235U快中子核反应截面协方差评价

Evaluation of Covariance Data for Neutron Cross Section of 235U in Fast Neutron Energy Region

  • 摘要: 本文基于最小二乘不确定度传递方法,建立235U中子裂变核反应截面模型依赖型与非模型依赖型协方差评价体系。通过针对实验测量较丰富的中子反应总截面、辐射俘获、(n,2n)等核反应实验数据不确定度源项分析,为协方差评价提供实验基础,并给出对应核反应截面的非模型依赖型协方差评价数据。通过开展快中子能区235U核反应理论模型参数灵敏度计算与分析,导出实验测量缺乏的核反应截面模型依赖型协方差评价数据。经上述系统评价,所得协方差数据与核反应截面中心值研究过程自洽、物理合理,并按国际标准ENDF-6格式输出,便于核工程用户使用。

     

    Abstract: With the development of the fourth generation nuclear power technology, clear requirements were put forward for the covariance of nuclear reaction cross section in order to satisfy the requirements of technical indicators such as safety and economy of nuclear devices. At the same time, in order to fill the covariance data vacancy of neutron induced actinide-nucleus nuclear reaction data in Chinese Evaluated Nuclear Data Library (CENDL), the covariance evaluation of neutron induced actinide-nucleus nuclear reaction cross section based on the least-square approach was researched, and the model dependent and non-model dependent covariance evaluation system of neutron induced 235U nuclear reaction cross section were established. First through the investigation and analysis of experimental data, the covariance evaluation methods of cross section of different reaction channels were determined. By comparing and recommending the experimental data of neutron induced 235U reaction total cross section, radiation capture cross section, (n, 2n) cross section and other reaction channels with abundant experimental data and analyzing the source of experiment uncertainty, the non-model dependent covariance evaluation data of corresponding nuclear reaction cross section were given, and the experimental basis for the model dependent covariance evaluation was provided. At the same time, taking the experimental data as the restraint condition, the optimized parameters of theoretical model and complete set of theoretical data of neutron induced 235U nuclear reaction were obtained by using the nuclear reaction code FUNF developed by China Nuclear Data Center (CNDC), which considers many physical models such as optical model, equilibrium and pre-equilibrium particle emission. Through the calculation and analysis of the optimized parameters’ sensitivity of neutron induced 235U nuclear reaction theoretical model in fast neutron energy region, and combined with non-model dependent covariance evaluation results, the model dependent covariance evaluation data of nuclear reaction cross section of which lacking experimental measurement were derived. Through the above systematic evaluation, the obtained covariance data are consistent with the research process of the central value of nuclear reaction cross section, and the physical results are reasonable. Next, the evaluation data and theoretical calculation data were put into the database together and conduct self-consistent processing, and combined with the covariance evaluation data results, output them in accordance with the international standard ENDF-6 format and carried out a series of inspections, such as format check and physical check.

     

/

返回文章
返回