The implementation and optimization strategies of the neutron tracking algorithms in the GPU-based continuous-energy Monte Carlo (MC) code PRAGMA are presented. The strategies consist of 1) a mixed precision technique, 2) an event-based tracking algorithm, 3) the history-based tracking algorithm improved for GPUs by imposing transition limits, 4) the region partitioning and energy sort schemes to vectorize macroscopic cross section calculations, 5) the unionized grid method improved by a linear hashing scheme, and 6) the GPU-specific implementation techniques such as the use of built-in vector types and an array-based race-free bank algorithm utilizing GPU atomic addition. The developed algorithms and strategies are examined for pin cell and full-core problems consisting of fresh and depleted fuels. PRAGMA turned out to be especially efficient in depleted fuel calculation; PRAGMA effectively overcame the performance drop in the depleted fuel calculation by vectorized cross section calculation. In the full-core calculations PRAGMA also rendered outstanding performance; calculations employing 11.5 billion histories and 20 consumer-grade GPUs could be finished within 15 min for a 3D APR1400 fresh core problem, and within half an hour for a mock-up depleted core problem.

介绍了基于 GPU 的连续能量蒙特卡罗 (MC) 代码 PRAGMA 中中子跟踪算法的实现和优化策略。这些策略包括 1) 混合精度技术，2) 基于事件的跟踪算法，3) 通过施加过渡限制为 GPU 改进的基于历史的跟踪算法，4) 用于矢量化宏观横截面的区域划分和能量排序方案计算，5) 通过线性散列方案改进的联合网格方法，以及 6) 特定于 GPU 的实现技术，例如使用内置向量类型和利用 GPU 原子加法的基于数组的无竞争银行算法。针对由新鲜燃料和耗尽燃料组成的针电池和全核问题，对开发的算法和策略进行了检查。事实证明，PRAGMA 在消耗燃料计算方面特别有效；PRAGMA 通过矢量化截面计算有效地克服了耗尽燃料计算中的性能下降。在全核计算中PRAGMA也呈现出优异的表现；对于 3D APR1400 新核心问题，使用 115 亿条历史记录和 20 个消费级 GPU 的计算可以在 15 分钟内完成，对于模型耗尽核心问题，可以在半小时内完成。