Nuclear reactor pressure vessel flaw distribution development. Phase 1, NDE capability and sensitivity analyses.

摘要

The Nuclear Regulatory Commission (NRC) has addressed pressurized water reactor vessel neutron embrittlement by imposing regulations on plant operation. Power plants failing to meet the operating criteria defined by the regulations are required, among other things, to analytically demonstrate continued safe operation. The initial flaw size or distribution of initial flaw size is a key input to the required vessel integrity analyses. A fracture mechanics sensitivity study was performed to quantify the effect of the assumed flaw distribution on predicted vessel performance and to determine the critical crack size. The analysis shows that vessel performance in terms of the estimated probability of failure under a given pressurized thermal shock transient is significantly sensitive to the assumed flaw distribution. The vessel flaw distribution recommended by the NRC for the plant-specific analyses is potentially over-conservative, may not represent the condition of domestic vessels, and does not take full advantage of the more recent and reliable inspection data available. This project aims at establishing the feasibility of developing a new and more appropriate flaw distribution from recent domestic vessel inservice inspection data. 25 refs., 11 figs., 12 tabs.