Modeling of creep behavior of Zircaloy-4 by considering metallurgical effect

The creep model for Zircaloy-4 has been improved by including the metallurg ical effect of Zircaloy cladding. Based on the experimental results in whic h the creep strain rate is highest for stress relief annealed cladding (SRA ) and lowest for recrystallized cladding (RXA), the annealing factor was in troduced and derived by iterative calculations until the best predictions f or all the rods were obtained. The creep model has been incorporated into t he KAERIs fuel performance code COSMOS and then verified with 4 cladding cr eep data, of which 3 cases exhibit creepdown and the other one creepout. Th e model predicts well the creep behavior of UO2 fuel rods in PWRs. The pred iction does not show any discernable difference between the high- and low-S n claddings. With satisfactory agreement between predicted and measured val ues, the comparison indicates no difference in creep behavior between MOX a nd UO2, fuel rods as expected. Although there are controversies over the ex perimental method and the analysis procedures for clad creepout, COSMOS gen erally well predicts the creep behavior, even in the case of creepout, if t he creepout factor is applied. (C) 2001 Elsevier Science Ltd. All rights re served.