Material Accountancy and NDA approach for U-Pu Co-Denitration Area at Rokkasyo Reprocessing Plant (RRP)

The construction of commercial reprocessing plant (maximum 8tPu/y or 800tU/y) in Japan had completed. The commercial operation will be scheduled in next year. The uranium test is being performed to check plant operating function including validity of material accountancy. There are 5 MBA structures (SF storage & Head-End, Main Process (PUREX), Waste Treatment & Storage, U-Pu Co-denitration (Conversion) and MOX/UO3 Product Storage) in the RRP. In U-Pu co-denitration area, Plutonium-Uranyl nitrate solution is converted to MOX powder by means of microwave heating. The material accountancy for this area is very important and difficult, because large amount of plutonium as the bulk material will be handled. In order to establish material accountancy properly, auto data collection and NRTA analysis computer have been installed to provide timeliness declaration. In order to credible material accountancy, high-precision manometer (0.1% for input), balance (0.05% for output), plutonium inventory measurement system (PIMS; 5% for process inventory), and waste drum assay system (WDAS; 7% for waste inventory) have been also installed. These systems have monitoring function as additional measures except for WDAS. Not only their improvement, but also NRTA concept and new nuclear loss calculation method are applied. And minimizing of operator’s efforts for the inspection and provision of operation data for the verification are considered. For instance, dual C/S for MOX product storage area will be introduced to avoid re-verification of the MOX at PIV. In this area, several NDA equipments are installed to provide effective and efficient safeguards such as PIMS, WDAS and temporary canister verification system (TCVS). PIMS measures Pu quantity inside equipments in glove boxes by total neutron counting. TCVS measures Pu amount of canisters inside temporary storage by neutron coincidence counting method. WDAS measures Pu amount of waste drums by neutron multiplicity counting with matrix correction. This paper presents nuclear material accountancy procedure and function of NDA systems.