Year
2019
Abstract
Pyroprocessing technology for nuclear spent fuel has been developed as one of the spent fuel management options. This novel technology produces a significant amount of special fissionable material in a unique form, blended with uranium, transuranium and rare earth elements - U/TRU/RE ingot. The mass of fissile isotopes in the ingot, especially plutonium, is of great interest for nuclear safeguards. In this regard, neutron multiplicity measurement has served as a non-destructive method to account for the mass of plutonium. In this study, neutron multiplicity and gamma-ray spectroscopy is measured and analyzed with MCNP6 to estimate the plutonium mass in the pyroprocessed ingots. Stilbene detectors are deployed for neutron detection and NaI for gamma-ray spectroscopy. A number of ingot samples were prepared with variations in initial enrichment, burn-up and cooling time with SCALE/ORIGEN-ARP. From passive neutron multiplicity counting, Cm-244 is the most dominant source of neutrons from spontaneous fission. Thus, it is difficult to determine the quantity of even-numbered plutonium isotopes only from passive method results. Therefore, the active neutron multiplicity method (with external neutron source interrogation) is used to calculate the mass of fissile (odd-numbered) plutonium isotopes. The gamma-ray spectroscopy is introduced to obtain relative abundance of plutonium isotopes. The active multiplicity method results combined with gamma-ray spectroscopy can yield the mass of even-numbered plutonium isotopes as well as verify the passive method results. The active and passive neutron multiplicity methods combined with gamma-ray spectroscopy enables more accurate and reliable assessment of plutonium quantity in the complex nuclear material such as pyroprocessed ingot.