Probabilistic and non-probabilistic failure assessment curves of primary coolant pipe contained internal circumferential surface crack in pressurized water reactor nuclear power plant

Structural integrity analysis of nuclear pipe containing defects should be maintained in the nuclear power plants. Deterministic approach has been often used for integrity evaluation even though there are many uncertainties to hinder a reasonable evaluation. Based on EPRI engineering estimation method, the formulas are derived to calculate the shape factor F′ and the full plastic solution coefficient h1′ of primary coolant pipe with cracks in this paper. Considering the uncertainties in assessment parameters, the probabilistic method is introduced to establish probabilistic failure assessment curve (PFAC) according to the probabilistic model. Usually, probabilistic approach has strong dependences on data which is sensitive to the probabilistic model. In this respect, non-probabilistic method that only needs the upper and lower limits of parameters is as a promising alternative. Non-probabilistic failure assessment curve (NPFAC) is also provided based on interval method. The comparison between PFAC and NPFAC indicates that NPFAC is an appropriate methodology to conduct safety assessment with defects when data information is inadequate. A numerical example is given to show the application of probabilistic failure assessment and non-probabilistic failure assessment, the results suggest that it is effective and feasible to use non-probabilistic method for assessment.