DEVELOPMENT OF HIGH CYCLE THERMAL FATIGUE EVALUATION METHOD BASED ON TIME INTERVAL OF PEAK-TO-PEAK OF FLUID TEMPERATURE

摘要

Hot and cold fluids are mixed at the core outlet of sodium cooled fast reactors. The temperature fluctuation causes high cycle thermal fatigue in structural components. The temperature fluctuation at the core outlet region does not have always a sinusoidal waveform but a sharp edged waveform. The temperature shows intermittent and sudden decrease and recovery like a spike form. It is necessary to take into account the spiky waveform of temperature fluctuation for the construction of an evaluation method of the high cycle thermal fatigue. The conventional method uses the amplitude and cycle number of waves without reference to the frequency of temperature fluctuation. In this study, the time interval of each wave based on the rainflow method was applied to consider frequency characteristics against the conversion from fluid temperature to thermal stress in structure. The thermal stress obtained from the new method was compared to the results of FEM analysis. It was found that the consideration of frequency characteristics of waves could evaluate the fatigue damage in structure. Furthermore, the frequency characteristics of waves in this method were expressed as the unified curve independent of the velocity. Hereby the new evaluation method could evaluate the thermal fatigue in the reactor.