A unified, microstructural creep law which simulates the transient creep deformation of Zircaloy at temperatures above 750 K has been used to follow the interaction of diffusional and dislocation creep with changes in material microstructure (grain size, recrystallization, phase fraction and anisotropy) under loss-of-coolant accident (LOCA) conditions. Comparison of a membrane sheath model using this creep law with a large number of tube tests (>700) in an inert environment has demonstrated good predictive capability.

This model has been extended to cover other aspects affecting deformation and failure of CANDU (CANada Deuterium Uranium) fuel sheaths such as: nonuniform structure distribution resulting from temperature profiles along the sheath length, oxidation of the fuel sheaths, cracking of the oxidized layers and localized straining, large strain failure, and failure by beryllium-assisted cracking.