Depleted Uranium from reactor cores would not be found in a drum at an airport or anywhere else other than a Reactor Fuel reprocessing plant or a nuclear waste facility.
You are correct in stating that the depleted Uranium from spent fuel would be mixed with the fission daughter nuclides of U235 and Pu239. This mixture would be radioactive enough that if in this drum would kill anyone with in that 150 foot radius in a few seconds.
A sufficient dose of radiation to kill “in a few seconds” does not exist. It may do its’ damage in a few seconds, but death takes, depending on dose, hours to weeks. . .