Microstructure evolution in Zr1Nb fuel cladding during high-temperature oxidation

► Microstructure inside Zr1Nb fuel cladding was observed. ► The α-Zr(O) thickness kinetics is slower compared to Zry-4 alloy. ► The (α + β)-Zr thickness kinetics is faster than parabolic. ► The oxide layer thickness kinetics changes depending on temperature.