[en] Since integrity is very important in Nuclear Power Plants, there have been a lot of researches and several rules are provided. But these are mostly based on the concept of the deterministic fracture mechanics and in many cases, those rules are unrealistic or conservative. Therefore, the concept of the probabilistic fracture mechanics considering the realistic failure of the structure and the quantitative failure probability is introduced in many fields. There have been many researches on the probabilistic fracture mechanics in world, but a few in Korea. The final object of our research os to develop the code years. In the first year study, we obtained the concept of the probabilistic fracture mechanics by reviewing the papers about the integrity evaluation of the nuclear pressure vessel on the base of the probabilistic fracture mechanics and selected the important random variables by comparing the effects of random variables on the failure probability using the existing code