literature. Comparison of ESP predictions with those of the SOLGASMIX Model.

One method of validating the ESP model is to examine its predictive capabilities for a system of critical interest to the Hanford tank wastes. One such system is sodium-fluoride-phosphate. Experimental solubilities have been measured by Herting for natrophosphate as a function of [OH]-.30 The solubility envelope was then predicted by Beahm, et al., using the SOLGASMIX model.32 ESP predictions can be compared to these recent studies.

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1.00 E.C. Beahm et al., 3 m OH-

0.90

ESP Prediction, 3 m OHE.C. Beahm et al., 1 m OH

Phosphate in Solution, (m)

0.80

ESP Prediction, 1m OH 0.70

E.C. Beahm et al. (in water) ESP Prediction (in water)

0.60 0.50 0.40 0.30 0.20 0.10 0.00 0.00

0.20

0.40

0.60

0.80

1.00

1.20

Fluoride in Solution, (m)

FIGURE 10.

Predicted solubility envelope for Na7F(PO4)2.19H2O.

Figure 10 provides results of the ESP and SOLGASMIX predictions of the solubility envelope for the Na-F-PO4 systems as a function of [OH].22,32 It is evident that the solubilities predicted by the two models for the pure components NaF and Na3PO4, differ. In water ESP predicts, the solubility of NaF as 0.823 m while the SOLGASMIX model estimates 0.974.m. The solubility of Na3PO4 from SOLGASMIX was determined to be 0.807 m while a value of 0.929 m was found using the ESP code. Differences in agreement were also found at the different hydroxide concentrations investigated and for the invariant points. For the mixed compositions, the ESP solubilities are larger than those from the SOLGASMIX model in pure water, agree well at 0.1 m [OH]-, and are lower than the solubilities from SOLGASMIX at the 0.3-m [OH]- condition. These differences are thought to reflect the sources of the fundamental thermodynamic data called by the respective codes. The invariant points, for example, which predict the existence of two solid phases and a liquid composition, is required information for understanding the behavior of the waste in the Hanford tanks. Knowledge of the solubility envelope for the Na-F-PO4, and other waste constitu-

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ents will prevent the fouling of transfer lines and components during retrieval operations. Incorporation of the fundamental data used in the SOLGASMIX modeling study within the ESP database will permit an assessment of the influence of the fundamental data on the code predictions. Modeling of saltcakes and comparison to experimental results. As

noted in the introduction, little is known about the pretreatment requirements and compositions of the saltcakes present in the Hanford inventory. A companion experimental program was begun at Numatec Hanford Corporation and results of these studies have been released.33 This work and the data obtained, provide a vehicle for additional comparison of the ESP model predictions with experimental data. The Hanford saltcakes examined were from tanks BY-106, BY102, and B-106 and were selected because of the unique character of the inventory in each. It was anticipated that these tanks would provide a measure of the application range of the ESP model by virtue of the widely differing composition in each tank, Table 3. TABLE 3. Major

anions present in select Hanford Tanks (in ppm). BY-106

BY-102

B-106

F-

5,130

18,000

1,540

Cl-

2,060

1,220

1,530

NO2-

32,100

13,900

7,840

NO3-

329,000

95,000

195,000

PO43-

5,270

27,000

75,700

TIC

7,360

27,800

370

SO42-

11,300

57,700

14,800

DIAL 40395-1

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Herting and Edmundson performed sequential dilution experiments on each saltcake sample. The concentrations of pertinent anions and cations were obtained and served, along with the temperatures and diluents investigated, as input to the ESP model. At each dilution Herting and Edmundson determined the specific gravity of the resulting supernate. The original sample weights and dilution conditions and the concentrations of the ionic species represented the initial data for comparison to the ESP code. An abbreviated discussion of the results obtained for the saltcake from Tank BY-106 is presented below. Full details of these and the other simulations involving the samples from Hanford tanks BY-102 and B-106 can be found in the report cited previously.22 Comparison of the model predictions and the experimental concentration determinations for the nitrate anion (NO3-2) are given in Figure 11. Quite noticeable in the calculated results is the increase in nitrate concentration that corresponds to the percent dilution where the sodium nitrate is predicted to completely dissolve. A similar result is observed in the experimental data, however, the maximum concentration is shifted toward slightly higher dilution. Experimentally it appears that all of the sodium nitrate in this saltcake sample will dissolve between 51% and 100% dilution. Some discrepancy is also observed with the absolute values of the nitrate anion concentration. One possible explanation for this disagreement rests on the electroneutrality constraint imposed on the ESP program. To maintain a balance of positive and negative charges the software will adjust the concentrations of various anions or cations. For this waste, and much of the other waste at Hanford, the main anion present is nitrate. Assuming an excess of sodium ions, but still remaining within experimental error, it is not unlikely that the model will add nitrate to achieve a net charge of zero.

DIAL 40395-1

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400 NO3, ESP

350

NO3, D. Herting Data

Concentration, g/L

300 250 200 150 100 50 0 0

100

200

300

400

500

Dilution, Weight Percent

Comparison of experimental and predicted results for nitrate anion concentration – Tank BY-106. FIGURE 11.

At dilutions greater than 100% (1:1 by weight) the agreement between the ESP model predictions and the experimental results is excellent. This behavior was observed to hold for other single salt anions, such as oxalate (C2O4-2) and chloride. Somewhat more complicated behavior was predicted for the phosphate and sulfate anions. Figure 12 is a plot of the concentration of the sulfate anion against percent dilution. At dilutions greater than about 200% the predicted concentration seems to be within 20% of the experimental result. In the lower dilution range a considerable difference between the results is observed. The sulfate may be partitioned in the solid phase between Na3FSO4 and Na6(SO4)2CO3. Both of these solids were predicted by the ESP model; however, as discussed in connections with the studies on the Na-F-PO4 system, some questions remain as to the results predicted by ESP for double salt systems. Further comparisons of the ESP data with the saltcake results will involve the determination of the solid phase constituent at NHC. From these data it will be possible to evaluate the solids speciation predicted by the code and determine if additional solids are present which compete for those anions, sulfate, phosphate and fluoride, that participate in double salt formation.

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7 SO4, ESP

6

Concentration, g/L

SO4, D. Herting Data 5 4 3 2 1 0 0

100

200

300

400

500

Dilution, Weight Percent

Comparison of experimental and simulation results for sulfate anion – Tank BY-106 (25°C). FIGURE 12.

Similar results were observed for the saltcakes from tanks BY102 and B-106. In most cases, the ESP prediction of anion concentrations from the single salts agrees with the experiments at high dilution (lower ionic strength). At low dilution values (high ionic strengths) the code predictions appear to require attention. These needs are being addressed in the experimental work and in further comparison of the model to other Hanford streams. Application of ESP to crust remediation options for Hanford Tank 241SY-101. Recent observations of the crust layer in Hanford tank 241-

SY-101 (SY-101) have indicated that the thickness is increasing. The growth of the crust has been estimated at 2 in. per quarter and the location of the surface is approximately 14 in. below the single-shell portion of the tank.34 Workers at Hanford have considered spraying 2M NaOH or inhibited water directly on the crust. In this manner it was thought that the crust volume, and, perhaps, the combined volume of the liquid/solid inventory in the tank could be reduced. Customers at the site requested the use of ESP for modeling the SY-101 crust problem. Initial efforts concerned the direct addition of diluent to the tank. These results are summarized below. Others simuDIAL 40395-1

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lations involving the transfer of 100,000 gallons of SY-101 liquid to a receiving tank (241-SY-102) were also considered. The results from both of the studies have previously been distributed as letter reports and are also contained in the report to the focus area.22-24 Data for the simulation were taken from the TWRS Best Basis Inventory for SY-101.35 The total weight of the various anions, cations and radionuclides were used with the reported total volume of liquid and solid inventory to estimate concentrations of the tank constituents. The temperatures of the tank are monitored, near the tank risers, using thermocouples.35 Averaging of these results yielded a temperature of 45˚C. The concentration data were reconciled for electroneutrality and the pH of the tank was calculated. These operations and conversion of the input ionic concentrations to a composite molecular stream was performed using the ESP Water Analyzer tool. A characterization of core samples from SY-101 was previously reported by Person.36 Initial comparison of the simulation results with the experimental solids distribution revealed poor agreement in the distribution of the organic carbon components. Thus, the ESP model was tuned by varying the ratio of oxalate to acetate. The resulting distribution along with that obtained by Person is collected in Table 4. TABLE 4. Comparison

of solid phase species observed in simulation with core sample analysis of Person.36 Species

ESP Prediction Weight %

Person3 Weight %

Cr(OH)3

4.1

5±1

NaNO3

35.0

21 ± 7

Ni(OH)2

0.2

NR

UO2(OH)2

ca. 10-1

NR

Ca(OH)2

0.4

NR

Na6(SO4)2CO3

3.4

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TABLE 4. Comparison of solid phase species observed in simulation with core sample analysis of Person.36

Species

ESP Prediction Weight %

Person3 Weight %

Na2C2O4

12.1

12 ± 4

Na2CO3 1H2O

35.5

31 ± 7

NaCl

0.1

NR

Na7F(PO4)2.19H2O

4.1

NaNO2

5.2

12 ± 3

Al(OH)3

Not observed

4±5

Na3PO4

4±3

Na2SO4

4±2

Good agreement is observed for chromium hydroxide, sodium carbonate, and sodium oxalate. The sodium nitrate weight fraction is larger than that reported by Person and the percentage of sodium nitrite predicted by ESP is from ca. 4% to 9% lower than that of the core sample. Using the upper limit error estimates from the laboratory data, the total sodium nitrate and sodium nitrite percentage would be 43%. This value is slightly higher than the corresponding total (40%) from the simulation. Fair agreement was also observed in comparing the double salt weight fractions and those of the base single salts reported by Person. For example, the fraction of sodium sulfate from the core sample (4 ± 2%) is consistent with the ESP prediction for the associated Na6(SO4)2CO3 double salt (3.4%). Adding either 2M caustic or inhibited water using an ESP Process Mix block simulated in situ dissolution of the SY-101 crust. The ESP model describes equilibrium chemistry. Simulation of the fate of any trapped gases, such as the hydrogen associated with the SY-101 crust, is outside of the basic thermodynamic framework. Within the code, it is possible to entrain solids in liquid or vapors in liquid; however, as soon as an equilibrium condition is achieved, the gas will be parti-

DIAL 40395-1

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tioned according to the specific solubility. Hydrogen has limited solubility in water at a pH of 15.2 and an accurate measure of the volume of hydrogen liberated, which will effect the total waste volume in the tank, relies on an assumption that the gas will be liberated at a rate consistent with solids dissolution. TABLE 5. Solid

phase species distribution - 2M NaOH addition. % of 2M NaOH Added (By Weight) 0

1

2

3

4

5

Cr(OH)3

4.07e+04

4.06e+04

4.06e+04

4.07e+04

4.07e+04

4.07e+04

NaNO3

3.46e+05

3.17e+05

2.81e+05

2.42e+05

2.03e+05

1.63e+05

Ni(OH)2

1.49e+03

1.49e+03

1.49e+03

1.49e+03

1.49e+03

1.49e+03

UO2(OH)2

5.32e+01

2.61e+01

Ca(OH)2

4.18e+03

4.18e+03

4.18e+03

4.19e+03

4.18e+03

4.18e+03

Na6(SO4)2CO3

3.38e+04

3.30e+04

3.20e+04

3.09e+04

2.97e+03

2.85e+04

Na2C2O4

1.20e+05

1.20e+05

1.20e+05

1.20e+05

1.20e+05

1.20e+05

Na2CO3 1H2O

3.52e+05

3.46e+05

3.39e+05

3.33e+05

3.25e+05

3.17e+05

NaCl

6.41e+02

Na7F(PO4)2.19H2O

4.04e+04

3.74e+04

3.68e+04

3.68e+04

3.67e+04

3.64e+04

NaNO2

5.11e+04

1.01e+04

Total Solids (kg)

9.9e+05

9.1e+05

8.55e+05

8.09e+05

7.34e+05

7.11e+05

Species*

Tables 5 and 6 provide the results of the simulations for in situ dissolution of the tank contents using 2M NaOH. Similar results were obtained for the addition of inhibited water and can be found in the original reference.23 The chromium, nickel, and calcium hydroxides were predicted to be insoluble at the pH and ionic strengths encountered. Weights for sodium oxalate and the sodium-fluoride-phosphate double salt were not predicted to change significantly over the range of dilutions studied. Major changes in the total mass of the solid

DIAL 40395-1

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phase arise from dissolution of the sodium nitrate and sodium carbonate. TABLE 6. Additional

simulation results for the 2M NaOH addition % 2 M NaOH Added (by Weight) 0

1

2

3

4

5

9.90e+05

9.09e+05

8.55e+05

8.09e+05

7.60e+05

7.11e+05

Solids Total Mass (kg) % Change

0.00

-8.14

-13.66

-18.30

-23.24

-28.18

Total Volume (l)

4.32e+05

3.95e+05

3.71e+05

3.51e+05

3.19e+05

3.07e+05

% Change

0

-8.47

-14.12

-18.82

-26.23

-28.82

Density (g/l)

2292

2301

2304

2307

2385

2313

5.80e+06

5.96e+06

6.08e+06

6.19e+06

6.31e+06

6.43e+06

Supernate Total Mass (kg) % Change

0.00

2.59

4.70

6.68

8.68

10.69

Total Volume (l)

3.97e+06

4.08e+06

4.16e+06

4.25e+06

4.33e+06

4.41e+06

% Change

0.00

2.59

4.78

6.87

8.98

11.08

Density (g/l)

1461

1461

1460

1458

1457

1456

Ionic Strength

21.81

21.74

21.52

21.27

21.03

20.81

pH

15.19

15.18

15.16

15.14

15.12

15.10

Process Information %Solids by Weight

14.58

13.23

12.33

11.56

10.75

9.96

Total Mass in Tank

6.79e+06

6.86e+06

6.93e+06

7.00e+06

7.07e+06

7.14e+06

Total Volume in Tank

4.41e+06

4.47e+06

4.53e+06

4.60e+06

4.65e+06

4.72e+06

Volume Inc %

0.00

1.50

2.93

4.35

5.52

7.17

Figure 13 compares the total solids weight for the two diluents. It is evident that the use of inhibited water results in a slightly larger dissolution of solids. This is expected, as the salts, which are dissolving, are sodium salts; thus, the introduction of sodium into the system via the use of 2M NaOH will suppress the dissolution of the nitrate and carbonate containing salts.

DIAL 40395-1

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1.1E+06

1.0E+06 2M NaOH Inhibited Water

Total Solids Weight (kg)

9.5E+05

9.0E+05

8.5E+05

8.0E+05

7.5E+05

7.0E+05

6.5E+05

6.0E+05 0

1

2

3

4

5

6

% Dilution by Weight

FIGURE 13.

Predicted solids mass in SY-101 during in situ dilution.

It has been estimated that 10% of the volume within SY-101 is composed of H2.37 All of the hydrogen must be in direct physical contact with the solid phase else it would be free to evolve from the tank. At 10% of the total tank volume the hydrogen would occupy 4.41 x 105 L. At an addition of 4% by weight of inhibited water, the ESP model predicts 7.10 x 105 kg of solids remaining in the tank. This amounts to a dissolution of roughly 2.8 x 105 kg of the original solid phase. By assuming a direct proportionality of H2 evolution to total solids mass, the amount of gas released upon addition of 4% by weight of inhibited water would be 1.29 x 105 L. Subtracting this value from the final tank volume predicted following the 4% (by weight) addition of inhibited water, yields a contents volume of 4.48 x 106 L. This value is larger than the current volume of 4.41 x 106 L and, consequently, other options for reducing the crust may be more appropriate.

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The additional studies on options for remediation of the SY-101 crust are contained in Ref. 24. These calculations describe the effects of solids entrainment; the diluent needed to prevent solids formation in the transfer line between SY-101 and the receiving tank, temperature effects, and the results of mixing the SY-101 transfer stream with the receiving tank contents. Further simulations on SY-101 are in progress to determine possible reasons for the recent waste changes and observed crust growth. Conclusions Considerable progress has been made in modeling the dissolution of saltcakes from three different Hanford tanks, and in evaluating various aspects of the ESP code. Model characterization efforts have been started by: •examining the fundamental thermodynamic constants inher-

ent to the compilations used in the software that are specifically applicable to the Hanford inventory; •performing experiments to obtain solubilities in systems which represent knowledge gaps in the data; •running and interpreting simulations on waste saltcakes that are being characterized at the site; and •modeling tank contents and remediation efforts. In examining the fundamental data it was noted that excellent agreement between the Gibbs free energy of formation and the enthalpy of formation was observed in comparing the data contained in the ESP databases and the critically evaluated NIST and CODATA compilations. For most systems evaluated, except for simple salts containing fluoride ion, the agreement with the standard state entropy values was reasonable. Data for the heat capacity are limited and scattered across all data sources.

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An experimental apparatus was developed and tested for determination of system solubilities. Studies on the Na-F-PO4 system were initiated with measurements on Na3PO4. The experimental results for this system were observed to be in good agreement with other literature data and with ESP model predictions. Some solubility discrepancies were noted in a composition/temperature regime where multiple crystal forms are expected. A comparison of the predictions of the ESP model with a second thermodynamic code (SOLGASMIX, ORNL) was performed for the Na-F-PO4 system. Differences in the phase behavior observed from the two models are thought to reflect the fundamental data used. Additional comparisons with the two codes are planned for other double salt systems and through further examination of the data. An extensive modeling effort was initiated on saltcake dissolution. The simulations correctly predicted the composition of the supernate phase, compared to the experimental results, at dilutions greater than 1:1. At lower dilution ratios, the code tended to underpredict the ions associated with double salts. One factor, which has been implicated in this work, is the lack of substantial information on the double salts. Finally, from a direct customer request, the ESP code was used to model remediation options for the crust layer in Hanford tank 241SY-101. Results presented here indicate good agreement between the code predictions and a previous core sample analysis. The original solids loading in the tank was calculated as 14.6%. Upon addition of 4% by weight of inhibited water, the solids loading is reduced to 11% by weight. The addition resulted in a total volume increase, assuming the trapped hydrogen in the crust would evolve in direct proportion to solids dissolution, compared to the original waste content level. Work on evaluating the effects of transferring a portion of the waste to a receiving tank have been reported elsewhere (Ref. 24) and additional simulations on SY-101 are continuing.

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Project Status Work on evaluation of saltcakes using ESP and on code validation is continuing. The Tank Focus Area has also asked us to participate in a study on feed stabilization, which is expected to begin in January. Work Planned Improved confidence in the predictive capabilities of the code relies on the quality of the fundamental data and on comparison of the results from the model to actual experimental data. The developed solubility apparatus will be used to continue the phase diagram work on the Na-F-PO4, Na-F-SO4, and Na-SO4-CO3 systems. Further evaluation of the ESP and SOLGASMIX models will be undertaken by examining the Na-F-SO4, and Na-SO4-CO3. Evaluating the variance in predictions at different error levels for selected input streams will assess model sensitivities. Continued experimental studies of Hanford saltcakes will be conducted at Numatec Hanford Corporation. The existing comparison is limited to the supernate phase and knowledge of the composition of the solid phase distribution will pinpoint those specific molecules that are effecting the ESP results. Some additional simulations designed to evaluate the processes that have occurred in Hanford tank 241-SY-101 are planned. A second Phase I feed tank will also be modeled. References 18.

MacLean, G. T., “Computer Simulation of Laboratory Leaching and Washing of Tank Waste Sludges,” WHC-SD-WM-E5-312, Westinghouse Hanford Company, Richland, Washington, October 1994.

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19.

Reynolds, D. A., “Practical Modeling of Aluminum Species in High-pH Waste,” WHC-EP-0872, Westinghouse Hanford Company, Richland, Washington, 1995.

20.

Kirkbride, R. A., ”Tank Waste Remediation System Operation and Utilization Plan,” HNF-SD-SP-012, Rev. 0, Numatec Hanford Corporation, Richland Washington, September 1997.

21.

“Data Presented at the Saltcake Dissolution Workshop,” DIAL, Mississippi State, MS, May 1998.

22.

Modeling, FY 1998 Status Report,” DIAL 40395-TR98-3, Diagnostic Instrumentation and Analysis Laboratory, Mississippi State University, October 1998.

23.

Lindner, J. S. and Toghiani, R. K., “Thermodynamic Simulation of Tank 241-SY-101 Dissolution-Part 1: in situ Crust Dissolution”, DIAL 40395TR98-1, Diagnostic Instrumentation and Analysis laboratory, Mississippi State University, August 1998.

24.

241-SY-101 Dissolution-Part 2: Supernate Transfer Followed by In-Tank Dilution,” DIAL 40395-TR98-2, Diagnostic Instrumentation and Analysis laboratory, Mississippi State University, October 1998.

25.

The NBS Tables of Chemical Thermodynamic Properties, J. Phys. Chem. Ref. Data.

26.

Supplement 2, (1982). Cox, J.D., and Wagman, D.D., CODATA KEY Values for Thermodynamics, Hemisphere, New York (1989).

27.

Nuclear Energy Agency website www.nea.fr/ml/science/chemistry/ www.tbd database.

28.

Wyatt, D. K. and Grady, L. T., “Determination of Solubility, Physical Methods of Chemistry, Vol. VI,” in Determination of Thermodynamic Properties, 2nd ed., Rossiter, B. W. and Baetzold, R.C., Eds. Wiley, New York, 1996.

29.

Zhang, L. et al.,” Measurement of Solid-Liquid Equilibria by a FlowCloud-Point Method,” J. Chem. Eng. Data, 43, 32 (1998).

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30.

Herting, D.L., “Clean Salt Process Final Report, Appendix A, WHC-EP0915, Numatec Hanford Corporation, Richland, Washington, 1996.

31.

Weber, C. F., “A Solubility Model for Aqueous Solutions Containing Sodium, Fluoride, and Phosphate,” Ph.D. Dissertation, The University of Tennessee, Knoxville, May 1998.

32.

Beahm, E. C., et al.,”Status Report on Solid Control in Leachates,” ORNL/ TM-13660, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1998.

33.

Herting, D. L. and Edmundson, D. W., “Saltcake Dissolution FY 1998 Status Report,” HNF-3437, Rev. 0, Numatec Hanford Corporation, Richland, Washington, 1998.

34.

Blain Barton, personal communication (July 3,1998)

35.

Twins II website, http://twins.pnl.gov:8001/htbin/TCD/getTableList.exe

36.

Person, J.C., “Effects of NaOH Dilution on Solution Concentrations in Tank 241-SY-101 Waste”, WHC-SD-WM-DTR-045, Rev. 0, December 1996.

37.

Meyer, P.A., et al., “Gas Retention and Release Behavior in Hanford Double-Shell Waste Tanks”, PNNL-11536, Rev. 1, May 1997.

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TASK 4

Product Acceptance Support

Subtask 4.1. Monitors for Idaho LAW Stream D. L. Monts, C. B. Winstead, G. P. Miller

Introduction Purpose Currently, Idaho is developing a design of a facility to immobilize HLW from the Idaho Chemical Processing Plant. Most of the HLW is in the form of a dry calcine, stored in bins. The present design calls for dissolution of the calcine, and separation of the fission products and actinides from the inert chemicals contained in the calcine. The resulting stream containing the inert chemicals will be immobilized by grouting, and then disposed of as low-level waste. This strategy is predicated on the success of the separations process. Currently, no method is available to directly determine the content of the TRU and other important elements in this product stream. As a result, a number of “surge” tanks have been included in the process to allow the product stream to be sampled, and then analyzed off-line elsewhere. Based on these analyses, a decision will be made of whether the low activity fraction of the dissolved HLW (LAW) can

DIAL 40395-1

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Task 4. Product Acceptance Support

be treated as low level waste. This determination will depend on the concentration of actinides in the LAW. DIAL will adapt an existing laser-based system so that it can be used to make this determination on-line in near real-time. This will greatly reduce the cost of the facility (by eliminating surge tanks), and improve the process cycle time. It will also help avoid the risk associated with handling these samples in highly radioactive facilities. DIAL currently has two laser-based techniques with the ability to distinguish isotopic species: high resolution laser-induced fluorescence (HR-LIF), and cavity ringdown spectroscopy (CRDS). The first year’s activities will concentrate on determining the detection limits of each technique for the isotopes of interest to INEEL. Based on the demonstrated detection limits of each instrument, a selection of the instrument concept to be utilized will be made. Subsequent efforts will concentrate on optimizing the instrument for field deployment. Based on the optimization, a prototype instrument will be used for a radioactive demonstration. This, in turn, will be the basis for s specification for a monitoring system. Methodology Two different techniques to address this need are being investigated: cavity ringdown spectroscopy and laser-induced fluorescence spectrometry. Cavity Ringdown Spectroscopy. Cavity

ringdown spectroscopy (CRDS) is a relatively new variant of absorption spectroscopy that has demonstrated extreme sensitivity in a variety of studies.38 The ringdown technique (Fig. 14) has been described in a number of publications, and will only be briefly summarized here. In “traditional” cavity ringdown spectroscopy, a laser pulse from a tunable pulsed laser is introduced through the end mirror of a stable optical cavity.

DIAL 40395-1

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This optical cavity is formed from two highly reflective mirrors, and serves to trap the fraction of the laser pulse that enters the cavity. The laser pulse propagates back and forth between the mirrors, where it can interact with an absorbing medium in the cavity over the course of thousands of round trips inside the cavity. Since the mirrors are not perfectly reflective, some of the laser light is transmitted through the mirrors each time the light is reflected. A photomultiplier tube is placed behind the second mirror to detect the intensity of laser light transmitted through the mirror as a function of time. The time for the pulse energy in the cavity to decay is determined by the reflectivity of the mirrors and by the absorption of the sample in the cavity. When the cavity is empty, the decay time yields a measurement of the cavity mirror reflectivities. As the absorption in the cavity increases, the decay time for the light in the cavity decreases. By inserting into the cavity an appropriate atomization source, such as an inductively coupled plasma (ICP) or graphite furnace, various chemical forms of TRU elements can be atomized and detected using CRDS.

FIGURE 14.

Schematic of cavity-ringdown spectroscopy technique.

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Laser-Induced Fluorescence Spectrometry. Laser-induced fluorescence (LIF) spectrometry is a well-established, robust technique for detecting species of interest at low concentrations. In the LIF technique (Fig. 15), an electronic state of the species of interest is excited with a tunable laser and the resulting fluorescence intensity is monitored as a function of laser wavelength. Since the mass of isotopes are different from one another, the corresponding atomic energy levels are slightly different (Fig. 16). Consequently, when a sufficiently high-resolution tunable laser is scanned across an atomic electronic transition, the resulting LIF spectrum contains a peak associated with each isotope present; the intensities of the isotopic peaks are directly related to the concentration of the isotopes. Hence the isotopic abundances can readily be obtained from the LIF spectrum. In order that the individual isotopic transitions can be resolved, it is necessary that the species of interest be in the gas-phase. For the TRU elements of interest, an atomization source is required in order to volatilize and atomize the sample. A calibration curve is obtained by recording the LIF signal intensity as a function of concentration. Using the calibration curve, unknown concentrations can be determined.

Narrowband Laser

Atomization Source Lens Spectrometer Detector

Schematic of the laser-induced fluorescence spectrometry technique. FIGURE 15.

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U-238

Isotope shift

U-235 U-238 U-235 U-235 U-238

FIGURE 16.

Emission Intensity

Wavelength λ

Schematic of isotopic energy shifts and the associated LIF

spectrum.

Work Accomplished Cavity Ringdown Spectroscopy The most critical elements necessary for assembling an ultrasensitive CRDS system are high-quality cavity mirrors. Typically to achieve extreme sensitivity, mirrors of greater than 99.9% reflectivity are required. However, atomic spectrometry requires the use of ultraviolet laser light, a region of the spectrum where mirror reflectivity is often relatively poor. Thus, the first challenge to be overcome for cavity ringdown in elemental spectrometry is obtaining high-reflectivity mirrors for ultraviolet wavelengths. While standard optical suppliers will only guarantee 99.5% reflectivity for ultraviolet wavelengths, a thorough search resulted in finding one company willing to quote 99.9% reflectivity mirrors for ultraviolet use. Figure 17 depicts a ringdown signal obtained using mirrors coated by this company for maximum reflectivity around 360 nm. (Uranium has a strong absorption at 358.4 nm). These mirrors have a 6-meter radius of curvature and were separated by 57 cm of air when this waveform was recorded. The depicted waveform has a decay time of 5 microseconds. After correcting for the amount of loss due to scatter from the air in the cavity, the reflectivity of the mirrors can be determined from this ringdown

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time and is ~99.965%. Thus contrary to statements in the literature, excellent mirrors are available for cavity ringdown at ultraviolet wavelengths. Mirrors with 99.9% reflectivity have also been obtained for 280 nm operation.

Relative Intensity

358 nm Mirrors

-5E-06

0

5E-06 1E-05 Seconds

2E-05

2E-05

Cavity ringdown decay for air with mirrors optimized for 360-nm operation. FIGURE 17.

The original plans for this project included measurements of uranium standards using cavity ringdown in both inductively coupled plasma and graphite furnace systems. However due to regulatory requirements, the use of uranium is not permitted at this time. Instead we have used chromium as a surrogate in the ICP for measurements at almost precisely the same wavelength as would be used for uranium, demonstrating the feasibility of using this spectral region for ICP ringdown measurements. Figure 18 depicts a cavity ringdown spectrum of the chromium absorption at 357.9 nm, obtained when a 1-ppm chromium standard solution was injected into the ICP. Due to difficulties beyond our control encountered upon installation of a new narrow linewidth laser system, this data was obtained with a laser linewidth that is broader than the absorption line. As with traditional

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absorption spectroscopy, using a broad linewidth source leads to a reduction in measurement sensitivity since only a fraction of the light is resonant with the strongest part of the atomic absorption. The new narrow linewidth laser system has now been successfully installed, allowing for detection limit determination in the near future. Ringdown Time (1 ppm Chromium)

Microseconds

1.4 1.2 1 0.8 0.6 0.4 3578

3578.5 3579 Wavelength (Å)

3579.5

Cavity ringdown spectrum of atomic chromium absorption at 357.9 nm. FIGURE 18.

We also have recently collected some preliminary data that demonstrates the utility of cavity ringdown for elemental spectrometry in graphite furnace sources. Using mirrors coated for 280-nm operation with 99.9% reflectivity, changes in ringdown time have been measured that are associated with the atomization of lead standard solutions. This preliminary data, which was acquired using a somewhat crude manual timing scheme for acquiring data (essentially a stopwatch), seems to indicate results comparable to commercial atomic absorption systems. This is very encouraging when considering that we have not yet optimized many experimental parameters (such as data acquisition timing and speed) and that the broad linewidth laser source was also used. The total atomization time in a graphite furnace

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is typically on the order of one second, so the fact that usable data is obtained with manual timing is a testament to the sensitivity of the ringdown method, as we almost assuredly were not measuring during the optimum atomization time. We are currently improving our acquisition system and are working toward a more quantitative analysis of this data. Finally, this work and other related atomic cavity ringdown efforts have been presented at the U.S. Department of Energy's Environmental Management Science Program (EMSP) workshop in Chicago and abstracts have been submitted to the Federation of Analytical Chemistry and Spectroscopy Societies Conference, the Gaseous Electronics Conference, and the Southeastern Section of the American Physical Society Conference. Laser-Induced Fluorescence Spectrometry During this reporting period, we concentrated on efforts to record and deconvolute the isotopic spectrum of a surrogate, copper, in order to demonstrate the deconvolution technique. Copper was selected because it has only two naturally occurring isotopes, both isotopes are present in significant abundance, and the separation of the isotopic transitions (although smaller than for uranium) should have been almost resolvable with our current dye laser system. In order to maximize the intensity, initial experiments were performed with high concentrations of copper. Deconvolution analysis of these spectra indicated that in addition to atomic transitions, molecular transitions also occurred in the spectra region, inhibiting resolution of the isotopic transitions. These experiments were repeated using lower concentrations. The resulting LIF spectra could not be resolved even using deconvolution because the linewidth of our tunable dye laser was broader than the isotopic separation for this copper transition. The linewidth of the dye laser was narrowed by inserting an etalon into the dye laser's oscillator cavity; however, it was discovered that the wavelength of the dye laser can no longer be scanned under computer

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control. We are currently modifying our dye laser so that the narrowlinewidth dye laser can be pressure scanned. This is done by pressurizing the dye laser oscillator cavity with an inert gas, such as nitrogen, to a pressure of up to 30 psig and then allowing the gas to escape. Since the index of refraction of the gas in the oscillator cavity is a function of pressure, changing the pressure in the oscillator cavity changes the lasing wavelength. The technique is simple, but it has three disadvantages: (1) since the rate at which the gas escapes the cavity is non-linear, the scan rate of the laser wavelength is also nonlinear; (2) since the operational conditions (exact initial pressure and how valve is opened) are slightly different from experiment to experiment, the scan rate differs from experiment to experiment; and (3) the wavelength range over which the dye laser can be pressure scanned in a single experiment is limited. The use of a pressure-scanned, narrowlinewidth dye laser will permit us to develop the methodology to handle isotopic LIF spectra, but will not be satisfactory for routine analysis. To the extent possible, we are attempting to perform these experiments using currently available equipment; what we are too frequently encountering in the laboratory is proof that the existing equipment is not adequate for these efforts. TRU elements are most commonly found in the oxide form. Laboratory flames are known not to efficiently atomize actinide oxides. Inductively coupled plasmas are more than sufficiently hot enough to atomize refractory oxides such as those of the actinides. The air ICP elemental analysis group at DIAL loaned us one of their ICP plasma systems. After the ICP system had been installed in our laboratory and preliminary experiments using surrogates had been performed to optimize operation, we learned that the university did not yet have a regulatory license to perform experiments with actinides and thus we were unable to record the LIF spectrum of uranium in an ICP.

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Work Planned Cavity Ringdown Spectroscopy The primary elements to demonstrate measurement of TRU elements using cavity ringdown have now been assembled. Very high quality mirrors have been located and obtained, and demonstration measurements have been performed in the ICP very near the uranium absorption wavelength. Graphite furnace cavity ringdown has been demonstrated as well. A new narrow-linewidth laser system is finally on-line and operational, and will allow the quantitative demonstration of ringdown detection limits for species such as uranium. Continuing progress into the sensitive measurements of TRU elements will be largely dependent upon MSU and DIAL securing the appropriate licenses to use uranium in these studies. It is anticipated that in the coming year, these detection limit measurements will be finalized. Test measurements of a surrogate for the low activity fraction of the INEEL high-level waste will also be investigated. Laser-Induced Fluorescence Spectrometry In order to make progress on the use of LIF for isotopic determination of TRU elements, there are three prerequisite needs that must be meet. The first is that the university must have a regulatory license to work with actinides The university is currently negotiating with the state regulatory agency and is purchasing the required monitoring equipment. It is currently anticipated that the university will have the appropriate regulatory license by March, 1999. Thereafter we will be able to work with uranium rather than with surrogates. The second need is the need for a sufficiently hot atomization source. Funds have recently been approved for an ICP atomization source; request for written bids have been distributed by the university's purchasing office and will be opened in early January, 1999; delivery of the ICP system is expected before the end of March, 1999. An ICP system capable of operating with air as the carrier gas is being purchased

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since many of the applications for which the LIF technique is applicable involve air. The third need is for a sufficiently narrow-linewidth, tunable laser system that can be reproducibly scanned. DIAL's cavity ringdown spectroscopy group will permit us to use their new moderately high-resolution dye laser system to perform some preliminary experiments on surrogates in an ICP plasma. If as expected these LIF experiments prove that such a moderately high-resolution tunable laser system has sufficient resolution for the TRU elements, then a comparable dye laser system will be purchased during spring, 1999; if the experiments indicate that even higher resolution is required, then additional funding will be sought in order to purchase an ultrahigh resolution tunable laser system. In the interim our efforts to pressure scan our current dye laser will continue. A high-resolution dye laser with computer-controlled scanning mechanism will overcome all these limitations. Nomenclature CRDS

cavity ringdown spectroscopy

DIAL

Diagnostic Instrumentation and Analysis Laboratory

HLW

high-level waste

ICP

inductively coupled plasma

LAW

low activity waste

LIF

laser-induced fluorescence

MSU

Mississippi State University

nm

nanometer

ppm

parts-per-million

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TRU

transuranic

References 38.

See, for example: G. P. Miller and C. B. Winstead. 1997. Journal of Analytical Atomic Spectrometry. 12:907; and J. J. Scherer, J. B. Paul, A. O’Keefe and R. J. Saykally. 1997. Chemical Reviews. 97:25.

Subtask 4.2. Pressure in Drums R. Daniel Costley and Mark Henderson

Introduction At most waste sites, transuranic (TRU), low-level (LLW), and mixed low-level (MLLW) wastes are stored in 55 gallon drums. Most of these drums contain organic materials as well. Radiolysis of the organic contents of the drums, or other physical or chemical decomposition mechanisms, may result in pressurization of the drums. In and of itself this pressurization can represent a serious safety hazard to the operator who has to open them. In some cases, however, the pressure may reflect flammable or explosive conditions inside the drum (e.g., from hydrogen generation), greatly increasing the hazard. Current DOE practice require opening and inspecting individual drums. In cases where pressurization has occurred, this practice is a danger to the worker. Personnel at DIAL have developed a simple non-intrusive technique that will detect pressures above ambient, and have demonstrated a first generation prototype at the Paducah and Oak Ridge sites. Based on feedback from users, a commercial-grade instrument is desired. This task will produce a commercial-grade instrument which can be used to provide both a warning of overpressurization, and a quantitative assessment of the pressure inside the

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drum. The general plan is to use the users’ feedback to upgrade the prototype, field test the unit, re-engineer the unit based on field testing, and then do proof testing of the re-engineered unit. After completion of this testing, the feasibility of extending this to larger packages will be investigated. Negotiations are already underway which should lead to commercialization of the technology. Representatives from the Paducah, Oak Ridge, and Savannah River Sites will assist in developing test plans for the current prototype, participate in field testing, and thus assist in refining the concept and expanding it to other types of containers. The objective of this task is to develop a commercial monitor for determining pressure inside closed drums. Work Accomplished In order to investigate the effect of drum pressurization on the lid vibration, several drums were configured so that they could be pressurized and so that this pressure could be measured. In order to do this, two fittings were inserted into the side of a drum near the top. A valve stem was put into one of these fittings. A pressure gauge was screwed into the other fitting. This arrangement allowed the drum to be pressurized and the pressure to be measured independently of the technique being developed. The vibration of the drum lid was detected by two means. An accelerometer, which was attached to the center of the lid with a magnetic coupler, detected the vibration of the lid directly. A microphone, which was mounted approximately 1 foot above the lid, detected the sound produced when the lid was tapped. Therefore, the microphone indirectly detected the vibration of the lid. An impact hammer with a soft tip was used to strike the lid and cause it to vibrate. The impulse from the impact hammer was used to trigger an oscilloscope. The data was then transferred from the oscilloscope to a microcomputer where it was processed and analyzed. The lowest mode of vibration of the drum lid was detected with the microphone

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since this mode radiates acoustically. Several other modes of vibration were detected with the accelerometer. The digitized signals were converted to frequency spectrums via a Fast Fourier Transform which allowed the frequencies of the different modes to be identified. The frequency of the lowest mode was correlated to the drum pressure for several different drum types. These drum types included drums lids with and without stiffening rings. The drums were also filled with water at varying levels, up to 80% full. These results show that the fill level did not influence the frequency response of the drum lid. The drum and drum lid were modeled using Finite Element Analysis. This allowed us to investigate the effects of drum thickness and other factors on the vibration response. There was good agreement between the FEA results and experiment. It was determined that the frequency response of the drum increased as the pressure within the drum increased. The frequency increased approximately 10 Hz/psi for drum lids with a stiffening ring and 20 Hz/psi for lids without stiffening ring. FEA showed that the frequency response increased as the thickness of the drum increased. However, both experimental and FEA showed that this change was small compared to the change caused by the stiffening ring. Conclusions It has been demonstrated that the frequency of vibration of the lid on a 55 gallon drum is proportional to the pressure inside the drum. This dependence of frequency on pressure is being used to develop an instrument that will detect pressurization within drums. It was shown, however, that different type drums may require different calibrations, i.e. those with and without stiffening rings. The ultimate goal of this work is to design an instrument that can test drums for pressure in the field. A prototype has already been built. This instrument would ideally be hand held, utilizing a microphone which has certain advantages over an accelerometer. By using a microphone an inspector would save time since contact with the drum would be minimized. The inspector would simply tap the drum, the signal would be

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recorded with a microphone that was either internal to the device or attached to a lapel, the signal would be recorded, and the inspector would move on to the next drum. Another advantage is that the spectrum from the microphone signal is usually much simpler, since many of the higher modes do not radiate acoustically. Thus, the spectrum is easier to interpret with software. Work Planned We plan to investigate the repeatability of the technique by taking data on many different drum lids. The effects of corrosion on the drum lid will also be investigated. A field test/demonstration is being planned at a DOE facility. Reference 39.

Patel, H., Costley, R.D., Henderson, M., Jones, E.W., and Tomlinson, A. 1999. Drum pressure monitor. To be published in Review of Progress in Quantitative Nondestructive Evaluation, Vol. 18, ed. by D.O. Thompson and D.E. Chimenti, New York: Plenum Press.

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TASK 5

Advanced Cleanup Support: Robust Immobilization Devices

Subtask 5.1. Hybrid Plasma Induction Cold Crucible Melter Dana Miles

Introduction Russian engineers have developed several melters which are more robust than current generation furnaces, and which can produce a wide variety of waste forms ranging from borosilicate glass to crystalline ceramics (Synroc). This technology potentially could be used for the orphaned spent fuel at SRS, Idaho, and Hanford. DOE has identified disposition of these materials as an “Unmet Need.” This technology appears to be a way to address this need in an expeditious manner, while also providing the capability to produce a second generation waste form in existing facilities. As part of the Cooperative Agreement, a “hybrid” Russian melter will be installed and tested at DIAL to determine its usefulness and limitations. It is similar to the new “next generation” melter, a cold crucible design with inductive heating. This requires certain components in the glass to allow current to flow, and thus effectively heat up the glass pool. The “hybrid” melter combines the cold crucible design

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Task 5. Advanced Cleanup Support: Robust Immobilization Devices

with a plasma torch to initially break down waste components fed to the melter, negating the need for current inducing components in the glass feed. Discussions continue for obtaining the next generation melter and testing it at DIAL. Future work calls for providing an appropriate control system for each system. After installation at DIAL, each melter will be tested with simulated spent nuclear fuel to determine the feasibility of producing a vitrified product (borosilicate glass) and a crystalline product (Synroc). Processing and product properties of the waste forms will be determined. Based on the testing, a recommendation will be made regarding the value of each of these systems for this application, and future testing. The objective of this task is to determine whether the Russian melters can be used to immobilize spent nuclear fuel and selected other waste streams. Work Accomplished The Diagnostic Instrumentation and Analysis Laboratory (DIAL) at Mississippi State University has begun evaluation of a hybrid plasma induction cold crucible melter (PICCM) for its potential success in processing spent nuclear fuel and other heterogeneous, metal containing waste. The hybrid plasma induction cold crucible melter was developed at the Russian Institute of Chemical Technology in Moscow. Though originally designed for producing chemically active, high purity metals, it was brought to the United States for research in treating radioactive wastes containing metal. The PICCM combines plasma heating for the non-metal portion of the waste and inductive heating for the metallic portion. A copper, water cooled crucible is loaded with waste that upon processing contains distinct separation of metal from an upper layer of slag. Radioactive components tend to concentrate in the slag phase which can be removed through an over flow spout. The metal layer can be removed as an ingot for

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reuse or for disposal as a low level waste. A simplified schematic is shown in Figure 19. The cold crucible design nullifies the problem of selecting/creating a refractory that can withstand glass and metal environments in high temperature processing.40 The PICCM, fabricated in Russia in 1994, was received at DIAL in May 1998 after a brief installation at Georgia Tech during 1996. The potential for success in this application supplies justification for immediate short term as well as long term research opportunities for the international collaboration between the Russian developers and DIAL.

Plasma Torch Feed

Glass-Slag

Induction Heating Coils

Metal Alloy

Glass-Slag Container

Cold Wall Crucible Extracation of Casting

FIGURE 19.

Schematic of hybrid plasma induction cold crucible melter.

System Description The PICCM is comprised of a melter vessel containing a 200-mm diameter, water cooled crucible with individually isolated cooper segments. The crucible is designed with an overflow spout for removing the slag layer during processing. The overflow spout drains into a stainless steel bucket (approximate volume = 4 gal.) that is housed on

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one side of the vessel. The bucket can be easily removed through a door way on the side of the vessel by rolling it on the fold out tracks. The vessel has a side port for off gas removal. Induction heating is supplied by the water cooled copper coil wrapping the crucible. The bottom of the crucible, also water cooled, is situated on a shaft that moves up or down as directed by the DC motor/controller. The shaft/ crucible bottom combination is known as the ram. The melter vessel is sealed on top with a cone-shaped lid. The lid has a small side view port and port on top to accommodate the torch; it is equipped with a rotary feeder. The feeder is activated with another DC motor/controller. Other items include a capacitor bank with eight capacitors of which two are not used, four hydroblocks to control the delivery of water to each water cooled elements in the system, an outside coil, a draw sill, an induction power supply, a torch power supply and 70kW torch, and an operator console. The operating frequency is 2.4 kHz with a 480-V, 60-Hz source. The power limit for the melt operation is about 500 kW. Experimental Set-up The first of two technical exchanges between DIAL personnel and Russian developers followed the PICCM arrival by approximately one month. The purpose of this meeting was to draft a plan for the unit’s installation. Procurement and establishment of structural and system support equipment at the new DIAL facility filled the interim between the technical collaborations. Two Russian scientists, Dr. Vitaliy Gotovchikov and Mr. Naum Gurvitch, visited DIAL near the end of the reporting period for the second exchange (one month) to complete installation and calibration of the PICCM. Preparations began with a layout of equipment in the high bay area for accommodating the PICCM and other test units at DIAL, a combustion test stand and two plasma torches. Once the layout was

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planned, the most immediate consideration became the design and fabrication of a 20-ft x 20-ft platform to support the melter and its water cooling units, the hydroblocks. The first technical exchange resolved questions regarding the platform and optimization of space in the high bay as well as provided a detailed plan for placement/orientation of the melter vessel, power supply, capacitor bank, and hydroblocks. The platform area was reduced to 18 ft x 18 ft and a design was produced to utilize donated metal grating. Use of this grating simplified the installation and reduced the labor required for the water cooling connections made during the second exchange. Placing the equipment on the platform prior to the developers’ arrival allowed the necessary electricity supply, water supply, emergency water supply, return water, and off gas piping installations to begin. The equipment location and proximity to other objects were surveyed for potential hazards; safeguards such as hand rails, warning signs, and hard-hat only areas for the platform area and underneath were constructed as needed. Assembly of the PICCM began with the arrival of Dr. Gotovchikov and Mr. Gurvitch. Based on DIAL’s experience with plasma torch operation, a decision was made to set-up the unit as an induction cold crucible melter (ICCM) and to explore top heating on an asneeded basis. Using an ideal waste composition in the start-up phase also diminishes the need for top heat. As a safety precaution, the hydroblocks had been anchored to the platform grating. The melter vessel sat on a 5/8-in. steel plate. Once the exact position was fixed, a hole was cut in the plate beneath the crucible for the adjustable height bottom (the ram) and water cooling lines to enter. Then the vessel was bolted to the steel plate. The vessel was connected to the capacitor bank through the outer coil, draw sill, and power supply cables to the inner coil. With these items in place, the individual water lines, 56 in all, to and from the hydroblocks were run. Other completed installations included the electricity supply, water supply, return water, emergency water, and off gas piping.

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The next phase of the ICCM installation was accomplished with point by point evaluations of the power supply and water supply systems. Leak checks with emergency water flow (a lower flow rate) were carried out first, then with the main water and return water pumps activated. The operating water flow rate is approximately 160 gpm. The power supply was inspected for any damage or loose connections resulting from shipping using a storage oscilloscope and a megger. Control of the power supply would be carried out at the unit because the torch and the operator console were eliminated from the start-up assembly. The operator at the vessel would direct the power settings from the platform area. A steel cylinder, 190-mm diameter with an 8-mm wall thickness, was loaded into the crucible for a series of quick burst calibrations. The ICCM was ready to begin processing. Results and Discussion The DIAL facility accomplished a tremendous amount of work to get the Russian melter installed in a one-month period. Every request for field fitting to enhance the assembly effort was quickly carried out. For both the electricity and water, the work entailed getting the supply to the melter area as well as making the necessary connections. It was, in general, a “from scratch” effort. Early on we experienced a bit of the “new building” syndrome; the main water tank could not be set until a concrete pad was poured, the water supply lines could not be run until the university physical plant gave permission for going through the high bay wall, a main breaker was set at half power which shutdown all power when the water system and power supply were checked simultaneously, and there was a short in the fluid cooler starting panel. Each difficulty was quickly worked through. The most important lesson learned involved the air-cooled heat exchanger; summer-like weather using this exchanger does not cool process water to mimic expected Russian water temperatures. Early morning runs could solve this problem combined with the fact that most melter tests do not exceed 30 minutes.

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Apart from the structural installation, several discussions and mock training sessions were held. Start-up, operating, and shutdown procedures were documented enabling DIAL personnel to operate the system once the exchange ended. In addition to trouble shooting guidelines, these procedures include the range of parameters for normal operation and upset conditions. Diagrams of the hydroblocks’ water cooling service to the various locations in the PICCM were produced as a quick reference for trouble shooting. Almost all communications took place through an interpreter. Work Planned •Perform melts with different combinations of metal and

borosilicate glass melts to condition the melter and train operating personnel. •Replace/repair items identified during the second exchange (i.e., hoses on capacitor bank, cooling mechanism for Cu bus bars, etc.) •Develop operating procedures/historical data for various materials (i.e., heterogeneous debris, simulated spent nuclear fuel). •Obtain thermal imaging of tests; measure particulate (amount and identity) in the off gas. •Upgrade electric, control, and water cooling systems by supplying modern instrumentation and data collection. •Investigate barriers to continuous operation; develop physical components and operating procedures to circumvent those barriers. References 40.

Schumacher, R. F., et al. 1995. High-Temperature Vitrification of LowLevel Radioactive and Hazardous Wastes. Savannah River Technology Center.

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Subtask 5.2. Hollow-electrode DC Arc Furnace for Mixed-waste Treatment Carlson C. P. Pian

Introduction The hollow-electrode DC (HEDC) arc furnace is another advanced melter concept which is more robust than current-generation furnaces. This technology could be considered for use on the mixed wastes and orphaned spent fuel at the various DOE sites. The plasma arc technology may also be used to destroy pesticide and chemical weapon stockpiles. The possible advantages of the hollow-electrode arc furnace for nuclear waste remediation were discussed previously in Ref. 41. HEDC arc furnaces are used commercially in the metals industries with demonstrated service life of over many years without repairs. The furnace electrodes are simple, inexpensive, and easily maintained. The simple electrode replenishment procedure is extremely advantageous in the treatment of radioactive wastes since it does not expose maintenance personnel to possible radiation hazards. Another advantage of HEDC arc furnace is its ability to handle all forms of wastes. Waste feeds can be in solid, liquid, and/or gaseous forms. Work Accomplished A feasibility study was carried out during this reporting period to investigate the use of a hollow-electrode DC-arc furnace for the treatment of mixed wastes. This test represents the first in a series of planned tests.

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Experimental Set-up The initial feasibility test was conducted at Montec Associates in Butte, MT, using an existing plasma torch furnace. The decision to test at Montec was based on several factors. They have in place a DC power supply capable of providing the high amperage (1250 amps) necessary to evaluate the electromagnetic effects that makes the hollow-electrode arc heating concept for waste remediation unique. Moreover, Montec has a plasma test cell that is suited for these tests, which would not require major modifications. They also had the capability for mounting the arc electrode assembly and for controlling its position. NITROGEN AIR

FEEDER

FLOWMETER COOLANT IN

NC

E

DILUTION

LA

HOLLOW ELECTRODE

COOLANT OUT

PITOT MEASUREMENT

OFF GAS

THERMOCOUPLE (TYPE K) FLOW PRESSURE

FIGURE 20.

DC arc furnace at Montec Associates, Butte, MT.

The arc furnace is shown in Figures 20 and 21. The test vessel consisted of a water-cooled steel dome, which is four feet in diameter. The hollow graphite electrode, eight inches in diameter, extends into the furnace through a port at the center of the dome. The lumen (inner passage) of the electrode was four inches in diameter. The feed material was delivered directly into the lumen at a controlled feeding rate by an auger-type feeder, positioned above the electrode. This feeder,

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shown in Figure 22, had a capacity for about 100 pounds of solid feed. The electrode and the feed system was mounted on a platform above the furnace. A roof-mounted crane/pulley system was used to raise and lower this platform, which in turn adjusts the height of the electrode relative to the melt surface.

DC arc furnace at Montec Associates, Butte, MT, July 1998. FIGURE 21.

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Feeder for the hollow-electrode DC arc heater experiment, Montec Associates, Butte, MT, July 1998. FIGURE 22.

Hollow-electrode dc arc heater at Montec Associates, Butte, MT, July 1998. FIGURE 23.

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An alternate lance feed system was also used during our test. An auxiliary port on the furnace dome was used for the lance feeder (see Figure 20). The purpose of this feeder was to provide baseline data (for the conventional method of dropping the waste materials into the melt) that could be used to compare with the new method of delivering the charge directly into the plasma arc. The furnace bottom consists of several layers of refractory brick, as shown in Figure 20. A simple steel anode design was used in our initial feasibility test for cost and material availability reasons. This anode consisted of a water-cooled circular base, 12 inches in diameter. Thin steel strips (fins) were welded onto the top surface of the electrode base and used as conducting paths for the electric current. The spaces between the bricks, and between the electrode fins were filled with a refractory ramming compound. This particular anode design configuration provided adequate lifetime (over 12 hours) for the initial feasibility tests. An anode design which uses conducting refractory material that does not require water cooling will be required for longer test durations or for actual waste processing applications. Ports in the off-gas line were used for gas sampling and for pitottube velocity measurements. Gas analyzers used in our test consist of a micro fuel cell oxygen analyzer, two dual carbon dioxide/carbon monoxide nondispersive infrared analyzers (for different concentration ranges of each species), and a total hydrocarbon analyzer. During certain segments of our test, an iso-kinetic sampling train was used to determine the particle concentration in the off-gas stream. Downstream of the sampling ports, an existing scrubbing device at Montec was used to clean and quench the exhaust gas. The heat-up period for each furnace test typically lasted about three to four hours. Initially, the furnace bottom was loaded with a layer of soil (about six to ten inches deep). To initiate the arc, a pile of scrap iron was positioned above the anode to provide a current path.

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The furnace operates initially in a joule-heating mode with the graphite electrode in direct contact with the soil/iron scraps. As the soil was heated up and began to melt, the graphite electrode was raised to establish the plasma arc. During the heat-up period, additional soil was added to the furnace until a deep pool of melt is obtained. Figure 23 shows a view of the hollow electrode through the viewing port after the power was turned off. 25

1400

O2 (%)

Potatoes

CO2 (%) CO (ppm)

1200

Oak Blocks 1000

15 800

600 10

Brickettes 400

Species Concentration (ppm)

Species Concentration (molar %)

20

5 200

Brickettes Bulk Addition Through Lumen

0 12:45

12:50

12:55

13:00

Bulk Addition Through Lance 0 13:05

13:10

13:15

13:20

13:25

13:30

Time (h:m:s)

Off-gas species concentration during bulk-solid addition, Montec Associates, Butte, MT, August 1998. FIGURE 24.

A substantial amount of dust was generated by the plasma arc during the heat-up period. The interior surfaces of the furnace and exhaust pipe were coated with a thick build-up of white powder. The composition of this dust was later analyzed and found to consist largely of silicon. The dust quickly clouded the quartz view-port window and caused considerable plugging problems for the gas sampling

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probes, resulting in decreased sampling time. Dust generation ceased once a melt of sufficient depth was established within the furnace. Preliminary Results One of the advantages of the HEDC arc furnace for treating wastes is its ability to handle fines. Fine grain materials can be fed directly without prior briquetting. The arc at the tip of the cathode acts as a continuation of the electrode/feeder cylinder and directs the flow of feed into the melt. Dust particles and untreated wastes are entrained into the bath thus avoiding carryover of particulates into the off-gas treatment system. To demonstrate this attribute of HEDC arc furnace in our test, alumina powder was fed into the furnace, first through the lumen, and later through the lance at the same feed rate, in order to determine if there was any difference in the off-gas dust loading between the two feeding methods. Gas samples were collected with an EPA Method 5 sampling train to determine the off-gas particle concentrations. Due to the limited test times, only three samples were collected: two samples during the period when alumina powder was fed through the lumen, and one during the period when feeding was through the lance. Analysis of the data indicated that particle concentration in the off gas decreased with increasing furnace operating time, and that the collected powder was mostly silicon. This appears to be an artifact of the initial period of silica dust generation and suggests that we might have initiated the alumina injection test before an adequate melt was established. As mentioned previously, dust generation from arc vaporization of the soil can be a problem prior to achieving a sizable melt in the furnace. Another advantage of the HEDC arc furnace for treating wastes is its ability to deliver the charge directly into the arc, resulting in very efficient arc heat transfer to the charge material. Also, when the feed materials are funneled through the hollow electrode, the cathode arc acts like a pump, pushing the materials downward and ejecting them

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towards the anode and into the melt. This acceleration force arises from the Maecker effect.42,43 To evaluate these attributes of the HEDC arc in our test, we compared the thermal treatment of bulk wastes using the HEDC arc feeder with that using a lance feeder. Three different forms of bulk wastes were tested: whole potatoes, blocks of wood (oak), and “heterogeneous debris” briquettes. The potatoes were about 1.5 to 2 inches in diameter. The oak blocks were about 1.5 inch squares. The briquettes were “pillow-shaped,” and have dimensions of about 2” x 1.2” x 0.75”. The ingredients of the briquettes were a mixture of approximately equal parts of PVC granules, pecan shell fines, glass beads, iron powder, Perlite, and alumina powder. A small amount of starch was used as binder material. The bulk-solid addition tests were carried out twice, once with the furnace view port opened for video taping and once with the port sealed for off-gas analysis. The visual observations portion of the test clearly showed that objects fed through the lumen were accelerated by the Maecker effect and thrusted into the melt. In some cases the objects appeared to have been shattered after they entered the melt. In other cases, the objects remained intact and were burned up at the arc/ melt interface. When the bulk solids were dropped through the lance, most of them came to rest on the crusty slag layer above the melt, where they were heated from below and slowly burned up. In few instances, the objects broke the slag crust and floated on the surface of the melt. The off-gas analysis also indicated more efficient thermal treatment of the bulk-solid wastes fed through the HEDC arc. Figure 24 shows the time variation of off-gas species concentrations during the bulk-solid addition portion of the test. Bulk addition through the lumen occurred between 12:53 and 13:03; and through the lance feeder between 13:08 and 13:26. Spikes in CO and/or CO2 concentrations and dips in O2 concentrations indicate times when objects were introduced into the furnace. Generally a group of five to seven objects were introduced at a time. The durations of the concentration spikes

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(or dips) suggest that objects fed through the lance took about five times longer to process than when they were fed through the lumen. The low CO concentration and high O2 levels measured prior to 12:55 may have been caused by an opened furnace port.

Dissolution of the refractory bricks. Hollow-electrode are furnace tests, Butte, MT, August 1998. FIGURE 25.

This test was terminated after about 13 hours of operation, due to a containment failure in the brick bottom. At the time of the failure, preparations were underway to initiate a test segment to evaluate HEDC arc furnace’s ability to thermally treat soil contaminated with diesel fuel. The failure of the brick containment was due to dissolution of the refractory bricks by the high temperature melt. Figure 25 shows a cross-sectional view of the damaged bricks. Lessons learned from our HEDC arc furnace test are summarized in Table 7. The test data indicate that treatment of bulk-solid wastes can be carried out much more efficiently in the HEDC arc furnace than in the conventional DC-arc or plasma-torch furnaces.

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TABLE 7. Lessons

learned (preliminary).

•Arc characteristic and stability are strong function of elec-

trode polarity. •Hollow cathode results in more stable arc. •Hollow anode results in simpler bottom electrode design. •Need to design furnace bottom (anode) without the necessity for water cooling. •Need to analyze acid/base characteristics of melt and refractory bricks and address their compatibility. •Overheating of melt can be a problem in shallow melt pools and during heat-up periods - leading to dust generation. •Limited data suggesting feeding through lumen can result in faster and more complete thermal treatment of bulk wastes. Work Planned Future tests are planned to accomplish the following: •Complete unfinished portion of test plan: diesel fuel laden

soil and Method 29 off-gas sampling. •Anode redesign without water cooling. •Redo alumina dust segment of experiment with soil/alumina mixture. •Determine effect of submerged electrode (dipped into melt) on dust generation and melt heating. •Characterize off-gas as a function of melt chemistry. •Quantify factors affecting off-gas dust loading. Pool size of melt, melt chemistry, arc power, and soil feed rate can all affect dust loading in exhaust.

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•Quantify Maecker effect. Six-inch diameter lumen, vary

magnitude of arc current, video/laser imaging of particles flowing through arc. •Measure temperature of melt. References 41.

Plodinec, M.J., et al. 1998. Application of Modern Diagnostic Methods to Environmental Improvement. Final Report to U.S. Department of Energy, Contract No. DE-FG02-93CH-10575, Reporting period July 30, 1993 March 31, 1998. Mississippi State University: Diagnostic Instrumentation and Analysis Laboratory.

42.

Maecker, H. 1995. Plasma Streaming in Arcs Due to Self-Magnetic Compression. Z. fur Physik (in German) 141:198-216.

43.

Pfender, E., et al. 1987. Plasma Technology in Metallurgical Processing, J. Feinman, Editor, Iron and Steel Society, Inc., Ch. 4, pp. 32-33.

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