Probabilistic assessment of structural integrity of reactor pressure vessel in severe loading conditions caused by various transients

Abstract
Assessment of reactor pressure vessel structural integrity is an important issue for long-term operation of nuclear power plant. In our work, the integrity of a pressure vessel structural integrity has been evaluated based on the relationship between stress intensity factor (KI) and fracture toughness (KIc) following 13 different scenarios. The changing of temperature margin and conditional probability of crack initiation in various transients are obtained to confirm the risk level in severe loading conditions including stuck open pressurizer relief valve, main steam line break and loss of coolant accident. The evaluation is performed by using probabilistic fracture mechanics analysis code PASCAL (PFM Analysis of Structural Components in Aging LWR).
The results of this analysis showed that comparing to other transients, a large break LOCA lead to the most severe pressurized thermal shock conditions, while the risk of SOV transients are strongly related to the re-pressurization in the pressurizer caused by the increase of water level due to the relief valve stuck open.
Keywords: reactor pressure vessel, structural integrity, probabilistic assessment, pressurized thermal shock.