Low cycle fatigue problem in RAPP fuel

In a nuclear power plant, the fuel sheath is subjected to power cycling during start-up and shut-down, and also during normal operation. Power reactors operating in relatively small electrical grids, as for example RAPS-1 are prone to large number of such power cycles. RAPS fuel sheath being of the collapsible design is subjected to high initial plastic strains. These environmental conditions pose serious low cycle fatigue problem in RAPS fuel operations. The limitations on fuel life due to low cycle fatigue are described. The low cycle fatigue behaviour of zircaloy under normal and irradiation is discussed. UO2 expansion model used for calculating plastic strains is also described. (author)