A safeguards approach for molten salt reactors: Direct gamma-spectrometry of 233U

Abstract

Multidimensional gamma-spectrometry is a potential solution for safeguarding future thorium-fuelled molten salt reactors (MSRs). A high-sensitivity system developed at Pacific Northwest National Laboratory (PNNL), the Advanced Radionuclide Gamma spectrometer​ (ARGO), has demonstrated direct 233U assay in freshly irradiated fuel salt samples using a dual-detector configuration and the 97.1 keV gamma-emission. These measurements were made using 1.4 × 106 Bq of 233U activity (at 1.4 × 108 fissions), at relatively high dead times (10.4%), and using short count durations of ∼800 s. Other major emissions were also evaluated (42.5 keV, 54.7 keV, 146.4 keV), in additional to limited (1.96%) Compton suppression, but provided less consistent determination of the 233U activity. Accurate 233U measurement was also demonstrated using its four-coincidence gamma-emissions (42.5 keV, 54.7 keV; 42.5 keV, 278.1 keV; 146.4 keV, 174.2 keV; 146.4 keV, 219 keV). Further improvements in coincidence measurements may be achievable with improvements in the detector configuration and nuclear data. Whilst this demonstration utilized the ARGO laboratory system, a similar dual-detector configuration could be utilized for online safeguards measurements.