In reactors employing daily load following, or other types of power cycling operation, the cladding accumulates fatigue damage. The accumulated damage, and hence the fatigue life, is dependent upon the cladding type, the number of cycles and the amplitude of the clad stress variations during each cycle. Further information on fatigue of zirconium alloy cladding can be found elsewhere (O’Donnell and Langer, 1964).

Cladding is also subject to fretting (wearing away of the cladding material by repeated relative motion of the cladding and material in contact with it). Grid-to-pin fretting wear may occur if flow-induced assembly vibration leads to relative motion between the grid straps and the fuel pins (although the aim is to eliminate this possibility by good fuel assembly design, i. e. by maintaining sufficient forces between grid straps and fuel pins by use of grid springs and dimples, and by optimising grid profiles to minimise vibrations). Debris-induced fretting wear of cladding is also possible. However, fuel assemblies are usually designed in such a way to prevent this, or at least to minimise the possibility of its occurrence. If fretting wear becomes too great the cladding can fail.