承压热冲击下反应堆压力容器的塑性失效分析

承压热冲击（PTS）使反应堆压力容器（RPV）的完整性面临极大的挑战，尤其是在喷嘴周围的环带区。考虑到瞬态温度处于零韧性参考温度之上，引入非线性材料性能来模拟一个真实RPV的混合温度场和应力场。应用扩展有限元法对喷嘴区中的裂纹扩展过程进行模拟，并得到了承压热冲击下的临界裂纹尺寸。结果显示，PTS初期的热应力效应显著，后期热-机械耦合作用产生的峰值应力很可能会引起结构失效。应用直接和间接耦合法得到的数值结果吻合，且后者的计算效率较高。在塑性极限承载状况下，裂纹尖端在靠近内壁的位置容易产生扩展。离内壁较远的裂纹尖端由于受热冲击影响较小，发生裂纹扩展的可能性相对较低。随着基体墙厚度的减小，容许的裂纹尺寸急剧缩小，接近临界承载状态时稳态裂纹扩展的程度明显降低。

Plastic failure analysis of a reactor pressure vessel subjected to pressurized thermal shock

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.