Clad ballooning, which is a plastic instability, results in sudden large deformation and thereby coolant flow blockage in case of transients in a nuclear reactor. We report the experimental findings in the present paper. Experiments have been carried out to investigate the effect of ballooning in fast reactors, where Fe-based alloys are used as clad material. Real-time X-ray imaging captured the evolution of ballooning and rupture, which occurred within a short duration. It was seen that there was material instability until the point of onset of ballooning and thereafter the plastic instability was observed. Microstructural investigations carried out on various regions of the failed specimen showed that there is significant grain coarsening and a drastic drop in the hardness values in the ballooned region when compared to the unaffected region. Fractography tests of the ballooned specimen confirmed the presence of fine dimples at the ballooned region, which is a signature of ductile failure.

包层膨胀是一种塑性不稳定性，在核反应堆发生瞬变的情况下会导致突然的大变形，从而导致冷却剂流动阻塞。我们在本文中报告了实验结果。已经进行了实验来研究快堆中膨胀的影响，其中铁基合金用作包覆材料。实时 X 射线成像捕获了在短时间内发生的膨胀和破裂的演变。可以看出，材料不稳定性直到膨胀开始点，然后观察到塑性不稳定性。对失效试样的各个区域进行的微观结构研究表明，与未受影响的区域相比，膨胀区域的晶粒显着粗化，硬度值急剧下降。