Stackable nuclear waste storage system

A method for forming a passively cooled nuclear waste system comprising:

• positioning a lower cask on an above grade concrete pad, the lower cask including a body comprising a first cavity;
• inserting a first canister containing nuclear waste emitting thermal energy in the first cavity of the lower cask;
• positioning an upper cask on the concrete pad, the upper cask including a body comprising a second cavity;
• inserting a second canister containing nuclear waste emitting thermal energy in the second cavity of the upper cask;
• positioning the upper cask on top of the lower cask, the second cavity being placed in fluid communication with the first cavity of the lower cask;
• and
• detachably coupling the upper cask to the lower cask in vertically stacked relationship.

A method for adding storage capacity to an existing nuclear waste storage system comprising:

• positioning a lower cask on an above grade concrete pad at a first point in time, the lower cask including a body comprising a first cavity and plurality of radial first air inlet ducts in fluid communication with the first cavity;
• inserting a first canister containing nuclear waste emitting thermal energy in the first cavity of the lower cask;
• detachably coupling a first closure lid on top of the lower cask, the first closure lid defining at least one air outlet duct in fluid communication with the second cavity of the lower cask;
• removing the first closure lid from the lower cask at a second point in time later than the first point in time;
• positioning an upper cask on the concrete pad, the upper cask including a body comprising a second cavity and plurality of radial second air inlet ducts in fluid communication with the second cavity
• inserting a second canister containing nuclear waste emitting thermal energy in the second cavity of the upper cask;
• lifting and positioning the upper cask on top of the lower cask;
• establishing fluid communication between the first and second cavities of the lower and upper casks, respectively;
• and
• detachably coupling the upper cask to the lower cask in vertically stacked relationship;
• wherein the upper cask comprises a perforated baseplate, and the step of inserting the second canister includes supporting the second canister from the perforated baseplate inside the second cavity of the upper cask.