Development of active neutron NDA techniques for nonproliferation and nuclear security (5). Delayed gamma-ray spectroscopy and inverse Monte Carlo analysis for fissile isotopic ratios

The JAEA is developing active neutron NDA techniques for future nuclear material (NM) applications using a pulsed D-T neutron source under collaboration with the JRC. These will be directed toward determining the Pu/U composition of purified NM (e.g. MOX fuel) and non-purified NM with high radioactivity (e.g. spent fuel, vitrified waste, melted fuel from reactor accidents, and next-generation fuel cycle materials). The delayed gamma-ray spectroscopy (DGS) technique being incorporated into the system has the potential to establish fissionable material nuclide ratios to relatively high precision by correlating the observed gamma rays to the unique fission product yield of each fissionable isotope. Many of the short-lived fission products generate specific, time-dependent, gamma-ray energy spectra that extend well above 3 MeV, which is a benefit when applied to the NM of interest that have high passive gamma-ray emissions below this energy. The measured data will be analyzed using an Inverse Monte Carlo (IMC) method that is well suited for highly difficult and time-limited measurements. This presentation will describe the DGS technique and the IMC analysis method, including preliminary measured data analysis results and systematic uncertainty calculation, along with how DGS will be used in conjunction with other techniques. (author)