中文摘要：

为准确划分应急等级,本文采用最佳估算模型,以源项计算耦合热工水力分析、堆芯物理分析程序对船用堆典型事故——大破口失水事故进行仿真,首先根据relap5/mod3.2程序计算出事故后临界管元件包壳峰值温度,同时找到包壳破损对应的临界功率因子;然后运用堆芯物理粗网格节块程序结合高阶多项式重构方法对所有组件进行精细功率重构,得到组件内的相对功率分布;根据堆内功率因子的分布,计算出破损元件份额,最后进行放射性后果分析,得到较为合理的源项结果,为应急决策提供依据。

英文摘要：

Aiming at defining the grade of nuclear emergency response,the best estimate model has been adopted;the simulation of large break loss of coolant accident（LBLOCA） has been carried out by the radioactive analysis software coupled with relap5/mod3.2 and core physics model.First,the peak clad temperature of the critical failure channel is calculated in relap5 code,and simultaneously its power factor is obtained.Second,pin power distribution of the fuel assemblies has been calculated in coarse-mesh nodal method.According to the pin power distribution in the whole core and the result gained above,the fraction of fuel element fracture is calculated.Finally,the radioactive analysis has been carried out and the reasonable source term is gotten,which can offer reference for the nuclear emergency decision making.