b'Figure 6. Nominal cladding thickness. Distribution of fission gas porosity in the fuel confirms that fuel deformation is driven by fission gasFigure 7. Reduced (50%) Figure 8. EOL shape of unconstrained induced swelling cladding thickness.two-slotted fuel (no cladding).Cladding Behavior Cladding ovalization depends on the cladding wall thickness (Cladding deformation (10 x magni-fied) when using two-slotted fuelCladding provides driving forcefor slot closure Simulation of unconstrained two-slotted fuel swelling shows non-closure of the slots Constraint of the fuel by the clad- Figure 9. EOL shape of constrained two-slotted fuel (with cladding).ding defines the nature of fuel deformationFuel Creep is the mechanism respon-sible for closure of the slotsFigure 10. Reduced fuel creep. BISON simulation performed assuming reduced fuel creep show non-closure of the slots and extreme cladding deformation Creep-resistant fuel compositions are no suitable for slotted fuel design Figure 11. Nominal fuel creep.2019|AFC ACCOMPLISHMENTS 225'