Liquid molten salt reactor has many features such as high economy, safety and on-line fuel processing. The emergency draining salt passive residual heat removal system (EDS-PRHRS) is a unique residual heat removal system design for liquid fuel molten salt reactor, in which safely export residual heat of the molten salt in the salt draining tank is the first requirement for EDS-PRHRS design.

This study aims to analyze the transient characteristics of EDS-PRHRS salt discharge tank during operation by simulation.

Firstly, the accident analysis of the passive residual heat removal system was carried out. The peak temperature of the molten salt was mainly found in the full heat discharge phase of the salt discharge tank. Then, a computational model of the molten salt coupled to the heat exchanger element was established for this stage of the discharge tank and numerical simulations were carried out by using computational fluid dynamics (CFD) analysis software Fluent. The Mixture model was used to simulate the boiling heat exchange of water in the heat exchanger element. Finally, different parameter sensitivity analysis scenarios were designed to investigate the effect on the transient.

The analysis results show that the heat exchange power of the heat exchange element gradually decreases with time, and the temperatures of the outer wall and the hot spot of molten salt have a peak with time.

By increasing the axial height of the thimble and enhancing the emissivity of the air gap layer, the temperature peak can be significantly reduced, and the peak value can be slightly reduced by delaying the salt discharge time. In addition, the triangular arrangement of can delay the local solidification time. The study results can provide some reference for EDS-PRHRS design.