Thermal Fatigue Analysis And Study On Thermal-Fluid-structure Interaction Characteristic Of Central Measurement Column In Fast Reactor Under Thermal Striping

In fast breeder reactor,due to the non-uniformity of core power and flow distribution,the coolant flows through fuel assemblies with different temperatures will be mixed at the core outlet and a complicated high frequency temperature fluctuation phenomenon will be generated near the central measurement column.When the temperature fluctuation of fluid is transferred to the abrupt position of structure,the structure will produce great deformation and stress intensity,which may cause thermal fatigue and thermal aging of the central measurement column,thus affecting the control and protection actions of the reactor.Compared with pressurized water reactor,the temperature difference and thermal conductivity of the fluid at the core outlet in fast reactor is larger,and the effect caused by the temperature fluctuation on structure is more serious.For the research on the temperature fluctuation at the core outlet,most of the researches at home and abroad are based on several simplified model of core outlet structure,and a large number of two-dimensional and three-dimensional numerical simulations and experimental researches only for fluid temperature fluctuation at core outlet have been carried.On the other hand,some researches have calculated the fatigue damage caused by temperature fluctuation to the central measurement column of fast reactors through a unidirectional thermal-structure interaction method.However,none of these researches involved the heat transfer effect between the fluid at core outlet and the central measurement column.Therefore,the calculation of thermal-fluid-structure interaction of the central measurement column of fast reactor under the thermal striping is of great significance to explore the influence of the fluid temperature fluctuation on the structure in the upper chamber of nuclear reactor and to evaluate the high cycle thermal fatigue of the central measurement column.In this paper,a simplified model of the lower head of central measurement column and the operating head of fuel assemblies have been established.Based on the finite element analysis method,the thermal-fluid-structure interaction calculation of the model is carried out to obtain the thermal-fluid-structure interaction characteristics between the structure and the fluid near the central measurement column of fast reactor under temperature fluctuation,and the high cycle fatigue of the central measurement column is analyzed.The results show that the fluid temperature fluctuation is affected by the surrounding fluid.The fluid temperature fluctuation range near the lower head of the central measurement column is about 10℃,and the temperature fluctuation frequency is within 10Hz,The temperature fluctuation trend of the surface of the lower head of central measurement column is similar to that of the fluid,with certain hysteresis and attenuation.The surface temperature amplitude of the structure is within 5℃,and the temperature fluctuation frequency is within 5Hz.When the fluid temperature fluctuation is transmitted to the structure thickness of 4mm,the temperature amplitude inside the structure has approximately decayed to 0.The maximum stress node of the structure appears at the welding position between the lower head and the conducting pipe.The structural stress continuously fluctuates with time,and the main frequency of the stress fluctuation is within 5Hz.The fatigue cumulative use factor of central measurement column is much less than 1,that is,the central measurement column of the fast reactor could operate safely during the design life without high cycle fatigue failure.In this study,the thermal-fluid-structure interaction calculation and high cycle fatigue analysis method in this study have certain academic significance and engineering application value.