Passive cooling device for casks containing nuclear fuel
A system for externally cooling a cask containing heat-emitting spent nuclear fuel includes the cask comprising a radiation shielding body defining an internal cavity configured to hold a canister containing the spent nuclear fuel. A continuously annular cooling jacket extends circumferentially around an external surface of the cask body. The cooling jacket may have a double shell construction including an internal cavity for a cooling medium which provides an external heat sink for absorbing heat radiated from the external wall surface of the cask generated by the spent nuclear fuel. The heat emitted by the spent nuclear fuel is absorbed by the cooling medium in the cooling jacket, thereby in turn cooling the cask. In one embodiment, the cooling medium may be dry ice which undergoes sublimation by absorbing the heat to change from solid to gaseous phase directly. The jacket may be formed of multiple segments.
1. A system for cooling high level radioactive waste, the system comprising:
a cask comprising a storage cavity containing the high level radioactive waste emitting heat; and
a cooling jacket at least partially surrounding the cask, the cooling jacket comprising a cooling medium cavity containing a cooling medium that sublimates at normal atmospheric pressure, the cooling medium providing an external heat sink for absorbing the heat emitted from the cask from the high level radioactive waste.
2. The system according to claim 1 , wherein the cooling jacket comprises a metallic inner shell and a metallic outer shell, the cooling medium cavity being defined between the inner and outer shells.
3. The system according to claim 2 , wherein the cooling jacket further comprises an annular top closure plate affixed to top ends of the inner and outer shells, and an annular bottom closure plate affixed to bottom ends of the inner and outer shells.
4. The system according to claim 3 , wherein the top closure plate includes an openable and closeable access hatch configured for filling the cooling medium cavity of the cooling jacket with the cooling medium.
5. The system according to claim 3 , wherein the cooling medium is dry ice and the top closure plate further includes a plurality of vents in fluid communication with the internal cavity of the cooling jacket, the vents circumferentially spaced apart and configured for venting gaseous carbon dioxide to atmosphere from the cooling medium cavity which is created by sublimation of the dry ice upon absorbing the heat emitted by the cask from the high level radioactive waste.
6. The system according to claim 2 , wherein the inner shell is formed of a material having a greater heat transfer coefficient than the outer shell.
7. The system according to claim 6 , wherein the inner shell is formed of copper and the outer shell is formed of a different material.
8. The system according to claim 2 , wherein the cooling jacket comprises a first semi-circular segment having ends abutted to end of a second semi-circular segment to form a continuous annular structure.
9. The cooling system according to claim 8 , wherein each of the first and second semi-circular segments comprises a pair of vertical end plates extending between the inner and outer shells arranged at opposing sides of each segment, the end plates the first semi-circular segment abutting the end plates of the second semi-circular segment at a flat-to-flat interface.
10. The system according to claim 1 , wherein the cooling jacket has a height which extends for at least a majority of a height of the cask.
11. The system according to claim 1 , further comprising a plurality of circumferentially spaced apart stiffening plates arranged in the cooling medium cavity of the cooling jacket and extending longitudinally and in a radial direction between the inner and outer shells, the stiffening plates extending for a majority of a height of the inner and outer shells to divide the cooling medium cavity into a plurality of cooling compartments each configured for holding the cooling medium.
12. The system according to claim 1 , wherein the cooling medium is a solid substance having a triple point at a pressure which is greater than normal atmospheric pressure such that the cooling medium sublimates at normal atmospheric pressure inside the cooling jacket.
13. The system according to claim 12 , wherein the cooling medium is dry ice.
14. The system according to claim 13 , wherein the dry ice is in pellet or block form.
15. The system according to claim 1 , wherein the cooling jacket is removably mounted to the cask.
16. The system according to claim 15 , wherein the cooling jacket further comprises a plurality of hangers extending upwards from a top end of the cooling jacket and having a hook shape configured to hang the cooling jacket from a top surface of the cask in a suspended manner.
17. The cooling system according to claim 16 , wherein the hangers comprise L-shaped brackets including a vertical section fixedly attached to the top end of the cooling jacket and a horizontal section extending inwards beyond an innermost surface of the cooling jacket to engage a peripheral top mounting flange of the cask.
18. The system according to claim 1 , further comprising a circumferentially-extending insulation jacket disposed on an external surface of the cooling jacket.
19. The system according to claim 1 , wherein the cooling jacket further comprises a plurality of circumferentially spaced apart spacers arranged on an internal surface of the cooling jacket, the spacers maintaining an empty annular interstitial space between the cooling jacket and the cask to allow some of the heat emitted from the cask to be removed by cooling air flow.
20. The system according to claim 19 , wherein the spacers comprising a first circular array of block-shaped spacers arranged on an upper half of the internal surface of the cooling jacket, and a separate second circular array of block-shaped spacers arranged on a lower half of the internal surface of the cooling jacket.
21. The system according to claim 1 , further comprising a canister loaded with the high level radioactive waste, the canister positioned within the storage cavity of the cask.