[en] The Model 48-14 protective overpack designed and fabricated by Nuclear Containers, Incorporated of Elizabethton, Tennessee, in a joint development with the US Department of Energy, is being considered for potential use in the shipment of UF₆ cylinders containing material enriched up to 4.5 wt % in ²³⁵UF₆. In order to partially satisfy licensing requirements, it must be satisfactorily demonstrated that the overpack and its contents can withstand thermal exposures specified for both normal transportation and accident conditions. Normal transportation conditions consist of exposures to -40⁰F ambient temperature in shade and to 130⁰F ambient temperature in direct sunlight. Accident conditions consist of a thirty-minute exposure to a 1475⁰F heat source followed by a three-hour cooldown period in still, 130⁰F ambient air in direct sunlight. Computer simulations using the HEATING5 heat conduction code were performed to determine the thermal response of the overpack and UF₆ cylinder to these exposures. Based on results of these analyses and engineering judgement, the overpack is expected to provide adequate protection in the transportation environment