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

摘要

The construction of commercial reprocessing plant (maximum 8tPu/y or 800tU/y) in Japanrnhad completed. The commercial operation will be scheduled in next year. The uranium test isrnbeing performed to check plant operating function including validity of material accountancy.rnThere are 5 MBA structures (SF storage & Head-End, Main Process (PUREX), WasternTreatment & Storage, U-Pu Co-denitration (Conversion) and MOX/UO3 Product Storage) in thernRRP. In U-Pu co-denitration area, Plutonium-Uranyl nitrate solution is converted to MOXrnpowder by means of microwave heating. The material accountancy for this area is veryrnimportant and difficult, because large amount of plutonium as the bulk material will be handled.rnIn order to establish material accountancy properly, auto data collection and NRTA analysisrncomputer have been installed to provide timeliness declaration. In order to credible materialrnaccountancy, high-precision manometer (0.1% for input), balance (0.05% for output), plutoniumrninventory measurement system (PIMS; 5% for process inventory), and waste drum assay systemrn(WDAS; 7% for waste inventory) have been also installed. These systems have monitoringrnfunction as additional measures except for WDAS. Not only their improvement, but also NRTArnconcept and new nuclear loss calculation method are applied. And minimizing of operator’srnefforts for the inspection and provision of operation data for the verification are considered. Forrninstance, dual C/S for MOX product storage area will be introduced to avoid re-verification ofrnthe MOX at PIV.rnIn this area, several NDA equipments are installed to provide effective and efficientrnsafeguards such as PIMS, WDAS and temporary canister verification system (TCVS). PIMSrnmeasures Pu quantity inside equipments in glove boxes by total neutron counting. TCVSrnmeasures Pu amount of canisters inside temporary storage by neutron coincidence countingrnmethod. WDAS measures Pu amount of waste drums by neutron multiplicity counting withrnmatrix correction.rnThis paper presents nuclear material accountancy procedure and function of NDA systems.