Several new fuel designs are currently being considered within the generation-IV gas-cooled fast reactor (GFR) project. One of them, which is the GFR reference design, is a ceramic plate matrix with a honeycomb inner structure containing small fuel cylinders. The fuel is mixed plutonium-uranium carbide, while the matrix material is silicon carbide. A two-dimensional approach to simulation of the thermal behaviour (for both steady-state and transient analysis) of such fuel, taking into account the inner heterogeneity, has been developed and benchmarked against detailed finite-element calculations. The resultant model can provide reliable fuel and matrix temperatures to determine neutronic feedbacks, as also to evaluate fuel integrity. As such, it has been integrated into PSIs coupled code system FAST, which aims at the comprehensive safety analysis of advanced fast reactor systems.[All rights reserved Elsevier].