PWR's core internals have aging due to IASCC (Irradiation Assisted Stress Corrosion Cracking). Using IASCC data and the results of an inspection of an actual plant's baffle former bolts, we have devised a formula for predicting IASCC. We have also applied this method to barrel former bolts and core barrel which have aging of IASCC. We divided these test objects into several groups based on a number of similar structure in order to conduct inspections efficiently. Our findings show that that at the fastest, baffle former bolts should be inspected by about 250,000 hours (30 years) after a plant begins operation. Barrel former bolts develop IASCC at a slower rate, and there is little possibility of the core barrels being affected by IASCC..
