A method for storing high level radioactive waste in a passively cooled cavity. In one embodiment, the invention comprises: (a) providing a container comprising an outer shell having an open top end and a hermetically closed bottom end, an inner shell forming a cavity, the inner shell positioned within the outer shell so as to form a space between the inner shell and the outer shell, and at least one opening in the inner shell that forms a passageway between the space and a bottom portion of the cavity; (b) lowering a hermetically sealed canister holding high level radioactive waste into the cavity via the open top end; and (c) positioning a lid having at least one inlet vent and at least one outlet vent atop the container such that the at least one inlet vent forms a passageway from an ambient atmosphere to the space and the at least one outlet vent forms a passageway from the cavity to the ambient atmosphere, the lid substantially enclosing the open top end.