Brittle fracture initiation in decommissioned boiling water reactor pressure vessel head weld
Zaiqing Que, M. Lindroos, Jari Lydman, Noora Hytönen, Sebastian Lindqvist, Pål Efsing, Pekka Nevasmaa, Pentti Arffman
Abstract
The brittle fracture initiation behavior and fracture toughness in the ductile-to-brittle transition region for a thermally-aged weld metal of a decommissioned reactor pressure vessel head (in operation at 288 °C for 23 effective full power years) and in the non-aged reference condition were investigated. The results show that brittle fracture initiated primarily from non-metallic inclusions. The correlation between fracture toughness and brittle fracture initiation type (inclusion debonding or breakage), initiator size, initiation location (as-welded or re-heated regions in the weld metal) were analysed. Despite that thermal ageing does not affect significantly the fracture toughness, it could promote the debonding as a brittle fracture primary initiation type. The influence of debonded inclusion on the evolution of cumulative damage and brittle fracture initiation was assessed using crystal plasticity modelling.