在反应堆上进行中子残余应力谱仪(RSND)的建设工程中，生物屏蔽是降低谱仪测量本底，保证工作人员安全的主要技术手段。为了对屏蔽系统进行优化设计，采用蒙特卡罗方法对其进行模拟计算。采用McStas和MCNP5两种计算程序，理论分析提高计算效率的方法和技巧，并分三步进行谱仪辐射场的计算。首先用McStas程序模拟热中子在导管中的输运过程，然后用MCNP程序计算了屏蔽块之间接合处的拼缝对谱仪辐射场的影响，最后建立整个谱仪屏蔽系统的MCNP模型，并进行计算。将经过用影响因素修正后的计算结果与现场剂量仪实测值进行比较，结果表明二者在允许的误差范围内基本一致。

The shielding is a key way to lower the measuring background and keep workers safe for residual stress neutron diffractometer (RSND) building on reactor. The shield plan was optimized with Monte Carlo codes. In view of its complexity, two programs, McStas and MCNP5, were used, with some good techniques to improve the computation efficiency. The calculation of radiating field in RSND was accomplished with three parts: the transmission of thermal neutron in guide was simulated with McStas, the radiating leakage was estimated with MCNP due to slits between shield blocks, and the whole shield plan for RSND was modeled in MCNP. Corrected with influencing factors, the simulated results were compared with data measured by dosimeter, and it was found that they fitted well and was within the permitted error.