Evaluation of thermomechanical behaviors of UO₂-5 vol% Mo nuclear fuel pellets with sandwiched configuration

Abstract

Deploying high thermal conductive materials as additives to UO₂ has been highlighted due to their enhanced thermal performance as a potential candidate of Accident-Tolerant Fuels (ATFs). Herein, we investigate thermomechanical behaviors of UO₂ - 5 vol% Mo fuel pellets with a sandwiched configuration where Mo layers are positioned on the top and bottom of a UO₂ part. The successfully fabricated sandwich-type UO₂ fuel pellets with an inclusion of 5 vol% Mo by using a conventional sintering method exhibit up to 3.0 and 2.5 times higher effective thermal conductivities at 800 degrees C than standard UO₂ and dispersion-type UO₂ - 5 vol% Mo fuel pellets, due to the effective heat transfer characteristics in the Light Water Reactor (LWR) fuel. Accordingly, the sandwich-type fuel pellets not only effectively reduce the thermal stress gradients across the pellets, but also significantly decrease the maximum tensile hoop stresses of fuel pellets. Finally, the radial deformation behaviors of the sandwich-type fuel pellets are also investigated under a simulated irradiation condition, showing that an hourglass-shaped deformation of UO₂ pellets are considerably mitigated.