During irradiation in a nuclear reactor, the UO₂ fuel and the Zr cladding come into contact due to fuel thermal expansion and cladding creep. The inner surface of the Zr cladding in contact with the UO₂ fuel therefore oxidizes. This paper analyzes the microstructure of zirconia formed at the Zr cladding/UO₂ interface in two samples with different burnups. It seems that the zirconia develops ‘normally’ until it comes into contact with the fuel. The development of internal zirconia is, however, constrained mechanically by the contact of the UO₂ fuel. Four different zones can be distinguished in the zirconia layer of each sample. In the medium-burnup sample (37 GWd/tU), the zirconia in the first zone in contact with the cladding exhibits the same kind of microstructure as ‘ordinary’ zirconium oxide formed on the cladding outer surface, which is characterized by columnar and equiaxed grains. Thereafter, two intermediate zones can be observed: a first composed of very small equiaxed grains and a second with a mixture of intermediate and large grains. In the high-burnup sample (61 GWd/tU), zirconia presents a wavy interface with some circumvolutions. The ZrO₂ in contact with the fuel is more developed in this case than in the medium-burnup sample, but it shows the same microstructure.

在核反应堆中辐照期间，由于燃料热膨胀和包壳蠕变，UO ₂燃料和 Zr 包壳接触。与UO ₂燃料接触的Zr包层的内表面因此被氧化。本文分析了两种具有不同燃耗的样品在 Zr 包层/UO ₂界面形成的氧化锆的微观结构。氧化锆似乎“正常”发展，直到与燃料接触。然而，内部氧化锆的发展受到 UO ₂接触的机械限制燃料。在每个样品的氧化锆层中可以区分四个不同的区域。在中等燃耗样品 (37 GWd/tU) 中，与包层接触的第一区的氧化锆表现出与包层外表面上形成的“普通”氧化锆相同的微观结构，其特征是柱状和等轴状谷物。此后，可以观察到两个中间区域：第一个由非常小的等轴晶粒组成，第二个由中等和大晶粒的混合物组成。在高燃耗样品 (61 GWd/tU) 中，氧化锆呈现出带有一些回旋的波浪形界面。在这种情况下，与燃料接触的 ZrO ₂比中等燃耗样品中的更发达，但它显示出相同的微观结构。