Concentric Annular Thermosyphon for Passive Cooling System of Spent Fuel Pool

Abstract

Since the Fukushima accident, safety issues about spent fuel pools(SFP) have been raised. Current cooling systems of SFP are vulnerable to an accident such as a blackout. Hence, lots of attempts to develop passive cooling systems of SFP have been made, and heat pipes can be used effectively to develop a new passive cooling system of SFP. An annular thermosyphon is similar to a conventional heat pipe except that the cross section of the pipe is annular instead of circular. The heat transfer area and heat transfer coefficient of the evaporator section of the annular thermosyphon can be increased significantly without increasing the outer diameter of a pipe. In this study, a new passive cooling system of SFP with the annular thermosyphon was designed, and experiments were conducted to optimize the thermal performance of the thermosyphon. Using R-134a as working fluid, we measured the temperatures of the evaporator section and the condenser section of the heat pipe by changing the charging ratio and the air velocity. And We measured heat transfer rate of heat pipe at the emergency cases. The result of experiments shows that the optimal charging ratio is 65%, and that heat transfer rate increases as air velocity and water temperature increases. The narrower clearance, the better thermal performance.