T型三通管道冷热流体混合作用下循环热疲劳评估方法OACSTPCD

With regards to T-shaped junctions commonly used for mixing hot and cold fluid in nuclear power stations,the previous studies mostly focused on the flow characteristics and temperature distribution of fluid mixture.A simplified assessment method for thermal fatigue was raised herein.The advantages and disadvantages of the JSME guideline for thermal fatigue assessment were analyzed.Furthermore,the mixing characteristics of the fluid were summarized through the laboratory tests.The tests show that temperature fluctuation strength increases with the increase of momentum ratio,the maximum normalized RMS temperature difference is 0.26;The temperature difference between hold and cold fluid has limited influence on temperature fluctuation strength,which is only 5%.Meanwhile,the tests show that there is no typical dominant frequency for the mixed fluid in the range of 0.05～2 Hz.Based on the above results,a simplified assessment method was obtained and proposed to simplify T-shaped junction as the axial symmetric pipe model,and simplify a series of sinusoidal thermal loads,the fluctuating temperature difference was defined as 75%of the nominal temperature difference.The tee junction with cracks found in the inspection of RHR system of a PWR nuclear station was analyzed.The accumulative running time of this component was evaluated to be about 726 h under the combined action of the hot and cold fluid with the temperature difference of more than 150℃,whereas the corresponding effective operation time is 450 h stipulated in the common RHR system operation guideline,so its fatigue risk can be well controlled;The fatigue life according to JSME guideline was 1 190 h,which is not conservative enough for this case;The fatigue life estimated by the method of this study was 587 h,which can better predict the fatigue life in this case,and further effectively identify thermal fatigue risk and guide operation and overhaul.