Research into Measured and Simulated Nondestructive Assay Data to Address the Spent Fuel Assay Needs of Nuclear Repositories

The Next Generation Safeguards Initiative Spent Fuel (NGSI-SF) Project started in 2009 with the intent to integrate nondestructive assay (NDA) signals in order to improve safeguards verifi- cation capabilities. This paper researches the integration of the following: (1) spectral-resolved passive gamma [154Eu and 137Cs], (2) total neutron and (3) Passive Neutron Albedo Reactivity (PNAR) in the context of encapsulation/repository facilities. For the first two NDA techniques listed, measured and simulated results are available, while for PNAR only simulated results are currently available. The measured results are from the Central Interim Storage Facility for Spent Nuclear Fuel (Clab) in Sweden where 50 spent fuel assemblies were measured in 2014 and 2015. The PNAR instrument is one of four non-traditional, spent fuel NDA techniques to be deployed at Clab in 2016 and 2017. The in- clusion of these non-traditional instruments, capable of estimating properties such as within-assembly neutron multiplication, makes this research unique and offers promising improvements to the current safeguards toolkit. Goals of the NGSI-SF Project include: (1) verifying the initial enrichment, burnup, and cooling time of the facility declaration; (2) detecting diversion or replacement of pins, (3) esti- mating the plutonium mass. Additional project goals that are concurrent with SKB’s interests are (4) estimating the decay heat, and (5) determining the multiplication/reactivity of spent fuel assemblies. In this paper, data mining techniques are applied to integrate both simulated and measured passive gamma and total neutron signals with the simulated PNAR signals to estimate various quantities for safeguards and non-safeguards purposes.