Research On Advanced Subgroup Method For Resonance Self-shielding Calculation Of Nuclear Reactor

Accurate cognition of the neutron reaction rule is an important guarantee of the safety and economy of nuclear power plant.Since the material composition and geometry configuration of the new type reactor has gradually become more complex,it brings severe challenges to the high-fidelity reactor physics calculation.The resonance self-shielding calculation provides effective cross section for the neutron transport and depletion calculation,so it is a key point in the reactor physics calculation.The precision of resonance self-shielding cross section is an important basis for analyzing neutron behaviors in the reactor.The subgroup method has relatively high efficiency and good geometry applicability,so it is commonly applied to commercial core analyzing programs.However,the conventional subgroup method still has deficiencies for resonance treatment,and cannot meet the increasingly stringent requirement for precise computation.To deal with this issue,the research on advanced subgroup method for resonance self-shielding calculation is made in this thesis.Firstly,the key points of the subgroup method are the subgroup parameter generation and the subgroup fixed source equation calculation,so this thesis focuses on these two topics and proposes relevant improvements for conventional subgroup method above all.To avoid the illposedness of the conventional subgroup method,the particle swarm algorithm is adopted for subgroup parameter generation,and the optimal solution is obtained by the random particle flying process rather than solving the conventional complicated nonlinear equation systems.To handle the non-uniform temperature distribution condition,the subgroup probabilities are shared for different temperatures and all subgroup parameters are calculated simultaneously,and make it feasible to carry out the subgroup resonance calculation in non-uniform temperature condition.Besides,the resonance integral is enhanced,and the influence of homogenous and heterogeneous resonance integrals to subgroup calculating accuracy is analyzed.To improve the efficiency of subgroup calculation,the equivalent one-group subgroup flux interpolation method is proposed.All resonance groups are averaged to an equivalent single group and the transport calculation is only solved for certain subgroup levels,then the actual subgroup fluxes in each resonance group are obtained by interpolation of escape cross section.The calculating burden is much reduced while the precision is guaranteed.Secondly,to handle the resonance interference effect,the two-level discrete by fine-mesh and subgroup strategy is proposed.The subgroup is adopted based on the fine energy structure for the further dispersion of the resonance range,and the calculating accuracy achieved by hundreds of groups could be commensurate with those of the ultrafine group structure.The fine-mesh in this work has 408 groups in total and 289 of them are resonant.The fine-mesh describes the distribution of resonance peaks of different resonant nuclides in detail.By applying the subgroup method to the fine-mesh,the resonance interference effect could be sufficiently handled and no more correction for the resonance cross section is needed.Then,the fine-mesh resonance cross section is condensed by the neutron slowing-down flux to get the effective multigroup cross section for the transport calculation.The 47-group structure is selected for the transport module and 16 groups are resonant.Through this method,better accuracy than the conventional Bondarenko method and the resonance interference factor method is achieved.Finally,the resonance-transport coupling calculation is researched combined with the method of characteristic(MOC).To avoid the repeated calculation of geometry treatment and MOC sweep for solving subgroup fixed source equations and slowing-down equations,the multigroup calculation method is proposed.The calculating performance is analyzed both on CPU and GPU platforms and the optimal calculating scheme is raised.Meanwhile,to treat the double heterogeneity geometry problems,the double heterogeneity module is developed based on the Sanchez-Pomraning method.This module is applied to amend the subgroup fixed source equation and slowing-down equation respectively,and the resonance cross section could be obtained accurately both for the fuel kernel and matrix.This module is also applied to the multigroup transport equation to carry out the eigenvalue calculation in the double heterogeneity condition.According to the above content,the resonance calculating module of the high-fidelity reactor physics calculating code ALPHA is developed.A series of benchmarks are adopted to verify the accuracy of resonance calculation,including typical PWR problems,complex fuel composition problems,complex geometry configuration problems,double heterogeneity problem,multi-lattice problems,and 3-dimensional problems.The numerical results indicate that the research content in this thesis is could carry out the resonance self-shielding treatment precisely for different multiple complex condition in nuclear reactors.This work is a key component of the numerical reactor core physics calculation and has important value for engineering application.