三维离散纵标和蒙特卡洛混合方法研究

Research on Three Dimensional Discrete Ordinate and Monte Carlo Hybrid Method

对于深穿透类型的屏蔽计算,为了得到较为可信的统计结果,蒙特卡洛(MC)方法需要模拟大量的粒子,巨大的计算时间是其存在的主要问题。源偏倚和权窗技巧能够有效地降低深穿透问题的计数误差。本文开展了三维离散纵标(SN)方法-MC混合方法研究,根据SN方法的共轭注量率计算并生成了源偏倚和权窗参数,编写了MCNP程序的源抽样子程序,并且在秦山核电厂一期测量值基础上进行了验证,成功应用到CAP1400反应堆压力容器快中子注量率计算中。数值结果表明,对于深穿透屏蔽计算问题,和无偏的MC方法相比,三维SN-MC混合方法能够在保证结果精度的前提下,提高计算效率1~2个数量级。

For deep-penetration shielding calculation, Monte Carlo （MC） method requires the modeling of a great number of particles to obtain reliable results, thus huge computation time is the main problem of the MC method. Source biasing and weight window technique effectively decrease the tally error of deep penetration problem. This paper studies the 3D Discrete Ordinate （SN）-MC hybrid method, generates source biasing factors and weight window parameters for the MC method by using the adjoint fluence rates of the SN method, develops source sampling subroutine for MCNP, and verifies the hybrid method in the measurements in Qinshan Nuclear Power Plant I. The method is then applied in the calculation of CAP1400 reactor pressure vessel fast neutron fluence rate. Numerical results show that 3D SN-MC hybrid method increases the calculation efficiency by I to 2 orders for deep-penetration shielding calculation with high precision compared with unbiased MC method.