A system and method for storing spent nuclear fuel that affords adequate cooling capabilities under "smart flood" criteria. In one aspect, the invention is a method of storing spent nuclear fuel comprising: providing a system comprising a structure forming a cavity for receiving and storing a spent fuel canister, the cavity having a top, a bottom, and a bottom surface, at least one inlet ventilation duct forming a passageway from an ambient air inlet to an outlet at or near the bottom of the cavity; and at least one outlet ventilation duct forming a passageway from at or near the top of the cavity to ambient air; lowering a canister loaded with spent nuclear fuel into the cavity until a bottom surface of the canister is lower than a top of the outlet of the at least one inlet ventilation duct; supporting the canister in the cavity in a position where the bottom surface of the canister is lower than the top of the outlet of the at least one inlet ventilation duct; and cool air entering the cavity via the at least one ventilation duct; the cool air being warmed by heat emanating from the canister; and warm air exiting the cavity via the at least one ventilation duct. In another aspect, the invention is a system comprising: a structure forming a cavity for receiving and storing a spent fuel canister, the cavity having a top, a bottom, and a bottom surface; at least one inlet ventilation duct forming a passageway from an ambient air inlet to an outlet at or near the bottom of the cavity; at least one outlet ventilation duct forming a passageway from at or near the top of the cavity to ambient air; and means to support a spent fuel canister in the cavity so that the bottom surface of the canister is lower than a top of the outlet; wherein the inlet ventilation duct is shaped so that a line of sight does not exist to a canister supported by the support means from the ambient air inlet.