Investigations on Crack-Like Leaks in Piping

Abstract

Methods to demonstrate break preclusion for pressure retaining components in nuclear power plants are summarized in the newly developed German safety standard KTA 3206, especially the requirements for the leak-before-break assessment of crack-like leaks. In this context numerical and simplified calculation methods for both the leak opening area and fluid flow rates of crack-like leaks were examined and validated on selected experiments. Second topic of the paper is an accident analysis for a postulated leak in form of a through-wall crack in the pressurizer surge line (SL) of a German PWR Konvoi type. The initial size of the leak as well as the changing size depending on system pressure and temperature during the postulated leak accident was calculated with a FEM analysis model of a cooling loop. The reduction of the leak area amounts in the examined transient to ca. 25 % after 1 h and leads also to an approximately 23 % smaller leak rate. These results depend on the assumed position of the leak and on the initial leak size. Therefore, the results of accident analyses due to postulated leaks can be influenced by the change of the leak size during the course of the accident.