Development of Analysis Method for Plutonium amount and Burn up by Measurement of Xenon Isotopic Ratio in Dissolver Off-gas at Reprocessing Facility

We have studied a new technique to evaluate the amount of Pu in spent fuel and burn up from the Xe isotopic ratio in off-gas at reprocessing facilities. The technique is applicable for both a new measurement method for the inspection of safeguards and burn up credit in achieving efficient criticality safety control. Six batches of dissolver off-gas (DOG) from a spent fuel dissolution process were sampled with a press pump from the main stack in the Tokai Reprocessing Plant (TRP) during BWR fuel (approx. 30 GWD/MTU) reprocessing. The Xe isotopic ratio was determined using a gas chromatograph-quadrupole mass spectrometer (GC/QMS). The amount of Pu and burn up were evaluated with NOVA, the Noble Gas Environmental Monitoring Application code, developed by the Los Alamos National Laboratory. The agreement between the declared burn up and the inferred burn up evaluated by Xe isotopic measurements and NOVA was at the 94% confidence level. We found that the Pu amount in spent fuel evaluated by our method agreed with the declared value calculated by the ORIGEN code within a range of -0.9% to 4.7%.