Creep assessment of Zry-4 cladded high burnup fuel under dry storage

Cladding creep rupture is thought to be the most likely and limiting failure mechanism of spent fuel in dry storage. In spite of being highly unlikely, the current trend towards high burnups is drawing further attention to the potential creep effect on cladding integrity of fuels burnt over 45 GWd/tU.This paper explores the burnup influence on cladding creep during dry storage by modelling two different high burnup scenarios (51 GWd/tU and 67 GWd/tU). In addition, sensitivity of the results to the in-reactor average power and power history has been conducted. The computation tool used in this study has been an extension of FRAPCON-3.4 capable of simulating dry storage scenarios. Burnup and average linear power have been shown to make creep grow quite substantially during the first two years in dry storage, adopting a quasi-asymptotic trend from then on. However, even though this profile seems to have a generic nature, the net creep value reached depends not just on integral and average variables, but also on magnitudes describing the entire irradiation history, like linear power history. In none of the cases explored creep approaches the 1% threshold. In-reactor FGR modelling has been highlighted as a key element to get accurate estimates of creep.