Patent Number: 
Section: claims

1. A storage apparatus with gamma radiation shielding for spent nuclear fuel comprising:a fuel basket comprising a plurality of elongated fuel storage tubes extending along a longitudinal axis, each of the tubes defining a cell configured to hold a nuclear fuel assembly;a plurality of gamma radiation attenuation inserts each one of which is nested inside a respective cell of at least some of the storage tubes of the fuel basket;each radiation attenuation insert comprising a longitudinally elongated tubular body including an open top end, a bottom end, and plurality of sidewalls extending between the ends;wherein the radiation attenuation insert is composed of a dense material operable to block gamma radiation;each radiation attenuation insert including a downwardly open flow cutout formed in each sidewall of the insert at its bottom end;each storage tube containing a radiation attenuation insert including a downwardly open flow cutout formed in each sidewall of the tube at its bottom end, the flow cutouts in the tube each being laterally aligned with and overlapping a corresponding one of the flow cutouts of the radiation attenuation insert;an elastically deformable spring angle clip affixed to each sidewall of each radiation attenuation insert, each angle clip protruding laterally outwards and downwards from the sidewall into the flow cutout of the radiation attenuation insert and engaging a corresponding locking edge formed by the flow cutout on its respective storage tube when the insert is fully inserted into the storage tube;wherein the flow cutouts of the storage tubes and radiation attenuation insert remain open after being engaged by one of the angle clips such that air or gas can pass through the flow cutouts. 2. The apparatus according to claim 1, wherein the radiation attenuation insert is formed of a non-ferrous material having a density greater than 8.0 grams/cubic centimeter. 3. The apparatus according to claim 2, wherein the non-ferrous material is selected from the group consisting of copper, aluminum bronze, Admiralty brass, and copper-nickel alloy. 4. The apparatus according to claim 2, wherein the non-ferrous material is copper. 5. The apparatus according to claim 1, further comprising a nuclear fuel assembly disposed in a longitudinally-extending internal chamber of a first insert of the plurality of radiation attenuation inserts, the first insert arranged in a gap between cell walls of a first tube of the plurality of tubes and the fuel assembly. 6. The apparatus according to claim 1, wherein the radiation attenuation inserts have a height substantially coextensive with heights of the storage tubes. 7. The apparatus according to claim 6, wherein the radiation attenuation inserts and the storage tubes are affixed to and supported by a common baseplate. 8. The apparatus according to claim 1, further comprising an elastically deformable locking member affixed to each sidewall of each radiation attenuation insert proximate to the bottom end of the insert, the locking member including an outwardly projecting locking protrusion configured to detachably engage a corresponding locking edge formed proximate to a bottom end of the storage tube in which the insert is inserted. 9. The apparatus according to claim 8, wherein each locking member has an undulating body formed of spring steel including an upper fixed end portion rigidly attached to an exterior surface of the radiation attenuation insert sidewall, and a resiliently deformable and cantilevered lower free-end locking portion which defines the locking protrusion. 10. The apparatus according to claim 9, wherein the locking protrusion has a triangular shape. 11. The apparatus according to claim 8, further comprising an outwardly flared and angled securement flange extending upwards from the top end of the sidewalls of each radiation attenuation insert sidewalls, the securement flanges arranged and configured to engage a top end of a respective storage tube in which each insert is inserted. 12. The apparatus according to claim 6, wherein the plurality of storage tubes includes peripheral outboard tubes forming a perimeter of the fuel basket and inboard storage tubes disposed in a central region of the fuel basket inside the outboard tubes, and wherein the radiation attenuation inserts are disposed in some of the outboard tubes. 13. The apparatus according to claim 1, wherein all of the peripheral outboard tubes contain a radiation attenuation insert forming a continuous barrier against radiation emanating in a lateral direction from the fuel basket. 14. A storage apparatus with gamma radiation shielding for spent nuclear fuel comprising:a canister comprising a baseplate and an elongated cylindrical shell defining an internal cavity;a fuel basket disposed in the internal cavity, the fuel basket comprising a plurality of metal fuel storage tubes extending upwards from the baseplate along a longitudinal axis and each defining a fuel storage cell;a gamma radiation attenuation insert nested inside a first cell of a first tube of the fuel basket;the radiation attenuation insert comprising a longitudinally elongated cuboid body including open top and bottom ends, and a plurality of sidewalls extending between the ends;an upper securement feature of the radiation attenuation insert engaging a top end of the first tube; andan elastically deformable lower securement feature on the radiation attenuation insert engaging a bottom end portion of the first tube and configured to detachably affix the radiation attenuation insert to the first tube;wherein the radiation attenuation insert is composed of a dense material operable to block gamma radiation;wherein the radiation attenuation insert further includes a downwardly open flow cutout formed in each sidewall of the insert at its bottom end;wherein the first tube also includes a downwardly open flow cutout laterally aligned with the flow cutout of the radiation attenuation insert;wherein the lower securement feature comprises an elastically deformable spring angle clip affixed to one sidewall of the radiation attenuation insert, the angle clip protruding downwards from the one sidewall into the flow cutout of the radiation attenuation insert and having a locking protrusion engaging a corresponding locking edge formed on a corresponding downwardly open flow cutout of the first tube when the insert is fully inserted into the first tube;wherein the flow cutouts of the first tube and radiation attenuation insert remain open after being engaged by the spring angle clip such that air or gas can pass through the flow cutouts. 15. The apparatus according to claim 14, wherein the upper securement feature comprises an angled securement flange flared outwards from the one sidewall of the radiation attenuation insert and engaging a top edge of the first tube. 16. The apparatus according to claim 14, wherein the radiation attenuation insert has a height substantially coextensive with the height of the first tube and is supported at its bottom end by the baseplate of the canister. 17. The apparatus according to claim 14, wherein the radiation attenuation insert is formed of a non-ferrous material having a density of at least 7.0 grams/cubic centimeter.