In liquid-fueled molten salt reactors, fuel (e.g., uranium, plutonium, or thorium salts) is dissolved within a carrier salt, which flows through the core, piping, pumps, and heat exchangers. During operation, this fuel salt is continuously changing due to irradiation (i.e., fission and transmutation), fueling, and passive and active elemental removal processes. Reactor physics tools designed and validated for predicting the isotopic change in light water reactor solid fuel have been extended to account for fueling and elemental removal processes and to track and decay isotopes that are removed from the fuel salt. Predicting fueling rates, removal rates, and waste storage burdens with these tools is critical for reactor system and fuel cycle design. In addition, changes in the elemental composition of the fuel salt drives changes in its thermophysical properties and corrosion potential. Predicting these changes provides for ensuring safe system operations and designing mitigation mechanisms to maintain acceptable fuel salt conditions. The thermophysical and chemical properties of the changing fuel salt help define the behavior of fuel salt constituent elements during a reactor event; the mobility and volatility of these elements directly impact the source term quantification included in a reactor licensing case. Leading fluoride and chloride molten salt reactor concepts target different fuel cycle outcomes, with fluoride concepts generally having a maximum burnup (e.g., fissions per initial uranium atom) similar to that of current light water reactor fuel at discharge. Leading chloride concepts target greater fuel cycle benefits that require a much higher burnup, resulting in the buildup of significantly more fission product elements within the fuel salt. The expected operating lifetime of these systems is over 7 years; ensuring the longevity and reliability of components and piping exposed to the fuel salt environment is crucial for the economic viability of the technology.

Liquid fueled molten salt reactor fuel salt composition evolution and implications for operations and performance

2019 Fall National Meeting

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