Churchill-Chu关系式在极薄金属层内传热的适用性研究

在假设的堆芯融毁事故中，反应堆压力容器的下封头内可能会形成分层的熔池结构。底部重金属层的形成会导致熔池顶部的金属层高度逐渐降低，使得顶部金属层的侧壁热聚焦效应逐渐增强，压力容器有可能会失效。本文通过开展HELM?LR试验，针对薄金属层在低高度条件下的传热进行了研究。结果表明，Churchill?Chu径向传热关系式在低高度的条件下依然适用。Churchill?Chu关系式在低高径比且以水为工质的条件下，计算结果偏不保守。将Churchill?Chu关系式运用到反应堆的熔池结构案例中发现，随着氧化物层衰变功率的增大和薄金属层高度的降低，氧化物层的等温边界假设将不再适用；虽然薄金属层侧壁的热聚焦效应仍会随其高度的降低而逐渐增强，但增加速度变缓慢。

Applicability of Churchill-Chu Correlation in Heat Transfer Calculation of Thin Metallic Layer with Extremely Low Aspect Ratio

In the postulated nuclear core melt accident, a stratified molten pool configuration would be formed in the lower head of the nuclear reactor pressure vessel. The formation of the heavy metallic layer leads to the decrease of the height of the thin metallic layer, consequently, the thermal focusing effect in the sidewall of the top metallic layer would be enhanced and it is possible for the vessel failure. The heat transfer behavior of thin metallic layer experiment for the low aspect ratio (HELM?LR) was performed to investigate the heat transfer in the thin metallic layer under the low aspect ratio condition. The experimental results indicate that Churchill-Chu correlation is still suitable for lateral heat transfer calculation under the low aspect ratio condition. Its calculated results are slightly less conservative under the condition of the low aspect ratio and water as the simulant. Applicating the Churchill-Chu correlation to the molten pool in the nuclear reactor case, it is found that increasing the decay power of the oxidic layer and decreasing the height of the thin metallic layer might lead to the failure of the hypothesis of isothermal boundary for the oxidic layer. The thermal focusing effect of the sidewall still increases with the decrease of the height of the thin metallic layer, but the increasing rate becomes slow.