Part I of this study introduced a novel methodology for the optimization of energy group structures to be used in diffusion calculations of Sodium cooled Fast Reactors. The goal of the optimization is to speed up calculations, particularly in transient analyses, while maintaining an acceptable accuracy of the results.

The proposed methodology is based by either direct or simulated annealing search techniques. The capabilities of the method were preliminarily demonstrated on a single core state of the Superphénix reactor by using the DYN3D nodal diffusion code.

The scope of Part II is the further demonstration of the methodology efficiency through its application to more challenging “real-life” cases. In this respect, a static Superphénix neutronic benchmark comprising 13 different core states and a transient test initiated by an increase of the core inlet temperature at the Phénix reactor are considered.

For both Superphénix and Phénix reactor cores, 2- to 12-group optimal condensed energy group structures are identified using the 24-group structure as a starting point. The obtained optimal structures are thus employed in DYN3D and compared to the reference 24-group DYN3D solutions.

The outcomes show that also for a broader range of core configurations and under transient conditions the optimal energy group structures allow for significant acceleration of the DYN3D performance with practically negligible degradation of the solution accuracy.

本研究的第一部分介绍了一种用于优化用于钠冷快堆扩散计算的能量组结构的新方法。优化的目标是加快计算速度，尤其是在瞬态分析中，同时保持可接受的结果准确性。

所提出的方法基于直接或模拟退火搜索技术。通过使用 DYN3D 节点扩散代码，在 Superphénix 反应堆的单核状态上初步证明了该方法的能力。

第二部分的范围是通过将其应用于更具挑战性的“现实生活”案例来进一步证明该方法论的效率。在这方面，考虑了包含 13 个不同堆芯状态的静态 Superphénix 中子基准测试和由 Phénix 反应堆堆芯入口温度升高启动的瞬态测试。

对于 Superphénix 和 Phénix 反应堆堆芯，以 24 族结构为起点，确定了 2 至 12 族最优凝聚能群结构。因此，在 DYN3D 中采用了获得的最佳结构，并与参考 24 组 DYN3D 解决方案进行了比较。

结果表明，对于更广泛的核心配置和瞬态条件下，最佳能量组结构允许显着加速 DYN3D 性能，而解决方案精度的降低几乎可以忽略不计。