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首页> 外文期刊>Nuclear Technology >EFFECT OF REPLACING HELIUM WITH A LIQUID METAL IN THE FUEL-CLADDING GAP ON FISSION GAS RELEASE
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EFFECT OF REPLACING HELIUM WITH A LIQUID METAL IN THE FUEL-CLADDING GAP ON FISSION GAS RELEASE

机译：包气隙中液态金属置换氦气对裂变气体释放的影响

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In light water reactors, a helium-filled gap between the fuel and the cladding accommodates fuel swelling and cladding creepdown. However, the low thermal conductivity of helium results in a large ΔT over the gap before closure occurs. To remedy this situation, Wright et al. proposed the use of a liquid metal (LM) bond in the fuel-cladding gap. The LM (33 wt% each of lead, tin, and bismuth) was chosen for its low melting point (～ 120℃), its lack of chemical reactivity with UO_2 and water, and its high thermal conductivity (～100 times that of He). The thermal resistance of the LM-bonded gap is nil. Prior to closure of a helium-bonded gap, the center-line fuel temperature can be hundreds of degrees hotter than that with an LM-bonded gap at the same linear heat rating. Since the diffusion of fission gas atoms depends strongly upon temperature, it is expected that with the high thermal conductivity pellet-cladding gap, the incubation time to fission gas release should be considerably delayed. A modified Booth Sphere model, which takes into account re-solution, is adopted. The amount of fission gas atoms collected at the grain boundary is calculated using realistic time-temperature histories taken from a recent U.S. Nuclear Regulatory Commission review. The saturation value of gas at the grain boundary proposed by Dowling to fission gas release is adopted. The results show that although the temperature in the LM-bonded case is substantially lower than the He-filled case when the gap is open, the temperatures in the two cases equalize when the gap vanishes. Correspondingly, the two cases exhibit a comparable amount of fission gas at the grain boundary. Calculated differences between the times to saturation with LM and He in the gap are as high as ～ 1 yr and as low as 1 to 2 days.
机译：在轻水反应堆中，燃料和包壳之间的充氦间隙可容纳燃料溶胀和包壳蠕变。但是，氦气的低导热率会导致在闭合之前在间隙上产生较大的ΔT。为了纠正这种情况，Wri​​ght等人。建议在燃料包层间隙中使用液态金属（LM）键。选择LM（铅，锡和铋各33 wt％）是因为它的熔点低（约120℃），与UO_2和水的化学反应性差，导热系数高（是He的100倍） ）。 LM键合间隙的热阻为零。在关闭氦键合间隙之前，在相同的线性热额定值下，中心线燃料温度可能比带有LM键合间隙的中心温度高数百度。由于裂变气体原子的扩散强烈依赖于温度，因此可以预期，由于具有高导热率的颗粒包覆层间隙，裂变气体释放的孵育时间应大大延迟。采用考虑了重新求解的改进的Booth Sphere模型。晶粒边界处收集的裂变气体原子的数量是根据最近美国核监管委员会的审查得出的真实的时间-温度历史来计算的。采用Dowling提出的裂变气体释放的晶界处气体饱和度值。结果表明，尽管在间隙打开时LM结合情况下的温度明显低于He填充情况，但当间隙消失时，两种情况下的温度相等。相应地，这两种情况在晶界处表现出相当数量的裂变气体。间隙中LM和He达到饱和的时间之间的计算差异最大为〜1年，最小为1至2天。

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