Research On Group Constants Generation By Reactor Monte Carlo Code

In the analysis method of reactor physics,the two-step method still is the mainstream approach.Since the homogenization group constants generated by lattice code are applied to the downstream nodel diffusion code directly,its accuracy is crucial to reactor core analyses.Compared to the deterministic method,generation of few group constants by Monte Carlo code not only has the advantage of preserving high-fidelity geometries but also free from complicated resonance shielding treatment which results from the directly accessing continuous-energy nuclear data.Given the inherent advantage of Monte Carlo,the homogenous group constants obtained by Monte Carlo is of higher accuracy theoretically.The two-step procedure Monte Carlo homogenization combined with diffusion code utilizing both the advantage of Monte Carlo and deterministic method.Thus,this paper focus on the method of homogenous group constants generation by Monte Carlo.In this paper,the generation of few group constants of fuel assembly with reflective boundary condition is studied based on continuous-energy Monte Carlo code cos RMC.The multigroup cross section is tallyed with track length method,and two methods of scattering matrix?Legengre components and g? calculation are included: Monte Carlo method and explicit method.In order to account for the non-physical infinite-lattice approximation,/N NB P methodology is adopted.The caculation of diffusion coefficient is quite difficult for Monte Carlo homogenization beacause there are no physical quantities correspondently in MC code.Three calculation methods of diffusion coefficient are implemented in this research:the outflow transport correction method;an leakage item of 1B /1P equation;1B equation combined with inflow correction.To keep the conservation of key physical quantities before and after homogenization,general equivalence theory is applied in cos RMC and discontinuity factors are obtained.In addition,a corrected discontinuity factors of reflector assembly calculated method is studied in this paper which results in an improvement of accuracy of homogenized group constants.The coupling system of cos RMC-SIMULATE5,forming the two step procedure cos RMC-SIMULATE5 which nodal diffusion code SIMULATE5 using group constants generated by cos RMC,is applied.The Kinf/Keff/ power distribution(radial & axial)obtained by two schemes cos RMC-SIMULATE5 and cosRMC one step shows good agreement with each other regarding to single assembly-mini core-full core level benchmark.These positive outcomes indicate that the few-group constants generated by cos RMC are highly accurate.