Fracture mechanical analysis of a reactor pressure vessel under thermal shock loading

Abstract

Improved knowledge of cooling conditions in nuclear power plants in the case of potential emergencies and increasing irradiation embrittlement of reactor pressure vessel materials are two reasons for the fact that the safety of plant components is under permanent observation. In a loss-of-coolant accident it is possible that the injected cooling water runs in stripes down the vessel wall. This causes high thermal stresses and high stress gradients in the wall combined with a decrease of fracture toughness of the ferritic material. Assuming a circumferential crack in this region the temperature and loadtime-dependent stress intensity factors along the crack front are to be determined and compared with the temperature and life-time-dependent material toughness for the evaluation of pressure vessel safety against unstable crack propagation. Considering a reactor pressure vessel in operation the necessary ADINA finite element analyses of (i) transient heat transfer through the wall of the vessel and (ii) the stress and strain fields for thermoelastic-plastic material behaviour are presented. The virtual crack extension method was used for the calculation of J-integral values along the crackfront, which were converted into the stress intensity factors being compared with the material toughness.