Development Of A Nondestructive Assay Design Concept For Molten Salt Reactor Material Accountancy

Molten salt reactors (MSRs) are a popular design concept for Generation IV nuclear reactors. Some variations in MSR design concepts that have been proposed concern the fuel cycle, liquid or solid fuel, coolant salt constituents, etc. One popular MSR design approach utilizes a liquid 232Th/233U fuel cycle. The design characteristics of liquid-fueled MSRs present many unique safeguards challenges. These include the presence of new diversion pathways due to in-line fuel processing (removal of fission products, online refueling, 233Pa separation/decay), difficulties in accounting for changes in fuel composition at different locations in the fuel pathways, and complications involving in-line nondestructive assay measurements taking place in transient, corrosive, and high-neutron background environments. The objective of this design concept is the development of an in-line safeguards system for liquid-fueled MSRs by identifying possible diversion pathways and utilizing effective nondestructive assay techniques to accurately assess the movement of special nuclear material in a facility. This was accomplished using state of the art codes in MSR burnup depletion modeling to model operational parameters and radionuclide inventory of a representative liquid 232Th/233U fuel reactor. The fission product composition of the fuel following burnup has been analyzed to identify potential isotopes for nondestructive assay analysis. The gamma spectra of the resulting fission products were identified. Following the identification of the isotopes of monitoring interest, a thermal and neutronic analysis was conducted to determine the required setup for an effective detection system in the MSR environment. Various materials, detectors, and configurations will be proposed and detection of the characteristic gammas from the fuel’s fission products will be evaluated for utility in nuclear material accountancy monitoring. Accurate knowledge of the location and amount of these elements is an essential part of preventing the proliferation of nuclear material towards undeclared military or malicious security activities.