Integrity assessment considering unified constraint for reactor pressure vessel under pressurized thermal shock

Abstract

The integrity assessment methodology based on a new unified constraint parameter Ad* and the Master Curve has been investigated for a typical Chinese reactor pressure vessel (RPV) containing axial surface cracks subjected to pressurized thermal shock (PTS). The thermal–mechanical analysis was carried out under two different PTS transients using finite element method. The integrity assessment has been conducted by comparing the KJ-T curve and KJc-T curve (KJ is elastic–plastic stress integrity, KJc is fracture toughness and T is the crack-tip temperature), and the safety margin was quantitatively analyzed. The results show that the Ad* value does not change with temperature and loads (thermal load and internal pressure load) during PTS due to its load and material independences, and which facilitates the constraint analysis for a RPV under PTS. For smaller size surface cracks usually occurring in the RPV, the integrity assessment considering unified constraint under PTS can reduce excessive conservatism of traditional assessment method. The safety margin of integrity assessment is mainly influenced by constraint levels, PTS transients and fracture toughness of irradiation materials, and methods for increasing safety margin are discussed.