Emergent thorium fuel cycles present an array of potential new reactors, materials, and isotopic mixtures that will fall under international safeguards, likely requiring new non-destructive assay (NDA) methods. This is especially true when 233U and 235U are both present (and must be assayed) in a sample and in the presence of strong gamma emissions from 232U progeny and fission products. Existing NDA methods are likely challenged in these scenarios because of the weak gamma and neutron emissions from 233U, and the similar neutron multiplicities of 233U and 235U. In this paper, we present the design of a multi-modal system for such measurements that leverages two techniques with recent practical advancements: neutron resonance transmission analysis (NRTA) and gamma-ray spectrometry. NRTA provides isotopic information about a sample by analyzing the magnitude and energy of absorption lines in transmitted time-of-flight neutron spectra and can also estimate the linear density of isotopes present in an object. NRTA has not been evaluated or developed for thorium fuel cycle relevant safeguards, and the isotopes of interest for thorium fuel cycles have distinct neutron resonance structures accessible with NRTA. Recent experimental work at The Massachusetts Institute of Technology (MIT) shows it is feasible to perform NRTA in the 1-40 eV range with commercially available, moderated deuterium-tritium (DT) neutron sources and short flight paths (~2 m) with practical measurement times ( PNNL-SA-170555
Year
2022
Abstract