A numerical study is performed to determine the thermal response of a reactor vessel lower head following a studden contact of the core melt with the vessel wall during a severe accident. The major objective is to determine the transient wall temperature distribution, including possible hot spots within the lower head. The mathematical formulation involves a nonlinear coordinate tansformation which serves the dual purpose of fixing the moving interface between the crust and the melt pool, and simplifying the computational domain by coverting the crust and wall regimes into two adjacement square regions of equal length. The system is nodalized using an ortogonal grid with equal spacing in both the crust and steel regions. Results from the actual crust thickness distribution indicate a sharp decline in thickness from 4.37 x 10~(-2) m at the bottom center to 3.04 x 10~(-3) m at the upper edge. These results indicate that a hot spot is likely to form at the upper edge of the vessel. However, it would take an increase in molten pool heat flux of 80
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机译：进行了一项数值研究，以确定在严重事故期间堆芯熔体与容器壁突然接触后反应堆容器下盖的热响应。主要目的是确定瞬态壁温分布，包括下压头内可能出现的热点。数学公式涉及非线性坐标变形，其双重目的是固定地壳和熔池之间的移动界面，以及通过将地壳和壁体覆盖到两个等长的相邻正方形区域中来简化计算域。使用在地壳和钢区域均等间距的正交网格对系统进行节点化。实际地壳厚度分布的结果表明，厚度从底部中心处的4.37 x 10〜（-2）m急剧下降到顶部边缘处的3.04 x 10〜（-3）m。这些结果表明热点可能在容器的上边缘形成。但是，熔池的热通量将增加80
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