Multi-Group Cross Section Generation For Shielding Calculation With The Contribution Theory

Accurate shielding calculation method is a significant foundation of radiation shielding design of nuclear system.The discrete ordinates method(SN)is one of the main deterministic transport methods at home and abroad,widely used in shielding calculations.Advanced nuclear devices puts forward higher requirements for shielding design.Numerical simulation not only requires efficient and accurate numerical solution methods,but reliable and compatible multi-group cross section data has also become a key affecting the accuracy of transport calculations.The strong resonance self-shielding effect in shielding materials for practical engineering problems cannot be ignored.Moreover,strong anisotropic scattering in high-energy neutrons and deep penetration problems also brings great difficulties to the generation of multi-group cross sections.The accuracy of multi-group cross section directly affects the calculation accuracy of transport simulation and the reliability of shielding design.For complex engineering shielding problems with resonance self-shielding effects and strong anisotropic scattering,this dissertation studies resonance multi-group cross section processing methods,energy group structure optimization,and the collapsed group strategy in strong anisotropic scattering media,to improve the accuracy of cross sections and efficiency of transport simulation.The resonance multi-group cross section processing methods are studied,which can effectively process the unresolved resonance energy based on the narrow resonance approximation theory,to accurately calculate multi-group resonance cross sections.An exponential interpolation method is proposed instead of the linear interpolation to calculate the temperature and background cross section interpolation,which effectively improves the accuracy and numerical stability of the self-shielding factor,and does not introduce additional cost.The negative cross section correction method is adopted to improve the shielding calculation accuracy for strong resonance problems.With complex three-dimensional shielding models,the optimization method of wide-group structure based on the contribution of energy groups is studied.The energy group contribution factor is used to guide energy group structure,to generate the optimal wide-group structure related to the problem.This method can solve the problems that the general energy group structure is not applicable in the specific problem,and balance the relationship between accuracy and efficiency of the transport simulation.Accurate collapsed group method in strongly anisotropic scattering called an angle-space dependent bilinear adjoint collapsed group is proposed.It fully considers angle-space effects on the multi-group cross section and ensures the accuracy of wide-group structures after collapsing,which extends the applicability for strong anisotropy shielding problems.The generation method of multi-group cross sections is studied and the multi-group cross section processing program ARES-MACXS is developed,which can generate multi-group working cross section libraries to be used directly in a variety of transport programs.Numerical results demonstrate that the resonance cross section processing based on the Bondarenko method can quickly and effectively handle the resonance multi-group cross sectionHowever,this method still has a slightly large error when calculating resolved resonance energy.At the same time,because the resonance interference effect between nuclides is not considered,the accuracy of the transport simulation in complex shielding problems may be reduced.The results in the AP1000 shielding problem demonstrate that for the interested parameters in the shielding calculation such as fast neutron fluence rate,detector response rate,and thermal neutron flux,the relative errors of the transport calculation results of the wide-group structure optimization method and that of fine-energy group structure are within 8%,which perform much better than that of the international common BUGLE-B7 energy group structure.It is no denying that initial fine-group energy group structures may disturb the process of the broad-group structure optimization,which affects the multi-group cross section accuracy and transport results to a certain extent.The results of the angle-space dependent bilinear adjoint collapsed group method illustrate higher transport calculation accuracy than traditional ones.In the VENUS-3 benchmark problem,the detector response rate under the wide-group structure is basically consistent with that under fine-group structure,and the maximum relative error is within 3%.In the IRI-TUB experimental benchmark,with the same or similar accuracy in neutron fluxes the calculation time of the optimized wide-group structure is reduced by more than 40%compared with the fine group structure,which demonstrates the engineering application prospect.The research of this topic has promoted the generation method of multi-group cross sections for shielding calculations,which is helpful to improve the reliability and efficiency for realistic shielding problems.This research has the potential and value of further application in large-scale complex shielding calculations.