深穿透屏蔽计算中MCNP减方差技巧应用及比较

Application and Comparison of MCNP Variance Reduction Techniques for Deep Penetration Shielding Calculation

在中子输运的深穿透屏蔽计算中,采用有效的MCNP减方差技巧可以有效缩减计算时间提高计算效率。以一维聚变反应堆(CFETR)平板模型作为深穿透屏蔽计算实例,分别应用了几何分裂与轮盘赌、源偏倚、强迫碰撞、权窗、指数变换等减方差技巧,对各种减方差技巧应用过程中遇到的如中子平分布问题,全零权窗问题等问题,进行了分析总结,并在此基础上提出了针对深穿透问题的新的解决思路。通过不同方法分析和组合,获得了权窗和指数变换的最佳组合,使计算效率加速了162倍。

For the neutron deep penetration problem, application of variance reduction （VR）techniques in MC- NP could increase the calculation efficiency and decrease the simulation time. For the one - dimensional fusion reactor（CFETR） slab model, geometry splitting and Russian roulette, biasing the source, forced collision, weight window and exponential transform were experimented and analyzed. Practical problem of VR application was reasoned and summarized, like particle flat distribution problem, all zeros in weight window problem. Some new thoughts of VR technique for deep penetration shielding problem were introduced. Through different combi- nations of VR techniques, the combination of weight window and exponential transform performed well that a- chieved 162 times than the analogue simulation.