STUDY ON EFFECTS OF NON-ISOTHERMAL CONDITION AND STRAIN HOLDING ON ENVIRONMENTALLY ASSISTED FATIGUE IN PWR PRIMARY WATER ENVIRONMENT (STEP Ⅲ)

摘要

To further understand the environmentally assisted fatigue (EAF) behavior of Type 316 austenitic stainless steels (SS) in a pressurized water reactor (PWR) primary water environment, the influence of non-isothermal transient conditions was investigated using hollow, small-scale fatigue specimens. In our previous study (Step I: PVP 2016-63798), isothermal and non-isothermal EAF tests were performed. The non-isothermal transient conditions for the fatigue tests investigated transients that consisted of both in-phase and out-of-phase temperature and strain variations. The result of this test series showed longer fatigue lives than those predicted using the modified rate approach and the EAF multiplier (F_(en)) presented in the draft of NUREG/CR-6909, Revision 1. In our follow-on study (Step Ⅱ: PVP2017-66233), one extra non-isothermal test was performed and application of the Weighted Stress Intensity Factor (K) Rate (WKR) method was discussed. In the latest Step Ⅲ testing, an extra non-is othermal test with periodic beachmarking has been performed. This paper discusses, based on the completion of all EAF tests performed in Steps Ⅰ - Ⅲ of this project, the effects of non-isothermal conditions and recommendations which are made for treatment of non-isothermal conditions in EAF assessments.