Development of indirect Plutonium Accounting Tag (iPAT) for Safeguards Purpose of MSRs

Molten salt reactors (MSRs) have limitations in implementing safeguards used in conventional light water reactors (LWRs) due to high-temperature operation and liquid fuel use. Therefore, this paper proposes a new safeguards methodology for nuclear material accounting and diversion scenario analysis by attaching the indirect Plutonium Accounting Tag (iPAT) to the outer wall of the reactor, which can indirectly estimate plutonium production rather than direct sampling. iPAT estimates plutonium production based on the boron isotope ratio by analyzing the 10 B/ 11 B ratio, which changes through the reaction between the neutrons leaking out of the reactor and the boron in iPAT. In addition, the characteristics of iPAT, including sealing, labeling, security, and miniaturization, were designed considering applicability and effectiveness. To analyze the research results, modeling and a 1,665 day burnup simulation was completed for the Molten Salt Reactor Experiment (MSRE), using Serpent 2. In this instance, key elements of MSRs, such as fission product removal, online fuel feeding and removal, were included. In addition, the diversion scenarios of 1 Significant Quantity (1 SQ) of nuclear materials were analyzed using the 10 B/ 11 B ratio change in iPAT. The results confirmed that the 10 B/ 11 B ratio provides significant information on plutonium production and diversion scenario detection.