Scoping evaluation of trace isotopic ratios within the noble metal-phase as indicators of reactor class

ORIGEN-ARP is used to simulate nine fuel types (six reactor classes) in a scoping study investigating potential isotopic indicators contained within the noble metal phase formed in used nuclear fuel. A concurrent effort compares predictions of these noble metal phase isotopic inventories to measured values in three approved testing materials (ATMs) of various burnups ranging from 28 to 70 MWd/kgM. The noble metal phase elements (Mo-Tc-Ru-Rh-Pd-Te) are chemically unreactive and remain undissolved following dissolution as a fine black residue. This characteristic is appealing for nuclear forensics or nuclear archeology, in which information is often sought regarding fuel burnup and reactor class in order to verify past operating declarations. Intra-element isotope ratio predictions that compare favorably to the chemical measurements of the three ATMs are plotted as a function of burnup to determine the feasibility to distinguish reactor class or burnup. This evaluation of intra-elemental isotope ratios specific to the noble metal phase provides a prospect to determine reactor class from remaining, undissolved solids following reprocessing. This would be particularly valuable in assessing the source of used nuclear fuel at an undeclared reprocessing facility. Results of predicted isotope ratios are reported that show promise as indicators at low burnups (<5 MWd/kgM) and are compared to the measurements at higher burnups for the three ATMs.