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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300pcm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。
NECP-SARAX is a neutron program system for fast neutron reactors developed by the Xi’an Jiaotong University NECP team. To accurately handle the complex neutron moderation effects caused by the scattering of medium-quality nuclides in fast neutron reactors and by inelastic scattering, the SARAX program originally used a continuous-energy Monte Carlo method to calculate neutron energy spectra for core calculations The effective multi-group cross-section. Due to the low computational efficiency of Monte Carlo code and the large deviation in the low energy segment, a new method of calculating the neutron moderation spectrum based on the ultrafine-point method based on point cross-section is proposed to avoid the defects of the Monte Carlo method. Multi-group neutron transport is used in core calculation, and the practicality of the program is improved by simplifying geometric modeling. A variety of perturbation methods were used to calculate the core reactivity coefficients. A virtual density method based on the neutron transport perturbation theory was proposed to calculate the reactivity changes caused by the deformation of the in-reactor components. In the transient calculation of the core, point piles and quasi-static quasi-static methods are used, which can be used in typical accident analysis of general fast reactor and fast spectrum ADS. A series of fast reactor benchmark tests released by the OECD show that the SARAX program has good accuracy in fast reactor calculation and has reached a level comparable to that of a famous fast reactor in foreign countries. The effective multiplication factor is less than 300pcm deviation from the Monte Carlo calculation of continuous energy. At the same time, due to the introduction of virtual density theory and three-dimensional space-time dynamics model, the function of the program is more perfect, which can better meet the requirements of fast reactor engineering design.