Research On The Subgroup Method For Treating Multiple-Complexity Neutron Resonance Problem

Neutron resonance calculation is a basic part of reactor physics calculation, and itdirectly influences the accuracy of physics calculation. With the fast development ofnuclear power, the design of reactor core is becoming more various, and thecomputation requirement of multiple-complexity resonance problems, with complexgeometry structure, complex fuel composition or multiple resonance regions, isinevitably increased.It is difficult for the traditional resonance calculation model based on equivalenceprinciple to fulfill the computation requirements of complex resonance problems. Onthe other hand, subgroup method has great potential in calculation accuracy, efficiency,and capability of handling complex geometry. These merits make subgroup method animportant choice to solve the problem. So this thesis focuses on subgroup method, andthe research contents are shown as below.Firstly, the subgroup method and the method of characteristics are combined toachieve the accurate computation of complex geometry resonance problems. The fittingmethod is used to obtain subgroup parameters, and the influence of subgroup number onfitting accuracy of subgroup parameters is analyzed. The approximate treatment ofsubgroup scattering matrix is also proposed.Secondly, two different methods for resonance interference effect calculation areproposed, which both improve the performance of subgroup method on handlingresonance interference effect. Stochastic interference correlated-probability method isproposed, which obtains correlated-probability by stochastic interference approximation,in order to extend correlated-probability method to compute resonance interferenceproblems with multi-temperature, multi-group, multi-isotope. The method based oncross-section modification produces nuclear cross-section which taking resonanceinterference effect into account approximately. This method enhances the resonancecalculation accuracy; meanwhile, it costs no additional computation time.Thirdly, new nuclear cross-section taking resonance effect of elastic scattering intoaccount is produced. Correlative subgroup parameters are obtained and applied tosubgroup method, and then the resonance calculation accuracy is further improved.Reasonable approximate technique is used to handle scattering matrixes of resonance isotopes, which solves the scattering cross-section conflicting problem in subgroupequation brought by the importing of resonance elastic scattering cross-section.Subgroup method&method of characteristics calculation code SGMOC isdeveloped, utilizing the aforementioned methods. The results of several benchmarksshow that: the SGMOC code is able to handle resonance problems with differentcomplexity degrees; both two correction methods, which are stochastic interferencecorrelated-probability method and the method based on cross-section modification, areable to enhance the accuracy of subgroup resonance interference effect calculation; andthe accuracy of subgroup method is further improved by taking resonance elasticscattering into account. Finally, the selection principle of quadrature set order and rayspacing on resonance calculation is proposed.This thesis improves the performance of subgroup method on resonanceinterference effect calculation, enhances the calculation accuracy of subgroup method,and finally constructs an advanced resonance calculation model which is able to handlemultiple-complexity resonance problems.