Lineal elastic fracture mechanics analysis applied for the evaluation of the structural integrity of a boiling water reactor vessel considering neutronic irradiation

This paper shows the methodology used for the evaluation of the structural integrity of a boiling water reactor (BWR-5). This evaluation is relevant, because this vessel is the coolant pressure boundary for cooling the nuclear core. In the case of this paper, an axial crack is postulated in the adjacent internal wall of a vessel to the core, which is denominated beltline. Such a crack is subjected to an internal pressure and neutron irradiation. Additionally, a crack on the inlet nozzle of the low-pressure coolant injection (LPCI) was also considered. The analysis presented in this paper, evaluated the transient conditions which take place during the start-up and shutdown of a BWR 5. The neutronic irradiation damage at the beltline was also incorporated to the analysis. It induces an embrittlement. Linear elastic fracture mechanics was applied with the requirements established at the Appendix G of ASME Code Section XI. The finite element method was used to simulate the transient conditions of the components considering the critical parameter, such as the service temperature, thickness, stresses and the material properties.