Abstract：Pressurized thermal shock (PTS) will produce a great challenge on the integrity of a reactor pressure vessel (RPV), especially in the beltline region around the inlet nozzles. So it is necessary to study the influence of PTS on the ultimate bearing capacity of a reactor pressure vessel (RPV) with defects. The current analysis methods are based on the assumption of linear elasticity or small range yield, and there is little research on the crack growth behavior and the ultimate bearing capacity of the RPV structure. Considering that the transient temperatures are above the nil-ductility reference temperature, the nonlinear material properties are adopted to simulate the combined temperature field and stress field of a real RPV. By using the XFEM, the process of the crack propagation in the nozzle region is simulated, and the critical crack sizes under the PTS are obtained. The results show that the thermal stress effect is significant in the early stage of the PTS transient, and the peak stress caused by thermal-mechanical coupling is very likely to cause structural failure. The numerical results obtained by the direct coupling method are in good agreement with the results obtained by the indirect coupling method, and the calculation efficiency of the latter is higher. In the plastic limit bearing condition, the crack tip close to the inner wall is easy to expand. For the crack tip which is far from the inner wall, the possibility of crack propagation is relatively low due to the weak thermal shock effect. With the decrease of the base wall thickness, the allowable crack sizes are drastically reduced, and the extent of the steady crack propagation is obviously reduced until the ultimate bearing state is reached. This study provides an important reference for the integrity and reliability assessment of the cracked RPV in the thermo-mechanical coupling field.
2017, Vol. 38 
