As the zircaloy cladding absorbs an excessive amount of hydrogen and cooled down under hoop stress, radial hydride may be precipitated by hydride reorientation phenomenon. There have been many previous studies about the threshold stress of the reorientation, but it is known that the quantitative degree of hydride reorientation rather than the threshold is important for the prediction of mechanical properties. A thermodynamic model for Radial Hydride Fraction (RHF) prediction has been developed in this study. The model calculates RHF with respect to temperature, cooling rate, hydrogen content, and applied stresses. Once the cooling rate is given, the solid solution concentration at each temperature is determined by Hydrogen-Nucleation-Growth-Dissolution model. Subsequently, the increment of radial hydride is derived by nucleation and growth theory. The code based on the thermodynamic theory can provide the prediction of RHF under hoop stress, as well as a change in precipitation behavior over time. RHF of the zircaloy cladding in long-term dry storage can be obtained by the implementation of the code and the degradation of the cladding is directly estimated according to the correlation between RHF and mechanical properties. Ongoing experimental validation of the developed model is discussed.

• Changhyun Jo(Seoul National University (SNU))
• Youho Lee(Seoul National University (SNU)) Corresponding author