Research On High-fidelity Resonance Self-shielding Calculation For Whole-core Problem

Resonance self-shielding calculation is the crucial component in the deterministic neutronics calculation,whose major objective is to predict the shape variation of neutron spectrum caused by the resonance peak and then provide the accurate multi-group cross-sections for the transport calculation.Since the trend that the direct whole-core high-fidelity transport calculation has become the research hotspot,it is essential to carry out the research of the high-fidelity resonance self-shielding method for whole-core scale problem.The conventional resonance self-shielding methods including the equivalence theory,the subgroup method,and the ultra-fine-group method.Unfortunately,these methods have no ability to fully meet the requirements appeared in the high-fidelity resonance self-shielding calculations for the whole-core problem independently since their deficiency in computing accuracy or efficiency.Therefore,the advanced resonance self-shielding methods which are the fusion of different conventional methods have appeared in recent years.And the fusion of the equivalence theory and the ultra-fine-group method becomes one of the hotspots of research due to the high-efficiency characteristic of the equivalence theory and the high-accuracy characteristic of the ultra-fine-group method are complementary.There are two concepts in the coupling scheme: the online coupling scheme and the heterogeneous resonance integral based on the offline ultra-fine-group calculations.Among them,the online coupling scheme has an efficiency problem when treating the resonance self-shielding problems during the depletion of the reactor core,while the heterogeneous resonance integral has the problem of the troublesome generation process and computing adaptability.Thus,based on the improvement of the equivalence theory,a resonance database is generated online through the adoption of heterogeneous ultra-fine-group calculations,and an advanced resonance self-shielding method named as the two-step resonance method is proposed in this study.In the two-step resonance method,the embedded self-shielding method with modification is employed to evaluate the global lattice effect of the target problem and establish the equivalence relationship between the heterogeneous pin-cell in the resonance database generation and the realistic fuel rod in the target problem.The number-density perturbation technique is adopted to treat the resonance interference effect during the depletion.A distributed parameter method is proposed to resolve the intra-pin radial self-shielding effect since the radial detail of self-shielded cross-section distribution which is washed out in the resonance database generation.In addition,the method of ultra-fine-group slowing-down solving based on the method of characteristics is proposed as a beneficial supplement for the two-step resonance method when treating local complicated resonance problems.And the corresponding accelerating techniques are proposed for its efficiency improvement.Based on the methodology of the two-step resonance method,the corresponding computing code named as TSR(Two-Step Resonance code)is developed.The basic computing ability of the two-step resonance method is tested through the TSR code on the computing of a series of problems including the UO2 and MOX pin-cell problems,the UO2 and MOX assembly problems,the reactor corner problem,and the whole-core problem.In addition,a lattice with local heterogeneity is calculated by the TSR code to test the ability of the two-step resonance method for the prediction of intra-pin self-shielding.Lastly,the ability of the two-step resonance method for the local complicated resonance problem is tested through a local interlaced slab problem.The numerical results show that the two-step resonance method is capable to meet the requirement of high-fidelity resonance self-shielding calculation for the whole-core problem with high computing efficiency.