The OpenFOAM Fuel BEhavior Analysis Tool, or OFFBEAT, is a multi-dimensional fuel performance code under collaborative development at the Laboratory for Reactor Physics and Systems Behaviour (LRS) of the EPFL and at the PSI. The code can be used both for studying complex 2D or 3D local effects and for more traditional 1.5D base irradiation analyses. OFFBEAT is based on the open-source C++ library OpenFOAM (R), thus the governing equations are discretized with modern finite volume techniques using unstructured meshes, and the solver is fully parallelized via geometrical domain decomposition. This paper presents the numerical framework, governing equations and solution strategy behind OFFBEAT and it gives a brief overview of the material properties and behavioral models already implemented. Finally, a set of experimental rods is chosen to provide the first validation results for the thermal behavior of low burnup axisymmetric rods, by comparing the fuel centerline temperatures with experimental data.