Feasibility Study of Technology for Pu Solution Monitoring including FP -Overview and Research Plan-

The International Atomic Energy Agency (IAEA) has proposed in its long-term research and development (R&D) plan, development of a real-time measurement technology to monitor and verify nuclear material movement continuously as part of an advanced approach to effectively and efficiently conduct safeguards for reprocessing facilities. The solution monitoring and measurement system (SMMS) being installed for safeguards in the reprocessing plant only monitors density and level continuously. Thus, direct Pu monitoring in the solution by SMMS is impossible. At JAEA, we designed and developed nondestructive assay (NDA) system (neutron coincidence method) to monitor Pu directly in solutions after purification and without fission products (FP). It has been confirmed that a total measurement uncertainty of less than 6% could be achieved, which could be applied as a partial defect verification. In the reprocessing plant, since solutions containing both Pu and FP exist, a new detector development project to monitor Pu with FP is being carried out from 2015 to 2017. This project is mainly conducted in the High Active Liquid Waste Storage (HALWS) in Tokai Reprocessing Plant (TRP). First, the design information of HALWS and radiation (type and intensity of radiation) were investigated to develop a calculation model using Monte Carlo N-Particle Transport Code (MCNP). Then, gamma rays and neutrons are continuously measured out of / into the concrete cell, where the High Active Liquid Waste (HALW) is located, to study placement of the detector and the radiation characteristics. Using these results, a computer model HALWS will be developed and the MCNP calculation will be performed. Based on the simulation analysis results and preliminary measurement results at the cell walls’ interior and exterior, candidate technologies will be considered. Some test detectors will be fabricated and checked for measurement function, then the conceptual design will be developed using the selected demonstration detector(s) based on the test results. In this paper, an overview of the technology development, simulation results of preliminary evaluation of the characteristics of radiation emitted from the HALW tank at TRP, and the future research plan are presented.