Developing the californium interrogation prompt neutron technique to measure fissile content and to detect diversion in spent nuclear fuel assemblies

²⁵²Cf Interrogation with Prompt Neutron (CIPN) detection is one of the fourteen nondestructive assay (NDA) techniques researched under the Next Generation Safeguards Initiative effort. CIPN is relatively low-cost and lightweight instrument, and it looks like a Fork detector combined with an active interrogation source. This study of CIPN evaluates its capability of measuring fissile content and detecting diversion of fuel pins in commercial spent nuclear fuel assemblies. The design and the underlying physics of the CIPN detector are described. The response of CIPN to a series of virtual spent fuel assemblies were quantified using MCNPX simulations. The net signal of CIPN is mainly due to multiplication of the Cf source neutrons; this multiplication is dependent on both the fissile content and the neutron absorbers present in spent fuel. Two novel corrections have been introduced to account for the absorption caused by neutron absorbers. With the help of empirical fitting developed in this work, the fissile content in a target spent fuel assembly can be determined from the CIPN signal. CIPN is also tested in a series of hypothesized diversion cases. Preliminary results show that CIPN can detect the replacement of at least eight fuel pins (3 percent of total mass) with depleted uranium provided the count rate of baseline case was previously measured. In short, CIPN shows promising capability for measuring fissile content.