Research On The Development Of High-accuracy Multi-group Cross Section Library For PWR

In the PWR nuclear design,we need first to know the cross section and related parameters for different nuclides ranging from 10-5eV and 10MeV.The nuclear data of these nuclides are stored in the multi-group cross section library.Therefore,the accuracy of the multi-group cross section has a great influence on the reactivity values.Now,the cross section processing code NJOY is used in the development of a multi-group cross section library based on the different requirements of nuclear design,which can read a point-wise cross section in the different versions of the evaluated nuclear data library.To increase the calculation efficiency,the typical neutron spectrum and simplified neutron transport equation are introduced in the NJOY code.The point-wise cross section is then combined into the energy dependent multi-group cross section.For most nuclides,the tendency of a cross section is smooth in different energy groups and it has less influence on the reactivity.However,some nuclides have a resonance self-shielding effect and anisotropic scattering effect（such as 238U and 1H,etc.）,which has a great impact on the final results.What’s more,during the development of multi-group cross section library,the different input parameters of cross section processing code and a variety of evaluated nuclear data libraries has great influence in reactivity predictions.So,the investigation is focused on the production method and theory model of multi-group cross section library.Then,the high-accuracy of multi-group cross section library is developed for the PWR system.The main content is as followed:First,this paper adopts the different transport correction methods to treat the anisotropic scattering effect in PWR light nuclides.For the strong anisotropic scattering cases（like control rod assembly and core benchmarks）,the traditional outflow transport approximation can introduce a large error in reactivity value.The inflow transport approximation of the moderator region can improve the accuracy of reactivity,but the neutron spectrum of Po order is different from the reference values.Therefore,the new inflow transport approximation is improved through the assembly homogenization techniques,which adopt the homogeneous cross section and accurate fission source data in the transport calculation.The results indicate that the new inflow transport approximation can both improve the accuracy of reactivity and neutron spectrum.Second,the resonance self-shielding effect is investigated in the PWR fuel and cladding region.The experimental reduction of absorption resonance integrals for 238U is used in the treatment of resonance self-shielding effect for fuel region,which is based on the ENDF/B-Ⅶ.0 evaluated nuclear data library and 70 energy group structure.On the other hand,the equivalence theory and subgroup method are used in the treatment of resonance self-shielding effect for cladding region.Compared with the traditional method for reference dilution cross section,the new method has higher accuracy and greater application in PWR cases.Furthermore,the different versions of evaluated nuclear data libraries（like CENDL-3.2,ENDF/B-Ⅷ.0,and JEFF-3.3,etc.）and NJOY input parameters（like maximum up-scattering thermal energy,neutron spectrum,and dilution cross section.）are selected in the typical PWR cases.Through the analy sis of these factors to the final results,we can finally acquire the most accurate combination of multi-group nuclear data library’s production values.Finally,the accurate multi-group cross section library for PWR is generated through the above improvements,which are then verified through the extensive PWR cases.The numerical results demonstrate that the improved library can reach a higher accuracy and greater application than traditional.libraries.It is close to the reference values.In summary,the research on the development of a high-accuracy multi-group cross section library for PWR is performed in this work.Firstly,based on the improved inflow transport approximation,the anisotropic scattering effect for PWR light nuclides can be accurately treated.Secondly,the experimental reduction of²³⁸U absorption resonance integrals can improve the accuracy of resonance self-shielding effect for fuel region through the ENDF/B-Ⅶ.0 evaluated nuclear data library and 70 energy group structure.Thirdly,the equivalence theory and subgroup method are valid for the treatment of the resonance self-shielding effect for the cladding region.Fourthly,the optimal combination values are investigated in the generation of a multi-group nuclear data library,which is based on the different versions of evaluated nuclear data libraries and NJOY input parameters.Finally,compared to the traditional multi-group cross section library,the improved.multi-group cross section library can reach higher accuracy and greater application in PWR cases,which has the engineering meaning and academic value in the PWR nuclear design.