A Summary of the Use of the BIC Set to Characterize Used Nuclear Fuel Assemblies for the Purpose of Nondestructive Assay

This paper summarizes a recent journal article that examines how the burnup, initial enrichment, and cooling time—collectively called the BIC set of variables—of a used nuclear fuel assembly are necessary and sufficient quantities to characterize it for the purposes of non-destructive assay (NDA). Though this fact has been vaguely recognized for many decades, this article re-examines it from a holistic standpoint. It collects, in one place, the effects that the BIC variables have on the physics properties of the fuel assemblies, rather than just their effects on the responses of specific detectors and instruments. This collection of information then sheds light on how different NDA techniques can and, in fact, must be integrated together to determine the isotopic content and residual reactivity of used nuclear fuel assemblies. Furthermore, the limitations of the applicability of the BIC set become apparent, so that corresponding limitations in the NDA techniques that rely on the BIC set are also highlighted. Two situations in which the logic fails include the presence of partial defects in the fuel assembly and the analysis of formerly molten nuclear fuel debris.