Research On Accurate Activation Calculation Method And Key Technology For Advanced Nuclear Reactors

A large number of neutrons are produced in nuclear reactor operation.These neutrons cause strong activation on structural materials and corrosion products,which will bring radioactive hazards on persons working on operation,maintenance and decommission.It is essential to develop an activation calculation method with high precision and high efficiency for the reactor design and safety analysis.With the development of advanced reactor technologies,the structure materials and the neutron energy spectra become more and more complex,which brings great challenges for improving the accuracy and efficiency of activation calculation.In order to solve these problems,this thesis studies the activation calculation method for advanced reactors based on Super Monte Carlo Program for Nuclear and Radiation Simulation(SuperMC).In this paper,Chebyshev Rational Approximation Method(CARM)based on exponential transformation is studied to improve the accuracy of CRAM in calculating the long decay problem.Based on the fine reaction chain model,the activation physical processes of 2231 nuclides and 66256 reactions were considered,and the effects of light nuclide yield,short-lived nuclides and excited-state nuclides on the activation calculation results were also taken into account.Varieties of material activation properties can be provided,including activity,decay heat,biological hazard,dose rate,and clearance index.The main innovation points of this paper are as following:(1)The dynamic construction method of transmutation chain based on depth-first search was developed.There are kinds of nuclides in a reactor and their conversion relationships are complicated.Besideas,each nuclide contains many reaction pathways.The degree of fine transmutation chain directly affects the result of calculation.Based on the neutron reaction information and decay information of the nuclide,the new method could search and add the activation products and construct the transmutation chain according to the initial calculation condition,which has the advantages of strong expansibility and high search efficiency.(2)Adaptive order reduction method for large scale matrix was proposed to improve the calculation efficiency.When solving the Bateman equation using CRAM,a large number of short-lived nuclides cause the coefficient matrix with the characteristics of large-scale and rigidity,affecting the efficiency and accuracy of numerical solution.By reconstructing the coefficient matrx,the new method can remarkably reduce the size and rigidity of the coefficient matrix and improve the efficiency of the activation calculation.Taking the international activation benchmark as an example,calculation results showed that the efficiency of solving the matrix by using the new method could be increased to more than 2 times,compared with the original calculation.Based on SuperMC,the activation calculation method of the the reaserch was realized.To verify the correctness of the method,a series of different test cases were selected in this study.Firstly,some test cases containing common decay reactions were validated,such as ?-and ?+.Secondly,a total of 90 kinds of natural nuclides form H to Th were selected to calculate the activation properties with irradiation scheme,including activity,decay heat,biological hazard,contact dose rate and clearance index.Results showed good agreement with the reference program.Finally,benchmarks of cladding materials in PWR and IAEA-ACB were used to validate the method in fission and fusion reactors' problems,respectively.The calculation results have good agreements with reference values.In conclusion,these consistent test results demonstrated the correctness of the developed activation calculation method and can be used in accurate activation calculation of advanced reactors.