各向异性散射截面对快堆敏感性系数计算影响研究

Study on Effect of Anisotropic Scattering Cross Section on Sensitivity Coefficient Calculation for Fast Reactors

快能谱反应堆由于中子能量较高,中子各向异性散射会对计算结果有重要影响。本文在计算弹性散射和非弹性散射截面敏感性系数时,研究了高阶散射截面扰动对弹性散射和非弹性散射截面敏感性系数计算的影响。从理论上分析了隐式敏感性产生的原因和相关近似条件,采用直接扰动方法计算了ZPR-6/7快能谱反应堆主要核素的主要反应道的敏感性系数。研究结果表明,对于ZPR-6/7快能谱反应堆,不扰动^(238)U高阶散射截面,总的弹性散射截面的敏感性系数比考虑高阶散射截面时的敏感性系数高44.3%,不考虑^(56)Fe高阶非弹性散射截面的扰动,会造成非弹性散射截面敏感性系数偏高28.9%,而对其他核素的弹性散射和非弹性散射的敏感性系数影响较小。考虑到高阶散射截面后,自主开发的程序SUFR计算的总的敏感性系数结果与国际同类程序ERANOS和MCNP的计算结果吻合很好,最大偏差不超过3.22%,同时^(238)U的弹性散射反应道和^(56)Fe的非弹性散射反应道对有效增殖因子不确定度分析的精度也有了很大提高。因此,快堆敏感性系数计算需要考虑高阶散射截面影响,同时敏感性和不确定度分析程序SUFR开发正确,针对于快能谱反应堆进行敏感性系数的技术路线可行,计算精度同国际同类程序的计算精度相当。

Due to the high energy of neutrons in fast-spectrum reactors,the anisotropic scattering of neutrons is with great effect on the calculation results.In this study,the effects of high-order scattering cross-section perturbation on the calculation of elastic and inelastic cross-section sensitivity coefficients are studied when calculating the elastic and inelastic cross-section sensitivity coefficients.The causes of implicit sensitivities and related approximate conditions were theoretically analyzed.The direct perturbation method was used to calculate the sensitivity coefficients of the main nuclides reaction channel of the ZPR-6/7 fast-spectrum reactor.The research results show that for the ZPR-6/7 fast-spectrum reactor,without disturbing the ^(238)U high-order scattering cross section,the sensitivity coefficient of the total elastic scattering cross section is 44.3%higher than that when the high-order scattering cross section is considered.Irrespective of the disturbance of ^(56)Fe high-order inelastic scattering cross section,it will cause the sensitivity coefficient of inelastic scattering cross section to be 28.9%higher,but it has less influence on the sensitivity coefficients of elastic scattering and inelastic scattering of other nuclides.After considering the high-order scattering cross section,the total sensitivity coefficient calculated by the independently developed SUFR program is in good agreement with the ERANOS and MCNP results.The maximum deviation does not exceed 3.22%.At the same time,the accuracy of the uncertainty analysis of the effective multiplication factor caused by the elastic scattering reaction channel of ^(238)U and the inelastic scattering of ^(56)Fe has also been greatly improved.Therefore,the calculation of fast reactor sensitivity coefficient needs to consider the influence of high-order scattering cross section.At the same time,the sensitivity and uncertainty analysis program SUFR is developed correctly.The technical route for the sensitivity coefficient of fast energy spectrum reactors is feasible,and the calculation accuracy is the same as that of the famous international program.