Effects of base salt additives on NaCl-UCl3-PuCl3 fuel systems: Insights from CALPHAD simulations

Abstract

The overall performance of molten salt reactor (MSR) fuels is governed by their chemical composition: the actinide content regulates fuel criticality; the base salt determines the fuel melting temperature, and the solubility of chemical species that evolves during the reactor's lifetime. In this study, Calculation of Phase Diagrams (CALPHAD) simulations were performed to investigate the effects of non-unary base salts on the performance of NaCl-UCl3-PuCl3 fuel systems. We specifically focused on the fuel liquidus temperature and the fuel response to compositional changes, such as the breeding of PuCl3 and the evolution of fission products. Our calculations indicate that non-unary base salt combina-tions can effectively decrease the liquidus temperatures of the proposed fuel systems up to the eutectic actinide composition of the KCl-UCl3-PuCl3 system. Moreover, we found that the response of the fuel liq-uidus to shifts in fuel chemistry depends largely on the interactions between the base salt and actinide content. Our results imply that an appropriate modification of the base salt chemistry in the fuel can bol-ster the safety, performance, and economics of molten salt reactors.