Thermal creep in Zircaloy-4 nuclear fuel cladding alloy

The prime objective of any safety action in a nuclear power plant is to maintain the structural integrity of nuclear fuel cladding, which encases the radioactive fuel undergoing nuclear fission. Of different acting degradation processes, creep is regarded as one of the life-limiting factors for zirconium nuclear fuel cladding in all light-water reactor systems. However, deformation, fracture, and structural processes in the thermal creep of zirconium nuclear cladding tubes remain poorly understood. This inconvenient situation is due to the relatively limited number of studies published in the open literature. This work mainly carried out uniaxial constant-stress creep tests of the zirconium Zircaloy-4 (Zr-Sn-Fe-Cr) alloy cladding tubes in the power-law and the power-law breakdown creep regimes. Fractographic and metallographic analyses of the crept specimens followed the creep tests. They were used to explain the observed thermal high-temperature creep behavior and to determine acting deformation and fracture processes. The analysis of the creep data indicates close links between creep deformation and fracture.