Theoretical effects on pellet cracking of friction at pellet-pellet interfaces

The most likely position for fracture to occur in the cladding on a nuclear fuel element was shown, in the earlier work, to be the point above the place where a radial crack emerges through the end face of the pellet. In this paper it is shown that friction between the contacting surfaces of two adjacent pellets will tend to make cracks propagate from one pellet to the other. This reduces the tendency for friction against a neighbouring pellet to restrain the opening-up of a radial pellet crack during an upward power excursion. The position where a propagating crack traverses the interface between two contacting pellets is the most likely site of failure in the overlying clad. Failure is less likely if the pellet-pellet friction coefficient is low, if the ratio of pellet length to pellet radius is large, and if the pellets contain a high number density of radial cracks. (Auth.)