IAEA-CN-184/57 Technical Challenge and Demonstration of Advanced Solution Monitoring and Measurement System (ASMS) A. Takaya, Y. Mukai, H. Nakamura, T. Hosoma, K. Yoshimoto Tokai Reprocessing Technology Development Center, Japan Atomic Energy Agency (JAEA) T. Tamura, T. Iwamoto Nuclear Material Management Department, Japan Nuclear Fuel Limited (JNFL)
[email protected] Abstract JNFL and JAEA have collaboratively started to develop an Advanced Solution Measurement and monitoring System (ASMS) as a part of technical challenge intended for next generation safeguards NDA equipment. After we completed feasibility study by using small detectors, the second stage of ASMS has installed into PCDF tank located in a cell, and then tested and calibrated by Pu nitrate solution experimentally. There was no experience measuring around 50kgPu inventory directly, so it was very challenging work. The conventional SMMS (Solution Monitoring and Measurement System) that is composed of precision manometers acquires density, level and temperature of solution, so that the sampling and analysis are essential to obtain the nuclear material amount in the tank. The SMMS has two weak points on verification and monitoring of the nuclear material flow and inventory; (1) Direct measurement of the inventory cannot be done, (2) Solution rework and reagent adjustment operation in actual plant will make miss-interpretation on the monitoring evaluation. The purpose of ASMS development is to establish quantitative plutonium mass measurement technique directly by NDA of high concentrated pure plutonium nitrate solution and monitoring capability for solution transfers in a process. The merits of ASMS are considered below; (1) Provide direct Pu measurement and continuous monitoring capability, (2) Eliminate sampling and analysis at IIV, (3) Reduce unmeasured inventory. The target of the measurement uncertainty of ASMS is set less than 6% (1sigma) which is equivalent to meet the detection level of the partial defect at IIV by NDA. Known-alpha coincidence counting technique is applied to the ASMS, which is similar to the NDAs for MOX powder as a principle measurement technique. Especially, three following points are key techniques to establish ASMS. (1) Pre-determination of plutonium isotopic composition because it impacts alpha and rho-zero values to obtain multiplication correction factor, (2) Establish detailed MCNP modeling for entire cell, tank and detectors to obtain an appropriate setting parameter, (3) Establish flat response profile for various solution heights. We could obtain successfully a calibration curve to derive plutonium mass from multiplication corrected doubles. The uncertainty was less than 6% with good counting statistics in the calibration of about 160gPu/L concentration solution. In addition to the quantitative viewpoint, superior monitoring capability clearly proves operation status in a tank. Though a few improvements are still remained, there is a possibility in this ASMS technology to be applied to the next generation safeguards equipment. 1. Introduction In reprocessing plant, high precision electromanometer [1] and solution monitoring system (SMMS) [2][3] are used for verification and process monitoring. Indeed this current system can measure solution volume and density with very small uncertainty (about 0.3%), but has weak points in plutonium mass determination and monitoring evaluation as mentioned above. The purpose to develop ASMS is to establish direct mass measurement technique of high concentrated plutonium nitrate solution and its monitoring capability in solution operation. As a technical challenge, JNFL and JAEA have collaboratively started to develop ASMS as the next generation safeguards NDA equipment. Prototype monitoring system ASMS-P had tested so far, but measurement uncertainty was insufficient due to low counting efficiency (about 0.1%) [4]. This paper 1
describes newly and optimally designed demonstration type monitoring system ASMS-D, its configuration, calibration results and monitoring capability.
2.Detector Designing and Installation ASMS-D is a demonstration system to measure plutonium mass using neutron coincidence known-alpha method, which is newly fabricated after the feasibility study using ASMS-P. In this monitoring system, more flat response profile for various solution heights and higher detection efficiency for singles and doubles count were required. To solve these issues, we performed MCNP–X (Monte Carlo N-Particle Transport Code) [5] calculation in this detector designing. Calculation model is shown in Figure 1 and Figure 2. We considered almost entire structure in this calculation including detector, solution tank, cadmium liner, boron containing raschig rings (homogenized in volume region) and cell concrete.
Cell concrete Neutron detector
Annular tank Raschig ring
Figure 1 MCNP model (vertical plane)
Figure 2 MCNP model (horizontal plane)
Table 1 Chemical Form Pu Concentration
Solution Characteristics for Designing Pu(NO3)4 210.3 (g/ℓ) 0.926 (Pu-238), 66.730 (Pu-239), 24.122 (Pu-240), Pu Isotopic Comp. 4.497 (Pu-241), 3.725 (Pu-242) (wt%) Am-241 Contents 6800 (ppm/Pu) Solution Density 1.44 (g/cm3) Acidity 3.85 (N) Volume Range 50.0 – 300.0 (ℓ) In order to investigate the most appropriate detector location, neutron flux distribution inside the entire cell was calculated in several neutron energy ranges. Solution characteristic used in this investigation is summarized in Table 1. The number of neutrons and energy spectrum were calculated by SOURCES-4C [6] code. Figure 3 shows the neutron flux distribution of horizontal plane at different neutron energy range. In the low neutron energy range, which is favorable for He-3 neutron counting without moderator, flux intensity is low and inadequate especially inside region of annular tank. This is due to neutron absorption by the cadmium liner attached inside the tank wall. In contrast, neutron flux is greater in higher neutron energy range inside the annular tank. Especially, for the range over 1 MeV, it is clear that the flux has an axisymmetrical distribution where the flux is lowest at the center of the tank. The flux reaches to 1000 n sec-1 cm-2 near the inside wall. Therefore, higher efficient singles and doubles counting can be expected at the location near the wall with appropriate neutron moderating condition.
[n/sec/cm 2] 1400 1200 1000 800 600 400 200 0
( E< 1.0e-7MeV)
( 1.0e+0
