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STATUS OF NUCLEAR DATA FOR ITER APPLICATIONS
Duane C Larson Oak Ridge National Laboratory P. O. Box 2008 Oak Ridge, TN 37831-6354 (615) 574-6119
Edward T. Cheng TSI Research, Inc. 225 Stevens Avenue Solana Beach, CA 92075 (619) 793-3567
Frederick M. Mann WHC P. O. Box 1970 Hanford, WA 99352 (509) 376-5728
Genn Saji ITER San Diego Co-Center 11025 N. Tony Pines Road La Jolla, CA 92037 (619) 622-5113
ABSTRACT
ITER needs, and Section VII has the summary and conclusions.
As the development of a near-term fusion reactor, such as the International Thermonuclear Experimental Reactor (ITER), enters the engineering design activity phase, one of the essential elements leading to the successful design, construction and operation of such a reactor is nuclear data. High quality nuclear data for all reactor materials relevant to ITER will be required in order to assess the nuclear performance, radiation damage, and safety and environmental aspects of all reactor components. In this paper we review the current ITER design, noting which materials and associated nuclear data are important in the various reactor components. We also review the contents of the Fusion Evaluated Nuclear Data Library (FENDL) accepted for use by ITER, and identify materials for which nuclear data improvements are required. I. INTRODUCTION Nuclear data play an important role in material choice, facility design, operation and maintenance, and ultimately, facility decommissioning. In Section II we review the reactor components of ITER, moving from the plasma region out to the magnet region. Section III describes the current materials under discussion for each of the component systems. Section IV discusses reactor design calculations which require nuclear data as input Section V describes the FENDL library chosen by ITER as their source of nuclear data, and outlines proposed areas of improvement. Section VI describes important nuclear data which requires further work to meet 1
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II. ITER COMPONENTS The ITER consists of the following reactor components, in the order of distance from the plasma: A Blanket - converts the kinetic energy carried by the 14 MeV neutrons into heat, extracts it, and breeds tritium if desired. B. Divertor - removes the ash alpha particles from the plasma. The present ITER design has a single-null divertor. C Vacuum Vessel - provides the high-vacuum environment for the plasma. As part of the vacuum vessel, a shield is attached to provide structural integrity to the vessel (and reactor), and provide additional shielding for the superconducting magnet region. D. Magnets - provide the necessary magnetic fields to confine the plasma and shape the particle flux for the divertor. The toroidal field (TF) coil in the inboard region is the most critical magnet component due to radiation damage and nuclear heating. III. REACTOR MATERIALS Two versions of ITER are under consideration; one that breeds tritium in the blanket, and one that does not. The reactor materials presently considered for ITER are: A. Blanket - a shielding blanket with no tritium breeding is of high design priority. The
blanket is made of SS316 and cooled by water. The first wall in this blanket includes thin layers of beryllium as the limiter, and copper as a high heat flux material to withstand plasma disruption. Divertor materials are similar to those of the blanket. The breeding blanket design uses a vanadium alloy as the structural material and includes tritium breeding with liquid lithium as the breeding material. A significant quantity of beryllium is used as a neutron multiplier as well as heat conduction material. The divertor coolant and structure could be materials other than vanadium alloy and liquid lithium. The materials considered for the ITER blankets and associated devices are: High priority - SS316 (Fe, Cr, and Ni) and water (H and O), beryllium and copper (minor) Normal priority - Vanadium alloy (V, Ti and Cr), lithium, and beryllium B. Vacuum vessel - A high-strength nickel based alloy, Inconel, is to be used as the structural material. A SS316 pebble-bed shield is constructed between two Inconel plates to form the vacuum vessel component The vessel is cooled by ordinary water. The materials considered for the vacuum vessel are: Inconel (Ni, Cr, and Fe), SS316 (Fe, Cr, and Ni), and water (H and O). C Magnets - The TF coils consist of copper conductor, Nb3Sn and NbTi superconductor, SS304 and Inconel908 structural alloys, and insulating material. The materials considered are: Cu, Nb3Sn, NbTi, SS304 (Fe, Cr and Ni), Inconel908 (Ni, Cr and Fe), and organic insulators (H, C and O mainly). IV. NUCLEAR DATA NEEDS The nuclear data needed are those for the following functions. A. Flux attenuation - Flux attenuation occurs as the 14 MeV neutrons pass through the blanket and shield/vacuum vessel to the magnet region. The attenuation must be known to determine breeding, heating, and radiation damage in these
components. The neutron spectrum covers the energy range from 14 MeV to thermal. B. Tritium breeding - For the breeding blanket, tritium production reactions from lithium isotopes and neutron multiplication from the beryllium (n,2n) reaction are important, in addition to the neutron attenuation reactions in the blanket C Radiation damage - Atomic displacement per atom estimates, and helium and hydrogen production data are very important at the maximum flux locations in the blanket, vacuum vessel and magnet components. For the magnet component, the radiation dose to the insulator and fast neutron fluence at the superconductor are also crucial. The materials subject to investigation are (a) blanket - Be, Cu, and SS for the shielding blanket, and vanadium alloy and Be for the breeding blanket, (b) Inconel alloy for the vacuum vessel plate, and (c) Cu dpa, radiation dose at the insulator, and fast neutron fluence at the superconductor, Nb3Sn and NbTi, for the magnet component D. Nuclear heating - The nuclear heating rate distribution in each reactor component is very important for the design of the cooling system. The total nuclear heating rate in each component also needs to be accurately calculated in order to assess the heat removal systems. The total nuclear heating in the TF superconducting magnet, primarily the copper conductor, is an important limiting factor for normal operation. The generally large low energy (few keV to MeV) neutron flux in this region will enhance capture reactions, resulting in high energy gamma radiation which is a major source of heating. E. Activation concerns - Activation products generated by the interaction of neutronfluxeswith the various reactor materials pose serious concerns in a number of areas such as radiological hazards due to decay-heat-induced consequences, maintenance due to biological dose rate and decay heat, and waste management due to decay heat and long-lived radionuclides. The dominating activation products which require special attention are: 5
SS316 - Co58, Co58m, Co57, Ni57, Co62m, C06O (from Ni), Mn56, Mn54, Fe55 (from Fe), Cx51 (from Cr), V52 (from Cr), Mo99 (from Mo), and Nb94 (from Nb and Mo). Inconel 625 - Co58, Co58m, Co57, Ni57, Co62m, Co60 (from Ni), Cr51 (from Cr),
Mn56, Mn54, Fe55 (from Fe), V52 (from Cr), Tal82 (from Ta), Mo99 (from Mo), Nb92m (from Nb) and Nb94 (from Nb and Mo). VCrTi - V52, V49, Ti51 (from V), Sc48, Sc47, Sc46, Ca45, Ar42 (from Ti), Cr51 (from Cr), and Nb94 (from Nb and Mo impurities). A recently identified problem concerns production of the 6.13 MeV gamma ray from the 016(n,p)N16 reaction, particularly at the first wall region, where the flux of neutrons with E > 11 MeV can be large. The N16 gamma ray may impose significant additional heating to the magnet region as the cooling water passes between the TF coils. n
V. FENDL NUCLEAR DATA LIBRARY Since ITER is an international undertaking, the IAEA organized an activity to develop an international fusion nuclear data library to support the ITER design effort. Materials for which evaluations are required were obtained from the ITER project, although it is understood that such lists are subject to change as new designs are studied. FENDL development was accomplished by reviewing available evaluations from the various existing national data libraries which were offered, selecting the best one for each material, and assembling them into a library for ITER design use. This process was a breakthrough, since for the first time contents of national data libraries were made available for direct comparisons via plots. Criteria were developed to aid in the selection process, and the selections were done by evaluation experts at a series of meetings organized by the IAEA. Candidate evaluations from the BROND, EFF-1, ENDF/B-VI AND JENDL-3 libraries were considered. This effort has resulted in a set of FENDL evaluations for materials listed in Table 1, along with the source library for each evaluated material. 3
Along with the library of basic evaluated data, libraries for activation, dosimetry, decay data, incident charged-particles, and processed libraries for Monte Carlo and multigroup representations, and uncertainties, are required to meet ITER needs for nuclear data. Some of these libraries have been developed, and others are in the development stage. Table 2 lists the set of libraries which will be available as part of the FENDL system. w
In addition to the General Purpose Library, FENDL/E-1.0, which provides data for transport,
radiation damage, etc calculations described earlier, material activation is an important concern in ITER design. The FENDL/A-1.1 Activation Library covers the energy range from 0-20 MeV, and includes more than 12,000 energetically possible reactions for over 800 isotopes. It includes all nuclides with a half-life > 5 days. Many of the results in the library were generated using nuclear models, as experimental data are very limited. To validate the library, the nuclear models are benchmarked against experimental data to test their adequacy. A processed version of the activation library is a part of FENDL/A-1.1. 7
Processed libraries are required for neutronics design calculations, and two are available; a Monte-Carlo library and a multigroup library in the VTTAMIN-J 175 group structure. Both libraries are processed from FENDL-E/1.0 via NJOY. To validate the processed libraries, a series of nineteen fusion benchmarks have been identified and compiled. They cover materials of importance to s h i e l d i n g and breeding/multiplication, and are chosen for the characteristics of simple geometry and material composition. Benchmarking activities are underway, and results will be fed back to the group working on development of FENDL/E-2.0, the next version of the General Purpose library. VL REMAINING NUCLEAR DATA NEEDS AND CONCERNS As design methods improve and detailed engineering studies of ITER are initiated, nuclear data issues become more important While scoping studies required less precise nuclear data, current activities must also support safety analyses requirements and environmental concerns. Several important pieces of nuclear data have been validated and declared satisfactory during the evaluation and testing process; the tritium production from lithium and the basic chargedparticle fuel cycle reactions being the most prominent Much work has gone into the nuclear data for the structural materials, but work remains to resolve inconsistent data. Examples include the (n,a) cross sections, neutron emission between 7 and 13 MeV, and capture cross sections. As lowactivation designs are pursued, activation cross sections become important for activities ranging from maintenance to ultimate disposal. For this work, many materials must be investigated since the presence of a small amount of an impurity can cause activation limits to be exceeded. For an
operating reactor, tritium inventory is important not only for breeding but also for accountability as a special nuclear material. As new designs evolve, new materials are studied. One of these presently under consideration is vanadium, for use in the blanket Vanadium has not traditionally been a material of interest to fission reactor programs, so its nuclear data base is inadequate. Evaluation documentation requests improvements in the data bases for the total cross section, capture, (n,p), (n,2n), and neutron and photon production data. Resonance parameters also require new data. Based on information from the last FENDL meeting (November, 1993), no plans have been announced for experimental or evaluation work on vanadium, due primarily to reduction in facilities available for measurement of fusion-related nuclear data. 6
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Other examples of nuclear data which need review include gamma-ray production from the 160(n,p)16N reaction, if the flux of En > 11 MeV neutrons is large in the vicinity of the TF coils. The capture cross section and associated gammaray spectra from copper also needs review in light of the importance of this reaction for heat loading in the copper components of the superconducting magnets. Additional nuclear data needs are discussed and summarized in References 1,3,44,6. VII. SUMMARY AND CONCLUSIONS Nuclear data needs for the proposed ITER fusion reactor have been outlined in terms of the present design and reactor components. Mostly traditional materials are expected to be used to construct the device. Some of the nuclear data have low enough uncertainties to meet design criteria, however, a number of specific needs still exist in the areas of activation, neutron emission, charged-particle emission and gamma-ray production. If vanadium is selected as a blanket material, much experimental work will be required to bring the nuclear data base for vanadium up to acceptable standards. ITER has selected the FENDL set of data libraries for use in their design work, and the scope and contents of FENDL has been outlined. Meeting experimental data needs for improving nuclear data evaluations is a concern because of the loss of several excellent facilities which have produced much of the differential data currently in use, and the retirement of many measurement experts.
Research sponsored by the Office of Energy Research, Division of Nuclear Physics, U. S. Department of Energy, under contract DE-AC0584OR21400 with Martin Marietta Energy Systems, Inc. REFERENCES: 1. F. M. Mann and E. T. Cheng, "International Workshop on Nuclear Data for Fusion Reactor Technology," Paper 7A.1 at this conference. 2.
ITER Director, "Detail of the ITER Outline Design Report, The ITER Machine," ITER San Diego Joint Site Meeting Report, January 10-12,1994.
3. D. C. Larson, "Report of Working Group I: Review of General Purpose File for FENDL2," in Summary Report of IAEA Advisory Group Meeting, Vienna, Austria, IAEA Report INDC(NDS)-260, March 1992. 4. E. T. Cheng, "Review of the Nuclear Data Status and Requirements for Fusion Reactors," Proc. ML Conf. Nuclear Data For Science and Technology, Mito, Japan, p. 187, June 1988. 5. E. T. Cheng, "Activation Cross Sections for Safety and Environmental Assessment of Fusion Reactors," Proc NEANDC Specialists' Meeting on Activation Cross Sections for Fission and Fusion Energy, Argonne, IL, USA, September 1989, Report NEANDC-259 'U', OECD, Paris, 1990. 6. D. C Larson, H. Vonach and P. G. Young, "Working Group 3 - Specifying Procedures for Improving FENDL," in Summary Report of IAEA Advisory Group Meeting, JAERI, Japan, November 1993, Report to be published by IAEA. 7. F. M. Mann, D. E. Lessor and L. L. Carter, "Processing of FENDL-PA/1.1," Report WHCEP-0727, Feb. 1994, Westinghouse Hanford Co., Richland, WA 99352.
TABLE 1. LIST OF FENDL/E-1.0 EVALUATIONS MATERIAL
LIBRARY
MATERIAL
LIBRARY
H-l H-2 H-3 Li-6 Li-7 Be-9 B-10 B-ll C-Nat N-14 N-15 0-16 F-19 Na-23 Mg-Nat Al-27 Si-Nat P-31 S-Nat Cl-Nat K-Nat Ca-Nat Ti-Nat V-Nat Cr-50 Cr-52 Cr-53 Cr-54 Mn-55
ENDF/B-VL1 BROND-2 ENDF/B-VLO ENDF/B-VL1 ENDF/B-VLO ENDF/B-VL0 ENDF/B-VL1 ENDF/B-VLO ENDF/B-VL1 BROND-2 BROND-2 ENDF/B-VL0 ENDF/B-VLO JENDL-3.1 JENDL-3.1 JENDL-3.1 BROND-2 ENDF/B-VLO ENDF/B-VLO ENDF/B-VLO ENDF/B-VLO JENDL-3.1 JENDL-3.1 ENDF/B-VLO ENDF/B-VL1 ENDF/B-VL1 ENDF/B-VL1 ENDF/B-VL1 ENDF/B-VLO (JENDL-3.1) ENDF/B-VL1 ENDF/B-VL1
Fe-57 Fe-58 Co-59 Ni-58 Ni-60 Ni-61 Ni-62 Ni-64 Cu-63 Cu-65 Zr-90 Zr-91 Zr-92 Zr-94 Zr-96 Nb-93 Mo-Nat Sn-Nat Ba-134 Ba-135 Ba-136 Ba-137 Ba-138 Ta-181 W-182 W-183 W-184 W-186 Pb-206 Pb-207 Pb-208 Bi-209
ENDF/B-VI.1 ENDF/B-VL1 ENDF/B-VI.2 ENDF/B-VI.1 ENDF/B-VI.1 ENDF/B-VI.0 ENDF/B-VI.1 ENDF/B-VI.1 ENDF/B-VI.2 ENDF/B-VI.2 BROND-2 BROND-2 BROND-2 BROND-2 BROND-2 BROND-2 JENDL-3.1 BROND-2 ENDF/B-VI.0 ENDF/B-VI.0 ENDF/B-VI.0 ENDF/B-VI.0 ENDF/B-VI.0 JENDL-3.1 ENDF/B-VI.0 ENDF/B-VI.0 ENDF/B-VI.0 ENDF/B-VI.0 ENDF/B-VI.0 ENDF/B-VI.1 ENDF/B-VI.0 JENDL-3.1
Fe-54 Fe-56
TABLE 2. FENDL LIBRARIES FENDL/E-1.0 FENDL/A-1.0 FENDL/DS-1.0 FENDL/D-1.0 FENDL/C-1.0 FENDL/MC-1.0 FENDL/MG-l.C1 FENDL/U-1.0
General Purpose Evaluation Library Activation Library Dosimetry Library Decay Data Library Incident Charged-Particle Library Processed Monte Carlo Library Processed Multigroup Library Processed Uncertainty Library
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