The methods and performance of a 3D pin-by-pin neutronics code based on the 2D/1D decoupling method are presented. The code was newly developed as an effort to achieve enhanced accuracy and high calculation performance that are sufficient for the use in practical nuclear design analyses. From the 3D diffusion-based finite difference method (FDM) formulation, decoupled planar formulations are established by treating pre-determined axial leakage as a source term. The decoupled axial problems are formulated with the radial leakage source term. To accelerate the pin-by-pin calculation, the two-level coarse mesh finite difference (CMFD) formulation, which consists of the multigroup node-wise CMFD and the two-group assembly-wise CMFD is implemented. To enhance the accuracy, both the discontinuity factor method and the super-homogenization (SPH) factor method are examined for pin-wise cross-section homogenization. The parallelization is achieved with the OpenMP package. The accuracy and performance of the pin-by-pin calculations are assessed with the VERA and APR1400 benchmark problems. It is demonstrated that pin-by-pin 2D/1D alternating calculations within the two-level 3D CMFD framework yield accurate solutions in about 30 s for the typical commercial core problems, on a parallel platform employing 32 threads.

介绍了基于 2D/1D 解耦方法的 3D 逐针中子学代码的方法和性能。该代码是新开发的，旨在提高精度和计算性能，足以在实际核设计分析中使用。根据基于 3D 扩散的有限差分法 (FDM) 公式，通过将预先确定的轴向泄漏作为源项来建立解耦平面公式。解耦的轴向问题用径向泄漏源项表示。为了加速逐针计算，实现了由多组节点方式 CMFD 和两组装配方式 CMFD 组成的两级粗网格有限差分 (CMFD) 公式。为了提高准确性，不连续因子方法和超均质化 (SPH) 因子方法均用于针状横截面均质化。并行化是通过 OpenMP 包实现的。逐针计算的准确性和性能通过 VERA 和 APR1400 基准问题进行评估。结果表明，在采用 32 个线程的并行平台上，两级 3D CMFD 框架内的逐针 2D/1D 交替计算可在大约 30 秒内为典型的商业核心问题提供准确的解决方案。