Comparison of Environmental Fatigue Evaluation Methods in LWR Water

Abstract

Many studies on the environmental fatigue of structural materials in LWR (Light Water Reactor) water have been carried out over the past 30 years. Early environmental fatigue tests were mainly carried out in Japan in the 1980s, and these results were reported to the ASME in 1988. After that, O. Chopra and W. Shack of ANL (Argonne National Laboratory) also carried out similar fatigue tests and reported that their data corresponded well to Japanese data. In the US, the PVRC (Pressure Vessel Research Council) started the CLEE Committee (Cyclic Life and Environmental Effect, Chair: Sumio Yukawa) for developing the environmental fatigue evaluation method in LWR water under the request from the ASME in 1991. This committee continued for 13 years and closed in 2004 after publishing the final report as WRC (Welding Research Council) Bulletin 487. After 1990 in Japan, the EFD Project (1993–1995) and the EFT Project (1994–2006) were carried out under the collaboration of electric utilities, plant vendors and government. A large number of environmental fatigue data have been generated in these projects, and these were offered to the US through the CLEE Committee. Based on Japanese and US fatigue data, environmental fatigue evaluation methods have been established in both countries that assess the effects of some parameters on fatigue life reduction in LWR water environments. This paper introduces the history of studies on the environmental fatigue in LWR water and the contributions of Sumio Yukawa to these activities. After that, the comparison of three major methods of environmental fatigue evaluation such as PVRC, JSME and MJREG/CR-6909 are reported.

Influence of strain range on fatigue life reduction of stainless steel in PWR primary water

“…It has been shown that the fatigue life reduction is dependent on the strain rate. 1,2,29 Then, the F en value is given as the function of strain rate as shown in Equation 2. Since the crack growth acceleration is responsible for the fatigue life reduction, the degree of crack growth acceleration depends on the strain rate.…”

“…Fatigue life of stainless steels in high‐temperature coolant water of nuclear power plants is shorter than that in air . To take the reduction in fatigue life into account for component designs, the fatigue life correction factor F en , which is the parameter representing the ratio of fatigue life in air to that in the environment, has been proposed .…”

Environmental effect of PWR primary water on fatigue life of stainless steel (influence of loading rate on fatigue life reduction)

“…It has been shown that the high‐temperature coolant water of nuclear power plants degrades fatigue life 1–5 . The fatigue life reduction factor F en is quoted to take into account the reduction in fatigue life when assessing fatigue according to the fatigue assessment codes published by the Japan Society of Mechanical Engineers (JSME) 6 and the American Society of Mechanical Engineers (ASME) 7 .…”

“…The fatigue life reduction factor F en is quoted to take into account the reduction in fatigue life when assessing fatigue according to the fatigue assessment codes published by the Japan Society of Mechanical Engineers (JSME) 6 and the American Society of Mechanical Engineers (ASME) 7 . F en represents the ratio of fatigue life in air to that in water 5 . The JSME code gives F en of stainless steel for the water environment of a pressurized water reactor (PWR) as where dε / dt (unit: %/s) and T (unit: °C) denote the strain rate and temperature, respectively.…”

Thermo-Mechanical and Isothermal Low-Cycle Fatigue Behavior of Type 316L Stainless Steel in High-Temperature Water and Air

“…Time to crack initiation of austenitic stainless steels in light water reactor (LWR) environments may be significantly shorter than in air, if certain conjoint threshold conditions with regard to temperature, strain rate and strain amplitude were simultaneously satisfied. [1][2][3][4][5][6] Based on laboratory investigations, different proposals [7][8][9] were established for incorporating environmental effects into the fatigue design procedure according to Section III of the American Society of Mechanical Engineers (ASME) boiler and pressure vessel (BPV) code or even implemented in certain national codes (e.g., in Japan). The practical application of these procedures is complex and also related to some uncertainties.…”