Safety margin predictions of reactor pressure vessel integrity assessment procedures for pressurized thermal shocks

• RPV Integrity assessment procedures are applied in two case studies. • These cases (generic Konvoi and VVER-440) reflect different designs and different LTO readiness. • The GRS PROST software is able to perform the assessment with the procedure-specific options. • The predicted safety margins differ significantly, which is related to the individual assessment options. The integrity assessment of a reactor pressure vessel in a loss of coolant scenario with pressurized thermal shock (PTS) loading of the vessel wall is a crucial part of the safety review for the long-term operation, since the embrittlement of the vessel steel due to neutron irradiation continues during the ongoing operation. The procedures for the safety demonstration in different countries select different options for this assessment, namely concerning crack postulates, weld residual stresses, fracture toughness model, and warm pre-stress model. In order to understand the impact of these differences, the deterministic procedures of eight European countries are applied to two different example cases, which are based on the Konvoi and the VVER-440 plant type but are partly fictitious and not reflecting any particular unit. The safety margin in terms of ductile–brittle transition temperature is computed for each assessment, allowing to draw conclusions regarding the impact of different options within an assessment. In addition, it is possible to identify general trends of the procedures concerning their safety margin prediction.