Update of CSFM Creep and Creep Rupture Models for Determining Temperature Limits for Dry Storage of Spent Fuel

Creep rupture is believed to be a dominant mode of cladding failure during dry storage of spent nuclear fuel. This paper describes a methodology to determine the maximum allowable temperature for dry SNF storage based on expected time-in-storage, cooling time after discharge, fuel rod inner pressure, burnup, and material properties of Zircalay cladding. The methodology employs a Monkman-Grant correlation to predict the time-to-rupture as a function of steady-state creep rate. The steady-state creep rate is calculated using different creep mechanisms developed from recently published experimental data. Several creep mechanisms were found to be active during dry SNF storage conditions. The methodology incorporates creep adjustment factors due to irradiation damage and thermal annealing.