As power-production nuclear fuel cycles propagate across the globe, a new generation of measurement technologies is needed to support safeguards monitoring of fuel reprocessing facilities. Currently, the fissile masses in spent fuel assemblies are not directly measured. Quantitative passive measurements confirm computational predictions for measurable isotopes (e.g. 137Cs and 244Cm) and by extension, infer the mass of fissile isotopes. Current assay methods are only viable when a detailed fuel pedigree (e.g. initial fuel composition and reactor operating history) is available to support the underlying computations.
A direct method, independent of reactor operating history, is needed. Motivations and challenges for fissile mass measurements, particularly Pu, will be presented. The focus will be on nondestructive assay (NDA); such measurements are difficult due to the extreme environment. The fuel is often housed underwater or in large gas-filled (“dry”) canisters. To maneuver assemblies for detector placement, cranes are necessary. In addition, the fuel is hot – both from a temperature and radiological perspective.