High-density underground storage systems for nuclear fuel and radioactive waste

Abstract

The underground, passively ventilated nuclear waste storage system includes an array of cavity enclosure containers, each including a cavity for holding a nuclear waste canister containing heat-generating radioactive waste. Each container includes at least one pair of air inlets, each fluidly coupled directly to a separate, vertical cooling air supply shell spaced apart from the container. The supply shell, in fluid communication with ambient air, operates to draw ventilation air that flows into the container by natural convection thermosiphon effect driven by heat emitted from the canister, which heats the container cavity. The containers are arranged in spaced-apart series in multiple parallel rows. The containers in each row are fluidly isolated from the containers in the other rows. Activation of the ventilation system further fluidly isolates the containers in each row from the other containers in that row. The containers may be part of an integrated interim storage facility for radioactive waste.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This patent application claims priority to U.S. Provisional Patent Application No. 63 / 118,350, filed November 25, 2020, and U.S. Provisional Patent Application No. 63 / 123,706, filed December 10, 2020, both of which are incorporated by reference in their entireties.

[0002] The present invention relates to a storage system for spent nuclear fuel and radioactive waste, and more particularly to such a system suitable for the consolidated intermediate storage of waste. [Background technology]

[0003] Spent or spent nuclear fuel and radioactive waste are currently temporarily stored "on-site" at operating nuclear power plants and at some decommissioned nuclear power plants until the federal government provides a central, permanent repository. For example, spent nuclear fuel (SNF) is removed from the reactor core and then stored in reactor fuel pools where it continues to generate decay heat. After a period of cooling in the pools, the fuel can be transferred to nuclear waste canisters, which are placed in thick-walled outer vessels, such as dry storage modules or casks, typically made of concrete, steel, or iron, for containment and radiation shielding. The casks are stored on the power plant site.

[0004] The concept of using Consolidated Interim Storage (CIS) is intended to provide a geographically distributed off-site storage facility for spent nuclear fuel and other high-level radioactive nuclear waste collected from multiple individual power plant sites, thereby augmenting widely dispersed waste stockpiles. The waste is stored in sealed nuclear waste canisters, such as the Multi-Purpose Canister (MPC) available from Holtec International Inc., Camden, New Jersey. The canister generally comprises an elongated cylindrical stainless steel shell, a base plate, and a lid hermetically seal welded to the shell, forming a boundary that confines the stored fuel assemblies disposed within the canister. A fuel basket disposed within the canister has a linear honeycomb structure that defines a number of open prismatic cells, each of which holds a nuclear fuel assembly. The fuel assembly is composed of a number of nuclear fuel rods or "cladding" containing uranium fuel pellets that continue to release significant decay heat even after removal from the reactor.

[0005] Nuclear waste canisters are initially transported from the power plant to the CIS facility for a period of time, with the ultimate goal of being transferred to a permanent nuclear waste repository once one becomes available from the government. These so-called Independent Spent Fuel Storage Facilities (ISFSI) are facilities designed for the intermediate storage of spent nuclear fuel, including solid and other associated radioactive materials, beyond reactor-related Class C waste. Each ISFSI facility typically maintains an inventory of a large number of waste canisters containing spent nuclear fuel and / or radioactive waste.

[0006] Some ISFSIs consist of multiple storage modules that store nuclear waste below ground / baseline and are ventilated by ambient natural cooling air. However, such existing underground nuclear waste storage systems do not meet all of the current needs of ISFSIs in all situations. For example, modules may be fluidly coupled to available ambient cooling air sources and / or to each other in a manner that may take from a particular module the ventilation air required for optimal cooling of the radioactive waste within each module.

[0007] Improvements to such underground ventilated nuclear waste storage systems are desirable. Summary of the Invention

[0008] The present application provides, in one aspect, a naturally ventilated, passively cooled radioactive nuclear waste storage system designed for storing fuel below ground / datum level. The system is comprised of a number of modules such as CECs (Cavity Enclosure Containers) that can be placed in an upright position on an underground concrete base pad located below the final graded overburden and / or artificial fill of the repository. Thus, the underground CECs are preferably positioned such that a majority of their total height is below ground level to protect against potential intentional or unintentional projectile impacts. In one embodiment, the CECs in the array can be spaced apart in a linear pattern, thereby forming a horizontally extending nuclear waste storage row along a common longitudinal axis. A number of parallel linear rows of CECs can be provided in a CIS facility, which can form an ISFSI facility.

[0009] In one embodiment, each CEC defines a cross-sectional area, in diameter, of an internal cavity configured to hold a single cylindrical spent nuclear fuel (SNF) canister. The canister holds SNF assemblies and / or other high-level radioactive waste as described hereinabove, which continue to emit significant amounts of heat that must be dissipated to preserve the structural integrity of the fuel assemblies or other waste. In certain other contemplated embodiments, multiple canisters may be stacked vertically, one above the other, within a single CEC, as disclosed in commonly owned U.S. Pat. No. 9,852,822, incorporated herein by reference. In this case, the CEC defines a cross-sectional area, in diameter, such that a single canister may be held at a single height in both the upper and lower positions within the CEC.

[0010] The CEC and canisters contained therein are cooled in a non-limiting preferred embodiment using a passive ambient air ventilation system that circulates cooling air through the CEC without the aid of a fan or blower. As the air in the annulus is heated by the canister due to heat emitted by the canister, a natural convective thermosiphon effect occurs that draws ambient air through the CEC cavity in the annulus between the CEC and the canister. In other possible embodiments, fans / blowers can be provided as needed, but are less preferred as an interruption in power to the CIS site may impede the ability to adequately cool the CEC and the radioactive nuclear fuel and / or other waste contained therein.

[0011] In a non-limiting preferred embodiment, each CEC includes at least two air inlets. In one embodiment, two air inlets are provided. The air inlets are directly fluidly connected to at least one direct cooling air source via laterally and horizontally extending flow paths (i.e., the air flow path defined by the flow paths between the cooling air source and the air inlets to the CEC does not include an intervening CEC). Additionally, each CEC is not directly fluidly coupled to other CECs (i.e., shell-to-shell) via flow paths. This advantageously minimizes fluid airflow interactions between adjacent CECs that may result in air pressure imbalances such that a CEC containing radioactive waste that releases more heat than other CECs may draw a disproportionate amount of available ventilation air in the system, causing other CECs to partially lack sufficient cooling air.

[0012] The cooling air source in some embodiments may be one or more vertically elongated tubular / hollow ambient cooling air supply shells. The air supply shells may have a smaller outer diameter than the CECs, allowing the CECs to be placed as closely together as possible to conserve the nuclear waste storage space available at the CIS facility within each row of CECs. Each air supply shell is in fluid communication with the ambient atmosphere at its top and is operable to draw cooling air into the shell from below by natural convection thermosiphon effect caused by heat released from the nuclear waste canisters in the CECs. The air flows through the flow passages into the CECs, is heated by the radioactive waste in the canisters, and is then discharged to the atmosphere through the top of the CEC, which may be located above ground to define an air outlet.

[0013] In some embodiments disclosed herein, each paired air inlet of the CEC can be fluidly coupled directly to a single, discrete, individual cooling air supply shell via a flow path. In other embodiments disclosed herein, the CEC is fluidly connected directly to the paired air supply shell via a flow path. In yet another embodiment disclosed herein, for nuclear waste that still loses extremely high levels of heat through thermal conduction through the nuclear waste canister walls, a high air flow system is provided in which each CEC is fluidly coupled to two pairs (i.e., four) of cooling air supply shells. In all of these embodiments, each air inlet of the CEC is fluidly coupled directly to the air supply shell via an individual, dedicated single flow path, rather than a shared branch or header type flow path configuration as in some past approaches, which may not receive the required amount / flow of cooling air in some circumstances.

[0014] In any of the three possible cooling air supply arrangements for the CECs and cooling air feeder shells described above, by providing each CEC with at least two separate air inlets fluidly coupled directly to one or more supply shells, the ability of natural ventilation to adequately cool each CEC to the extent necessary to preserve the structural integrity of the SNF assemblies and / or other high-level nuclear waste stored within the canisters of the CEC is advantageously improved. Because the ambient cooling air flowing to each CEC from one or two cooling air supply shells does not first pass through an upstream intervening CEC as employed in some conventional systems, the flow rate of ambient cooling air directly fed to the CEC to naturally ventilate the interior space or cavity and cool the SNF canisters is not reduced. This prevents a situation as in conventional ventilation systems where a vertically oriented CEC or storage shell located at the end of multiple CECs fluidly interconnected in series may not receive an adequate amount of cooling air. This is due to the fact that the upstream side of the CEC may cause an imbalance in the amount of available cooling air flowing to the ventilation system. Instead, by directly coupling each CEC to at least one cooling air supply shell in accordance with the present disclosure, the amount of cooling air required to adequately cool the canisters in each CEC is ensured via thermosiphonic fluid flow effects regardless of the level of decay heat generated by the radioactive waste in each CEC, thus avoiding pressure imbalances between the CECs due to different decay heat levels.

[0015] In a nuclear waste storage system such as a CIS facility with a passive ambient air ventilation system according to the present disclosure, in which parallel linear rows of CECs are provided, the CECs in one row are not fluidically coupled directly or indirectly (i.e., through intervening CECs or flow paths) to the CECs in other adjacent rows or to the cooling air supply shell. As previously described herein, fluid interactions between the CECs in adjacent rows that could result in potential pressure and flow imbalances and thereby cause unequal cooling of some CECs compared to other CECs are prevented. Furthermore, it should be noted that the use of parallel rows of CECs that are not fluidically interconnected can advantageously simplify the expansion of existing CIS facilities, since it is not necessary to partially excavate existing rows of CECs to create new fluid connections to existing buried CECs.

[0016] An array of CECs according to the present disclosure may form part of an Independent Spent Fuel Storage Installation (ISFSI) installation suitable for a CIS system that may include any suitable number of CECs as desired. The CECs may be part of a CIS system such as the HI-STORM UMAX (Holtec International Storage Module Underground Maximum Safety), an underground Vertical Ventilated Module (VVM) dry spent fuel storage system designed to be fully compatible with all currently certified Multi-Purpose Canisters (MPCs). Each HI-STORM UMAX Vertical Ventilated Module stores MPCs in a vertical configuration within a cylindrical cavity that is all located below the top of the grade of the ISFSI. The VVMs resemble above-ground overpacks and are composed of CECs, each of which includes a removable top closure lid according to the present disclosure.

[0017] Nuclear waste canisters usable with the current CEC, which may contain both spent or spent nuclear fuel (SNF) and / or non-fuel radioactive waste, may be stainless steel multipurpose canisters (MPC) available from Holtec International of Camden, N.J. Other canisters may also be used.

[0018] Current underground nuclear waste storage systems aim to provide safety by keeping radiation levels at the site boundary negligible in the event of a catastrophic event. As an underground system, the system utilizes the surrounding soil / artificial fill or roadbed to provide radiation shielding, physical protection, and a low center of gravity for a stable storage installation.

[0019] According to one aspect, an underground passively ventilated nuclear waste storage system includes a first cavity enclosure container having a horizontal longitudinal axis, an underground concrete base pad, a vertically elongated first cavity enclosure container positioned on said base pad and said longitudinal axis, said cavity enclosure container defining a vertical centerline axis and including a first air inlet, a second air inlet, an air outlet, and an interior cavity, said cavity of said first cavity enclosure container configured to hold a nuclear waste canister containing heat emitting radioactive nuclear waste, and an air outlet configured to be connected to an air outlet through an air outlet and an interior cavity. a first vertically elongated cooling air supply shell in fluid communication with the first cavity enclosure container and operable to draw in ambient air, the first cooling air supply shell fluidly coupled directly to a first air inlet of the first cavity enclosure container via a first flow passage, and a second vertically elongated cooling air supply shell in fluid communication with the ambient atmosphere and operable to draw in ambient air, the second cooling air supply shell fluidly coupled directly to a second air inlet of the first cavity enclosure container via a second flow passage. In one form, the first cavity enclosure container is not directly fluidly coupled to any other cavity enclosure container.

[0020] According to another aspect, an underground passively ventilated nuclear waste storage system includes a subsurface concrete base pad having a horizontal longitudinal axis, a first vertically elongated cavity enclosure container located on said base pad and on said longitudinal axis, a second vertically elongated cavity enclosure container located on said base pad and on said longitudinal axis, said second cavity enclosure container spaced apart from said first cavity enclosure container, said first cavity enclosure container and said second cavity enclosure container each defining a vertical centerline axis, said second cavity enclosure container including a first air inlet, a second air inlet, an air outlet, and an interior cavity, and a nuclear waste canister disposed in the interior cavity of each of said first cavity enclosure container and said second cavity enclosure container; a nuclear waste canister, the canister dissipating heat; and a vertically elongated cooling air supply shell disposed on a longitudinal axis between the first cavity enclosure container and the second cavity enclosure container, the cooling air supply shell in fluid communication with the ambient atmosphere and operable to draw in ambient air, the cooling air supply shell being fluidly coupled directly to a first air inlet of the first cavity enclosure container via a first flow path and the cooling air supply shell being fluidly coupled directly to a first air inlet of the second cavity enclosure container via a second flow path, the first cavity enclosure container not being directly fluidly coupled to any other cavity enclosure container and the second cavity enclosure container not being directly fluidly coupled to any other cavity enclosure container.

[0021] According to another aspect, an integrated intermediate storage facility for nuclear waste comprises a plurality of elongated cavity enclosure containers, each of which is erected on an underground base pad and extends vertically upward therefrom to a concrete top pad, and an artificial fill disposed between said base pad and said top pad, said cavity enclosure containers being arranged in an array of linear rows of a plurality of cavity enclosure containers extending longitudinally parallel to each other, each row defining a longitudinal axis, each of the cavity enclosure containers being disposed on the longitudinal axis, said integrated intermediate storage facility for nuclear waste further comprising: the cooling air supply shells comprising a plurality of vertically elongated cooling air supply shells, each arranged in a row on a longitudinal axis, one cooling air supply shell interposed between and directly fluidly coupled to a pair of cavity enclosure containers on either side of said cooling air supply shell, each said cooling air supply shell being in fluid communication with the ambient atmosphere, said one cooling air supply shell operable to draw in ambient air and distribute said air directly to each pair of cavity enclosure containers, wherein each row of said cavity enclosure containers is fluidly isolated from the cavity enclosure containers in any other row.

[0022] According to another aspect, an underground passively ventilated nuclear waste storage apparatus for an integrated interim storage facility includes a vertically elongated cavity enclosure container supported by an underground base pad and extending vertically upward therefrom to a concrete top pad, an artificial fill disposed between said base pad and said top pad, a nuclear waste canister disposed in an interior cavity of said cavity enclosure container, said canister releasing decay heat to heat air within an annular space formed between said cavity enclosure container and said canister, and a vertically elongated hollow cooling air distribution shell disposed to a side of said cavity enclosure container, said cooling air distribution shell being in fluid communication with the ambient atmosphere and operable to draw in ambient air, said cooling air distribution shell being configured to distribute said cooling air through said cavity enclosure container and said canister. and a cooling air supply shell, the cooling air intake shell being fluidly coupled directly to a lower portion of a cavity by a first air inlet of the cavity enclosure container via a first flow path, the cooling air supply shell being further fluidly coupled directly to a lower portion of a cavity by a second air inlet of the cavity enclosure container via a second flow path, the first flow path and the second flow path being fluidly coupled to a lower portion of the cooling air supply shell, defining a cooling air flow path whereby ambient cooling air is drawn into the cooling air supply shell, flows through the first flow path and the second flow path to a lower portion of the cavity enclosure container cavity, flows upwardly through an annular space, is heated by the canister, and exits an air outlet at a top of the cavity enclosure container for release to atmosphere. [Brief description of the drawings]

[0023] Features of the exemplary embodiments of the present invention will be described with reference to the following drawings, in which like elements are numbered like, and in which:

[0024] [Figure 1] FIG. 1 is a perspective view of an ISFSI facility comprising a first embodiment of a nuclear waste storage system according to the present disclosure for the consolidated intermediate storage of spent nuclear fuel and other high-level radioactive nuclear waste materials.

[0025] [Diagram 2] FIG.

[0026] [Diagram 3] FIG. 3 is a perspective view of one of the nuclear waste storage rows of the ISFSI facility of FIGS. 1 and 2.

[0027] [Figure 4] FIG. 2 is a first cross-sectional view of a second embodiment of a nuclear waste storage system showing a cavity enclosure container (CEC) and its cooling air distribution shell.

[0028] [Diagram 5] FIG. 2 is a second cross-sectional view of a single CEC.

[0029] [Figure 6] FIG. 11 is a plan view showing an arrangement of multiple CECs in the second embodiment.

[0030] [Figure 7] FIG. 13 is a perspective view of one row of nuclear waste storage according to the second embodiment.

[0031] [Figure 8] FIG. 4 is a top perspective view of the first embodiment of the nuclear waste storage system of FIGS. 1-3, illustrating one of the modular nuclear waste storage units including a CEC, a pair of directly fluidly coupled cooling air supply shells all mounted to a common support plate.

[0032] [Figure 9] FIG.

[0033] [Figure 10] FIG.

[0034] [Figure 11] This is a second side view thereof.

[0035] [Figure 12] This is a front view.

[0036] [Figure 13] FIG. 1 is a top view of the CEC with the top cover in place.

[0037] [Figure 14] FIG. 1 is a top view of the CEC with the top lid removed to show the internal cavity.

[0038] [Figure 15] FIG. 1 is a top view of the upper intake housing removed from a pair of cooling air supply shells to reveal an array of radiation attenuating plates therein.

[0039] [Figure 16] FIG.

[0040] [Figure 17] FIG. 1 is a cutaway perspective view showing a modular nuclear waste storage unit installed on a concrete base pad below ground level, a concrete top pad, and the engineered soil fill between them.

[0041] [Figure 18] FIG.

[0042] [Figure 19] FIG. 4 is a side cross-sectional view of a portion of the nuclear waste storage array of FIG. 3 showing multiple CECs and cooling air distribution shells.

[0043] [Figure 20] FIG. 13 is a plan view of a third embodiment of a nuclear waste storage system according to the present disclosure showing a pair of CECs and a cooling air distribution shell.

[0044] All drawings are schematic and not necessarily to scale. A part labeled with a reference numeral in one figure may be considered to be the same part as that shown in the other figures without the reference numeral for the sake of brevity, unless specifically labeled with a different part number and explained in the specification. Any designation in this specification that includes multiple numerals of the same integer but with different alphabetic suffixes shall be construed as a general reference numeral for all numerals sharing the same integer, unless otherwise indicated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The features and advantages of the present invention are illustrated and described herein with reference to exemplary (exemplary) embodiments. This description of exemplary embodiments is intended to be read in conjunction with the accompanying drawings, which are to be considered as part of the entire written description. Thus, the present disclosure should not be expressly limited to the exemplary embodiments shown in several possible non-limiting combinations that may exist alone or in other combinations of features.

[0046] In describing the embodiments disclosed herein, references to directions or orientations are merely for convenience of description and are not intended to limit the scope of the invention in any way. Relative terms such as "lower", "top", "horizontal", "vertical", "upper", "down", "upper", "lower", "top", "bottom", and derivatives thereof (e.g., "horizontal", "downward", "upward", etc.) should be construed as referring to the orientation as shown in the drawings being described or discussed at the time. These relative terms are for convenience of description only and do not require that the devices be constructed or operated in a particular orientation. Terms such as "mounted", "fixed", "connected", "coupled", "interconnected", etc., indicate a relationship in which components are movably or fixedly attached to one another, either directly or indirectly through intervening components, unless otherwise specified.

[0047] Throughout, the ranges disclosed herein are used as shorthand to describe each value within the range. Any value within the range can be selected as the range endpoint. Additionally, all references to prior patents or patent applications cited herein are incorporated herein by reference in their entirety. In the event of a discrepancy between a definition in this disclosure and a definition in a reference, this disclosure controls.

[0048] 1 and 2 show a plan view of an ISFSI facility comprising a passively cooled underground Integrated Intermediate Storage (CIS) system 100 according to the present disclosure. The system 100 comprises an array of underground vertically ventilated cavity enclosure containers (CECs) 110, each holding a single nuclear waste canister 150 containing radioactive nuclear waste, and a vertically elongated cooling air distribution shell 130 between and fluidly coupled to the CECs according to the present disclosure. The CECs and air distribution shell are configured to form an integrated part of an unpowered natural convection ventilation system that operates by thermosiphon effect to cool the nuclear waste fuel stored in each CEC, as described further herein.

[0049] 4 and 5 show an embodiment of the CEC 110 and more specifically the cooling air supply shell 110 of a nuclear waste storage system according to the present disclosure. The CEC 110 and cooling air supply shell 130 are installed on and supported by a thick, horizontally extending subterranean bottom base pad 101 located below the removed top surface or grade "G" of the natural soil "S" of the CIS system site. In one embodiment, the base pad 101 can be made of reinforced concrete. However, in other embodiments, other materials such as compacted gravel can be used, so long as they provide a stable and strong base to support the CEC and air supply shell. In the case of concrete as shown in the illustrated embodiment, the CEC and air supply shell can be securely fastened to the base pad via a number of anchor members 103, such as heavy-duty J-fasteners (threaded or otherwise) or other suitable types of anchors commonly used to fasten structures to concrete. The base pad 101 is preferably of suitable thickness and construction to be strong enough to withstand anticipated seismic events and maintain safe support of the CEC 110 and containment of its nuclear waste contents.

[0050] A horizontally and longitudinally extending concrete top pad 102 is formed on top of the artificial fill 140, described below, which is placed after the base pad 101 is poured. The top pad 102 thus projects and rises above the removed grade G of the surrounding natural soil S. The top pad is vertically spaced from the lower grade base pad 101. The top pad defines an upwardly facing top surface 102a that is elevated above ground level to prevent infiltration of standing water from the surrounding natural soil S into the CEC 110 due to rainfall. The top surface 102a is substantially parallel to the upwardly facing top surface 101a of the base pad 101 (the term "substantially" taking into account small variations in the levels of the surfaces 101a, 102a and recesses and / or contours formed in the surfaces for various purposes). The top pad 102 preferably extends beyond the periphery of the CEC 110 to at least one CEC outer diameter. A gradually sloping topography of the natural soil S around the upper pad is preferred to facilitate drainage of storm water from the CEC.

[0051] The vertical gaps or spaces formed between the base pad 101 and the top pad 102, including the open horizontal / lateral spaces between adjacent CECs 110 and cooling air distribution shells 130, are filled with a suitable "artificial fill" 104 to provide bilateral radiation shielding of the nuclear waste inside the CECs 110 and sufficient lateral structural support for the CECs and cooling air distribution shells 130. Any suitable artificial fill can be used, such as, but not limited to, flowable CLSM (Controlled Low Strength Material), a self-compacting cementitious fill material often used in the industry as backfill in place of conventional compacted earth fill. Regular concrete can also be used as the fill material for the gaps between CECs and from the base pad to the top pad if further radiation dose blocking capability of the CIS system is required. Other types of fill materials that provide radiation shielding and lateral support for the CECs and air distribution shells can also be used.

[0052] 4 and 5, each CEC 110 comprises a vertically elongated metal shell body 111 extending between an upper end 112 and a lower end 113 of the body to define a vertical centerline axis VC1. The upper portion 111a of the shell body defining the upper end 112 can be embedded in the concrete upper pad 102, including between the upper surface 102a and the bottom surface 102b of the upper pad 102 as shown. Several embodiments are shown in FIGS. 4 and 5 and 17-19. The upper end 112 of the CEC shell body 111 can terminate at the upper surface 102a of the upper pad. In either case, the body 111 of the CEC 110 can be cylindrical having a circular cross-sectional shape in a non-limiting preferred embodiment. However, other non-polygonal and polygonal bodies can be used in other acceptable embodiments. The shell body 111 of each CEC 110 defines an interior cavity 120 extending vertically between ends 112 and 113 that is configured to hold a cylindrical nuclear waste canister 150. As previously described herein, the waste canister 150 defines an interior space that holds spent fuel assemblies and / or other high-level radioactive waste from a nuclear reactor.

[0053] The nuclear waste canister 150 stored within the CEC 110 includes a vertically elongated hollow cylindrical shell 151, a top closure plate 152, and a bottom closure plate 153. The top and bottom closure plates are hermetically seal welded to the top and bottom ends of the shell 151 to form an airtight containment boundary for the nuclear waste stored within the canister. The canister 150 (i.e., shell and closure plates) may be formed of stainless steel for corrosion resistance in a preferred embodiment. The canister 150 has a height H3 that is less than the height H2 of the CEC shell body 111 such that the top of the canister is vertically spaced downward from the bottom of the concrete top pad 102 (see, e.g., FIG. 3). This helps both to prevent lateral radiation flow outward at the top of the CEC 110 and to provide impact protection from projectiles (e.g., missiles, etc.). Canister 150 may be any type of nuclear waste / SNF canister, including, but not limited to, a multipurpose canister (MPC) available from Holtec International of Camden, New Jersey.

[0054] The CEC 110 further includes a base plate 114 that is hermetically seal welded to the bottom end 113 of the shell body 111. A plurality of metallic radial support lugs 124 are welded to the base plate 114 and / or the inner surface of the CEC shell body 111 at circumferentially spaced locations at the bottom of the cavity 120. The lugs are formed of a suitable metal (e.g., stainless steel or other) and serve to support and elevate the canister 150 above the base plate. This provides an open space between the top of the base plate 114 and the bottom closure plate 153 of the canister 150 to allow cooling ventilation air to circulate underneath the canister to remove heat emitted from the bottom by the nuclear waste stored therein.

[0055] In one embodiment, the support lugs 124 may be generally L-shaped with a horizontal portion 124a welded to the base plate 114 and an integral adjacent vertical portion 124b welded to the inner surface of the CEC shell body 111. The vertical portions 124b each define a radially extending lower seismic restraining member that engages the sides of the canister 150 to hold the canister 150 in a centered position within the cavity 120 of the CEC 110, particularly during a seismic event (e.g., an earthquake). A plurality of radially extending upper seismic restraining members 123b project inwardly from the shell body 111 within the cavity 120 to hold the top of the canister 150 in a centered position. The restraining members 123b may be formed by circumferentially spaced metal plates or lugs welded to the inner surface of the CEC shell body 111.

[0056] When the canister 150 is placed into the cavity 120 of the CEC 110, an air ring 121 is formed therebetween that extends the entire height of the canister. The air ring is in fluid communication with the bottom cooling air supply shell 130 via passages 160 and an air outlet plenum 152 formed in the CEC cavity 120 above the canister.

[0057] The shell body 111 and base plate 114 of each CEC 110 may be formed from a suitable metal, such as stainless steel, for corrosion resistance.

[0058] The top end 112 of the CEC 110 is surrounded by a removable thick radiation shielding lid 115 that is removably attached to the top of the CEC shell body 111. The lid can have a metal and concrete composite construction including an outer shell 115a formed of steel, such as stainless steel, and an inner concrete lining 115b. This robust construction not only shields radiation, but also protects against projectile impact. In one configuration, the lid 115 includes a cylindrical circular upper portion 116a and an adjacent cylindrical circular lower portion 116b having an outer diameter D4 that is smaller than the outer diameter D3 of the upper portion. An annular stepped shoulder 116c is formed between the upper and lower portions of the lid. Diameters D3 and / or D4 in some embodiments may be greater than the outer diameter D2 of the CEC shell body 111.

[0059] The lower portion 116b of the lid 115 is insertably positioned within a corresponding upwardly opening circular recess 117 formed in the upper surface 102a of the upper pad 102 around the upper end 112 of each CEC 110 as shown (see, e.g., FIGS. 4 and 5). The diameter D5 of the recess 117 is greater than the outer diameter D2 of the CEC shell body 111. In one embodiment, the upper portion 111a of the CEC 110 (i.e., the shell body 111) can include a diametrically enlarged upper cylindrical section 111b having the same diameter D5 as the recess 117, which in fact defines the recess in this embodiment shown in FIGS. 14 and 16. The lid is slightly raised and ajar from the upper pad 102 within the recess in the upper pad 102 to form an air outlet 118, thereby forming an exit path between the lid and the CEC 110 for ventilation air rising from the CEC cavity 120 back to the ambient atmosphere. The air outlet 118 is configured to form a circuitous, multi-angled path to eliminate a direct line of sight from the cavity 120 to the atmosphere for radiation to escape (i.e., radiation streaming). In one embodiment, the outlet 118 may be configured in a double L-shape for this purpose, as shown in Figure 2, although other circuitous shaped paths may be used.

[0060] In some embodiments, as shown in Figures 16-18, the top section 111b of the CEC shell body 111 can further include a flat radially projecting annular seating flange 111c that is configured to engage and rest against the upper surface 102a of the concrete top pad 102.

[0061] Each cooling air supply shell 130 is a tubular hollow structure comprising a metallic vertically elongated body 131 defining a vertical centerline axis VC2 and a bottom closure plate 132 welded to the bottom end 134 of the shell. The vertical centerlines VC2 and VC1 of the CEC 110 are parallel to one another. The body 131 may be cylindrical having a circular cross-sectional shape in a non-limiting preferred embodiment. However, other non-polygonal and polygonal bodies may be used in other acceptable embodiments. The body 131 of each feeder shell defines an open vertical air passage 133 extending between the bottom end 134 and the top end 135 of the shell 130 to draw ambient cooling air downwardly through the shell. In some embodiments, the top end of the shell 130 may terminate at the top surface 102a of the concrete top pad 102. A perforated air intake housing 136 is coupled to the top end 135 of the shell 130 which projects vertically upward from the top pad 102 as shown. In one embodiment, the housing 136 may be formed of a cylindrical shell perforated to form multiple side openings extending 360 degrees circumferentially for drawing air laterally into the feeder shell 130. A circular cap 137 surrounds the top of the air inlet housing 136 to prevent rain ingress. The air feeder shell 130, bottom closure plate 132, intake housing 136, and cap 137 may be formed of a metal such as stainless steel to prevent corrosion. In other embodiments, other shapes of caps and intake housings may be used.

[0062] To minimize rising air exiting the top of the cavity 120 of the CEC 110 heated by the canister 150 from being drawn back into the intake housing 136 of the cooling air supply shell 130, in some embodiments it is preferred that each supply shell be spaced a sufficient lateral / horizontal distance, such as the distance of at least the outer diameter D1 of one supply shell, from the shell body 101 of an adjacent CEC.

[0063] 4 and 5, the cooling air supply shell 130 has a height H1 that is at least the same as the height H2 of the CEC shell body 111. As one non-limiting example, H2 and H1 may be approximately 227 inches (576.6 cm). In one embodiment, the shell 130 may have a height H1 (measured between the bottom end 134 and the top end 135) that is slightly greater than the height H2 (measured between the bottom end 113 and the top end 112 of the body, including the top) of the CEC shell body 111.

[0064] The canister 150 has an overall height H3 (including top and bottom closure plates 152, 153) that is less than the height H2 of the CEC shell body 111, such that an air outlet plenum 154 is formed between the bottom of the CEC lid 115 and the canister's top closure plate 152. The top of the canister, defined by the top closure plate 152, terminates below the CIS system's concrete top pad 102 at a height that can fit within the vertical extent of the artificial fill 140. This helps prevent "skyshine" radiation from leaking into the surrounding environment.

[0065] As shown in Figures 1 and 2, the cavity enclosure containers 110 and cooling air supply shells 130 in one embodiment can be arranged in a tightly packed array to minimize spatial installation requirements in a CIS facility. The array includes a plurality of parallel longitudinally extending linear nuclear waste storage rows R, each row R including a plurality of CECs 110 and cooling air supply shells 130. For ease of illustration, the arrangement in Figures 1 and 2 shows only five rows R. However, it will be appreciated that more or fewer rows of CECs and air supply shells can be provided as needed. Each row defines a respective horizontally extending longitudinal axis LA. The geometric center of each CEC intersects with the vertical centerline axis VC1 and intersects with the respective longitudinal axis LA of each row such that the CECs 110 can be considered to lie on the longitudinal axis. For ease of reference, a transverse axis TA can be defined as oriented perpendicular to the longitudinal axis LA in each row extending back and forth between the rows R in the array (see, for example, FIG. 2).

[0066] The nuclear waste storage rows R of the CECs 110 are spaced apart, parallel to one another, and define longitudinally extending access aisles AI, allowing access for commercially available motorized wheeled or track driven lifting devices, such as, but not limited to, cask crawlers or other devices, that carry, manipulate, and raise / lower the canisters 150 for insertion and removal from the CECs 110. These devices may span the row of CECs 110, with wheels or tracks traveling on the aisles AI on either side of the row. Such devices are well known to those skilled in the art without needing to be described in further detail. The low-exposure vertical profile of the CECs 110 (described further herein) allows these devices to navigate over a row of CEC modules to the desired CEC for canister insertion or removal.

[0067] 4-7 show a first possible embodiment and arrangement of the CECs 110 and cooling air supply shells 130. In this embodiment, each CEC 110 in each row R is directly fluidly coupled to a pair of cooling air supply shells 130 by horizontally / laterally extending flow passages 160. Each of the supply shells 130 is on either side of the CEC along the longitudinal axis LA as shown. In another perspective, each air supply shell 130 can be considered to be centrally located between the pair of CECs. Each CEC thus includes a pair of air inlets 125 forming openings on either side that extend through the shell body 111 of the CEC 110 to the internal cavity 120. The air inlets 125 are thus formed in and through the lower portion 111d of the CEC (i.e., the shell body 111) for introducing cooling air to the bottom of the CEC cavity 120 and the ventilation annulus 121. In a preferred but non-limiting embodiment, each air inlet 125 is constructed and arranged to introduce cooling ventilation air tangentially into the cavity 120 of each CEC 110 as shown. This tangential introduction of cooling air and flowing circumferentially around the inner surface of the CEC to quickly fill the CEC cavity and ventilation has the advantage of less pressure drop than introducing air radially and vertically into the canister shell 151.

[0068] The flow paths 160 comprise horizontally extending sections of metal piping that span between the cooling air supply shell 130 and its respective CEC 110. The flow paths fluidly couple each CEC air inlet 125 to its respective air supply shell 130 "directly," meaning that the cooling air flows from the air supply shell to its respective CEC without passing through other CECs or air supply shells on the way. As described earlier herein, this configuration advantageously maximizes the amount of cooling air each CEC 110 receives depending on the level of heat given off by the canisters in each CEC, which may differ. Thus, no CEC is starved of the cooling airflow required by the upstream CEC. Because the CECs and their nuclear waste contents are passively cooled by convection through the natural thermosiphon effect, as described earlier herein, pressure imbalances in the cooling air ventilation system that may adversely affect the proper cooling of each CEC are avoided by this cooling arrangement. By providing two air inlets 125 for each CEC 110, with each inlet having a separate cooling air source (i.e., supply shell 130), each CEC can be more reliably cooled and the greatest possible amount of heat generated within the cavity can be removed.

[0069] For the same reasons discussed above of ensuring that each CEC 110 receives the required amount of cooling air based on the particular heat load generated by the nuclear waste canisters 150 therein, it should further be noted that there are no interconnecting flow paths between the CECs or cooling air supplies anywhere. Thus, each nuclear waste storage row R is fluidly isolated from all other rows.

[0070] Although perhaps not immediately apparent from the figure, it should also be noted that when the ambient air cooling ventilation system is operational (i.e., when nuclear waste canisters 150 located within the CECs create active airflow through the ventilation system due to the thermosiphon effect described earlier herein), each CEC 110 in a single row R is fluidly isolated from adjacent CECs and all other CECs in the same row. For example, as shown in FIG. 4, ambient cooling air is drawn downwardly within the centrally located air supply shell 130 and then flows laterally outward through flow passages 160 toward each of the two illustrated CECs 110 (see airflow direction arrows). Cool air enters the bottom of the CEC and flows vertically upward as the air within the CEC cavity 120 is heated by the canisters 150 (see, e.g., FIG. 2). Thus, considering the direction of flow through these nuclear waste storage system components, air cannot flow in the opposite direction from one CEC 110 through the centrally located air supply shell 130 and into the other CEC. Thus, the CECs are effectively fluidly isolated from one another.

[0071] As previously mentioned, the flow paths 160 may include sections of metal piping, such as stainless steel, of suitable diameter. In a preferred but non-limiting embodiment, the flow paths are configured to prevent radiation streaming by having no straight line of sight between each cooling air supply shell 130 and any of the respective pairs of cavity enclosure containers 110 fluidly coupled thereto. This simultaneously ensures that there is no straight line of sight between any of the CECs 110 in row R through the supply shells 130. In one configuration, the flow paths 160 may each comprise an angled transverse section 162 oriented transversely to the longitudinal axis LA and an adjacent longitudinal section 161 oriented parallel to the longitudinal axis. A welded mitre joint 163 may be formed between the transverse section and the longitudinal section (see, for example, FIG. 6). An oblique angle is formed between these two sections of the flow paths. In other possible embodiments, a curved piping elbow may be used in place of the straight piping mitre joint section to prevent straight line of sight.

[0072] Since each cooling air supply shell 130 only needs to have a diameter necessary to supply cooling air to a pair of CECs 110, the diameter of the supply shell can be minimized to allow each row of CECs to be closely packed. This allows for more CECs and nuclear waste to be packed into each row R. Thus, in a preferred but non-limiting embodiment, the outer diameter D1 of the supply shell 130 may be smaller than the outer diameter D2 of the CECs 110. As one non-limiting example, D1 may be about 30 inches (76.2 cm) and D2 may be about 84 inches (213.4 cm). For size comparison, the flow passage 60 may have a smaller diameter than D1 or D2. For example, but not by way of limitation, in one embodiment, it is about 24 inches (61 cm). Other diameter sizes may be used in other embodiments and are not intended to limit the invention.

[0073] To summarize the operation of the nuclear waste storage system and ambient cooling air ventilation system, a nuclear waste canister 150 containing radioactive waste material (e.g., radioactive waste and / or other high-level radioactive waste removed from a nuclear reactor) is loaded into the CEC 110. A lid 115 is then placed on the CEC to enclose the CEC and its internal cavity.

[0074] When a canister is placed in a CEC and the lid is in place, the air in the ventilation ring 121 between the canister and the shell body 111 of each CEC 110 is heated by the canister. The heated air rises and collects in the air outlet plenum 154 above the canister in the CEC cavity 120, exits the CEC and returns to the atmosphere through air outlets 118 formed through the CEC lid 115 (see air flow direction arrows in Figures 4, 5 and 18).

[0075] The upward convection of air within the cavity 120 of each CEC 110 creates a negative pressure that draws ambient air into the cooling air supply shell 130 via a known thermosiphon effect or mechanism. The CEC draws air from the bottom of the air supply shell through passages 160 into its interior cavity 120 and lower portion of the ventilation annulus 121, completing the ventilation airflow circuit. This natural air flow is not assisted by powered fans or blowers, thereby avoiding operational costs associated with electricity consumption, but importantly, ensuring continued cooling of the CEC 110 to prevent overheating of the CEC in the event of a power outage and to maintain containment of the nuclear waste.

[0076] FIG. 20 illustrates a second alternative embodiment and arrangement of a nuclear waste storage system and corresponding ventilation system. In this embodiment, each CEC 110 is fluidly coupled to only a single cooling air supply shell 130 by a pair of angled / curved flow paths 160 to prevent radiation streaming as previously described herein. The CEC includes two air inlets 125 arranged to introduce ventilation air tangentially into the interior cavity of the CEC. The bifurcated ventilation air supply effectively creates a curtain of cooling air around the nuclear waste canisters 150 inside the CEC with minimal flow resistance to maximize air flow for cooling the radioactive waste. This alternative embodiment may be appropriate if a particular canister 150 still emits extremely high levels of thermal energy (heat) that must be dissipated to protect the structural integrity of the canister and the nuclear waste therein. Multiple pairs of fluidly isolated CECs 110 and cooling air supply shells 130 of FIG. 20 can be arranged as a row R of a CIS installation. The CECs 110 and air distribution shells 130 are disposed on the longitudinal axis LA of each row R, which may be an array of CECs.

[0077] It should be noted that some CIS installations may combine some rows of CECs 110 and air supply shells 130 according to the configuration shown in Figure 20 for nuclear waste canisters that emit high thermal energy, and some other rows of CECs 110 and air supply shells 130 according to the configuration shown in Figures 4-7 for nuclear waste canisters that emit low thermal energy. In still other embodiments, the two different arrangements of CECs and air supply shells may be mixed within a single row R. Thus, a great number of variations are possible depending on the particular nuclear waste storage needs and the level of thermal energy emitted by the canisters 150.

[0078] 1-3 and 8-19 show yet another alternative third embodiment and arrangement of a nuclear waste storage system and corresponding air ventilation system. This is a high air flow configuration of a passively cooled nuclear waste storage system with a thermosiphon driven ventilation system suitable for radioactive nuclear waste that emits very high levels of heat that must be dissipated by the ambient cooling air to protect the radioactive waste (e.g., SNF fuel assemblies, etc.) in the nuclear waste canister 150. The cooling air requirements of these high heat load CECs may even exceed the high air flow capacity provided by the CEC of FIG. 20 with its dedicated separate twin cooling air supply shells 130 shown.

[0079] Thus, the CECs 110 in this third embodiment of high air flow capacity may each be fluidly coupled to two pairs (i.e., four) of cooling air supply shells 130 by air flow conduits 160 (see, e.g., FIGS. 1-3 and 14). With continued reference to FIGS. 1-3 and 8-19, generally, one pair of supply shells 130 may be located on one side of the CEC and the remaining pair of supply shells may be located on the opposite, other side, as shown. The CEC includes four air inlets 125, each of which is fluidly coupled to one of the four cooling air supply shells 130 by a flow passage 160. The flow passage 160 may be configured and arranged similarly to the previous embodiments of the fresh air ventilation system previously described herein to introduce ventilation air tangentially at the lower / bottom of the interior cavity 120 of the CEC 110 to achieve the same air flow benefits.

[0080] It should be noted that each CEC 110 in a single row R need not necessarily be coupled to four cooling air supply shells 130 as seen in Figures 1-3. For example, one CEC 110 located at one end of row R is shown fluidly coupled to only a pair of cooling air supply shells 130 because it may not have as high a heat load as the remaining CECs in the illustrated row, which may require a higher ambient ventilation air flow rate or velocity (e.g., CFM - cubic feet per minute) to dissipate the higher heat emissions from the canisters 150 stored therein. Thus, the present passively cooled nuclear waste storage and ventilation system allows for considerable flexibility in configuration so that it can be customized to accommodate the specific and differing heat load dissipation needs of the CECs.

[0081] 1-3 and 8-19, the configuration and construction details of the CEC 110 in this third embodiment and arrangement of the passively cooled nuclear waste storage system may be similar to the previous embodiments, except for the additional cooling air inlets 125 to accommodate the two pairs of cooling air supply shells 130. Therefore, for the sake of brevity, the description of the CEC structure, including the lid 115, will not be repeated here. Accordingly, the features or parts of the CEC in the presently shown third embodiment of the nuclear waste storage system are numbered the same as in the figures of the first and second embodiments.

[0082] In the high airflow embodiment of the invention shown in Figures 1-3 and 8-19, however, the CEC 110 and cooling air distribution shells 130 are structurally integrated into an easily transportable and installable modular nuclear waste storage unit 200 (best shown in Figures 8-16). The modular unit 200 is a free-standing, portable assembly or structure that includes a common or shared support plate 202 formed of a suitable metallic material of suitable strength (e.g., stainless steel or other). The support plate 202 has a horizontally extending, flat body 201 that is configured to be attached and secured to an upper surface of an underground concrete base pad 101, such as via anchors 103 that are screw fasteners or other types of fastening / mounting devices. A CEC 110 and a pair of cooling air distribution shells 130 on either side of the CEC are fixedly attached to the common or shared support plate 202, such as by welding. The support plate 202 can have any suitable configuration, such as, in one non-limiting embodiment shown, a mixed U-shaped polygonal and non-polygonal configuration.

[0083] To ensure that the vertically tall shell body 111 of the CEC 110 and the pair of cooling air supply shells 130 are structurally stable and reinforced so that they can be lifted and transported as a single freestanding unit, a number of horizontally extending cross-support members 204 (e.g., appropriately shaped structural beams) are provided to structurally rigidly connect the CEC shell body and the supply shells. In one embodiment (as variously shown in Figures 8-16), the CEC 110 in each modular nuclear waste storage unit 200 is structurally connected to each of the pair of cooling air supply shells 130 and is laterally reinforced by a number of vertically spaced cross-support members 204. In the non-limiting illustrated embodiment, three cross-support members are shown connecting each of the lower portion 111d, middle portion 111e, and upper portion 111a of the CEC to each of the two supply shells 130. More or fewer cross-support members 204 may be used. The pair of cooling air distribution shells 130 are similarly structurally connected to one another and laterally supported by vertically spaced cross-support members 204, which may be the same or different type as the cross-support members connecting the CEC 110 to the cooling air distribution shells 130. In one non-limiting embodiment, W-beams may be used as the cross-support structural members 204, although other suitable types / shapes of structural members may be used.

[0084] The modular nuclear waste storage unit 200 is manufactured under conveniently controlled conditions in a work area within a manufacturing facility, and then transported to an installation site (e.g., an integrated interim storage facility). The CEC 110 and pair of cooling air supply shells 130 are essentially palletized on a common support plate 201, so that installation at the installation site requires only piping connections to the flowpath 160. This allows for rapid installation and deployment of the modular nuclear waste storage unit.

[0085] To install the modular nuclear waste storage units 200 at a location such as a CIS site or facility in the manner shown in FIG. 3, the installation process or method includes pouring a concrete base pad 101 and positioning and mounting a first storage unit 200 on the pad when cured and hardened. A second storage unit 200 is then positioned and mounted on the base pad adjacent to the first storage unit, spaced longitudinally along row R. A piping connection can now be made to the first storage unit. Each of the four cooling air supply shells 130 is then fluidly coupled directly to the CEC 110 of the first storage unit by a separate flow passage 160. The piping connection between the CEC and the supply shell 160 can be welded or, preferably, a bolted piping flange type connection, which can be made more conveniently than a welded connection. During operation of the ventilation system, the air flowing through the flow passage 160 is at most a slight negative pressure (subatmospheric) of the outside air, so the flange type connection is suitable for these conditions of use. Additional third, fourth, ... nuclear waste storage units 200 can then be added and installed in a similar manner. Once all units are attached to the base pad 101 and fluidly coupled to their respective cooling air supply shells 130, flowable artificial fill 140 can be installed over the base pad and around the CEC and supply shells of the CIS facility to fill the voids between the equipment for lateral support and radiation attenuation / blocking, as shown in Figures 17-19 (note that for clarity, the artificial fill is not shown in Figure 3).

[0086] A concrete top pad 102 may then be formed over the engineered fill. The modular nuclear waste storage unit 200 is now ready to receive a nuclear waste canister 150 in each cavity 120. In some embodiments disclosed in U.S. Pat. No. 9,852,822, incorporated herein by reference, a pair of canisters 150 may be stacked vertically within each CEC 110 and supported therein in the manner described. It should be noted that the CEC 110, whether holding a single canister 150 or two vertically stacked canisters 150, has a cross-sectional area sufficient to hold only a single canister at a single height (i.e., not side-by-side).

[0087] It should be noted that, preferably, in a non-limiting embodiment, the aforementioned CECs 110 of the plurality of modular nuclear waste storage units 200 are preferably disposed on the longitudinal axis LA of the storage row R (i.e., the vertical centerline axis VC1 intersects the longitudinal axis LA). This is similar to the two previously described embodiments of the nuclear waste storage system 100 shown in Figures 4-7 and 20. In this embodiment shown in Figures 1-3, the first and second cooling air supply shells 130 of the first pair of supply shells can be disposed perpendicular to and laterally spaced apart on either side of the longitudinal axis LA. The first and second supply shells are disposed on a first side of the first CEC 110. The third and fourth cooling air supply shells of the second pair of supply shells can be disposed laterally spaced apart in a similar manner and disposed on a second side opposite the first side of the first CEC 110.

[0088] The first, second, third and fourth cooling air supply shells 130 are preferably fluidly coupled directly to the first CEC by separate metallic flow conduits 160 as shown in Figure 3 (see also various portions of Figures 8-19), thus eliminating any intervening CEC or cooling air shell. The flow channels 160 may be formed by sections of piping as previously described herein.

[0089] In this third embodiment, each of the flow passages 160 may comprise a horizontally extending straight piping section that fluidly couples a lower portion of the cavity 120 of the first CEC 110 with a respective lower portion of the cooling air supply shell 130. The flow passages 160 of each straight piping section define a horizontal centerline axis Hc that is inclined at an acute angle A1 with respect to the longitudinal axis LA (see, for example, FIG. 14). Positioning the cooling air supply shell 130 at this angle with respect to the longitudinal axis is sufficient to ensure that there is no line of sight between the first CEC 110 and a next adjacent CEC mounted on a different support plate 201. In certain embodiments, the angle A1 may be between about 10 degrees and 20 degrees.

[0090] As also shown in FIG. 14, each pair of cooling air supply shells 130 on either side of the illustrated CEC 110 is on either side of the longitudinal axis LA. The geometric vertical centerline VC2 of each supply shell lies on a horizontal reference line R1 at an acute angle A2 relative to the longitudinal axis LA of the nuclear waste storage row R. The angle A2 may be approximately 30 degrees (+ / - 5 degrees). It should be noted that positioning the flow passages 160 and cooling air supply shells 130 at angles A1 and A2, respectively, relative to the longitudinal axis LA favors closer spacing between the CECs 110 and the supply shells in each row. This allows more CECs to be packed tightly in each row R.

[0091] 15-19. Each cooling air supply shell 130 in some embodiments may include an array 170 of vertically elongated radiation attenuating plates 171. The plates 171 may be flat and are structurally joined together (e.g., by welding, via clips / brackets, etc., etc.) as shown and arranged in an orthogonal grid. The plates 171 are positioned within the vertical air passages 133 of the cooling air supply shell 130 and form vertically extending grid openings therebetween through which ventilation air is drawn downwardly through the shell. The attenuating plates 171 may extend vertically across a majority of the H1 of the cooling air supply shell. In one embodiment, the attenuating plates extend vertically downwardly from the top end 135 to the bottom end 134 of the shell, terminating at a point adjacent just above the top of the flow passage 160 so as not to impede ventilation air flow from the shell 130 to the CEC 110. In one embodiment, the attenuating plates 171 may be formed of steel. However, other suitable materials may be used, including boron-containing materials and metals. The attenuation plate 171 is advantageously adapted to prevent the flow of radiation into the environment surrounding the nuclear waste storage system.

[0092] In operation, the ambient cooling air ventilation system of the high air flow capacity embodiment of the present invention shown in Figures 1-3 and 8-19 functions similarly to the previously described embodiments and follows a similar general path. Each of the air inlets 125 is constructed and arranged to introduce cooling ventilation air tangentially into the cavity 120 of each CEC 110 as shown. The ambient ventilation air is drawn downwardly through damping plates 171 in each cooling air supply shell 130 and then flows horizontally / laterally through flow passages 160 towards the CEC 110, cooling the canisters 150 within each CEC via the convection natural thermosiphon effect previously described herein.

[0093] In the present embodiment of Figures 1-3 and 8-19, an alternative air outlet 220 is shown that is formed directly through the lid 215, rather than between the perimeter of the lid and the top 111a and top pad 102 of the CEC 110, as in the previously described lid 115 in the previous embodiment shown in Figures 1-4 herein. In this embodiment, the air outlet 220 forms an internal, tortuous, angular passageway (see, e.g., Figure 18 and air flow direction arrows) that terminates in an air release housing 216 attached to the top surface of the lid. To accommodate this internal air outlet 220 passageway, the lid 215 is configured slightly differently than the lid 115 previously described herein.

[0094] The air exhaust housing 216 of the lid 215 of the present invention comprises a perforated cylindrical metal shell that projects vertically upward from the top surface of the lid 215 as shown. In one embodiment, the housing 216 comprises multiple lateral openings extending 360 degrees around the circumference for exhausting laterally outwardly and returning air to the surrounding environment. A circular cap 217 surrounds the top of the air exhaust housing 216 to prevent rain from entering. The air exhaust housing 216 and cap 217 may be formed of a metal such as stainless steel to prevent corrosion. In other embodiments, other shapes of caps and air intake housings may be used.

[0095] The lid 215 of the present invention may have a composite metal and concrete structure and configuration similar to the previously described lid 115 in Figures 4-7, including an exterior shell 215a formed of steel, such as stainless steel, and an interior concrete lining 215b. This robust structure not only provides radiation shielding, but also provides protection against projectile impact. In one configuration, the lid 215 includes a circular upper portion 218a and an adjacent circular lower portion 218b having an outer diameter smaller than that of the upper portion, similar to the previously described lid 115. The lid 215 of the present invention effectively seals the upwardly opening recess 117 formed in the upper surface 102a of the upper pad 102 around the upper end 112 of each CEC 110 by the diametrically enlarged upper cylindrical section 111b of the CEC.

[0096] In cooling operation, air rising upward in the vent annulus 121 between the heat generating canister 150 and the shell body 111 of the CEC 110 flows to the bottom of the lid 215 (see, e.g., FIG. 18 and the air flow direction arrows). The air then flows radially outward and turns upward around the lower portion 218b of the lid, which is a smaller diameter in the air outlet 220. The air then flows radially inward and makes a 90 degree turn upward toward the housing 216. The heated air exits the housing 216 in a lateral radial direction through a hole and is returned to the surrounding atmosphere. The cooling cycle continues to operate via the thermosiphon as long as the nuclear waste canister 150 continues to release heat generated by the nuclear waste therein.

[0097] While the foregoing description and drawings represent exemplary embodiments of the present disclosure, it will be understood that various additions, modifications, and substitutions can be made without departing from the spirit and scope of the appended claims and the scope of equivalents. In particular, it will be apparent to those skilled in the art that the present invention can be implemented in other shapes, structures, arrangements, proportions, sizes, and with other elements, materials, and components without departing from the spirit or essential characteristics thereof. Furthermore, many variations of the methods / processes described herein can be made within the scope of the present disclosure. Those skilled in the art will further appreciate that embodiments with many changes in structure, arrangement, proportions, sizes, materials, and components that are particularly adapted and operable in particular environments and operating conditions can be used without departing from the principles described herein. Thus, the presently disclosed embodiments should be considered in all respects as illustrative and not restrictive. The appended claims should be broadly construed to include other variations and embodiments of the present disclosure that may be made by those skilled in the art without departing from the scope and scope of equivalents.

Claims

1. 1. An underground passively ventilated nuclear waste storage system comprising: A horizontal longitudinal axis; an underground concrete base pad; a vertically elongated first cavity enclosure container positioned on said base pad and on said longitudinal axis, said cavity enclosure container defining a vertical centerline axis and including a first air inlet, a second air inlet, an air outlet, and an interior cavity; a first cavity enclosure container, the cavity of the first cavity enclosure container being configured to hold a nuclear waste canister containing heat-emitting radioactive nuclear waste; a vertically elongated first cooling air supply shell in fluid communication with the ambient atmosphere and operable to draw in ambient air, said first cooling air supply shell fluidly coupled directly to a first air inlet of said first cavity enclosure container via a first flow passage; a vertically elongated second cooling air supply shell in fluid communication with the ambient atmosphere and operable to draw in ambient air, said second cooling air supply shell being directly fluidly coupled to a second air inlet of said first cavity enclosure container via a second flow passage; Equipped with 1. An underground, passively ventilated nuclear waste storage system, comprising: a first cavity enclosure container structurally coupled to the first cooling air distribution shell and the second cooling air distribution shell by a plurality of horizontally extending cross-support members that act as lateral supports.

2. 10. The system of claim 1, wherein the first cavity enclosure container is not directly fluidly coupled to any other cavity enclosure container.

3. 2. The system of claim 1, wherein said first cooling air supply shell and said second cooling air supply shell are structurally coupled to one another by a plurality of horizontally extending cross support members that act as lateral supports.

4. 4. The system of claim 1, wherein the first cavity enclosure container and the first and second cooling air supply shells are fixedly attached to a common support plate to form a freestanding, transportable modular unit, the common support plate configured for fixing onto the concrete base pad.

5. 2. The system of claim 1, wherein the first flow path and the second flow path each comprise a section of horizontally extending straight piping fluidly coupling a lower portion of the cavity of the first cavity enclosure container with a lower portion of each of the first and second cooling air supply shells.

6. 6. The system of claim 5, wherein the first flow path and the second flow path are oriented at an acute angle relative to the longitudinal axis.

7. The system further comprises a vertically elongated second cavity enclosure container having an identical configuration to the first cavity enclosure container; 7. The system of claim 5 or claim 6, wherein the first air inlet and the second air inlet of the first cavity enclosure container and the second cavity enclosure container are configured to introduce cooling air tangentially into internal cavities of the first cavity enclosure container and the second cavity enclosure container.

8. 2. The system of claim 1, wherein the first and second cooling air supply shells are spaced apart and disposed on a first side of the first cavity enclosure container, the first side belonging to one of two spaces divided by a plane that includes a vertical central axis of the first cavity enclosure container and is perpendicular to the horizontal longitudinal axis.

9. The system described in claim 8, further comprising third and fourth cooling air supply shells spaced apart and positioned on a second side of the first cavity enclosure container, the third and fourth cooling air supply shells being fluidly coupled directly to the first cavity enclosure container by third and fourth flow paths, respectively, and the second side belonging to the other of the two spaces divided by a plane that includes the vertical central axis of the first cavity enclosure container and is perpendicular to the horizontal longitudinal axis.

10. The system of claim 9 , wherein said third and fourth cooling air supply shells are directly fluidly coupled to a second cavity enclosure container by fifth and sixth flow passages, respectively.

11. The system described in claim 10, characterized in that the second cavity enclosure container is positioned on the longitudinal axis, and the first, second, third, and fourth cooling air supply shells are not positioned on the longitudinal axis.

12. The system described in Claim 11, characterized in that the first and third cooling air supply shells are arranged on one side of two spaces divided by a plane including the vertical center axis and the horizontal longitudinal axis of the first cavity enclosure container, and the second and fourth cooling air supply shells are arranged on the other side of the two spaces divided by a plane including the vertical center axis and the horizontal longitudinal axis of the first cavity enclosure container.

13. 10. The system of claim 1, further comprising a concrete top pad defining an upper surface, said top pad being spaced parallel to said base pad, said top pad being filled with artificial fill soil between said top pad and said base pad.

14. 14. The system of claim 13, wherein the first cavity enclosure container comprises a top recessed in the top pad and a removable top lid covering the interior cavity of the first cavity enclosure container.

15. 15. The system of claim 14, wherein the air outlet of the first cavity enclosure container is defined by an air flow outlet path extending between the top cover and the interior cavity of the first cavity enclosure container.

16. 16. The system of claim 14 or claim 15, wherein the top cover is partially disposed in an upwardly opening recess formed in the top pad.

17. 17. The system of claim 13, wherein the first cavity enclosure container comprises a body having a height extending upwardly from the base pad to the upper pad, and the first and second cooling air supply shells each have a height extending upwardly from the base pad to an upper surface of the upper pad.

18. The system of claim 17, wherein said first and second cooling air supply shells are each at least flush with a body of said first cavity enclosure container.

19. 19. The system of claim 17 or claim 18, wherein the first and second cooling air supply shells each include a perforated intake housing disposed on an upper surface of the upper pad.

20. 20. The system of claim 1, wherein the first and second cooling air supply shells and the first cavity enclosure container are cylindrical, and the first and second cooling air supply shells each have an outer diameter that is smaller than an outer diameter of the first cavity enclosure container.

21. 2. The system of claim 1, further defining a cooling air flow path configured such that ambient cooling air is drawn vertically downward into the first and second cooling air supply shells, flows horizontally through the first and second flow passages, respectively, into the first cavity enclosure container, flows vertically upward within the cavity of the first cavity enclosure container, and flows laterally out the air outlet within the first cavity enclosure container back to the ambient atmosphere.

22. 22. The system of claim 21, wherein the cooling airflow is induced by natural convection thermosiphon effect without the aid of a blower or fan.

23. 23. The system of any one of claims 1-22, wherein the first and second cooling air supply shells and the first cavity enclosure container are formed from stainless steel.

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