The NECP-SARAX code developed by NECP research team is used for the fast reactor analysis.In order to consider the complex neutron slowing down effects from scattering resonance of nuclides with medium mass and inelastic scattering, the Monte-Carlo method was used previously but brought big uncertainty in tallying the spectrum in low energy.Besides, the efficiency is extremely low.In the improvement, a new resonance method based on ultra-fine group and point-wise cross section was involved.It generated effective multi-group cross sections with similar accuracy of Monte-Carlo method but avoided its disadvantages.In the core calculation, the multi-group cross sections were used for the 3D transport calculation.The first-order and exact perturbation theories were used in calculating the reactivity coefficients of fast reactor.To be capable of handling the geometric distorting in fast reactor, a new pseudo density method based on neutron transport and perturbation theory was proposed.Both the point kinetic and quasi-steady method were used in the transient calculation as two options to fit the requirement of fast reactor and ADS.The OECD fast reactor benchmarks were tested to verify the SARAX code, the results show good accuracy in the fast reactor calculations, which is similar to other widely accepted fast reactor code.The relative error of keff is less than 300 pcm compared with the Monte-Carlo code.Based on the pseudo density model and three-dimensional spatially dependent kinetics model, the SARAX code has more complete functions to fit the requirements of fast reactor design better.%NECP-SARAX是西安交通大学NECP团队开发的用于快中子反应堆的中子学程序系统.为准确处理快中子反应堆中中等质量核素散射共振以及非弹性散射导致的复杂的中子慢化效应,SARAX程序最初采用连续能量的蒙特卡罗方法计算中子能谱从而获得堆芯计算使用的有效多群截面.由于蒙特卡罗程序计算效率低,且在低能量段统计偏差较大,提出采用基于点截面的超细群方法计算中子慢化能谱,避免了蒙特卡罗方法产生参数时存在的缺陷.堆芯计算采用多群中子输运,通过优化简化几何建模,改进了程序的实用性.采用多种微扰方法计算堆芯各种反应性系数,提出了基于中子输运微扰理论的虚拟密度方法以计算堆内组件变形导致的反应性变化.在进行堆芯瞬态计算时,采用了点堆和改进准静态两种方法,可用于一般快堆和快谱ADS的典型事故分析.OECD发布的一系列快堆基准题测试表明,SARAX程序在快堆计算中具有良好的精度,达到了与国外著名快堆程序相当的水平.有效增殖因子与连续能量的蒙卡计算结果相比偏差在300 pcm以内.同时,由于引入了虚拟密度理论和三维时空动力学模型,程序功能更加完善,可以更好地满足快堆工程设计的需求.
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