Experimental study on transient performance of heat pipe-cooled passive residual heat removal system of a molten salt reactor

A heat pipe-cooled passive residual heat removal system (PRHRS) of a molten salt reactor (MSR) is proposed by employing high-temperature heat pipe technology. This system can significantly improve the passive safety of an MSR during abnormal transients. In the study, an experimental system is constructed to verify the feasibility of using a PRHRS in molten salt reactors. A eutectic salt mixture of 46.5 mol%LiF-42 mol%KF-11.5 mol%NaF composition, termed as FLiNaK, is selected as the working fluid because it has similar thermo-physical properties to real salt 67 mol% LiF-33 mol%BeF₂, termed as FLiBe. The transient responses of the designed PRHRS for an MSR are studied from the following two aspects. 1) The temperature distribution of molten salt in the drain tank with different heat pipe cooling schemes during transients is analyzed. 2) The effect of key parameters such as height of the air stack, number of heat pipes, initial salt temperature, and different decay power on the transient performance of the PRHRS is investigated. Experimental results indicate that the heat pipe system significantly removes the residual heat of molten salt in the drain tank, although part of the heat pipes does not operate normally. The residual heat is released in 5–10 h until the molten salt reaches its freezing point, thereby indicating the feasibility of the designed PRHRS for an MSR. The study provides valuable experimental data and suggestions for the design and analysis of a PRHRS for an MSR.