In order to enhance the ability of severe accident mitigation for Pressurised Water Reactor (PWR), different kinds of severe accident mitigation strategies have been proposed. In-Vessel Retention (IVR) is one of the important severe accident management means by External Reactor Vessel Cooling. Reactor cavity would be submerged to cool the molten corium when a severe accident happens. The success criterion of IVR strategy is that the heat flux which transfers from the corium pool must be lower than the local critical heat flux (CHF) of the reactor pressure vessel (RPV) outside wall and the residual thickness of the RPV wall can maintain the integrity. The residual thickness of RPV is determined by the heat flux transfer from the corium pool and the cooling capability of outer wall of the RPV. There are various factors which would influence the CHF and the cooling capability of outer wall of the RPV. In order to verify the optimized design which is beneficial to the heat transfer and the natural circulation outside the actual reactor vessel, a large-scale Reactor Vessel External Cooling Test (REVECT) facility has been built. A large number of sensitivity tests were carried out, to study how these sensitivity factors affect CHF value and natural circulation. Based on the test results, the structure of the test section flow channel has an obvious effect on the CHF distribution. The flow channel optimized can effectively enhance the CHF value, especially to enhance the CHF value near the “heat focus” region of the molten pool. The water level in the reactor pit has also a great impact on the natural circulation flow. Although natural circulation can be maintained with a low water level, it will lead to a decrease of the cooling capacity. Meanwhile, some noteworthy test phenomena have been found, which are also essential for the design of the reactor pit flooding system.

中文翻译：

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先进压水堆反应堆腔注水系统自然循环特性关键影响因素研究

为了提高压水堆（PWR）的严重事故缓解能力，已经提出了各种缓解严重事故的策略。船内滞留（IVR）是通过外部反应堆容器冷却进行的重要严重事故管理手段之一。当发生严重事故时，反应堆腔将被淹没以冷却熔融的皮质。IVR策略的成功标准是从皮质池传递的热通量必须低于反应堆压力容器（RPV）外壁的局部临界热通量（CHF），并且RPV壁的剩余厚度可以保持诚信 RPV的剩余厚度取决于从皮质池传出的热通量和RPV外壁的冷却能力。有多种因素会影响RPV的CHF和外壁的冷却能力。为了验证优化设计，该设计有利于实际反应堆容器外部的热传递和自然循环，已建造了大型反应堆容器外部冷却测试（REVECT）设施。进行了大量的敏感性测试，以研究这些敏感性因素如何影响CHF值和自然循环。根据测试结果，测试段流道的结构对CHF分布有明显影响。优化的流道可以有效地提高CHF值，特别是提高熔池“热焦点”区域附近的CHF值。反应堆坑中的水位对自然循环流量也有很大影响。尽管可以在低水位的情况下保持自然循环，但会导致冷却能力下降。同时，发现了一些值得注意的测试现象，这对于反应堆坑注水系统的设计也是必不可少的。