基于中子均方位移守恒的平均散射角余弦计算

In the two-step calculation of reactor physics, the average scattering cosine is determined using the scalar flux as the weighting function in the Monte Carlo method for generating group constants, which introduces additional errors. Therefore, starting from the relationship between the mean square displacement and average scattering cosine, this paper proposes a novel method that calculates the average scattering cosine, conserving the mean square displacement of neutrons. It is realized based on the Monte Carlo particle transport procedure NECP-MCX. Several fast reactor problems with strong anisotropy are selected to test the validity of the proposed method. Compared with the traditional method, the biases of multiplication factors decrease from 588×10^-5 ~ 796×10^-5 to -31×10^-5 ~ 266× 10^-5. The maximum relative biases of relative fission reaction rates decrease from 3. 754% ~ 4. 675% to -0. 990% ~ 0. 920%, and the root mean squared biases decrease from 1. 864% ~ 2. 444% to 0. 569% ~ 0. 612%. The results show that the proposed method can effectively reduce the biases introduced by the traditional method, and has certain application values.