基于蒙特卡罗-离散纵标双向耦合方法的堆坑粒子注量率计算

为有效解决大型复杂核设施屏蔽计算问题，研究了三维蒙特卡罗(MC)-离散纵标（S_N）双向耦合方法，通过自主开发接口程序实现MC粒子概率分布与S_N角通量密度之间的相互转换，实现MC-S_N双向耦合计算。将基于MC-S_N双向耦合方法的程序用于某反应堆堆坑底部粒子注量率计算。利用MC程序建立堆芯及堆坑处的精细模型进行计算，三维S_N程序用于堆芯下表面与压力容器底面之间区域的计算。通过MC-S_N-MC两步耦合计算，给出堆坑通道及小室内的中子和光子注量率。三维MC-S_N双向耦合方法计算结果与单一MCNP程序结果吻合较好，初步验证了该方法是解决大型复杂核装置屏蔽问题的有效工具。

Particle Fluence Rate Calculation of Reactor Pit Based on MC-SN Bidirectional Coupled Method

In order to effectively solve the shielding problem with complex geometric and bulk shields of nuclear facility, the three dimensional Monte Carlo (MC)-discrete ordinates (S_N ) bidirectional coupled method was developed. The transform between particle probability distribution of MC and angle flux density of S_N was realized by a self-developed interface program to achieve the coupling calculation. The test calculation was taken by the application of the MC-S_N bidirectional coupled method on the particle fluence rate calculation of reactor pit bottom. Monte Carlo code was employed to accurately simulate the structure of core and the model of reactor pit, while the 3D S_N code was used for the calculation from the core bottom surface to the pressure vessel bottom region. Neutron and photon fluence rates of reactor pit channel and indoor were calculated by MC-S_N-MC two step coupled method. The calculation results were compared with results of MCNP and satisfactory agreements were obtained. The results demonstrate that the method is an effective tool to solve the shielding problem of large complex shielding of nuclear facility.