Research On The Characteristic And Effect Of Core Outlet Temperature Fluctuation For Lead Based Reactor

In a lead-based reactor,the coolant that flows out of the reactor core subassemblies may result in a temperature fluctuate,which causes a high cycle thermal fatigue at the solid wall such as cover plate and endangers reactor safety.However,so far there is no research about the temperature fluctuation of lead-based reactors.And some study results about temperature fluctuations of the water cooled reactors are not suitable for the lead-based reactor.Thus,the detailed analysis of temperature fluctuation of lead-based reactor is very important.In this paper,large eddy simulation(LES)approach was employed by using CFD method for the accurate simulation of temperature fluctuations for lead-based reactor core outlet.(1)The normalized amplitudes of temperature fluctuations and frequencies of lead,Lead-Bismuth Eutectic(LBE)and sodium were analysed in triple jet model.It is concluded that the amplitudes of lead-based materials fluctuations are larger compared with that of sodium temperature fluctuations.And thermal stress due to temperature fluctuation should thus be paid more attention to in lead-based reactor than sodium cooled reactor such as the layout of instruments and thermocouples.(2)The simulation was performed by using lead coolant as the fluid medium in triple jet model.The results show that for the central location between the cold and hot fluid outlet while closer to hot fluid,the temperature fluctuation amplitude is largest when velocity ratio is 0.5.Therefore,it is suggested that the instruments should be arranged at the exit right above of the fuel assembly exit when the coolant velocity is smaller.(3)In order to analyze the temperature fluctuation sensitivity for the fuel assembly design parameters,five simplified geometry models were constructed.It is found that the temperature fluctuation intensity is enhanced with the increase of the gap size between adjacent fuel assemblies and the opposite edge width of each fuel assembly.So small size design of the fuel assembly exit is advantageous for preventing from the coolant temperature fluctuation.(4)The 1/4 10WMth lead-based reactor core outlet model was constructed to investigate the core outlet temperature fluctuation distribution characteristics along the axial and radial direction.It is found that the amplitude and frequency of six monitoring points are higher in radial direction from core outlet.The amplitudes and the frequency of temperature fluctuation are decreasing with the axial height along the axial direction.Therefore,it is concluded that these monitoring points should be avoided when the instruments and thermocouples are arranged at the core outlet.What'more,the arrangements should be far away from the core outlet.The innovation of this paper provided as follows:(1)The temperature fluctuation for lead-based reactor core outlet is studied systematically in this paper firstly.The effects of the flow parameters and structural parameters are researched comprehensively which can cover the range of parameters commonly used in engineering.(2)In the present study,the effect of velocity ratio for temperature fluctuation is analyzed from the view of the fluid dynamic govering equations by combinating the Coanda effect in the parallel triple jet to study the mechanism of temperature fluctuation deeply.The analysis results would provide important design references for mass flow rate assignment,fuel assembly design,instruments arrangement such as thermocouple,and safety analysis at core outlet and future practical operation of lead-based reactors.