本報告在探討液態金屬次通道內燃料棒表面的溫度分佈，分為兩種事故分析。首先為正常案例分析，其液態金屬在緊密排列的燃料棒三角形次通道內流動；另一種為偏心案例分析，此案例重點在於典型燃料棒組件裡中心燃料棒偏移的影響。本研究利用計算流體力學(Computational Fluid Dynamics)軟體FLUENT，在穩態熱傳導、完全發展流且考慮局部流體混合的條件下來進行模擬分析。
在正常案例的分析裡，數值結果顯示在燃料棒表面的環向溫度分佈是不均勻的，可以想像此種現象在偏心燃料棒組件裡會更加嚴重。研究結果顯示燃料棒表面溫度在次通道空間較窄的區域會有較高的溫度，此現象在緊密排列的偏心燃料棒組件裡會更加明顯。即使中心燃料棒偏移的程度僅有一點點的距離，中心燃料棒表面的最大溫度差還是會高達54K左右，其燃料棒的直徑為4.7mm。這種現象是非常嚴重的，可能會產生不必要的熱應力，嚴重的話還會導致燃料元件失效。

A numerical study on fuel rod surface temperature distributions in liquid metal cooled sub-channel flow is presented in this paper. There are two kinds of accident analysis. First is normal case, liquid metal is arranged to flow through triangular sub-channels in rather compact fuel rod lattice. Another accident is eccentric case, it is focused on the effects of misaligned central fuel rod in typical fuel rod cluster geometries. Numerical models based on FLUENT, a Computational Fluid Dynamics (CFD) commercial software, are developed to model steady state fuel thermal conductions, fully-developed turbulent convective flows, and local flow mixing.
In normal case, the numerical results show the temperature distributions in the azimuthal direction are non-uniform. One could imagine that such situations will be more apparent when one has eccentric geometry in a misaligned fuel lattice. Numerical results show that fuel rod surface temperatures are higher for surfaces facing the narrow gap of the sub-channel. Situations are worse for cases where misaligned fuel rods exist in tightly packed fuel rod clusters. Even for a small amount of rod center deviation, such temperature differences can be as high as 54 K around a fuel rod whose diameter is only 4.7 mm. The situations could be very serious and might generate unnecessary thermal stresses and cause fuel failure.

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