Examination of Molten Salt Reactor Relevant Elements Using Hydrothermal Synthesis

The structural chemistry of elements relevant to the FLiBe molten salt reactor, Th, U, Np, and Zr, including Ce and Nd (as analogues for Pu and Am, respectively), have been examined using hydrothermal synthesis at 200 °C. These reactions serve to model the reaction of molten salts under hydrolysis conditions. The results show that U and Np formed LiAnF₅, while Ce formed Li₄CeF₈. The source of U also controlled the crystal quality, where UO₂ gave small crystals, while UO₃·2H₂O gave very large crystals. It is likely that Be incorporation was not observed because of the high solubility of [BeF₄]^2- in water. Zr formed a third product, Li₆BeF₄ZrF₈, which features isolated [BeF₄]^2- and [ZrF₈]^4- units bridged by Li⁺. Additionally, Li₂BeF₄ was regularly isolated. When little to no alkali metal was included in the reaction, M₃F₁₂(H₂O) was isolated for Np, U, and Ce.