Fresh fuel transport casks are used to temporarily store or transport fresh fuel assemblies. A fresh fuel transport cask typically features a double-layer structure. Under accident transport conditions, the cask may fall to the ground or be impaled by sharp objects. According to the regulations of IAEA, the most severe accident condition is considered, that is the outer container ruptures and flames can cover the surface of the inner container. A simplified two-dimensional model of the inner container is built to analyze the burning process in transport accidents. The radiative heat transfer and the effect of gravity are considered. To reduce the computation size of the external flow region, the outer flow path is constructed artificially. The temperature variations of the fuel clads and neutron absorption plates are monitored during the burning process and the flow field development inside the inner container is analyzed. Finally, the effects of gap size and gravity on the thermal behavior are discussed.