High-Accuracy Measurement of Plutonium Mass by Non-Destructive Assay: An Improved Approach for the Effectiveness and Efficiency of Safeguards

The Japan Atomic Energy Agency (JAEA) has worked on highaccuracymeasurement of plutonium mass by non-destructive assayunder a joint study program with the Los Alamos NationalLaboratory (LANL) in order to improve the effectiveness and efficiencyof safeguards. As a part of this approach, we have developedthe Epithermal Neutron Multiplicity Counter (ENMC) toimprove measurement accuracy of 240Pu effective mass (g) (m240e ) andimproved the estimation accuracy of 242Pu by the existing highresolutiongamma-ray spectrometer (HRGS) to improve measurementaccuracy of 240Pu effective mass (percent) ( f240e ). Followingthese improvements, it was confirmed that the combinedENMC-HRGS could measure plutonium mass with high accuracy,providing an approximate total measurement uncertainty of0.7 percent. This value is nearly equivalent to the InternationalTarget Value of Isotope Dilution Mass Spectrometry for plutoniummass in MOX samples of 0.72 percent, which includes thesampling error of the measurement.It is expected that the combined ENMC-HRGS wouldimprove the measurement accuracy of scrap samples with lowhomogeneity and reduce the number of required destructiveanalysis samples, and this would contribute to improvement ofthe effectiveness and efficiency of safeguards.