Patent Number: 
Section: claims

1. A method of retrofitting an overhead crane assembly at a nuclear facility into a mobile nuclear cask transfer assembly, comprising steps of: (a) removing a prexisting trolley from at least one travel rail of an overhead crane assembly;  (b) installing a mobile nuclear cask transfer assembly onto said at least one travel rail, said mobile nuclear cask transfer assembly comprising a trolley assembly, a first single failure proof lifting mechanism mounted for movement with said trolley assembly for engaging and lifting a transfer cask in which a canister of spent nuclear fuel is temporarily positioned, and a second single failure proof lifting mechanism mounted for movement with said trolley assembly for engaging and lifting the canister of spent nuclear fuel. 2. A method of retrofitting an overhead crane assembly at a nuclear facility into a mobile nuclear cask transfer assembly according to  claim 1 , wherein step (a) is performed within a building. claim 1