To improve the capability of the SAS4A code, which simulates the initiating phase of core disruptive accidents for MOX-fueled Sodium-cooled Fast Reactors (SFRs), the authors have investigated in detail the physical phenomena under unprotected loss-of-flow (ULOF) conditions in a previous paper (Kawada and Suzuki, 2020) [1]. As the conclusion of the last article, fuel stub motion, in which the residual fuel pellets would move toward the core central region after fuel pin disruption, was identified as one of the key phenomena to be appropriately simulated for the initiating phase of ULOF.

In the present paper, based on the analysis of the experimental data, the behaviors related to the stub motion were evaluated and quantified by the author from scratch. A simple model describing fuel stub motion, which was not modeled in the previous SAS4A code, was newly proposed. The applicability of the proposed model was validated through a series of analyses for the CABRI experiments, by which the stub motion would be represented with reasonable conservativeness for the reactivity evaluation of disrupted core.

为了提高 SAS4A 代码的能力，该代码模拟 MOX 燃料钠冷快堆 (SFR) 堆芯破坏性事故的起始阶段，作者详细研究了无保护流量损失 (ULOF) 下的物理现象前一篇论文中的条件（Kawada 和 Suzuki，2020 年）[1]。作为上一篇文章的结论，燃料棒运动，其中残余燃料芯块在燃料棒破裂后向核心中心区域移动，被确定为 ULOF 起始阶段需要适当模拟的关键现象之一。

在本文中，基于对实验数据的分析，作者从头开始评估和量化与短柱运动相关的行为。新提出了一个描述燃料短管运动的简单模型，该模型在以前的 SAS4A 代码中没有建模。通过对 CABRI 实验的一系列分析验证了所提出模型的适用性，通过这些分析，短截线运动将以合理的保守性来表示，用于被破坏的岩心的反应性评估。