Research Of Fine Activation Calculation Method Of Nuclear Reactor Structural Materials

During the operation of the reactor,neutron activation reaction will cause a large amount of radionuclides to be produced in the reactor structural materials,which directly affects the reactor shielding design,maintenance plan,refueling plan,and decommissioning strategies,etc.With the development of advanced reactors,reactor geometry,material layout,and neutron energy spectrum have become more and more complex,which has led to more complex activation calculations.It is necessary to carry out research on fine activation calculation methods for nuclear reactor structural materials.The spatial gradient changes of neutron flux is not been considered in traditional cell-based R2 S method,so the method cannot describe the non-uniform spatial effect of activation of structural materials in cell.Aiming at the problem of fine activation calculation of reactor structural materials,this paper conducts research on mesh-based fine activation calculation method,considering the neutron fluence rate and the spatial effect of the activation process,and realizes the fine mesh of the activation source and decay gamma source of structural materials.Firstly,the method of monte carlo neutron transport of structural materials based on mesh tally is carried out.Secondly,the activation source term based on fine mesh is established.Thirdly,based on the secondary development of the MCNP program,the mesh-based gamma source sampling method is built,and the radiation dose field calculation of the decay gamma source based on the mesh source term was carried out.Finally,an activation analysis program for the structural materials in the reactor based on fine mesh is been established.In order to verify the correctness of the method in this paper and the Mc Fis MA program,the M5 cladding activation model,stainless steel activation model and NUREG/CR-6115 PWR are used.The result of atomic density,photon source intensity,and shutdown dose rate are consistent with the reference value.In order to verify the application of the program to PWR,NUREG/CR-6115 and VVER are carried out.The result shows that the distribution of dose field converged with the increase of mesh density.There is a critical value of mesh density,exceeded which dose field distribution dose not converge significantly.In this paper,an activation calculation method and program for reactor structural materials with mesh-based analysis capabilities have been developed.The program can provide theoretical and technical support for the precise activation calculation of structural materials and the accurate evaluation of decay gamma radiation fields.The code has engineering application value for ensuring the radiation safety of personnel in the process of reactor maintenance,refueling,and decommissioning.