Patent Number: 
Section: description

FIG. 1 illustrates prior art ventilated vertical overpack (xe2x80x9cVVOxe2x80x9d) 2. Prior art VVO 2 comprises flat bottom 17, cylindrical body 12, and lid 14. Lid 14 is secured to cylindrical body 12 by bolts 18. Bolts 18 also serve to restrain lateral sliding of lid 14 with respect to cylindrical body 12 if prior art VVO 2 were to tip over. Cylindrical body 12 has top ventilation ducts 15 and bottom ventilation ducts 16. Top ventilation ducts 15 are located at or near the top of cylindrical body 12 while bottom ventilation ducts 16 are located at or near the bottom of cylindrical body 12. Both bottom ventilation ducts 16 and top ventilation ducts 15 are located around the circumference of the cylindrical body 12. Referring to FIG. 2, cylindrical body 12 of prior art VVO 2 forms chamber 25. Chamber 25 is adapted so as to be capable of receiving a canister loaded with spent nuclear fuel when lid 14 is removed. Referring to FIG. 3, prior art VVO 2 is illustrated partially in section with canister 13 loaded in chamber 25 for storage. Prior art VVO 2 has pedestal 19 located at the bottom of chamber 25. When canister 13 is placed in chamber 25 of prior art VVO 2 for storage, canister 13 rests on pedestal 19. Bottom ventilation ducts 16 are positioned on cylindrical body 12 so that canister 13 is above the elevation of bottom ventilation ducts 16 when canister 13 is placed in chamber 25. Top ventilation ducts 15 are positioned on cylindrical body 12 so that canister 13 is below the elevation of top ventilation ducts 15 when canister 13 is placed in chamber 25. This positioning mitigates the extent of radiation emanating through both bottom ventilation ducts 16 and top ventilation ducts 15 to the external environment. Cylindrical body 12 and portions of lid 14 are made of gamma absorbing material such a concrete 22. When lid 14 is secured to cylindrical body 12 with canister 13 resting in chamber 25, ventilation of chamber 25 (and thus cooling of the spent nuclear fuel) must occur. In prior art VVO 2, cold air 30 enters bottom ventilation ducts 16, flows upward passed canister 13 removing heat energy form canister 13 by convention, and exits prior art VVO 2 as warm air 31 through top ventilation ducts 15. Referring to FIG. 4, in order to transfer loaded canister 13 from transfer cask 27 to prior art VVO 2, transfer cask 27 is positioned above and stacked atop prior art VVO 2 by overhead crane 26. Referring to FIG. 5, transfer cask 27 has a retractable bottom 28 capable of opening so that loaded canister 13 can be lowered directly into chamber 25 of prior art VVO 2 while transfer cask 27 is stacked atop and secured to prior art VVO 2. During this lowering operation, canister 13 will pass by top ventilation ducts 15 (FIG. 1), creating a direct path for radiation to escape. Referring to FIG. 6, in order to block this radiation from escaping through top ventilation ducts 15 during lowering, temporary shield plugs 29 are installed in the openings of top ventilation ducts 15 before transfer cask 27 is positioned above prior art VVO 2. Temporary shield plugs 29 are made of gamma absorbing material such as concrete. Referring to FIG. 7, upon fully lowering canister 13 into prior art VVO 2, transfer cask 27 is removed. Temporary shield plugs 29 must then be removed before lid 14 is again secured to cylindrical body 12 so that chamber 25 can be properly ventilated. Once temporary shield plugs 29 are removed, lid 14 is secured to cylindrical body 12 by bolts 18 (FIG. 1). FIG. 8 illustrates an embodiment of the system of the present invention, ventilated vertical overpack (xe2x80x9cVVOxe2x80x9d) 40. Ventilated vertical overpack 40 comprises cylindrical body 43, bottom 44, and ventilated lid 41. Cylindrical body 43 and bottom 44 form chamber 46 which is capable of receiving a canister of spent nuclear fuel. Cylindrical body 43 also has lower ventilation ducts 45 located at or near the bottom of cylindrical body 43 for ventilating chamber 46. However, unlike cylindrical body 12 of prior art VVO 2 (FIG. 1), cylindrical body 43 of VVO 40 does not have upper ventilation ducts located at or near its top. Instead, ventilated lid 41 has one or more lid ventilation ducts 42 for ventilating chamber 46. Referring to FIG. 9, because cylindrical body 43 does not have upper ventilation ducts, top surface 47 of cylindrical body 43 is approximately a flat horizontal surface, providing a gamma absorbing shield all around its top. As such, when canister 13 is fully lowered into chamber 46, cylindrical body 43 does need to extend taller than canister 13 to ensure that radiation does not emanate directly into the external environment. Moreover, this flat top surface 47 eliminates the need for installing temporary shield plugs 29 (FIG. 6) during canister 13 lowering operations being that there are no openings through which radiation can escape once a transfer cask is properly secured to top surface 47. However, as in the prior art VVO 2 (FIG. 1.), lower ventilation ducts 45 are positioned on cylindrical body 43 elevationally below canister 13 when canister 13 is placed in chamber 46. Body shear ring 20 is attached to top surface 47. Body shear ring 20 has an upper surface that is also a substantially flat horizontal surface. Loaded canister 13 of spent nuclear fuel is stored in VVO 40 by placing canister 13 in chamber 46 (FIG. 8) of ventilated vertical overpack 40 and securing ventilated lid 41 to cylindrical body 43 so that the air within chamber 46 is warmed by the heat of the spent nuclear fuel, cold air enters through lower ventilation ducts 45 and exits as warmed air through the lid ventilation ducts 42. Ventilated lid 41 can also be bolted to cylindrical body 43. Referring to FIG. 10, ventilation lid 41 has four lid ventilation ducts 42 on side wall 30. Ventilated lid 41 has a bottom surface 51 that is a substantially flat horizontal surface. Ventilation lid 41 also comprises lid shear ring 21 attached to bottom surface 51. Lid shear ring 21 has a lower surface that is a substantially flat horizontal surface. Referring to FIG. 9, cylindrical body 43 has body shear ring 20 secured to its top surface 47. When ventilated lid 41 is placed atop cylindrical body 43, the lower surface of lid shear ring 21 (FIG. 10) contacts top surface 47 to form a first substantially horizontal interface. Concurrently, the upper surface of body shear ring 20 contacts bottom surface 51 of ventilated lid 41 to form a second substantially horizontal interface. As such, lid shear ring 21 and body shear ring 20 interact to restrain lateral motion of ventilated lid 41 with respect to cylindrical body 43, even if bolts 18 are not secured. Ventilated lid 41 is secured to cylindrical body 43 by extending bolts 18 through ventilated lid 41 and threadily engaging bolt holes 48 of cylindrical body 43. Alternatively, shear rings do not have to be used. In this alternative embodiment, the bottom surface of the lid and the top surface of the overpack body will be in direct contact so as to form a substantially horizontal interface. Referring to FIG. 11, ventilated lid 41 can be constructed so that ventilated lid 41 comprises two pieces, lid cap 49 that substantially encloses chamber 46 and lid body 50 which contains the means to ventilate chamber 46, illustrated as lid ventilation ducts 42. Lid ventilation ducts 42 are located within side wall 30 (FIG. 10) of lid body 50. When constructed as lid cap 49 and lid body 50, lid cap 49 can be removed from cylindrical body 43 without removing lid body 50. In such an embodiment, lid body 50 is an annular ring-like structure capable of being removed and secured to cylindrical body 43 independent of lid cap 49. Alternatively, ventilated lid 41 can be constructed so that it is one rigid piece that must be removed in its entirety. The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. As will be understood by those skilled in this art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.