Systems and methods for storing radioactive materials that afford adequate ventilation of the cavity in which the radioactive materials are stored. In one aspect, the invention is a method of storing radioactive materials comprising: a) positioning a system comprising a shell forming a cavity and at least one inlet ventilation duct extending from an inlet to an outlet at a bottom portion of the cavity in a below grade hole so that the inlet of the inlet ventilation duct is above grade and the outlet of the inlet ventilation duct into the cavity is below grade; b) introducing engineered till into the hole to circumferentially surround the shell; c) lowering a canister containing radioactive materials into the cavity; and d) subsequent to the canister being lowered into the cavity, placing a lid on the shell.