Preliminary analysis and design of the energy conversion system for the molten salt fast reactor

Abstract

The unique design features of the molten salt fast reactor (MSFR) should enable higher coolant temperatures than in conventional water reactors, with a significant improvement in the achievable thermodynamic performance. The use of a molten salt as both fuel and coolant, however, poses several advanced heat transfer challenges, such as the design of innovative heat exchangers and energy conversion systems. In this work, we address a preliminary but quantitative analysis of the energy conversion system for the MSFR, based on reference design data from the SAMOFAR H2020-EURATOM project. We consider three main technologies, i.e., the supercritical steam cycle, the closed helium cycle and the helium/steam combined cycle. Preliminary design results are presented for each technology, based on a simplified modelling approach. The considered cycles show promising efficiency improvements, with the best performance being proven by the supercritical steam cycle. The analysis also highlights the critical issue related to the risk of freezing of the molten salts within the secondary heat exchangers, due to the low inlet temperatures of the working fluids. Results show potential incompatibility between the freezing point of molten salts and the temperatures typical of steam cycles, while helium cycles offer the best chances of freezing avoidance. The combined cycle promises intermediate performance in terms of thermodynamic efficiency and thermal compatibility with molten salts comparable with closed helium cycles.