Composite Material Properties Simulation for the Fuel Performance Evaluation of Gd₂O₃-Cored UO₂ Fuel

The use of burnable absorbers in previous fuel designs includes the application of boron-containing materials as coatings on fuel pellets as used in Integral Fuel Burnable Absorber (IFBA) or in separate fuel pellets like Wet Annular Burnable Absorber (WABA). Urania-Gadolinia mixed oxide fuel is also used widely as it provides additional characteristics. Since the burnable absorber exists within the fuel not in separate holes in the fuel assembly, therefore it reduces the handling exposure and decreases the water displacement. Several exclusive characteristics of lumping Gd₂O₃ into small-size particles embedded in the UO₂ pellet make this fuel design a desired option among the advanced nuclear fuel designs. This design enables the control of Gadolinium burning as the surface area is decreased when compared Gadolinia mixed oxide fuel. In this study, the thermal behaviour of Gd₂O₃-cored UO₂ fuel has been evaluated. The preliminary proposed pellet design is a heterogeneous configuration of Gd₂O₃ sphere in the UO₂ fuel pellet. Therefore, composite material properties are necessary to be obtained through experimental measurements, theoretical model calculations for heterogeneous composites such as the rule of mixtures, or simulation using Finite Element Methods (FEM). For this reason, COMSOL Multiphysics, a FEM modeling software, is used to obtain these properties. In this paper, the thermal analysis for one of the promising designs of the Gd₂O₃ cored UO₂ has been shown. The mechanical analysis results are anticipated to be the next step. The thermal analysis shows the effect of Gd₂O₃ sphere addition to the UO₂ fuel pellet thermally by comparing the temperature profile through the pellet of Gd₂O₃ cored UO₂ and the traditional UO₂ fuel pellets. In this study, the thermal performance of a selected design of Gd₂O₃ cored UO₂ fuel pellet was performed though the radial heat transfer analysis. A comparison between the thermal behavior of a standard UO₂ and the newly-designed Gd₂O₃ cored UO₂ pellets was presented. The results of the thermal analysis show a negligible difference in the temperature profiles between the Gd₂O₃ lumped pellet and the standard UO₂ pellet. In addition, as the anticipated next step is the stress analysis, it is expected that the elastic stress analysis results would address minimal stress distributions between the Gd₂O₃ sphere and UO₂ fuel since the thermal expansion mismatch between the two materials is insignificantly small. The preliminary elastic stress analysis showed matching results to the anticipated behavior, but more analysis is needed for the results to be presented.