Characterization of a Proof-of-Concept Imager to Safeguard Spent Nuclear Fuel Using Passive Fast Neutron Emission Tomography

A primary part of nuclear nonproliferation and nuclear security principles involves verification of spent fuel to ensure no material diversion has occurred. As a result, various verification technologies have been developed to detect when irradiated fuel pins have gone outside of regulatory control. One proposed method of spent nuclear fuel verification includes using a fast neutron emission tomography system for spent nuclear fuel. This system would allow for imaging of individual fuel pins and quantifications of neutron source strength. A proof-of concept fast neutron emission tomography system for verification of spent nuclear fuel was constructed at ORNL. An analytic neutron response model used in MLEM reconstructions was created based on the system’s geometry and results from MCNP simulations. In order to ensure accurate reconstructions of spent fuel, a series of measurements were performed to characterize the as-built imager. Results from this data were incorporated into the analytic neutron response model to match the analytic responses to the real response of the system. Characterization measurements were made to improve neutron detector efficiency values, collimator penetration of neutrons, and collimator slit scattering values. Using the data collected, these values were incorporated into the analytic response model and new reconstructions of mock fuel pins were created.