Abstract The article presents the results of three-dimensional numerical analysis to assess the natural convection heat transfer in pool-type sodium-cooled fast reactors during post-accident heat removal. To improve the coolability of the destroyed core, suitable modifications in core catcher design are suggested. The equations for conservation of mass, momentum and energy are solved in their transient form using finite volume based discretization in ( r , θ , z ) system. Turbulence is modeled using the k − ω SST model based on sensitivity analysis of different turbulence models and validation exercises. A comparative analysis of 3-D and 2-D simulations is carried out. Various feasible geometrical arrangements for core collection trays are analyzed in detail for better coolability of the core debris by natural convection. Multiple debris collection trays with and without cooling pipes are studied towards achieving coolability of core debris in case of core disruptive accident. Results show that better safety margins are achieved by using 3-D as compared to 2-D simulation. The incorporation of cooling pipes in distributed heat sources on multiple trays leads to enhanced coolability of the debris within the vessel. Maximum temperatures on the core catcher/collection trays and in the core debris (with the selected core catcher design) are 860 K and 932 K respectively. These are substantially below the acceptable thermal design limits. Furthermore, detailed insight of the flow field confirms the turbulence in the lower plenum, partly due to impingement of passive jets from multiple cooling pipes on core debris and partly due to flow bypass through the slots at upper tray. It is established that the use of passive pipes and multi-tray concept for core catcher can successfully accommodate the whole core debris arising from core disruptive accidents within the main vessel without exceeding the safe thermal design limits.

中文翻译：

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在快堆中使用被动方法增强来自发热堆芯碎片的热传递：3-D CFD 分析

摘要 本文介绍了三维数值分析的结果，用于评估池式钠冷快堆在事故后除热过程中的自然对流换热。为了提高被破坏的堆芯的冷却能力，建议对堆芯收集器的设计进行适当的修改。质量、动量和能量守恒方程在 (r, θ, z) 系统中使用基于有限体积的离散化以瞬态形式求解。湍流使用基于不同湍流模型和验证练习的敏感性分析的 k − ω SST 模型进行建模。进行了 3-D 和 2-D 模拟的比较分析。详细分析了岩心收集盘的各种可行几何布置，以通过自然对流更好地冷却岩心碎片。研究了带和不带冷却管的多个碎片收集托盘，以在发生堆芯破坏事故时实现堆芯碎片的冷却。结果表明，与 2-D 模拟相比，使用 3-D 可以实现更好的安全裕度。在多个托盘上的分布式热源中加入冷却管可提高容器内碎屑的冷却能力。岩心捕集器/收集盘和岩心碎片（采用所选岩心捕集器设计）的最高温度分别为 860 K 和 932 K。这些大大低于可接受的热设计限制。此外，对流场的详细观察证实了下气室中的湍流，部分原因是来自多个冷却管的被动射流撞击堆芯碎片，部分原因是流经上塔盘的槽道。确定使用被动管道和多托盘概念进行取芯器可以成功地容纳主容器内堆芯破坏事故产生的整个堆芯碎片，而不会超过安全热设计限制。