Internal stress analysis of irradiated graphite cores in a gas-cooled microreactor

The structural integrity of core graphite under high-temperature irradiation conditions is crucial for the safe operation of the reactor. This paper presents a simulation of the hexagonal core graphite structure, developed using the UMAT program. Design factors, including irradiation, high temperature, dimensional strain, and creep strain, are analyzed separately through the control variable method. The results indicate a positive correlation between the magnitude of the irradiation field gradient and the resulting stress effects. Stress concentration within the temperature field is observed to occur near the inner side of the hexagonal prism. Among the four types of graphite examined, PCIB demonstrates the least stress and deformation, making it more suitable for specific applications. The selection of graphite should consider the particular service period requirements. Choosing a graphite material that exhibits minimal shrinkage and a high turnaround dose is advisable. The primary creep parameter is negligible when compared to the secondary creep parameter; selecting graphite with a larger secondary creep parameter enhances reactor safety. The findings of this study provide a solid foundation for the design of a graphite core and offer recommendations for graphite candidates in the development of microreactors in China.