Safety design approach for sodium-cooled fast reactor coupled to thermal energy storage system with sodium-molten salt heat exchanger improving heat transfer performance

A sodium-cooled fast reactor (SFR) can make flexibility with variable renewable energy by coupling a thermal energy storage (TES) system with molten salt. One of technical issues for the SFR coupled with TES is a heat exchanger (HX) between sodium and molten salt. In particular, a safety design approach in case of heat transfer tube failure is necessary. On that account, since 2022, a three-year project has been performed to develop a safety design approach and risk assessment of the SFR with TES, to achieve heat transfer improvement of an HX between sodium and molten salt, and to clarify chemical reaction characteristics between sodium and molten salt. This paper summarizes the three-year project outcomes. First, safety design recommendations were proposed by a failure mechanism analysis based on the available information. This study quantified the failure occurrence frequency of key components as the basis of the risk assessment. Computational fluid dynamics analysis improved the sodium-salt HX design, comparable to a sodium-sodium HX. The chemical reaction clarified a mild exothermic reaction characteristic between sodium and molten salt, which suggested the safety design approach in case of the heat transfer tube failure.