Numerical investigation of thermal stress in the fuel element of high-temperature air-cooled nuclear reactor

Abstract

The direct-cycle nuclear reactor cooled by the air can be adopted in the aircraft of near space. The operation conditions are with high temperature and heat flux which can lead to the generation of thermal stress and result in the crack of the fuel element. To confirm the effect of air parameters and heating conditions caused by nuclear reactor on the thermal stress of the new type of reactor, the numerical investigation based on the multi-physics coupling method is conducted. Firstly, the boundaries and main physical properties of the fuel element are determined. Subsequently, the coupled methods of Computational Fluid Dynamics and Computational Structural Mechanics are adopted after being validated. Afterwards, the effects of cosine heating, heat flux, inlet temperature and pressure on thermal stress of the fuel element are investigated. The results reveal that the position with maximum thermal stress is close to the position with maximum heat flux. The condition with low heat flux can be adopted to obtain the sketchy thermal stress under high heat flux conditions ranging from 221 kW/m2 to 1.013 MW/m2 before the crack of the fuel element. The effect of the inlet temperature on thermal stress can be ignored compared with the heat flux. The effect of pressure on thermal stress is limited, but higher pressure is recommended. The research can lay the basis for the design of the reactor cooled by air.