A Direct Nondestructive Assay for the Pu of U/TRU Ingot in Pyroprocessing Using ²⁴⁴Cm Neutron Albedo Reactivity Technique and Its Error

The transuranic (TRU) ingot is considered to be the most prominent target material of pyroprocessing in terms of safeguards since it contains almost all of the Pu of the feed spent fuel. Due to the high density, excessively high neutron emission rates, and high neutron multiplication of the U/TRU ingot, it is impractical to apply gamma-ray spectroscopy or neutron coincidence counting techniques to the quantification of the Pu content of the U/TRU ingot. Since the passive neutron albedo reactivity (PNAR) technique is known to be sensitive to the total fissile mass of target material and the uncertainty of its singles Cd ratio is independent of the accidental coincidence coming from the high neutron emission rate, the capability of the PNAR technique for the quantification of the Pu content of the U/TRU ingot has been investigated using the MCNPX code with a spent fuel library with 81 different cases of various kinds of initial enrichment, burnup, and cooling time. The MCNPX simulation results for the Cd ratio versus Pu content of the U/TRU ingot show the maximum error in the Pu mass between the linear fit and the real Pu content in the U/TRU ingot is 2.14% for 4.5 wt% initial enrichment cases. The results of this study show that the PNAR technique can be one possible method for the direct nondestructive assay for the Pu of the U/TRU ingot.