Simulated imaging of spent nuclear fuel using associated-particle-neutron-induced gamma rays

This work demonstrates the use of 14.1-MeV fast-neutron interrogation in associated particle (AP) mode for the nondestructive assay of SNF canisters. We performed Monte Carlo simulation-based studies to inspect BWR GE (Boiling Water Reactor General Electrics)-14 fuel assemblies in an MPC-68 canister and basket and reconstructed a cross-sectional view of a quarter canister. Detection of the time-correlated characteristic gamma rays emitted by neutron inelastic scattering allowed us to perform elemental imaging of selected materials, such as iron, which would reveal damages to the canister structure and other steel components of the canister. Using this method, structural damages located in the peripheral or central area of an empty canister can be imaged in a 7.7-days measurement, and in a 52-days measurement in a fully loaded canister, when using a commercial AP neutron generator with a source strength of 10⁸ n/s. Additionally, single-pin resolution can be obtained using this method when detecting the scattered gamma rays in the 50 keV–15 MeV energy range. As AP generator technology advances and higher source strengths will become available, shorter measurement times will be possible. This unique approach to inspecting the integrity on the fuel and ancillary canister structures is highly penetrating, non-destructive, material-specific, and does not require the detector to be directly in contact with the outer canister surface.