Abstract
The reactor pressure vessel (RPV) is one of the most important components in a nuclear power plant which is exposed to various transients associated with high neutron fluence during operation. The neutron irradiation may cause the vessel material to become more brittle especially for the weld and plate materials in the beltline region corresponding to the reactor core. After years of operation, the structural integrity of the degraded RPV becomes crucial and needs to be evaluated to ensure the nuclear safety. This paper is to study the effects of copper and nickel content variations and non-uniform temperature distribution causing by inlet water on the fracture probability of the pressurized water reactor (PWR) pressure vessel subjected to pressurized-thermal-shock (PTS) transients. The probabilistic fracture mechanics (PFM) code, FAVOR, which was developed by the Oak Ridge National Laboratory in the United States, is employed to perform the analyses. Some PTS transients analyzed from Beaver Valley Unit 1 for establishing the USNRC’s new PTS rule are applied as the loading conditions. It is found that the content variation of copper and nickel will significantly affect the radiation embrittlement and the fracture probability of PWR pressure vessels. The results can be regarded as the risk incremental factors for comparison with the safety regulation requirements on vessel degradation as well as a reference for the operation of PWR plants in Taiwan. We also consider about the effect of non-uniform temperature distribution, plume effect, caused by cold cooling water inlet on the fracture probability of the three loop PWR pressure vessel subjected to PTS events. It is found that the plume effect will not have a significant impact on the fracture probability of the PWR under the injection of three loops cooling water at the same time consist with the IAEA-TECDOC-1627 report., However, it would increase the fracture probability even if there is only one loop failure.