Experimental Investigation of Heat Pipes as a Passive Cooling System for a Spent Fuel Pool: The Effects of Air Velocity and Temperature

Abstract

A passive cooling system, utilizing heat pipes and an air cooling tower, has been designed, which can serve as one of accident mitigation systems in a nuclear power plant, even in scenarios where electricity is unavailable, such as Station Black Out (SBO) accident. Particularly designed for application in a spent fuel storage pool, the system plays a crucial role in maintaining the cooling of spent fuels, effectively managing the continuous release of decay heat. The heat pipe features a unique design with condenser tubes acting as manifolds to increase the effective heat transfer area. To assess the feasibility and thermal performance of the heat pipe under accident conditions, an experimental facility was established. This facility included a water pool with a cartridge heater (heat source), a heat pipe, and an air circulation chamber (heat sink). Pressure transmitter and thermocouples were strategically placed at the evaporator and condenser sections of the heat pipe. The heat transfer performance of the heat pipe was evaluated based on the measurement results, and an analysis of the thermal characteristics inside the heat pipe was conducted as a function of air velocity and air temperature. The findings indicated a proportional relationship between air velocity and heat transfer performance, with an inverse relationship observed between air temperature and the performance. Furthermore, the temperature oscillations in both the inner fluid and on the outer surface were observed especially at the evaporator section, attributed to the differences in thermal-hydraulic characteristics between pool boiling and falling film boiling regions.