Consideration of Beyond Design Basis Earthquake on the Flaw Evaluation of Pipes

This study is basically consisted of steps of methodology to evaluate the flawed piping under beyond design basis earthquake. The objective of this study is to suggest the methodology to estimate the allowable flaw size with consideration over design basis earthquake using FEM with ASME code criteria. This could be applied in various flaw and pipe circumstances. The next step should be obviously actual analysis with real pipe model and date. In the overall steps, elaborate finite element analysis to estimate of the seismic load is needed. Further study pursues the flaw evaluation for the piping in OPR 1000. Integrity of plant piping has critical importance to the safety of nuclear power plants. So there are some non-destructive examination methods for to detect the flaws, but they have to wait for reactor shutdown, around 10 years. And there is an allowable size criterion of the crack to judge the continuation operation of the plant. But in practice, many cracks have been detected whose depth is larger than the code allowable size especially in weldment of the pipes. Considering the crack growth rate in PWR operation environment, the cracks in dissimilar welds could grows unusually fast especially during earthquake. After Fukushima accident, the riskiness due to the unexpected seismic events has been well known. Design basis earthquake of the some Korean old plants is 0.2g, but in the latest stress tests for the old plants which are the follow-up measures, 0.3g seismic load is assumed to secure more high confidence of the plant. In this point of time, seismic consideration on the flaw evaluation is also needed