Experimental investigation of transient behavior in sodium heat pipe system for microreactor

Abstract

Heat pipe cooled microreactors rely on passive heat removal through multiple heat pipes, and the thermal response of individual heat pipes under transient conditions is important for reactor thermal management and safety evaluation. However, experimental investigation on the transient thermal behavior of sodium heat pipe systems under representative operational and accident-related conditions remains limited. In this study, experimental investigations were conducted on a sodium heat pipe system under vertical and horizontal orientations to examine transient thermal behavior during start-up, steady-state operation, shutdown, loss of cooling, and inclination angle change scenarios. Temperature responses along the heat pipe and heater surface were measured to evaluate orientation dependent thermal characteristics. The results showed orientation-dependent differences in temperature distribution and deactivation behavior. During steady-state operation, the vertical configuration exhibited a more uniform temperature distribution in the condenser section and lower temperatures compared with the horizontal configuration. Under shutdown and loss of cooling conditions, temperature fluctuations associated with geyser boiling behavior were observed in the vertical orientation. The results provide experimental database for the transient thermal response of sodium heat pipe systems and contribute to understanding heat removal characteristics relevant to the thermal management and safety evaluation of heat pipe cooled microreactors.