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.