Studying the Pipeline Crack Growth in the Analysis of Nuclear Power Plant Internal Flooding and Estimating the Maximum Possible Leak Rate

Abstract

Regulations concerned with the deterministic analysis of the impact of flooding on the NPP safety stipulate the need to evaluate the degradation degree of defense-in-depth (DiD) levels. The results of this analysis serve as input data for the probabilistic safety assessment (PSA) and selection of technical solutions. To estimate the flooding zone and the list of dependent failures, it is necessary to postulate the size of a pipeline or tank leak. The leak flowrate has an essential effect on the analysis result: the flooded zone size, the list of failed equipment components, and the characteristics of protective measures. The currently effective Federal Codes and Regulations of the Russian Federation do not stipulate procedures for estimating the consequences of flooding in the framework of a deterministic approach, and the use of foreign calculation procedures (ANSI / ANS-58-2, NUREG / CR-3464) yields ambiguous results. The conservatism level of foreign approaches is evaluated taking into account the laws of fracture mechanics. To this end, the maximum allowable sizes of defects in pipelines of various standard sizes that do not lead to a guillotine rupture and limit the maximum flowrate values are estimated. The results of the comparative analysis and calculations will be applied as part of the safety justification of Russian and foreign NPP projects.