Life Management of Reactor Coolant Piping — Probabilistic Calibration of Partial Safety Factors in Flaw Acceptance Criteria: Application to Cast Duplex Stainless Steel Components

Abstract

The RSE-M Code provides rules and requirements for in-service inspection of the components of the French PWR power plant. The Code gives non mandatory guidance for analytical evaluation of flaws, comprising fracture mechanics analyses based on engineering methods, flaw acceptance criteria and codification of material characteristics. Based on a probabilistic calibration methodology, partial safety factors on the main random variables involved in flaw assessments (loading, crack size, yield strength and material toughness) are given in Appendix 5.5 of the Code for each category of operating conditions (A, C or D) and for the possible failure modes (ductile tearing or brittle fracture). These partial safety factors should be used with the material characteristics specified in Appendix 5.6 of the Code, to insure the consistency of the methodology. The criteria of the RSE-M Code have been implemented for the acceptance of generic flaws in cast duplex stainless steel elbows of the Reactor Coolant System. Statistical analyses of the mechanical properties of the base-metal have been carried out to get their characteristic values consistent with the Code criteria: • tensile properties comprising yield strength, ultimate tensile strength and non dimensional reference true stress - true strain curves taking into account thermal ageing, • value of the J-integral in the ductile regime at the onset of crack extension (J0.2 after 0.2 mm of crack extension), J-Δa curves in the ductile regime taking into account thermal ageing in the hot leg conditions, • fatigue crack growth rates. The results show that the aged cast duplex stainless steel elbows satisfy the Code criteria for each category of operating conditions.