| Abstract: | Pellet—clad mechanical interaction adjacent to the mouths of radial cracks in the pellet can lead to local clad strain intensification. in particular, if during operation bonding has occurred between the pellet and the clad, preventing relative azimuthal motion, very high strains would result and many clad failures would be expected. These are however not observed. We present here the results of a detailed analysis of the stress field in the region of the mouth of the pellet crack. These show there to be very high radial tensile stresses, not previously predicted, acting on the bond. Such stresses provide a highly plausible mechanism for the failure of the bond. These will permit the strain associated with the opening of pellet cracks during power ramps to be distributed over a relatively large arc of the cladding, and thus explain the low failure rate observed. |
