Development of thermal stress evaluation method and fatigue damage evaluation method for thermal stratification oscillation
栗林 大 Hiroshi KURIBAYASHI 鈴木 正昭 Masaaki SUZUKI 笠原 直人 Naoto KASAHARA
Frequency response function High cycle thermal fatigue Thermal fatigue damage Thermal stratification oscillation Thermal stress
In nuclear power plants, a lot of failure cases by high cycle thermal fatigue are reported, which is induced by temperature fluctuation of the coolant. To ensure the safety of nuclear power plants, thermal fatigue should be evaluated adequately. To evaluate thermal fatigue, frequency response functions were developed by Kasahara et al... These functions were derived theoretically to calculate thermal stress caused by thermal striping and thermal stratification oscillation, which are main causes of high cycle thermal fatigue. Recently the function for thermal stratification oscillation was proposed in the ideal condition where the thickness of stratification could be ignored. Consequently, calculated thermal stress in could be too conservative. Therefore influence of the thickness on occurrence mechanism of thermal stress was investigated by conducting finite element simulation. Based on the clarified mechanism, the frequency response function was improved for adequate evaluation of thermal stratification. By using the improved function, stress time series can be obtained, from which thermal fatigue damage was evaluated.