Material Control and Accounting for Liquid-Fueled Molten Salt Reactors: Material Control and Holdup Considerations

The US Nuclear Regulatory Commission (NRC) will likely require license applicants for liquid-fueled molten salt reactors (MSRs) with circulating fuel to submit a nuclear material control and accounting (MC&A) plan or detailed MC&A program description as a part of their application. Special Nuclear Material (SNM) within circulating fuel in MSRs is in bulk form compared to item form within discrete fuel assemblies in light water reactors. MC&A plans for existing NRC-licensed bulk nuclear material handling facilities, such as fuel fabrication facilities, have relied heavily on quantitative measurements for nuclear material accounting. However, nuclear material accounting with material balance evaluations is more challenging for reactors with rapidly changing inventory from fuel transmutation and depletion, and specifically so for MSRs with circulating fuel. Additionally, many areas in MSRs are inaccessible due to high temperature and high radiation environments, making measurements challenging. Previous MSR work recommended reliance on material control around the reactor confinement, which is consistent with the MC&A approach in light water reactors. This research  expands on this previous recommendation with four key tasks: (a) identifying the locations for deploying nuclear material control elements, such as tamper safing and surveillance, at the boundaries of the high temperature and high radiation areas of MSRs to monitor special nuclear material; (b) identifying and characterizing potential areas of holdup within high temperature and high radiation areas; (c) identifying the material control elements and assessing their performance when applied to MSRs for MC&A; and (d) developing solutions to accurately quantify holdup. This paper discusses the research results for the first two tasks and the plans for future work on the remaining two tasks. Overall, this effort provides the technical assessments in support of one of the domestic safeguards objectives of the NRC: to prevent and detect theft of SNM.