| The Chinese spallation neutron source is a large scientific device for observing the microscopic world through neutron heat dissipation technology.The target station is an important part of it.With the increase of the beam power of the Chinese spallation neutron source,the safety of the target station is also improved accordingly.How to deal with the accident conditions plays a necessary role in the safety of the target station.Therefore,it is particularly important to grasp the temperature change inside the target under the accident,and provide guidance and suggestions for the upgrading of the target station.Firstly,based on the target model in the first phase of China Spallation Neutron Source Project,the physical and mathematical modeling is carried out to study the internal flow and heat transfer process of the target under different accidents.The finite volume method is used to verify the grid independence and time step of the calculation model by grid convergence index(GCI),and the optimal number of grids is selected.UDF programming through the decay heat equation.The corresponding assumptions and boundary conditions of different working conditions are given under the accident conditions,and verified with the experimental results of beam power 125 k W.The results show that the heat dissipation of the convective heat transfer on the outer surface of the target container is very small under the power failure accident,which has little effect on the temperature of the target.The main heat dissipation method is the natural convection of the internal fluid.When the mixed heat transfer condition is adopted,the flow caused by both natural convection and residual pressure change is in good agreement with the experimental values.Secondly,in order to improve the beam power need to increase the beam section,need to change the target section size,design to meet the beam power of500 k W target,to ensure that after the accident pressure relief,the target internal cooling water will not occur boiling for the design conditions,and the rated working condition velocity field,temperature field analysis.The proton beam offset along the x-axis and z-axis in the positive and negative directions is simulated,and the temperature field is compared with the rated conditions.The results show that the proton beam is offset in the positive and negative directions of the x-axis and z-axis,and the proton beam offset along the z-axis has the most serious influence on the target temperature,resulting in an abnormal increase in the temperature of the proton beam window.When the proton beam offset increases,the temperature of the proton beam window increases,and the temperature distribution is uneven,increasing the thermal stress and other effects.The deviation of the proton beam will not lead to the increase of the outlet temperature of the cooling water,and the outlet temperature of the cooling water cannot be used as the basis for judging the abnormal proton beam.Finally,the simulation calculation of the power-off condition and the complete loss of flow condition under the beam power of 500 k W is carried out.Firstly,the heat source of the target body changes from the normal heat source to the decay heat source.Secondly,the forced convection heat transfer is lost under these two accident conditions,mainly through natural convection cooling,and the cooling capacity is reduced.Due to the high heat carried by the target body in the event of an accident,it is not easy to discharge and the target body will continue to release heat,so it is necessary to grasp the internal temperature change.The results show that boiling vaporization of internal cooling water occurs in the case of power failure,and the main vaporization position is located in the sixth flow channel.In order to avoid vaporization under power failure,it is necessary to start the emergency power supply for water cooling before 1.5 s.Under the condition of complete loss of flow,it is necessary to drag the trailer into the hot chamber for cooling before the target temperature reaches 350 ℃,so as to ensure that the temperature of the remaining parts inside the target station will not exceed the temperature and avoid more serious accidents. |
