Abstract: Spent nuclear fuel storage casks, particularly a protective and venting cover for such storage casks which are stored above ground. The protective and venting cover may be assembled from annular or doughnut-shaped cast concrete members stacked one upon the other and/or steel members extending the height of the storage cask. The annuli are axially indexed with respect to the storage cask, such that a venting annulus is formed about the storage cask and the annulus contributes to a defocusing geometry against armor piercing weapons, such an anti-tank "shaped charge" weaponry.