PWSCC initiation and propagation in a CRDM penetration nozzle

• Published in: Journal of mechanical science and technology Vol. 31; no. 11; pp. 5387 - 5395
• Main Authors: Kang, Seok Jun, Lee, Hoomin, Choi, Jae Boong, Kim, Moon Ki
• Format: Journal Article
• Language: English
• Published: Seoul Korean Society of Mechanical Engineers 01.11.2017; Springer Nature B.V; 대한기계학회
• Subjects: Computer simulation; Control; Crack initiation; Crack propagation; Cracking (fracturing); Damage assessment; Dynamical Systems; Empirical equations; Engineering; Finite element method; Fracture mechanics; Hoop stress; Industrial and Production Engineering; Mathematical models; Mechanical Engineering; Nozzles; Nuclear power plants; Penetration; Pressure head; Pressurized water; Residual stress; Strain rate; Stress analysis; Stress corrosion cracking; Stress propagation; Thermal stress; Vibration; Welding; 기계공학; Alloy 600; PWSCC; Nuclear power plant; CRDM penetration nozzle; XFEM
• ISSN: 1738-494X; 1976-3824
• DOI: 10.1007/s12206-017-1033-0

In the winter of 2012, several cracks were detected in the penetration nozzles of the reactor pressure vessel closure head in a pressurized water reactor in Korea. Primary water stress corrosion cracking in the CRDM penetration nozzle is usually initiated due to a combination of a particular alloy, temperature, boric acid and weld residual stress. Garud et al. suggested an empirical equation for PWSCC initiation time based on a strain rate damage model. In this study, the authors introduce a user subroutine to apply Garud’s simplified SRDM model and XFEM to simulate PWSCC crack initiation location and growth. The suggested model includes a new algorithm to track cracks and update crack domains by simulating primary water contact conditions. A finite element model of the CRDM penetration nozzle were constructed to simulate such phenomena. Only one quarter of the nozzle were modeled because of its geometrical symmetry. In order to calculate the welding residual stress, a heat transfer analysis with a model change function followed by a thermal stress analysis were performed. Adopting the calculated welding residual stress as initial condition, the PWSCC crack initiation and propagation analysis were done for over 11 cycles of normal operating conditions. After 11 cycles of normal operation, the crack depth and length were measured and compared with the reported cracks from operating nuclear power plants in Korea. A comparison of PWSCC driving force among hoop stress, von Mises stress and maximum principal stress were investigated. Also a comparison of PWSCC dimension between two different Alloy 600 material conditions (MA, CW) were investigated.