基于EFEN-SP_3方法的pin-by-pin中子动力学计算方法研究

Study on Pin-by-pin Neutron Kinetics Calculation based on EFEN-SP_3 Method

为能直接给出安全分析所需的最热棒功率而不引入组件均匀化近似和精细功率重构近似,本文研究了基于栅元均匀化的pin-by-pin中子动力学计算方法。通过全隐式向后差分对多群时空中子动力学方程组的时间变量进行离散,采用指数函数展开节块-SP_3(EFEN-SP_3)方法求解含裂变介质的多群中子固定源方程组,通过高阶源展开技术消除了中子源分布与缓发中子先驱核分布形状不一致的问题。采用Ks因子、LW外推和粗网再平衡等加速技术提高计算效率。三维pin-by-pin中子动力学问题的数值结果表明:pin-by-pin中子动力学计算能直接给出单棒功率密度分布;高阶源展开技术可有效抑制计算偏差随时间步的累加效应;加速技术可将SP_3动力学计算的求解速度提高134.9倍。

To provide the hottest pin power for safety analysis without introducing the assembly homogenization and pin-power reconstruction,a three-dimensional pin-by-pin neutron kinetics calculation method was researched.The time-variable of the multi-group time-dependent neutron kinetics equations was discretized by using the fully-implicit backward finite difference method.The EFEN-SP3(exponential function expansion nodal-SP3)method was employed to solve the multi-group neutron fixed source equations containing fission medium.To eliminate the inconsistency between neutron source distribution and precursor solution distribution,the EFEN-SP3 method was improved with high-order source expansion technique.To enhance the computing efficiency,acceleration technologies including Ks factor,LW extrapolation and coarse-mesh rebalancing were adopted.Numerical results based on three-dimensional pin-by-pin neutron kinetics calculation show that pin-by-pin neutron kinetics calculation can directly provide the pin-by-pin power distribution.The high-order source expansion can suppress the deviation increasing in terms of time steps effectively.A speedup of 134.9 times can be provided by the acceleration technologies.