The non-uniform high-temperature oxidation of Zr–1%Nb cladding – A numerical model

Highlights: • LOCA. • E110. • Cladding. • Modelling. • Zirconium. In this article it is examined how the non-uniform oxidation and the resulting change in the properties of the ballooned cladding in a LOCA scenario relate to the assumption of a "uniform ballooning" used in the LOCA criteria. This was achieved by creating a code that calculates how steam diffuses through the opening in the cladding after the burst, what happens during oxidation if the cladding wall thickness is non-uniform, and how this affects the load-bearing capacity of the fuel rod. The results were compared to experimental data and results of calculations using uniform geometry. With this program the severity of oxidation for different geometries and scenarios was calculated. The results show that local values differ significantly for uniform and non-uniform oxidation. We have also examined the variation in the load bearing capacity in different scenarios and we have found that for a design basis LOCA accident the remaining thickness of the beta layer in the zirconium cladding will prevent brittle failure.