Abstract
Fatigue is a phenomenon identified as a significant degradation mode which affects industrial facilities, in particulier the lifespan of nuclear power plants. As one of its important branches, the environmentally assisted fatigue (EAF) considers not only effects of unfavorable mechanical and thermal conditions, but also PWR primary water environment in nuclear components. This phenomenon can accelerate fatigue related structure failure for common materials in nuclear components such as austenitic stainless steels and nickel-based alloys.
Within this frame of reference, the RCC-M code formulated by AFCEN has included probationary phase rules named RPP-2 and RPP-3. EDF and CNNC/NPIC have hence established a specific collaboration on environmentally assisted fatigue to contribute to validation and improvement of these rules in the RCC-M code.
Part 1 of the paper states the context of the collaboration between EDF and CNNC/NPIC and the methods used by each side. Part 2 presents the satisfactory results of code comparison based on the AFCEN-provided benchmark case. As the third part, this paper presents the comparison based on an industrial case close to an HPR1000 nozzle under pressurized thermal shock (PTS) provided by CNNC/NPIC, where the RCC-M code is applied in a situation equivalent to the engineering practice.
By following the methodology of the Part 2, EDF and CNNC/NPIC use respectively their proper tools code_aster POST_RCCM and FAC_NPIC to calculate the cumulative fatigue usage factor with or without considering the effect of EAF following the comparison between RCC-M RPP and NUREG/CR-6909 rev.1. The comparison focuses on the technical details of transient combination method and temporal discretization of transients. Analysis concerning pressurized thermal shock type transients is also discussed.
Comparisons show some differences between the results of the two parts. Some could be attributed to the various calculation processes between EPRI Guidelines and RCC-M RPP-3. Minor differences could be attributed to engineering practices like thermal time stepping.
