NRC SFST ISG-12: Buckling of Irradiated Fuel Under Bottom End Drop Conditions

Fuel rod buckling analyses under bottom end drop conditions have traditionally been performed
to demonstrate integrity of the fuel following a cask drop accident. The methodology described
by Lawrence Livermore National Laboratory (LLNL) to analyze the buckling of irradiated spent
fuel assembly under a bottom end drop in their report UCID-21246 is a simplified approach. It
assumed that buckling occurred when the fuel rod segment between the bottom two spacer
grids reached the Euler buckling limit. The weight of fuel pellets was neglected in the analysis;
only the weight of the cladding was considered. Material properties for irradiated cladding were
used. The buckling analysis also neglected the stiffness of the pellets which could have been
fused or locked to the cladding. It assumed the total weight of the cladding to be on top of the
fuel rod segment between the bottom two spacer grids. In addition, it also assumed that the
fuel rod segment between the bottom two spacer grids was pin-connected. The restraint and
lateral support of the fuel basket structure to the fuel assemblies were ignored in the analysis.

Revision 1