Experimental study on heat transfer performance between fluoride salt and heat pipes in the new conceptual passive residual heat removal system of molten salt reactor

In order to improve the passive safety performance of molten salt reactor, a new conceptual design of passive residual heat removal system (PRHRS) has been proposed using heat pipe technology. In this paper, an experimental system has been constructed to verify the PRHRS design of molten salt reactors. An eutectic salt mixture of 46.5 mol%LiF-11.5 mol%NaF-42 mol% KF compositions called FLiNaK is selected as working fluid. Tests on the natural convection between the fluoride salt and a vertical array of heat pipes in the drain tank have been conducted. The temperature field of fluoride salt in the tank with different heat pipe spacing is analyzed. Comparisons have been made on the heat transfer characteristics between the natural convection with a single heat pipe and the vertical array of heat pipes. In addition, the empirical correlation for the Nusselt number is obtained within the range of Rayleigh numbers from 5.7×106 to 1.31×107. A good agreement between the proposed correlation and the experimental data is obtained with the deviation of −2.9%-1.7%. This work could provide valuable experimental data and suggestions for the design and analysis of PRHRS of MSR.