Year
2017
Abstract
The International Atomic Energy Agency (IAEA) has proposed in its long-term R&D plan, the development of technology to enable real-time flow measurement of nuclear material as a part of an advanced approach to effective and efficient safeguards for reprocessing facilities. To address this, Japan Atomic Energy Agency (JAEA) has designed and developed a neutron coincidence based nondestructive assay system to monitor Pu directly in solution after purification process that contain very little fission products (FPs). As a next step to improve the quality of further safeguards activity, a new detector to enable monitoring of Pu in solution with numerous FPs is being developed as a joint research program with U.S. DOE at the High Active Liquid Waste Storage (HALWS) in Tokai Reprocessing Plant (TRP). According to the development plan, LANL has developed a newly customized ion chamber type of gamma detector (thruster type) in order to know the actual dose rate and the distribution inside the concrete cell. This thruster can be lowered down directly to the tank through detector guides manually at different axial positions. By using the ion chamber in the thruster, JAEA successfully conducted dose rate measurements at various positions in January 2017. The High Active Liquid Waste (HALW) in the tank contains a significant amount of Pu and FPs and is located inside a thick concrete cell for shielding purposes. These measurements indicated that the dose rate next to the HALW tank was ~20 Sv/h which was very informative, not only for the safety review about degradation of material, but also for safeguards technology development. Using this data, the validity of the Monte Carlo N-Particle Transport Code (MCNP) model will be improved by comparing several dose rate measurements as a benchmark. The results will be used to develop a new prototype neutron detector as well as a gamma spectroscopy detector. Since the measured dose rate was extremely high, the data will be used to design the appropriate amount of gamma shielding for each detector type. In this paper, we report the results of dose measurements with the Ion chamber inside concrete cell storing HALW tank, comparison with MCNP simulation results and the future plans.