Simulation of Mechanical Behavior of Fuel Pellets With Different Geometries

Typical Pressurized Water Reactors (PWR) fuel rods are manufactured using zirconium-based alloys as cladding and slightly enriched UO2 sintered pellets as fuel. However, in the last years efforts have been made to develop Accident Tolerant Fuels (ATF) focusing mainly in new materials to replace the cladding in order to avoid the exothermic reaction with steam experienced by zirconium-based alloys under accident conditions as observed during the Fukushima Daiichi accident. In this sense, iron-based alloys appear as a possibility to replace conventional zirconium-based alloys, and the effect of the pellet geometry in the performance of iron-based alloys fuel rods shall be investigated. The fuel pellet geometry experiences changes due to irradiation can promote early gap closure, mechanical loadings to the cladding and/or bamboo effects due to the combination of loads and irradiation creep, and all these effects depend also on the cladding properties. The objective of this paper was to address the influence of geometric parameters in the fuel pellet behavior of a stainless steel fuel rod by means of structural mechanical analysis using the well-known ANSYS software. The parameters evaluated in this paper considered fuel pellet with and without chamfer and dish. The data related to the fuel pellet performance under irradiation were obtained using a modified version of the FRAPCON code considering stainless steel as cladding. Results obtained from mechanical evaluation considering the effects through the responses of the axial, radial, plastic deformations, and resulting tensions were evaluated.