基于MCNP的缓发裂变中子衰减时间谱模拟计算

摘要

Based on the idea that the nuclear fission reaction occurring and delayed fission neutron emitting can be separated in time dimension,the delayed fission neutron time spectrum in the range of 0-100 s in uranium contained formation was calculated by MCNP.Firstly,the 235U and 238U nuclear fission reaction space distributions in sphere geometry were simulated.Then delayed fission neutron's emission position and direction,originated fission nuclide,delayed fission neutron group and emission time,and initial energy were sequentially sampled with the assistance of SOURCE subroutine in MCNP.The result shows that the time feature of the calculated delayed fission neutron time spectrum is in accordance with the group parameters of delayed fission neutron of uranium nuclides.The relationship between accumulative delayed fission neutron count and formation uranium concentration was linearly fitted.The adjusted-R square of fitting result is greater than 0.998 5,which verifies the credibility of uranium concentration linear model.%基于核裂变反应发生与缓发裂变中子发射这两个物理过程在时间上可相互分离的思想,利用MCNP程序计算得到了含铀地层0～100 s范围内的缓发裂变中子衰减时间谱.模拟计算了球体几何模型中235U与238U核裂变反应率空间分布;借助SOURCE子程序依次对缓发裂变中子的发射位置、发射方向、发生核裂变反应的核素、缓发裂变中子所在的群组、发射时间及其初始能量等参数进行了抽样.结果表明,计算得到的缓发裂变中子衰减时间谱的时间特征与铀核素的缓发裂变中子群参数相符合.对缓发裂变中子总计数与地层铀含量之间的关系进行了线性拟合,拟合结果的相关系数平方值大于0.998 5,该结果从理论上验证了缓发裂变中子测井铀含量线性模型的正确性.