Study On Analysis Method Of Thermal Stratification Effect Of Surge Line Of The Pressurizer Under Ocean Condition

The surge line of pressurizer is an important pipe connecting the hot section of the main pipe of PWR coolant system with the pressurizer.It is also an important part of the second safety barrier of nuclear power plant to prevent the leakage of radioactive materials,and belongs to the nuclear safety class I pipeline.The surge line contains high-temperature and high-pressure coolant.During operation,it not only bears internal pressure,self weight,thermal expansion,earthquake and other loads,but also bears thermal stress caused by thermal stratification under some operating conditions.It is an important content in reactor design to evaluate the stress characteristics and fatigue performance of the surge line considering thermal stratification effect.In this paper,the unidirectional fluid structure coupling analysis technology is used to simulate the thermal stratification in the surge line with or without considering the influence of typical ocean conditions.On this basis,the influence of typical ocean conditions on the thermal stratification and stress fatigue life in the surge line is analyzed.In this paper,firstly,the surge line and the internal fluid region are modeled,and a group of typical outsurge operation conditions are selected to simulate and analyze the thermal stratification phenomenon of the surge line under the outsurge condition.In order to study the effects of the typical ocean conditions,rolling motion and different positions of the rolling axis on the thermal stratification in the surge line,two rolling directions,rolling and yawing,are considered.Using the unidirectional fluid structure coupling analysis technology,the results of flow numerical simulation are taken as the load of static analysis.After determining the calculation grid and constraint scheme,the stress of typical nodes of surge line is calculated.According to the requirements of relevant sections of ASME code,the primary and secondary stress limit values of three kinds of outsurge conditions are evaluated,and the cumulative usage factors under different combinations of conditions are calculated.The influence of thermal stratification effect and rolling motion on the fatigue life of surge line is analyzed.The results show that: the thermal stratification phenomenon is very obvious and lasts for a long time under the normal transient condition,In the same section,the maximum temperature difference between cold and hot fluid is 132.79℃,and the maximum temperature difference between pipe wall is 97.89℃.The rolling motion can alleviate the phenomenon of thermal stratification obviously,which shows that the heat transfer between cold and hot fluids is accelerated,and the temperature difference is reduced.The maximum temperature difference of fluid is decreased by 48.26℃,and the maximum temperature difference of pipe wall is decreased by 39.71℃.The effect of yawing motion on thermal stratification in this study is not obvious,even worse.The results of stress assessment under three operating conditions show that the primary and secondary stress amplitudes are qualified under normal transient outsurge condition and two rolling conditions.According to the calculation results of cumulative usage factors of three working conditions,the pipeline fatigue assessment is qualified under the stress amplitude.