SAFENR - a two dimensional axisymmetric finite element code for predicting behaviour of PHWR fuel

Fuel elements for the pressurized heavy water reactors in India use thin zircaloy cladding of collapsible design. A thin cladding will be deformed from the beginning of life by the external coolant pressure and by change in pellet outer geometry, as the irradiation progresses. A two dimensional axisymmetric finite element computer code SAFENR has been developed to analyse the fuel in pin behaviour. The code can predict pellet and clad deformations and stress and strain distributions within the pellet and cladding. The code uses eight noded isoparametric elements for fuel pellet and cladding. One of the most intricate problems encountered in fuel modelling is at the fuel sheath interface. In our model the friction between pellet and cladding has been introduced by the use of six noded, isoparametric, interface elements in the pellet clad gap. This element is highly versatile in simulating the pellet clad axial and radial interaction, at the same time a method of debonding is used to allow for pellet clad slip. (orig./RW)