Post-transient examination of performance of uranium silicide fuel and silicon-carbide composite cladding under reactivity-initiated accident conditions

•First transient testing of accident-tolerant fuel designs under transient nuclear heating reactivity-initiated accident conditions.•Claddings experienced dimensional changes but maintained primary rod-like geometries.•Elemental species diffusion from the U3Si2 fuel to the zircaloy cladding was observed.•No elemental species diffusion from the U3Si2 fuel to the silicon-carbide cladding was observed.•Through wall thickness cracking observed in the silicon-carbide cladding resulting from pellet cladding interaction from thermal expansion of the pellet. New fuels are being developed for light water nuclear reactors with the initial goal of improving accident tolerance. More recently, these new fuel systems are also being recognized for their potential to support higher fuel burnups and thus improved economics for reactor plants through improved fuel utilization. Fuel safety testing of these new fuels systems is being conducted under transient irradiation conditions in the Transient Reactor Test facility at Idaho National Laboratory. A test campaign including two rodlets of U3Si2 fuel in Zircaloy-4 cladding and two rodlets of U3Si2 fuel in Silicon-Carbide Composite cladding has been performed to begin the development of fuel-safety criteria in design-basis reactivity-initiated accident conditions. Post-Transient-Irradiation Examinations have been performed and found that the accident tolerant materials maintained their primary rod-like geometry. Elemental species diffusion was found to occur in the Zircaloy rodlets indicating rapid diffusion kinetics at the temperatures achieved. No elemental species diffusion was found in the Silicon-Carbide rodlets. However, through-wall thickness cracks were observed due to displacement loading of the cladding from thermal expansion of the fuel pellets. This work presents the first experimental evidence of the performance of these fuel systems under transient nuclear heating and representative reactivity-initiated accident energy depositions.