SYSTEM, METHOD AND APPARATUS FOR PROVIDING ADDITIONAL RADIATION SHIELDING TO HIGH LEVEL RADIOACTIVE MATERIALS

• US 20110172484A1
• Filed: 11/05/2010
• Published: 07/14/2011
• Est. Priority Date: 11/05/2009
• Status: Active Grant

• Current Assignee: Holtec International, Inc.
• Original Assignee: Holtec International, Inc.
• Inventors: Agace, Stephen J., Anton, Paul Stephan, Singh, Krishna P.
• Granted Patent: US 8,995,604 B2
• Time in Patent Office: Days
• US Class Current: 588/16
• CPC Class Codes: G21F 5/002 Containers for fluid radioactive wastes
• CPC Class Codes: G21F 5/06 Details of, or accessories to, the containers
• CPC Class Codes: G21F 5/10 Heat-removal systems, e.g. using circulating fluid or cooling fins

Abstract

A system, method and apparatus for providing additional radiation shielding to a ventilated cask for holding high level radioactive materials. The invention utilizes a tubular shell that is ancillary to the ventilated cask that circumscribes the ventilated cask to add radiation shielding protection while improving heat removal by natural convective air flow. Because the tubular shell and cask are non-unitary and slidably separable from one another, crane lifting capacity is not affected. In one aspect, the invention is an apparatus for providing additional radiation shielding to a cask holding high level radioactive materials comprising: a tubular shell extending from an open bottom end to an open top end, the tubular shell having an inner surface that forms a cavity about a longitudinal axis; a plurality of primary apertures forming passageways through the tubular shell and circumferentially arranged in a spaced-apart manner about the tubular shell; a plurality of secondary apertures forming passageways through the tubular shell and circumferentially arranged in a spaced-apart manner about the tubular shell; and an annular seal coupled to the tubular shell and extending from the inner surface of the tubular shell; wherein the secondary apertures are located at an axial height above the annular seal and the primary apertures are located at an axial height below the annular seal.

Claims

1. A system for containing high level radioactive materials comprising:

a cask extending along a longitudinal axis and having an internal cavity for holding high level radioactive materials, the cask comprising at least one inlet vent at a bottom end of the cask for allowing cool air to enter the internal cavity and at least one outlet vent at a top end of the cask for allowing heated air to exit the internal cavity;

a tubular shell extending from a bottom end to a top end, the tubular shell positioned to circumferentially surround the cask in a spaced apart manner so that an annular gap exists between the tubular shell and a sidewall of the cask, the tubular shell comprising at least one primary aperture forming a passageway through the tubular shell and at least one secondary aperture forming a passageway through the tubular shell; and

an air flow barrier extending between the tubular shell and the sidewall of the cask that separates the annular gap into;

(1) a first chamber that forms a passageway between the primary aperture and the inlet vent of the cask; and

(2) a second chamber that forms a passageway between the secondary aperture and an opening at the top end of the tubular shell, wherein cross-flow of air between the first and second chambers of the annular gap is prohibited by the air flow barrier.

2. The system of claim 1 wherein the air flow barrier is an annular plate that separates the annular gap into an upper chamber and a lower chamber.

3. The system of claim 2 wherein the tubular shell comprises a plurality of the primary apertures circumferentially arranged in a spaced-apart manner about the tubular shell and a plurality of the secondary apertures circumferentially arranged in a spaced-apart manner about the tubular shell, wherein the secondary apertures are located at an axial height above the air flow barrier and the primary apertures are located at an axial height below the air flow barrier.

4. The system of claim 3 wherein the primary apertures are notches in a bottom edge of the tubular shell.

5. The system of claim 1 wherein the inlet vent comprises an inlet opening in the sidewall of the cask, the primary aperture of the tubular shell being radially offset from the inlet opening of the inlet vent.

6. The system of claim 1 further comprising:

the tubular shell comprising a plurality of the primary apertures circumferentially arranged in a spaced-apart manner about the tubular shell;

the cask comprising a plurality of inlet vents, each of the inlet vents comprising an inlet opening in the sidewall of the cask, the inlet openings of the inlet vents circumferentially arranged in a spaced-apart manner about the bottom end of the cask; and

wherein the inlet openings of the inlet vents are radially offset from the primary apertures of the tubular shell.

7. The system of claim 6 wherein the primary openings are notches formed in a bottom edge of the tubular shell.

8. The system of claim 6 wherein the tubular shell comprises a plurality of the secondary apertures circumferentially arranged in a spaced-apart manner about the tubular shell;

wherein the primary apertures and the inlet opening are located at a first axial height, and wherein the secondary apertures are located at a second axial height that is different than the first axial height.

9. The system of claim 1 wherein the outlet vent terminates in an outlet opening in the sidewall of the cask in the second chamber of the annular gap.

10. The system of claim 1 wherein the tubular shell comprises a plurality of tube segments arranged in a stacked-assembly so that a surface contact interface is formed between a top edge and a bottom edge of adjacent tube segments, the system further comprising a collar located at each surface contact interfaces and extending above and below the surface contact interface.

12. The system of claim 10 wherein the primary aperture and the secondary aperture are located in a bottom-most tube segment of the stacked assembly.

13. The system of claim 12 wherein the air flow barrier is coupled to the bottom-most tube segment of the stacked assembly.

14. The system of claim 10 wherein the collar prohibits the adjacent tube segments from becoming axial misaligned while allowing the adjacent tube segments to be separated from one another through relative movement between the adjacent tube segments in the axial direction.

15. The system of claim 10 wherein each of the tube segments comprise a plurality of spacers circumferentially arranged in a spaced-apart manner about the tube segment and protruding from an inner surface of the tube segment to maintain the annular gap.

16. The system of claim 15 wherein each of the spacers comprise a means for facilitating engagement and lifting of the tube segment.

17. The system of claim 1 wherein the annular gap circumscribes the cask.

18. The system of claim 1 further comprising an annular top ring defining a central opening and coupled to a top end of the tubular shell, the annular top ring extending radially inward from the tubular end wall beyond the sidewall of the cask and spaced from a top surface of a lid of the cask, the central opening of the annular top ring being the opening at the top end of the tubular shell.

19. The system of claim 1 wherein the tubular shell has a height measured from the top end of the tubular shell to the bottom end of the tubular shell, the cask having a height measured from the top end of the cask to the bottom end of the cask, the height of the tubular shell being greater than the height of the cask.

20. The system of claim 19 wherein the tubular shell is a free-standing structure.

21. The system of claim 1 wherein the tubular shell is slidably removable from the cask by imparting axial movement to the tubular shell.

22. The system of claim 1 wherein the air flow barrier is coupled to the tubular shell and is flexible.

23. A system for containing high level radioactive materials comprising:

a cask extending along a longitudinal axis and having an internal cavity for holding high level radioactive materials, the cask comprising a plurality of inlet vents at a bottom end of the cask for allowing cool air to enter the internal cavity and a plurality of outlet vents at a top end of the cask for allowing heated air to exit the internal cavity;

a tubular shell extending from a bottom end to a top end, the tubular shell positioned to circumferentially surround the cask in a spaced apart manner so that an annular gap exists between the tubular shell and a sidewall of the cask, the tubular shell comprising a plurality of primary apertures forming passageways through the tubular shell and a plurality of secondary apertures forming passageways through the tubular shell; and

a flexible annular seal coupled to the tubular shell that separates the annular gap into;

(1) an upper chamber that forms a passageway between the primary aperture and the inlet vent of the cask; and

(2) a second chamber that forms a passageway between the secondary aperture and an opening at the top end of the tubular shell, wherein cross-flow of air between the first and second chambers of the annular gap is prohibited by the flexible annular seal.

24. The system of claim 23 wherein the primary apertures are circumferentially arranged in a spaced-apart manner about the tubular shell and the secondary apertures are circumferentially arranged in a spaced-apart manner about the tubular shell, wherein the secondary apertures are located at an axial height above the flexible annular seal and the primary apertures are located at an axial height below the flexible annular seal.

25. The system of claim 24 wherein each of the inlet vents comprise an inlet opening in the sidewall of the cask, the primary apertures of the tubular shell being radially offset from the inlet openings of the inlet vents.

26. The system of claim 25 wherein each of the outlet vents terminate in an outlet opening in the sidewall of the cask in the upper chamber of the annular gap, wherein the primary apertures and the inlet opening are located at a first axial height, the secondary apertures are located at a second axial height, and the outlet openings are located at a third axial height, and wherein the first, second and third axial heights are different.

27. The system of claim 23 wherein the tubular shell comprises a plurality of tube segments arranged in a stacked-assembly so that a surface contact interface is formed between a top edge and a bottom edge of adjacent tube segments, the system further comprising a collar located at each surface contact interfaces and extending above and below the surface contact interface.

28. The system of claim 27 wherein each of the tube segments comprise a plurality of spacers circumferentially arranged in a spaced-apart manner about the tube segment and protruding from an inner surface of the tube segment to maintain the annular gap.

29. The system of claim 28 wherein each of the spacers comprise a means for facilitating engagement and lifting of the tube segment.

30. The system of claim 23 further comprising an annular top ring defining a central opening and coupled to a top end of the tubular shell, the annular top ring extending radially inward from the tubular end wall beyond the sidewall of the cask and spaced from a top surface of a lid of the cask, the central opening of the annular top ring being the opening at the top end of the tubular shell.

31. The system of claim 23 wherein the tubular shell has a height measured from the top end of the tubular shell to the bottom end of the tubular shell, the cask having a height measured from the top end of the cask to the bottom end of the cask, the height of the tubular shell being greater than the height of the cask.

32. The system of claim 23 wherein the tubular shell is a free-standing structure that is slidably removable from the cask by imparting axial movement to the tubular shell.

33. An apparatus for providing additional radiation shielding to a cask holding high level radioactive materials comprising:

a tubular shell extending from an open bottom end to an open top end, the tubular shell having an inner surface that forms a cavity about a longitudinal axis;

a plurality of primary apertures forming passageways through the tubular shell and circumferentially arranged in a spaced-apart manner about the tubular shell;

a plurality of secondary apertures forming passageways through the tubular shell and circumferentially arranged in a spaced-apart manner about the tubular shell;

an annular seal coupled to the tubular shell and extending from the inner surface of the tubular shell; and

wherein the secondary apertures are located at an axial height above the annular seal and the primary apertures are located at an axial height below the annular seal.

34. The apparatus of claim 33 wherein the annular seal is flexible.

35. The apparatus of claim 33 wherein the tubular shell comprises a plurality of tube segments arranged in a stacked-assembly so that a surface contact interface is formed between a top edge and a bottom edge of adjacent tube segments, the system further comprising a collar located at each surface contact interfaces and extending above and below the surface contact interface.

36. The apparatus of claim 35 wherein the primary aperture, the secondary aperture and the annular seal are located in a bottom-most tube segment of the stacked assembly.

37. The system of claim 35 wherein the collar prohibits the adjacent tube segments from becoming axial misaligned.

38. The system of claim 35 wherein each of the tube segments comprise a plurality of spacers circumferentially arranged in a spaced-apart manner about the tube segment and protruding from an inner surface of the tube segment to maintain the annular gap.

39. The system of claim 38 wherein each of the spacers comprise a means for facilitating engagement and lifting of the tube segment.

40. The system of claim 33 further comprising an annular top ring defining a central opening and coupled to a top end of the tubular shell, the annular top ring extending radially inward from the tubular end wall.

41. A method of containing high level radioactive materials comprising:

a) positioning a cask on a support surface, the cask extending along a vertical axis and having an internal cavity containing high level radioactive materials, the cask comprising at least one inlet vent at a bottom end of the cask allowing cool air to enter the internal cavity and at least one outlet vent at a top end of the cask allowing heated air to exit the internal cavity; and

b) sliding a tubular shell over the cask, the tubular shell circumferentially surrounding the cask in a spaced apart manner so that an annular gap exists between the tubular shell and a sidewall of the cask, the tubular shell comprising at least one primary aperture forming a passageway through the tubular shell, at least one secondary aperture forming a passageway through the tubular shell, and an air flow barrier extending between the tubular shell and the sidewall of the cask that separates the annular gap into;

(1) a first chamber that forms a passageway between the primary aperture and the inlet vent of the cask; and

(2) a second chamber that forms a passageway between the secondary aperture and an opening at the top end of the tubular shell, wherein cross-flow of air between the first and second chambers of the annular gap is prohibited by the air flow barrier.

42. The method of claim 41 further comprising:

c) cool air entering the first chamber via the primary aperture of the tubular shell, the cool air within the first chamber being drawn into the internal cavity of the cask via the inlet duct, the cool air within the internal cavity becoming warmed within the internal cavity from heat emanating from the high level radioactive materials and exiting the internal cavity of the cask via the outlet duct as warmed air; and

e) cool air entering the second chamber via the secondary aperture, the cool air within the second chamber being warmed by heat emanating from the cask and rising within the second chamber as warmed air; and

wherein the warmed air exiting the outlet duct and the warmed air rising within the second chamber converge and exit the tubular shell via the opening at the top end of the tubular shell.

43. The method of claim 41 wherein step b) comprises sliding a plurality of tube segments over the cask and stacking the tube segments to form a stacked assembly that forms the tubular shell.