Abstract The paper proposes an overview of an R&D program for Gen4 Sodium Fast Reactors that was launched in 2012 at CEA to investigate Na boiling dynamics under an Unprotected Loss of Flow scenario. Part of the program motivation was an incident periodic two-phase flow pattern (limit cycle) along the transient that was calculated at first. If proven, such a stable phenomenology could indeed attractively improve reactor safety by providing a time-window for recovering pumping power. The paper is restricted to the thermal–hydraulic side of the R&D initiative that targeted to credit prediction of the boiling flow dynamics. First, the 1-D numerical achievements obtained by simulating with CATHARE3 thermal hydraulic system code, some out-of-pile programs from the 70–80 s, are detailed. The latter were indeed already very informative on two-phase flow stability scenarios, by so offering a first sound qualification basis. Related benefits allowed by a recent air–water experimental program that supported some modifications of wall and interfacial closure laws, are pointed out. The second part of the paper outlooks the next technical route and its early advances. Part of it, is 3-D simulation by subchannel code TrioMC which first application shows its added-value to perform a detailed analysis of a scaled experiment. Predictive capabilities of 3-D approach will be also central to credit a full-scale transposition. Progress on flow stability analysis, including subcooled condensation as well as connected channel reflooding and pressure wave aspects, could be as such expected from recent developments on CFD. Indeed, advances for an all flow regimes representation opportunely suit Na boiling physics. Bifurcation and stability analysis with the developed BACCARAT model is finally identified as providing a tailored mathematical approach to connect the periodic flow pattern with a Hopf bifurcation. Its ability to provide a mechanistic view of the scenarios shift on a natural convection test-case, is reported. On the experimental side, the scope of a new program planed with IPPE on a wire-spaced 19 pins bundle, is briefly introduced. HARIBO program suits some Gen4 hydraulic design specifics and targets CATHARE3 and TrioMC qualification.

中文翻译：

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Na沸腾动力学的一些数值成果及下一步技术路线

摘要 本文概述了 2012 年在 CEA 启动的第 4 代钠快堆研发计划，以研究无保护流动损失情景下的 Na沸腾动力学。项目动机的一部分是沿着最初计算的瞬态的事件周期性两相流模式（极限循环）。如果得到证实，这种稳定的现象确实可以通过提供恢复泵送功率的时间窗口来有吸引力地提高反应堆安全性。该论文仅限于研发计划的热工水力方面，该计划旨在对沸腾流动动力学进行信用预测。首先，详细介绍了通过使用 CATHARE3 热力液压系统代码模拟获得的一维数值成果，以及一些 70-80 s 的堆外程序。通过提供第一个可靠的鉴定基础，后者确实已经为两相流稳定性场景提供了非常丰富的信息。指出了最近的空气-水实验计划所允许的相关好处，该计划支持壁和界面闭合定律的一些修改。论文的第二部分展望了下一条技术路线及其早期进展。其中一部分是通过子通道代码 TrioMC 进行的 3-D 模拟，第一个应用程序显示了它的附加值，以执行缩放实验的详细分析。3-D 方法的预测能力也将成为全面换位的核心。流动稳定性分析的进展，包括过冷冷凝以及连接的通道回灌和压力波方面，可以从 CFD 的最新发展中得到预期的进展。确实，所有流态表示的进展恰好适合 Na 沸腾物理学。使用开发的 BACCARAT 模型进行的分岔和稳定性分析最终被确定为提供了一种量身定制的数学方法，以将周期性流动模式与 Hopf 分岔连接起来。据报道，它能够提供自然对流测试用例上场景变化的机械视图。在实验方面，简要介绍了在 19 针线束上使用 IPPE 规划的新程序的范围。HARIBO 程序适合某些 Gen4 液压设计细节，并针对 CATHARE3 和 TrioMC 资格。使用开发的 BACCARAT 模型进行的分岔和稳定性分析最终被确定为提供了一种量身定制的数学方法，以将周期性流动模式与 Hopf 分岔连接起来。据报道，它能够提供自然对流测试用例上场景变化的机械视图。在实验方面，简要介绍了在 19 针线束上使用 IPPE 规划的新程序的范围。HARIBO 计划适合某些 Gen4 液压设计细节，并针对 CATHARE3 和 TrioMC 资格。使用开发的 BACCARAT 模型进行的分岔和稳定性分析最终被确定为提供了一种量身定制的数学方法，以将周期性流动模式与 Hopf 分岔连接起来。据报道，它能够提供自然对流测试用例上场景变化的机械视图。在实验方面，简要介绍了在 19 针线束上使用 IPPE 规划的新程序的范围。HARIBO 计划适合某些 Gen4 液压设计细节，并针对 CATHARE3 和 TrioMC 资格。