Optimization of coolant arrangement for fusion-fission hybrid reactor and analysis of ex-core nature circulation

The simulation and numerical computation with FLUENT code are conducted for the fuel zone of fusion-fission hybrid reactor. Two coolant flowing arrangement schemes, uniform flow, and proportional flow based on the gross heat of each fuel cell, are compared for optimization. The results of the numerical computation show that the heat conduction between adjacent fuel cells is weak and the heat is carried away by the coolant in the duct, and it is almost completely equal to the heat produced by corresponding fuel cell except the fuel cell 1. Then the value of heat structure of the coolant duct is the gross heat of each fuel cell that means there is no need to remodel the fuel zone with system analysis program. The fuel zone has lower maximum temperature and more even temperature distribution in the case of proportional flow compared with uniform flow, but the effect of flattening temperature is not obvious. The capacity of heat transfer of ex-core nature circulation in the imaginary LOCA is also evaluated. The results show that the reactor core will be melted within 520 s after shut-down without the nature circulation and the maximum temperature in the fuel region will be only elevated to 584.4℃ within 1000 s after shut-down if with the nature circulation. (authors)