Patent Number: 
Section: claims

1. A method of storing high level radioactive waste comprising:(a) providing a body portion comprising a floor, an open top end, an inner shell extending upward from the floor and forming a cavity, an outer shell extending upward from the floor and surrounding the inner shell so as to form a space therebetween, and at least one opening in the inner shell that forms a passageway from a bottom of the space into a bottom of the cavity;(b) placing a canister containing high level radioactive waste into the cavity, the canister passing through the open top end from a location external to the body portion; and(c) positioning a lid having at least one outlet vent atop the inner and outer shells so as to enclose the open top end of the body portion and the at least one outlet vent forms a passageway from a top of the cavity to the ambient atmosphere; andwherein at least one inlet vent forms a passageway from an ambient atmosphere to a top of the space to facilitate natural convective cooling of the canister containing high level radioactive waste. 2. The method of claim 1 wherein the space is an annular space that circumferentially surrounds the inner shell. 3. The method of claim 1 wherein the canister is a hermetically sealed multi-purpose canister. 4. The method of claim 1 wherein the cavity has a horizontal cross-section that accommodates no more than one canister. 5. The method of claim 1 wherein step (a) comprises positioning the body portion so that at least a major portion of a height of the inner and outer shells are below grade, and wherein step (b) comprises lowering the canister containing high level waste into the cavity until the entire canister is below grade. 6. The method of claim 5 wherein step b) comprises positioning a transfer cask containing the canister above the cavity, and lowering the canister from the transfer cask into the cavity. 7. The method of claim 5 wherein step a) further comprises providing a concrete pad around a portion of the outer shell that protrudes above grade. 8. The method of claim 1 wherein the lid comprises the at least one inlet vent.