A special finite element for leak-before-break analysis

Leak-before-Break is increasingly being used as part of safety justifications, particularly within the nuclear industry. In order to make a Leak-before-Break case for a pressurised component, it is necessary to determine leak rates through cracks under the operating load conditions. The R6 assessment procedure provides equations to calculate leak rates from a known crack opening area. Leak rates evaluated from this calculational route, however, can be subject to safety factors being applied due to various uncertainties. As such there is a strong motivation to better understand the factors affecting leak rates through cracks in pipes, so that there is less conservatism in the leak rate estimation. To perform the investigations into these factors, a special finite element has been developed. This element uses the extended finite element method to model cracks with boundary conditions on the faces due to the leaking fluid. Previous work has shown that leak rates through a crack are affected by closure of the crack, which is due to convective heat transfer from the leaking fluid to the crack faces. Therefore the new 2-D element is used to investigate this and it shows the effect of heat transfer and pressure acting on the crack faces. The first results of leak rate evaluations, using this new element, are presented in the paper.