Numerical study on thermal shock of central measuring shroud with fluid–solid thermal coupling in the “Monju” reactor

Abstract

Thermal shock threatens the safe operation of the fast reactor and damages the structural integrity of the fast reactor. The stress of central measuring shroud under thermal shock accident in the “Monju” reactor is studied in this paper. The method of fluid–solid thermal coupling is adopted to solve the temperature field by fully coupling, while the stress field by one-way coupling. By comparing the temperature field with the experimental data, it is found that the temperature field is in good agreement with the error range within 3.44%. Under thermal shock condition, the core outlet temperature decreases with time, and the stress field shows a law consistent with the temperature field. The maximum stress position is located at the junction of the lower head and the sleeve. Based on the 1/3 model, thermal shock can be divided into three stages. At the initial stage of thermal shock, in the first 5 s after the thermal shock begins, the temperature gradient of the inner and outer walls increases with time, and the stress increases with time in the first 7 s after the thermal shock begins, reaching a maximum value of 345.67 MPa in 7 s. In the middle stage of thermal shock, between 5 and 15 s, the temperature gradient of the inner and outer walls decreases with time. Between 15 and 23 s, the temperature gradient of the inner and outer walls is small. The stress decreases with time between 7 and 24 s, reaching a minimum of 144.15 MPa in 24 s. At the end of thermal shock, after 23 s, the temperature gradient of the inner and outer walls increases with time. The stress increased with time after 24 s and reached a maximum of 339.62 MPa at 60 s. The maximum deformation is 23.38 mm in 8 s. Considering that the stress value is significant, further low-cycle fatigue analysis is recommended throughout the life cycle, which is very important.