A Review of Recent Studies of Nondestructive Assay Methods for Irradiated Nuclear Fuels

Implementation of safeguards against diversion of special nuclear materials from peaceful uses to weapons often requires nondestructive assay of fuel materials at various stages in the fuel cycle to obtain information on fissile material burnup, detailed fuel history, and content of ²³⁵U, ²³⁹Pu, and ²³³U. Past, current, and proposed efforts to elicit the required information have included direct gamma-ray spectrometry of fuel materials (by means of scintillation and, more recently, solid-state detectors); indirect gamma-ray spectrometry (magnetic analysis of external conversion electron spectra, Compton spectrometry by semiconductor detection pulse-height analysis); x-ray emission spectrometry; activation analysis of stable (or very long-lived) fission products; use of external monitors for neutron flux and/or fission and breeding rates; fast/slow neutron-fission counters; neutron transmission measurements; fission-neutron counting and spectrometry (prompt and delayed); photonuclear response measurements; and calorimetry. The various methods are described and compared for accuracy and precision, for the kind of information elicited, and for probable cost and portability of equipment required.