Effect of Void in Lithium Coolant on Heat Transfer of Space Reactor Cooldown and Startup Processes

To analyze the safety characteristics of liquid metal cooled space reactor restarting in orbit, the effects of shrinkage void on both lithium coolant freezing and melting processes were investigated using a numerical scheme, which was based on a single (solid/liquid) cell approach. Results show that void formation at the wall appreciably reduces the solid-liquid interface melting velocity, and the center void has little effect on the freezing and melting processes. Meanwhile, the wall void causes a substantial rise in the wall temperature during melting process. However, in the case of Li, the maximum wall temperature is much lower than the melting temperature of PWC-11, which is used as the structure material in the space reactor system. Hence, it is concluded that a formation of hot spots is unlikely during the startup or restarting of the space reactor system.