Abstract:
A module for storing high level radioactive waste includes an outer shell, having a hermetically closed bottom end, and an inner shell forming a cavity and being positioned inside the outer shell to form a space therebetween. At least one divider extends from the top to the bottom of the inner shell to create a plurality of inlet passageways through the space, each inlet passageway connecting to a bottom portion of the cavity. A plurality of inlet ducts each connect at least one of the inlet passageways and ambient atmosphere, and each includes an inlet duct cover affixed atop a surrounding inlet wall, the inlet wall being peripherally perforated. A removable lid is positioned atop the inner shell and has at least one outlet passageway connecting the cavity and the ambient atmosphere, the lid and the top of the inner shell being configured to form a hermetic seal therebetween.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a U.S. national stage application under 35 U.S.C. 371 of PCT Application No. PCT/US2013/037228, filed on Apr. 18, 2013, which claims the benefit of U.S. Provisional Patent Application 61/625,869, filed Apr. 18, 2012, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The field of the present invention relates systems and methods for storing high level waste (“HLW”), such as spent nuclear fuel, in ventilated vertical modules. 
     BACKGROUND OF THE INVENTION 
     The storage, handling, and transfer of HLW such as spent nuclear fuel, requires special care and procedural safeguards. For example, in the operation of nuclear reactors, it is customary to remove fuel assemblies after their energy has been depleted down to a predetermined level. Upon removal, this spent nuclear fuel is still highly radioactive and produces considerable heat, requiring that great care be taken in its packaging, transporting, and storing. In order to protect the environment from radiation exposure, spent nuclear fuel is first placed in a canister. The loaded canister is then transported and stored in large cylindrical containers called casks. A transfer cask is used to transport spent nuclear fuel from location to location while a storage cask is used to store spent nuclear fuel for a determined period of time. 
     In a typical nuclear power plant, an open empty canister is first placed in an open transfer cask. The transfer cask and empty canister are then submerged in a pool of water. Spent nuclear fuel is loaded into the canister while the canister and transfer cask remain submerged in the pool of water. Once fully loaded with spent nuclear fuel, a lid is typically placed atop the canister while in the pool. The transfer cask and canister are then removed from the pool of water, the lid of the canister is welded thereon and a lid is installed on the transfer cask. The canister is then properly dewatered and filled with inert gas. The transfer cask (which is holding the loaded canister) is then transported to a location where a storage cask is located. The loaded canister is then transferred from the transfer cask to the storage cask for long term storage. During transfer from the transfer cask to the storage cask, it is imperative that the loaded canister is not exposed to the environment. 
     One type of storage cask is a ventilated vertical overpack (“VVO”). A VVO is a massive structure made principally from steel and concrete and is used to store a canister loaded with spent nuclear fuel (or other HLW). VVOs stand above ground and are typically cylindrical in shape and extremely heavy, weighing over 150 tons and often having a height greater than 16 feet. VVOs typically have a flat bottom, a cylindrical body having a cavity to receive a canister of spent nuclear fuel, and a removable top lid. 
     In using a VVO to store spent nuclear fuel, a canister loaded with spent nuclear fuel is placed in the cavity of the cylindrical body of the VVO. Because the spent nuclear fuel is still producing a considerable amount of heat when it is placed in the VVO for storage, it is necessary that this heat energy is able to escape from the VVO cavity. This heat energy is removed from the outside surface of the canister by ventilating the VVO cavity. In ventilating the VVO cavity, cool air enters the VVO chamber through inlet ventilation ducts, flows upward past the loaded canister, and exits the VVO at an elevated temperature through outlet ventilation ducts. 
     While it is necessary that the VVO cavity be vented so that heat can escape from the canister, it is also imperative that the VVO provide adequate radiation shielding and that the spent nuclear fuel not be directly exposed to the external environment. U.S. Pat. No. 7,933,374, issued Apr. 26, 2011, the disclosure of which is incorporated herein by reference in its entirety, discloses a VVO which meets these shielding needs. 
     The effect of wind on the thermal performance of a ventilated system can also be a serious drawback that, to some extent, afflicts all systems in use in the industry at the present time. Storage VVO&#39;s with only two inlet or outlet ducts are especially vulnerable. While axisymmetric air inlet and outlet ducts behave extremely well in quiescent air, when the wind is blowing, the flow of air entering and leaving the system is skewed, frequently leading to at reduced heat rejection capacity. 
     SUMMARY OF THE INVENTION 
     A module for storing high level radioactive waste includes an outer shell having a hermetically closed bottom end and an inner shell disposed inside the outer shell so as to form a space between the inner shell and the outer shell. At least one divider extends from a top of the inner shell to a bottom of the inner shell, the at least one divider creating a plurality of inlet passageways through the space, each inlet passageway connecting to a bottom portion of the cavity. A plurality of inlet ducts each connect at least one of the inlet passageways to ambient atmosphere. The inlet ducts are configured such that when the module is inset into the ground, the air pressure about each inlet duct is substantially the same. A removable lid is positioned on the inner shell, and the lid having at least one outlet passageway connecting the cavity and the ambient atmosphere. The lid and the top of the inner shell are respectively configured to form a hermetic seal at a top of the cavity. 
     In a first separate aspect of the present invention, each inlet duct comprises an inlet duct cover affixed over a surrounding inlet wall, with the inlet wall being peripherally perforated. The inlet wall may be peripherally perforated to have a minimum of 60% open area. 
     In a second separate aspect of the present invention, the lid further includes an outlet duct connecting the at least one outlet passageway and the ambient atmosphere. The outlet duct includes an outlet duet cover affixed over a surrounding outlet wall, with the outlet wall being peripherally perforated. The outlet wall may be peripherally perforated to have a minimum of 60% open area. 
     In a third separate aspect of the present invention, a hermetically sealed canister for containing high-level waste is positioned within the cavity, wherein the cavity has a horizontal cross-section that accommodates no more than one canister. 
     In a fourth separate aspect of the present invention, the top of the upper shield extends to or above the inlet ducts. 
     In a fourth separate aspect of the present invention, at least four dividers extend from a top of the inner shell to a bottom of the inner shell, thereby forming a plurality of the inlet passageways, and each divider includes an extension portion extending into the cavity, the extension portion configured as a positioning flange for a canister disposed within the cavity. 
     In a fifth separate aspect of the present invention, each of the inlet ducts maintains an intake air pressure independently of each of the other inlet ducts. 
     In a sixth separate aspect of the present invention, each of the inlet ducts maintains an intake air pressure substantially the same as each of the other inlet ducts. 
     In a seventh separate aspect of the present invention, a system including a plurality of the modules is employed, with the inlet ducts of a first of the modules maintains air pressure independently of the inlet ducts of a second of the modules. 
     In an eighth separate aspect of the present invention, a method of storing high level waste includes providing a module having an outer shell having a hermetically closed bottom end and an inner shell disposed inside the outer shell so as to form a space between the inner shell and the outer shell. At least one divider extends from a top of the inner shell to a bottom of the inner shell, the at least one divider creating a plurality of inlet passageways through the space, each inlet passageway connecting to a bottom portion of the cavity. A plurality of inlet ducts each connect at least one of the inlet passageways to ambient atmosphere. The inlet ducts are configured such that when the module is inset into the ground, the air pressure at each inlet duct is substantially the same, and the air pressure at each inlet duct is independent of the air pressure at the other inlet ducts. A canister containing high level radioactive waste is placed into the cavity. A lid is positioned over the cavity, with the lid having at least one outlet passageway connecting the cavity and the ambient atmosphere. The lid and the top of the inner shell are respectively configured to form a hermetic seal at a top of the cavity. 
     In a ninth separate aspect of the present invention, one or more of the preceding separate aspects may be employed in combination. 
     Advantages of the improvements will be apparent from the drawings and the description of the preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the exemplary embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown in the following figures: 
         FIG. 1A  is a partially exploded perspective view of a HLW storage container. 
         FIG. 1B  is a top plan view of the HLW storage container of  FIG. 1 . 
         FIG. 2  is a sectional view of the HLW storage container of  FIG. 1  along the line II-II. 
         FIG. 3  is a partial sectional view of the HLW storage container of  FIG. 1  along the line III-III. 
         FIG. 4A  is a partial sectional view of the HLW storage container of  FIG. 1 . 
         FIG. 4B  is a sectional view of the HLW storage container  FIG. 5A  along the line IV-IV-B. 
         FIG. 5A  is a partial sectional view of the HLW storage container of  FIG. 1  having a canister positioned in the cavity. 
         FIGS. 5B-5D  are detailed views of the indicated parts of  FIG. 5A . 
         FIG. 6  is an isometric view of a lid for a HLW storage container. 
         FIG. 7  is a sectional view of the lid of  FIG. 6 . 
         FIG. 8  is a plan view of an array of HLW storage containers. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “left,” “right,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are illustrated by reference to the preferred embodiments. Accordingly, the invention expressly should not be limited to such preferred embodiments illustrating some possible non-limiting combinations of features that may exist alone or in other combinations of features; the scope of the invention being defined by the claims appended hereto. 
       FIG. 1  illustrates a high level waste (“HLW”) storage container  10 , encased in surrounding concrete  11 , as it would be in an installation.  FIG. 2  illustrates the storage container  10  in a sectional view, still with the surrounding concrete  101 . While the HLW storage container  10  will be described in terms of being used to store a canister of spent nuclear fuel, it will be appreciated by those skilled in the art that the systems and methods described herein can be used to store any and all kinds of HLW. 
     The HLW storage container  10  is designed to be a vertical, ventilated dry system for storing HLW such as spent fuel. The HLW storage container  10  is fully compatible with 100 ton and 125 ton transfer casks for HLW transfer procedures, such as spent fuel canister transfer operations. All spent fuel canister types engineered for storage in free-standing, below grade, and/or anchored overpack models can be stored in the HLW storage container  10 . 
     As used herein the term “canister” broadly includes any spent fuel containment apparatus, including, without limitation, multi-purpose canisters and thermally conductive casks. For example, in some areas of the world, spent fuel is transferred and stored in metal casks having a honeycomb grid-work/basket built directly into the metal cask. Such casks and similar containment apparatus qualify as canisters, as that term is used herein, and can be used in conjunction with the HLW storage container  10  as discussed below. 
     The HLW storage container  10  can be modified/designed to be compatible with any size or style of transfer cask. The HLW storage container  10  can also be designed to accept spent fuel canisters for storage at an Independent Spent Fuel Storage installations (“ISFSI”). ISFSIs employing the HLW storage container  10  can be designed to accommodate any number of the HLW storage container  10  and can be expanded to add additional HLW storage containers  100  as the need arises. In ISFSIs utilizing a plurality of the HLW storage container  10 , each HLW storage container  10  functions completely independent form any other HLW storage container  10  at the ISFSI. 
     The HLW storage container  10  has a body  20  and a lid  30 . The lid  30  rests atop and is removable/detachable from the body  20 . Although an HLW storage container can be adapted for use as an above grade storage system, by incorporating design features found in U.S. Pat. No. 7,933,374, this HLW storage container  10 , as shown, is designed for use as a below grade storage system. 
     Referring to  FIG. 2 , the body  20  includes an outer shell  21  and an inner shell  22 . The outer shell  21  surrounds the inner shell  22 , forming a space  23  therebetween. The outer shell  21  and the inner shell  22  are generally cylindrical in shape and concentric with one another. As a result, the space  23  is an annular space. While the shape of the inner and outer shells  22 ,  21  is cylindrical in the illustrated embodiment, the shells can take on any shape, including without limitation rectangular, conical, hexagonal, or irregularly shaped. In some embodiments, the inner and outer shells  22 ,  22  will not be concentrically oriented. 
     The space  23  formed between the inner shell  22  and the outer shell  21  acts as a passageway for cool air. The exact width of the space  23  for any HLW storage container  10  is determined on a case-by-case design basis, considering such factors as the heat load of the HLW to be stored, the temperature of the cool ambient air, and the desired fluid flow dynamics. In some embodiments, the width of the space  23  will be in the range of 1 to 6 inches. While the width of space  23  can vary circumferentially, it may be desirable to design the HLW storage container  10  so that the width of the space  23  is generally constant in order to effectuate symmetric cooling of the HLW container and even fluid flow of the incoming air. As discussed in greater detail below, the space  23  may be divided up into a plurality of passageways. 
     The inner shell  22  and the outer shell  21  are secured atop a floor plate  50 . The floor plate  50  is hermetically sealed to the outer shell  21 , and it may take on any desired shape. A plurality of spacers  51  are secured atop the floor plate  50  within the space  23 . The spacers  51  support a pedestal  52 , which in turn supports a canister. When a canister holding HLW is loaded into the cavity  24  for storage, the bottom surface of the canister rests atop the pedestal  52 , forming an inlet air plenum between the underside of the pedestal  52  and the floor of cavity  24 . This inlet air plenum contributes to the fluid flow and proper cooling of the canister. 
     Preferably, the outer shell  21  is seal joined to the floor plate  50  at all points of contact, thereby hermetically sealing the HLW storage container  10  to the ingress of fluids through these junctures. In the case of weldable metals, this seal joining may comprise welding or the use of gaskets. Most preferably, the outer shell  21  is integrally welded to the floor plate  50 . 
     An upper flange  77  is provided around the top of the outer shell  21  to stiffen the outer shell  21  so that it does not buckle or substantially deform under loading conditions. The upper flange  77  can be integrally welded to the top of the outer shell  21 . 
     The inner shell  22  is laterally and rotationally restrained in the horizontal plane at its bottom by support legs  27  which straddle lower ribs  53 . The lower ribs  53  are preferably equispaced about the bottom of the cavity  24 . The inner shell  22  is preferably not welded or otherwise permanently secured to the bottom plate  50  or outer shell  21  so as to permit convenient removal for decommissioning, and if required, for maintenance. 
     The inner shell  22 , the outer shell  21 , the floor plate  50 , and the upper flange  77  are preferably constructed of a metal, such as a thick low carbon steel, but can be made of other materials, such as stainless steel, aluminum, aluminum-alloys, plastics, and the like. Suitable low carbon steels include, without limitation, ASTM A516, Gr. 70, A515 Gr. 70 or equal. The desired thickness of the inner and outer shells  22 ,  21  is matter of design choice and will determined on a case-by-case basis. 
     The inner shell  22  forms a cavity  24 . The size and shape of the cavity  24  is also a matter of design choice. However, it is preferred that the inner shell  22  be designed so that the cavity  24  is sized and shaped so that it can accommodate a canister of spent nuclear fuel or other HLW. While not necessary, it is preferred that the horizontal cross-sectional size and shape of the cavity  24  be designed to generally correspond to the horizontal cross-sectional size and shape of the canister-type that is to be used in conjunction with a particular HLW storage container. More specifically, it is desirable that the size and shape of the cavity  24  be designed so that when a canister containing HLW is positioned in the cavity  24  for storage (as illustrated in  FIG. 4A ), a small clearance exists between the outer side walls of the canister and the side walls of the cavity  24 . 
     Designing the cavity  24  so that a small clearance is formed between the side walls of the stored canister and the side walls of the cavity  24  limits the degree the canister can move within the cavity during a catastrophic event, thereby minimizing damage to the canister and the cavity walls and prohibiting the canister from tipping over within the cavity. This small clearance also facilitates flow of the heated air during HLW cooling. The exact size of the clearance can be controlled/designed to achieve the desired fluid flow dynamics and heat transfer capabilities for any given situation. In some embodiments, for example, the clearance may be 1 to 3 inches. A small clearance also reduces radiation streaming. 
     The inner shell  22  is also equipped with multiple sets of equispaced longitudinal ribs  54 ,  55 , in addition to the lower ribs  53  discussed above. One set of ribs  54  are preferably disposed at an elevation that is near the top of a canister of HLW placed in the cavity  24 . This set of ribs  54  may be shorter in length in comparison to the height of the cavity  24  and a canister. Another set of ribs  55  are set below the first set of ribs  54 . This second set of ribs  55  is more elongated than the first set of ribs  54 , and these ribs  55  extend to, or nearly to, the bottom of the cavity  24 . These ribs  53 ,  54 ,  55  serve as guides for a canister of HLW is it is lowered down into the cavity  24 , helping to assure that the canister properly rests atop the pedestal  52 . The ribs also serve to limit the canister&#39;s lateral movement during an earthquake or other catastrophic event to a fraction of an inch. 
     A plurality of openings  25  are provided in the inner shell  22  at or neat its bottom between the support legs  27 . Each opening  25  provides a passageway between the annular space  23  and the bottom of the cavity  24 . The openings  25  provide passageways by which fluids, such as air, can pass from the annular space  23  into the cavity  24 . The openings  25  are used to facilitate the inlet of cooler ambient air into the cavity  24  for cooling a stored HLW having a heat load. As illustrated, eight openings  25  are equispaced about the bottom of the inner shell  22 . However, any number of openings  25  can be included, and they may have any spacing desired. The exact number and spacing will be determined on a case-by-case basis and will dictated by such considerations as the beat load of the HLW, desired fluid flow dynamics, etc. Moreover, while the openings  25  are illustrated as being located in the side wall of the inner shell  22 , the openings can be provided in the floor plate in certain modified embodiments of the HLW storage container. 
     The openings  25  in the inner shell  22  are sufficiently tall to ensure that if water enters the cavity  24 , the bottom region of a canister resting on the pedestal  52  would be submerged for several inches before the water level reaches the top edge of the openings  25 . This design feature helps ensure thermal performance of the system under accidental flooding of the cavity  24 . 
     With reference to  FIG. 3 , a layer of insulation  26  is provided around the outside surface of the inner shell  22  within the annular space  23 . The insulation  26  is provided to minimize heating of the incoming cooling air in the space  23  before it enters the cavity  24 . The insulation  26  helps ensure that the heated air rising around a canister situated in the cavity  24  causes minimal pre-heating of the downdraft cool air in the annular space  23 . The insulation  26  is preferably chosen so that it is water and radiation resistant and undegradable by accidental wetting. Suitable forms of insulation include, without limitation, blankets of alumina-silica fire clay (Kaowool Blanket), oxides of alimuna and silica (Kaowool S Blanket), alumina-silica-zirconia fiber (Cerablanket), and alumina-silica-chromia (Cerachrome Blanket). The desired thickness of the layer of insulation  26  is matter of design and will be dictated by such considerations such as the heat load of the HLW, the thickness of the shells, and the type of insulation used. In some embodiments, the insulation will have a thickness in the range ½ to 6 inches. 
     As shown in  FIGS. 2 and 3 , inlet ducts  60  are disposed on the top surface of the upper flange  77 . Each inlet duct  60  connects to two inlet passageways  61  which continue from under the upper flange  77 , into the space  23  between the outer and inner shells  21 ,  22 , and then connect to the cavity  24  by lower openings  62  in the bottom of the inner shell  22 . Within the space  23 , the inlet passageways  61  are separated by dividers  63  to keep cooling air flowing through each inlet passageway  61  separate from the other inlet passageways  61  until the cooling air emerges into the cavity  24 .  FIGS. 4A and 4B  illustrate the configuration of the inlet passageways  61  and the dividers  63 . Each inlet passageway  61  connects with the space  23  by openings  64  in the top of the outer shell  21 . From the openings  64 , the cooling air continues down the in the space, via the individual inlet passageways  61  created by the dividers  64 , and into the cavity  24 , where it is used to cool a placed HLW canister. The dividers  63  are equispaced within the space  23  to aid in balancing the air pressure entering the space  23  from each inlet duct and inlet passageway. Also, as shown in the figures, each of the lower ribs  53  is integrated with one of the dividers  63 , such that the lower ribs form an extension of the dividers, extending into the cavity  24 . 
     Referring back to  FIG. 3 , each inlet duct  60  includes a duct cover  65 , to help prevent rain water or other debris from entering and/or blocking the inlet passageways  61 , affixed on top of an inlet wall  66  that surrounds the inlet passageways  61  on the top surface of the upper flange  77 . The inlet wall  66  is peripherally perforated around the entire periphery of the opening of the inlet passageways  61 . At least a portion of the lower part of the inlet ducts are left without perforations, to aid in preventing rain water from entering the HLW storage container. Preferably, the inlet wall  66  is perforated over 60% or more of its surface, and the perforations can be made in any shape, size, and distribution in accordance with design preferences. When the inlet ducts  60  are formed with the inlet wall  66  peripherally perforated, each of the inlet ducts has been found to maintain an intake air pressure independently of each of the other inlet ducts, even in high wind conditions, and each of the inlet ducts has been found to maintain an intake air pressure substantially the same as each of the other inlet ducts, again, even in high wind conditions. 
     The lid  30  rests atop and is supported by the upper flange  77  and a shell flange  78 , the latter being disposed on and connected to the tops edge of the inner shell  22 . The lid  30  encloses the top of the cavity  24  and provides the necessary radiation shielding so that radiation does not escape from the top of the cavity  24  when a canister loaded with HLW is stored therein. The lid  30  is designed to facilitate the release of heated air from the cavity  24 . 
       FIG. 5A  illustrates the HLW storage container  10  with a canister  13  placed within the cavity  24 . As shown in the  FIG. 5B  detailed view, the bottom of the canister  13  sits on the pedestal  52 , and the lower ribs  53  maintain a space between the bottom of the canister  13  and the inner shell  22 . Similarly, the  FIG. 5C  detailed view shows that the upper ribs  54  maintain a space between the top of the canister  13  and the inner shell  22 . 
     The  FIG. 5D  detailed view shows the lid  30  resting atop the upper flange  77  and the shell flange  78 . The lid  30  includes a closure gasket  31  which forms a seal against the upper flange  77  when the lid  30  is seated, and a leaf spring gasket  32  which forms a seal against the shell flange  78 . 
       FIGS. 6 and 7  illustrate the lid  30  removed from the body of the HLW storage container. Referring first to  FIG. 6 , the lid  30  is preferably constructed of a combination of low carbon steel and concrete (or another radiation absorbing material) in order to provide the requisite radiation shielding. The lid  30  includes an upper lid part  33  and a lower lid part  34 . The upper lid part  33  preferable extends at least as high as, if not higher than, the top of each inlet duct  60 . Each lid pan.  33 ,  34  includes an external shell  35 ,  36  encasing an upper concrete shield  37  and a lower concrete shield  38 . One or more outlet passageways  39  are formed within and around the body parts  33 ,  34  to connect the cavity with the outlet duct  40  formed on the top surface of the lid  30 . The outlet passageways  39  pass over the lower lid part  34 , between the upper and lower lid parts  33 ,  34 , and up through a central aperture within the upper lid part  34 . The outlet duct  40  covers this central aperture to better control the heated air as it rises up out of the. By being disposed on the top of the lid  30 , the outlet duct  40  may also be raised up significantly higher than the inlet ducts, using any desired length of extension for the outlet duct. By raising up the outlet duct higher, mixing between the heated air emitted from the outlet duct and cooler air being drawn into the inlet ducts can be significantly reduced, if not eliminated altogether. 
     The outlet duct  40 , which is constructed similar to the inlet ducts, includes a duct cover  41 , to help prevent rain water or other debris from entering and/or blocking the outlet passageways  39 , affixed on top of an outlet wall  42  that surrounds the outlet passageways  39  on the top surface of the upper lid pan  33 . The outlet wall  42  is peripherally perforated around the entire periphery of the opening of the outlet passageways  39 . At least a portion of the lower part of the outlet duct is left without perforations, to aid in preventing rain water from entering the HLW storage container. Preferably, the outlet wall  42  is perforated over 60% or more of its surface, and the perforations can be made in any shape, size, and distribution in accordance with design preferences. 
     The external shell of the lid  30  may be constructed of a wide variety of materials, including without limitation metals, stainless steel, aluminum, aluminum-alloys, plastics, and the like. The lid may also be constructed of a single piece of material, such as concrete or steel for example, so that it has no separate external shell. 
     When the lid  30  is positioned atop the body  20 , the outlet passageways  39  are in spatial cooperation with the cavity  24 . As a result, cool ambient air can enter the HLW storage container  10  through the inlet ducts  60 , flow into the space  23 , and into the bottom of the cavity  24  via the openings  62 . When a canister containing HLW having a heat load is supported within the cavity  24 , this cool air is warmed by the HLW canister, rises within the cavity  24 , and, exits the cavity  24  via the outlet ducts  40 . 
     Because the inlet ducts  60  are placed on different sides of the lid  30 , and the dividers separate the inlet passageways associated with the different inlet ducts, the hydraulic resistance to the incoming air flow, a common limitation in ventilated modules, is minimized. This configuration makes the HLW storage container less apt to build up heat internally under high wind conditions. 
     A plurality of HLW storage containers  100  can be used at the same ISFSI site and situated in arrays as shown in  FIG. 8 . Although the HLW storage containers  100  are closely spaced, the design permits a canister in each HLW storage container  10  to be independently accessed and retrieved easily. In addition, the design of the individual storage containers  100 , and particularly the design and positioning of the inlet and outlet ducts, enables the inlet ducts of a first of the storage containers to maintain air pressure independently of the inlet ducts of a second of the storage containers. Each storage container therefore will operate independently of each of the other storage containers, such that the failure of one storage container is unlikely to lead directly to the failure of other surrounding storage containers in the array. 
     While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. Thus, the spirit and scope of the invention should be construed broadly as set forth in the appended claims.