基于动态差分法的压水堆一回路放射性核素浓度分析

摘要

本文通过分析一回路冷却剂在堆芯辐照区、非辐照区、稳压器及化容控制系统中的流动特性,建立核素浓度的动态差分数学模型,模型特征参数可根据实际操作情况进行调整,将每次取水测量值对数学模型计算初始值进行修正,以准确地反映核素浓度变化情况.应用所建立的动态差分数学模型针对某一典型压水堆的实际运行工况进行计算,并将计算结果与Profip5程序计算值进行对比,验证了所建立的数学模型的准确性.然后,对压水堆一回路放射性核素浓度进行计算分析,得到一回路冷却剂核素浓度和辅助系统中核素平衡浓度,以及各系统核素浓度随时间的变化规律和停堆时一回路核素的浓度变化规律.结果表明,所建立的动态差分数学模型冷却剂核素计算值与Profip5计算值相差不大,化容控制系统对一回路放射性核素的净化率与国家标准中提供的净化率相吻合,方程组可用于压水堆不同工况下冷却剂核素浓度计算,在燃料破损监测时,对分析破损发生的时间、预估破损后冷却剂核素浓度峰值、计算破口所在燃耗区域及大小均有重要意义.%The method to construct the dynamic differential equations of radionuclide concentration in primary loop was introduced in the paper.The data detected from coolant in primary loop were assigned to the equations' initial value and the parameters of the equation could be adjusted by actual operation to reflect the real change of the concentration.The equations whose parameters were based on the actual operation situation from typical PWR were proved applicable compared with the results calculated by the current existing algorithm Profip5.Through analysis of the concentration of radionuclides calculated by the equations,the equilibrium value and the trend of concentration in primary loop and auxiliary systems were shown.The regular pattern of change for radionuclide concentration in primary loop under the cold down condition was also revealed in this paper.The results show that the calculated values of dynamic differential equations agree well with the results from Profip5,and the purification rate of radionuclides in primary loop by the chemical and volume control system conforms to the national standards.That means the equations can be used to calculate the concentration of radionuclides in the coolant.When detecting the fuel element failure,calculated concentrations have important significance to ascertain the time when failure happens and deduct the maximal value of actual concentration,the burnup area and size of the break.