Plutonium Signatures in Molten-Salt Reactor Off-Gas Tank and Safeguards Considerations

Abstract

Fluid-fueled molten-salt reactors (MSRs) are actively being developed by several companies, with plans to deploy them internationally. The current IAEA inspection tools are largely incompatible with the unique design features of liquid fuel MSRs (e.g., the complex fuel chemistry, circulating fuel inventory, bulk accountancy, and high radiation environment). For these reasons, safeguards for MSRs are seen as challenging and require the development of new techniques. This paper proposes one such technique through the observation of the reactor’s off-gas. Any reactor design using low-enriched uranium will build up plutonium as the fuel undergoes burnup. Plutonium has different fission product yields than uranium. Therefore, a shift in fission product production is expected with fuel evolution. The passive removal of certain gaseous fission products to the off-gas tank of an MSR provides a valuable opportunity for analysis without significant modifications to the design of the system. Uniquely, due to the gaseous nature of the isotopes, beta particle emissions are available for observation. The ratios of these fission product isotopes can, thus, be traced back to the relative amount and types of fissile isotopes in the core. This proposed technique represents an effective safeguards tool for bulk accountancy which, while avoiding being onerous, could be used in concert with other techniques to meet the IAEA’s timeliness goals for the detection of a diversion.

Cradle to grave: the importance of the fuel cycle to molten salt reactor sustainability

“…The design will dictate the waste generation. For instance, the off-gas system could be enclosed for some reactor designs or have limited throughput (Dunkle et al, 2023), but most will have a flowing cover gas that continuously removes volatile radionuclides similarly to the Molten Salt Reactor Experiment (MSRE) at Oak Ridge National Laboratory (Guymon, 1973). Online processing could include removal of insoluble materials such as graphite particles and noble metals or actinide recovery from the liquid phase.…”

On the Employment of a Chloride or Floride Salt Fuel System in Advanced Molten Salt Reactors, Part 2; Core Inventory, Fuel Burnup, and Salt Clean-Up System

“…There is a strong need for a comprehensive assessment of these parameters throughout the reactor lifetime since their evolution can significantly affect the safety margins of the reactor. Considering the importance of evaluation of the MSRs burnup and its reactor core-related parameters, various research studies have been conducted that belong to one of the following categories: all employing burnup as the main parameter; (i) burnup and core inventory calculations , (ii) burnup optimization [15,[22][23][24], (iii) salt clean-up systems [25][26][27][28][29], and, finally, (iv) waste transmutation [30][31][32][33][34].…”

Exploring the Complex Chemistry of Uranium within Molten Chloride Salts

“…Specifically, the use of ultraviolet–visible (UV–vis) absorbance and Raman spectroscopy is discussed for the characterization of uranium behavior within chloride-based melts. UV–vis and Raman are well-known techniques for characterizing actinides and lanthanides in a wide range of chemical systems. ,− Furthermore, the integration of these techniques into the harsh molten salt environment has been well demonstrated on the small scale. ,− However, this work aims to explore the poorly understood realm of U behavior under complex conditions. Particularly, in chloride-based salts without active redox control, the dynamic speciation and redox behavior of U is unknown.…”

“…Molten salt reactors (MSRs) are an example of this . Notably, these reactors may also have the option of online processing, allowing for internal recycling of fuel and possibly harvesting of critical materials. − …”