内部内部保留（IVR）作为严重的事故管理策略

介绍

During a rare accident involving severe core damage in a Nuclear Power Plant (NPP), if the molten core material can be contained within the boundary of the reactor vessel, the severity of the accident is expected to be greatly reduced. Therefore, the severe accident management strategy based on in-vessel retention (IVR) of molten core debris is highly desirable, and has been adopted by advanced reactor designs such as VVER, AP1000 and APR1400. In these designs, the IVR strategy requires NPP operators to perform specific actions including: a) Opening valves to depressurize the reactor vessel and reduce the stress in the reactor vessel lower head b) Flooding the reactor cavity to a certain high level to ensure the reactor vessel is covered and cooled by water from the outside c) Injecting water into the reactor vessel after the vessel is fully depressurized to increase the probability of IVR success One of advantages of the IVR strategy is that the actions required in this strategy can be performed without AC power.

Issues Related to IVR Success

IVR的成功取决于从熔融核心材料（Corium）到反应器容器壁的热通量。热通量不得超过使容器失败的机械和热极限。机械限制是由于必须将反应器容器壁烧杯至非常小的厚度，以使热通量通过其进行。但是，如果容器壁太薄，则无法支撑下部头部墙壁的皮rium毛的重量。在这种情况下，船只将逐渐失败。热极限是由于以下事实，即热通量不得超过反应堆容器壁外表面上的临界热通量（CHF）。如果热通量超过CHF，则反应器容器壁温将迅速升高并导致故障。

从血管内到反应堆容器的热通量沿容器壁不均匀。在IVR研究人员中已经商定了最高的热通量可能发生在西果的顶部，在西果池的顶部，在那里，在那里，在那里，在那里，海池中的金属材料与较重的氧化材料隔离以形成金属层。金属层越薄，越大通量向墙壁，导致所谓的“聚焦效果”。理想情况下，将有足够数量的金属，包括钢和未氧化的ZR，可以在顶部形成厚的金属层。但是，在某些条件下，海rium中的非氧化ZR可以降低r骨中的UO2形成U金属。共晶U，ZR和钢比氧化材料重，并留在骨的底部形成重金属层。假定重金属以除去顶部（轻）金属层中的钢，从而使轻质金属层变薄，“聚焦效果”更糟。

Capabilities of MAAP5 Code for IVR Analysis Application

IVR analysis is challenging and, in many situations, requires simulations using integral a severe accident thermal hydraulic code. An appropriate code is the Modular Accident Analysis Program (MAAP), which is owned by the Electric Power Research Institute (EPRI) and developed and maintained by Fauske & Associates, LLC (FAI). The latest official revision of the MAAP5 code, MAAP5.03, is equipped with comprehensive models of the corium pool in the lower plenum, reactor vessel and in- and ex-vessel heat transfer. The key features of the models are discussed below. Page 1 Technical Bulletin No: N-16-07 In-Vessel Retention (IVR) as a Severe Accident Management Strategy By: Quan Zhou, Ph.D., Sr. Nuclear Engineer, Fauske & Associates, LLC

如图1（a）所示，MAAP5假设金属材料一旦骨出现在下部头部。如果海rium进入水液的下头，则由于燃料冷却液相互作用（FCI），皮菌可能会碎裂。碎片的冷冻石灰颗粒作为分隔金属层和氧化层的地壳顶部的颗粒床。随着粒子床的融化，熔融质量被添加到光金属层和氧化层中，最终导致了两层模型，如图1（b）所示。在某些情况下，可以在氧化层的下部形成重金属层，然后将rui池建模为三层结构，如图1（c）所示。