Evaluation of high temperature tensile and creep properties of light waterreactor coolant piping materials for severe accident analyses

It has been pointed out that the reactor coolant system piping could fail p rior to the melthrough of the reactor pressure vessel in a high pressure se quence of pressurized water reactor severe accidents. In order to apply to the evaluation of the piping failure which influences the subsequent accide nt progression, models for the strength of piping materials at high tempera tures were examined. It was found that 0.2% proof stress and ultimate tensi le strength above 1,073K obtained from tensile tests was reproduced by a qu adratic equation of the reciprocal absolute temperature. Short-term creep r upture time and minimum creep rate at high temperatures were well correlate d by the modified Norton's Law as a function of stress and temperature, whi ch implicitly expressed the effect of the precipitation and the resolution of precipitates on the creep strength. The modified Norton's Law gave bette r results than the conventional Larson-Miller method. Relating applied stre ss vs. minimum creep rate and tensile properties vs. applied strain rate ob tained from the creep and tensile tests, a temperature range where the dyna mic recrystallization significantly occurred was evaluated.