Burst rupture tests have been carried out on irradiated fuel pin cladding to determine the effect of intergranular attack on burst rupture strength and ductility and so to assess the ability of the weakened cladding to withstand power surge or loss of coolant conditions. The results from this series of tests indicate that the burst rupture strength or yield strength is not drastically reduced by localized attack extending through as much as 35% of the cladding thickness. Ductility values, however, do appear to be substantially reduced. In terms of reactor operation, this suggests that in a transient stress situation the cladding would be able to withstand higher stresses than previously predicted using a wall thinning criteria, based on the maximum depth of cladding attack, but would tolerate far less deformation than unattacked cladding before failure.