Prediction of Zircaloy-2 Fuel Cladding Strain during Temperature Transients

To obtain a basic understanding of deformation behavior of Zircaloy-2 fuel cladding during anticipated transients in BWRs, a new description of the strain response was developed, using the Larson-Miller parameter (LMP) life-fraction approach. Thermal transient and isothermal tests were made on internally/externally pressurized tubes to determine the diametral strain. Strain data for constant heating rate tests were converted to LMP values, based on the life-fraction rule, in which the assumption was made that a given strain would occur at a life-fraction of unity. It was found that a good correlation between LMP and hoop stress was obtained for each given strain, that is, the same LMP could lead to the same strain for a given stress. By using the LMP correlations, strain can be expressed as a function of life-fraction for various given thermal transient and isothermal conditions. The LMP-life-fraction approach will be useful to evaluate cladding integrity after complex load-time-temperature histories.