Clad data for fuel-element simulation models

In fast reactors, clad voidage dominates the fuel-element behaviour. Empirical fits have mainly been used to express voidage experimental data. A semi-empirical method is now available and extrapolations to conditions outside the experimental range can be made with more confidence. The clad behaviour is also controlled by thermal and irradiation creep. Although an estimate of the magnitude of irradiation creep has been made, its variation with temperature is not yet known. Several theoretical models have been put forward and their likely effect on clad deformation profiles is described. Thermal creep is potentially more damaging than irradiation creep, but its role in fuel-element deformation is less certain than that of irradiation creep. The likely range of its effects, together with the present uncertainty in its value are described. (author)