Final Proposal of Environmental Fatigue Life Correction Factor (Fen) for Structural Materials in LWR Water Environment

Abstract

Low cycle fatigue life of structural materials diminishes remarkably as functions of various parameters in high temperature water simulating LWR coolant. Such reduction was estimated by the fatigue life reduction factor (Fen) and the equations to calculate Fen were developed and have undergone revision over the past ten years. The authors have endeavored to establish the method assessing fatigue damage at LWR power plants for the past 13 years in the Japanese EFT (Environmental Fatigue Tests) project under the financial support from the JNES (Japan Nuclear Safety Organization). The project terminated at the end of March in 2007. Final proposals of Fen equations were established for carbon, low-alloy, and austenitic stainless steels and nickel base alloys based on all the data obtained in the project. As the results, a small change in saturated strain rate for carbon and low-alloy steels in highly dissolved oxygen water and newly revised equations including slight change in saturated strain rate for stainless steels in BWR water as well as those for nickel base alloys were proposed. The difference between revised and previous model is essentially not large.

Effects of mixed strain rates on low cycle fatigue behaviors of austenitic stainless steels in a simulated PWR environment

“…In addition, the results of LCF test with mixed strain rate (0.24-0.024%/s) also indicate that the fatigue life in air is not dependent on strain rate. Both observations are consistent with the previous results by ANL [1][2][3][4], Japanese researchers [5][6][7], and authors [13,14]. Fig.…”

“…5 shows the fatigue life of 316LN SS tested in RT air and 310°C air with a constant strain and mixed strain rates. According to the published LCF results, the fatigue life of austenitic SSs in air is not dependent on strain rate or temperature [1][2][3][4][5][6][7]. Before the mixed strain rate tests in PWR water, we performed a few tests at a strain rate of 0.024%/s to confirm such behaviors for 316LN SS.…”

“…A significant reduction in low cycle fatigue (LCF) life of metallic materials in nuclear power plant (NPP) environments has been reported by the Argonne National Laboratory (ANL) [1][2][3] and Japanese researchers [4][5][6][7]. Such a phenomenon was named as an ''Environmental Fatigue'' and has been a significant safety concern for the NPPs.…”

“…One of possible explanations for the discrepancy between lab test results and field experience is the fact that nearly all of the environmental fatigue e-N data were obtained under simple loading histories with constant strain rate which is far from the actual loading conditions in NPPs [1][2][3][4][5]. Previously, limited amount of tests with varying strain rate and strain holding were conducted to incorporate the actual plant operation transient condition in boiling water reactor (BWR) condition [6,7]. But the effects of complex loading such as a varying strain rate and holding at tensile strain are still unknown due to the lack of relevant test data and study.…”

Evaluation Methods for Corrosion Damage of Components in Cooling Systems of Nuclear Power Plants by Coupling Analysis of Corrosion and Flow Dynamics (I)

“…Vibration magnitude and frequency are calculated with computational flow dynamics (CFD) codes for singleand two-phase flows and then the calculated results are applied to estimate the residual lifetime by using the fatigue curves approved by the American Society of Mechanical Engineers (ASME) with environmental factors to calibrate corrosion factors. 9,10) The procedures for FIV due to single-phase flow are a proven type of approach (Fig. 4).…”