Salt Composition Selection for Molten Salt Reactors: Required Pumping Power, Heat Exchanger Size, and Other Considerations

A consequential design parameter of all molten salt reactor (MSR) designs is the composition of the primary fuel/coolant salt. Given the wide range of proposed salt compositions, understanding the tradeoffs associated with each composition is beneficial. Correspondingly, the primary objective of this foundational study is to conduct analyses and provide information to support the selection of salt compositions for MSRs. Neutron activation and cost and supply considerations are explored, and the absorption cross section is provided for the candidate fluoride salt components. The required pumping power and physical size of a molten salt heat exchanger are examined for several candidate fluoride salt compositions. Both clean (i.e. without fissile material) coolant salts, and fuel salts are analyzed. The required pumping power and heat transfer surface area were found to differ substantially among the candidate clean salts, but not for salts with a high fraction (22% mol fraction) of UF₄.

Highlights

1. Optimization of circulation velocity considering pumping requirements for, and the physical size of, a molten salt heat exchanger.

2. Salt composition selection considerations for MSRs: parasitic absorption, cost, activation, heat transport.

3. Screening process identified Li, Na, K, Be, Zr, and F as feasible constituent components.

4. Candidate coolant salts exhibited substantial differences in thermophysical performance while the differences between uranium-bearing salts were comparatively minor.