The influence of cooling thimble size on the heat transfer rate in a molten salt reactor residual heat removal system

A thimble-type heat transfer element is an essential part of the drain salt tank in the passive residual heat removal system (PRHRS) of a molten salt reactor (MSR). An experimental loop is designed and built with a single heat transfer element to analyze the heat transfer and flow characteristics. In this research, the influence of the size of a three-layer thimble-type heat transfer element on the heat transfer rate is analyzed. Two methods are employed to obtain the heat transfer rate, with a difference between them of approximately 5%. The gas gap width between the thimble and the bayonet has a large effect on the heat transfer rate. As the gas gap width increases from 1.0 mm to 11.0 mm, the heat transfer rate decreases from 5.2 kW to 1.6 kW. The conduction heat transfer rate accounts for a large proportion in the total heat transfer rate by contrast with the radiation heat transfer rate. (author)