压水堆三维全堆芯Pin-by-pin瞬态分析

Three-Dimensional Pin-by-pin Transient Analysis for PWR-Core

为了保证核反应堆在瞬态过程中的安全性,需要进行三维全堆芯的瞬态分析,给出安全分析关注的燃料棒功率分布。本研究建立了压水堆三维全堆芯Pin-by-pin核热耦合瞬态分析的理论模型:采用全隐式向后差分方法和指数函数展开节块法实现了三维全堆芯Pin-by-pin时空中子动力学计算;采用栅元尺度的多通道模型进行三维全堆芯Pin-by-pin热工反馈计算;采用Picard迭代实现了核热紧耦合迭代计算;利用信息传递接口(MPI)并行技术,采用统一的空间区域分解方式,实现了核热耦合瞬态过程的并行计算。基于理论模型,开发了相应的程序Bamboo-Transient2.0,采用基准题和多组件问题对程序进行验证,并将其应用于商用压水堆瞬态分析。结果表明:Pin-by-pin瞬态分析程序较之组件均匀化的粗网扩散程序结果更加精细,有效改善了棒功率分布的偏差,同时能够给出栅元尺度下的各状态参数分布情况,可直接满足安全分析需求。

In order to ensure the safety of nuclear reactor in transient process,it is necessary to carry out three-dimensional transient analysis of the whole core to obtain the power distribution of fuel rods concerned in the safety analysis.In this paper,a theoretical model of the pin-by-pin neutronic-thermohydraulic coupling transient analysis for PWR-core is established:the threedimensional pin-by-pin spatio-temporal neutron dynamics calculation of PWR-core is realized by fully implicit backward difference method and exponential function expansion nodal method;the multi-channel model of cell scale is used to calculate the thermal feedback of three-dimensional full core pin-by-pin;the Picard iteration is used to realize the iterative calculation of neutronicthermohydraulic tight coupling;using the parallel technology of message passing interface(MPI)and the unified spatial domain decomposition method,the parallel calculation of neutronicthermohydraulic coupling transient process is realized.Based on the theoretical model,the corresponding code called Bamboo-Transient 2.0 was developed and verified by the benchmark and multi-assemblies questions,and it was then applied to the transient analysis for commercial PWRs.The results show that the pin-by-pin transient analysis code has more fine results than that of the traditional coarse-mesh diffusion code based on assembly homogenization,and it can reduce the deviation of power distribution of pin-cell.Meanwhile,it can provide the distribution of state parameters at cell scale,which can directly meet the requirements of safety analysis.