High-density subterranean storage system for nuclear fuel and radioactive waste

An underground ventilated system for storing nuclear waste materials. The system includes a storage module having an outer shell defining an internal cavity and an inner shell. A majority of the height of the outer shell may be disposed below grade. The outer shell may include a hermetically sealed bottom. First and second canisters are positioned in lower and upper portions within the cavity respectively in vertically stacked relationship. A centering and spacing ring assembly is interspersed between the first and second canisters to transfer the weight of the upper second canister to the lower first canister. The assembly may include centering lugs which laterally restrain the first and second canisters in case of a seismic event. A natural convection driven ventilated air system cools the canisters to remove residual decay heat to the atmosphere. In one non-limiting embodiment, the shells are made of steel.

FIELD OF THE INVENTION

The present invention relates to spent nuclear fuel and radioactive waste storage systems, and more particularly to such a system suitable for consolidated interim waste storage.

BACKGROUND OF THE INVENTION

Used or spent nuclear fuel and radioactive waste materials are presently stored on an interim basis “on site” at commissioned and some decommissioned nuclear generating plants until the federal government provides a central permanent repository. For example, spent nuclear fuel is stored in the reactor fuel pool after removal from the core where it continues to generate decay heat. The fuel can be transferred after a period of cooling in the pool to canisters which are placed in dry storage casks (i.e. overpacks) typically constructed of concrete, steel, and iron, etc. to provide containment and radiation shielding. The casks are stored on site at the generating plant.

The concept of using consolidated interim storage (CIS) is intended to provide geographically distributed off-site storage facilities for spent nuclear fuel and radioactive wastes (collectively “waste”) gathered from a number of individual generating plant sites, thereby providing greater control over the widely dispersed waste stockpiles. The waste materials would initially be transported to the CIS facility from the generating plants for a period of time, with the eventual goal of a final move to a permanent nuclear waste repository when available. Such so called independent spent fuel storage installations (ISFSI) are facilities designed for the interim storage of spent nuclear fuel comprising solid, reactor-related, greater than Class C waste, in addition to other related radioactive materials. Each ISFSI facility would typically maintain an inventor of a multitude of waste canisters containing spent nuclear fuel and/or radioactive waste materials.

SUMMARY OF THE INVENTION

The present disclosure provides a below-ground used or spent nuclear fuel storage system designed for the compact dry storage of a large number of used fuel canisters in a small land area. In a non-limiting exemplary embodiment, two or more elongated canisters may be stored in vertically oriented and stacked relationship in each of a plurality of underground vertical ventilated storage modules which provide an overpack. The storage modules may be diametrically sized to fit a single canister therein at a given elevation, as further described herein. The collective array of storage modules defines an independent spent fuel storage installation (ISFSI) facility suitable for CIS that may include any number and arrangement of modules.

The canisters may contain both radioactive used nuclear fuel and/or non-fuel waste materials in some embodiments. In one embodiment, the canisters may be Multi-Purpose Canisters (MPCs) available from Holtec International of Marlton, N.J.

The underground storage system is intended to provide vanishingly low site boundary radiation dose levels and safety during catastrophic events. As an underground system, the system takes advantage of the surrounding soil or subgrade to provide shielding, physical protection, and a low center of gravity for a stable storage installation. Each vertical storage module provides storage of canisters in a vertical configuration inside a cylindrical cavity located entirely below the top-of-grade in the storage facility. The vertical modules may each be generally comprised of a cavity enclosure container formed by an outer shell, an inner divider shell, and a top closure lid in addition to various interfacing structures and features, as further described herein.

The canister storage system is further configured to provide passive heat removal from the canisters via natural convection during storage in the modules, thereby rejecting the used fuel's decay heat emitted to the ambient air above the module. Radiation emitted from the used nuclear fuel is substantially contained within the soil fill in which the modules are disposed and canisters stored.

Advantageously, stacking two canisters in each vertical ventilated storage module according to the present disclosure ultimately cuts the required storage area in half. For example, a 14 acre ISFSI for CIS can store 4,000 canisters containing more than 50,000 tons of uranium. This significantly reduces siting requirements. The radiation released to the environment from such a CIS facility storing used fuel may be negligible.

According to one exemplary embodiment, a system for vertically-stacked storage of nuclear waste canisters includes an elongated outer shell defining a vertical axis and an internal cavity; a first canister positioned in the cavity in a lower position; a second canister vertically stacked above the first canister in an upper position, the first and second canisters being concentrically aligned with the vertical axis; a centering and spacing ring assembly interspersed between the first and second canisters; and a removable top lid mounted on top of the outer shell covering the cavity. The centering and spacing ring assembly is arranged and operable to transfer weight of the second canister to the first canister.

According to another embodiment, a storage module for vertically-stacked storage of nuclear waste canisters includes an elongated outer shell defining a vertical axis and an internal cavity; an elongated inner shell disposed in the internal cavity; a first annular space formed between the inner and outer shells, the first annular spacing defining a vertical downcomer ventilation shaft operable to convey ambient cooling air downwards to the cavity; a first canister positioned in the cavity in a lower position; a second canister vertically stacked above the first canister in an upper position, the first and second canisters being concentrically aligned with the vertical axis; a middle centering and spacing ring assembly interspersed between the first and second canisters, the middle centering and spacing ring assembly operable to transfer weight of the second canister to the first canister; a second annular space formed between the first and second canisters and the inner shell, the second annular space defining a vertical riser ventilation shaft operable to convey cooling air upwards across outer surfaces of the canisters; and a removable top lid mounted on top of the outer shell covering the cavity, the top lid being in fluid communication with the riser ventilation shaft and configured to form an airflow pathway to atmosphere through the lid.

According to another embodiment, an underground storage module for vertically-stacked storage of nuclear waste canisters includes an elongated vertical outer shell defining vertical axis and an internal cavity, the outer shell having a top and a hermetically sealed bottom, the outer shell being disposed below grade for a majority of its height; a common inlet air plenum disposed at the top of the outer shell, the air plenum arranged to draw ambient cooling air through a plurality of air inlets in fluid communication with the air plenum; an annular-shaped vertical downcomer ventilation shaft arranged to convey the cooling air from the inlet air plenum downwards along the outer shell to a bottom of the cavity; a first canister positioned in the cavity in a lower position; a second canister vertically stacked above the first canister in an upper position, the first and second canisters being concentrically aligned with the vertical axis; an elongated inner shell disposed inside the outer shell and cavity; an annular-shaped vertical riser ventilation shaft formed between the inner shell and the canisters, the riser ventilation shaft being in fluid communication with the downcomer ventilation shaft near the bottom of the outer shell and arranged to convey cooling air upwards across outer sidewall surfaces of the canisters for removing decay heat; and a removable top lid mounted on top of the outer shell covering the cavity, the top lid in fluid communication with the riser ventilation shaft and configured to form an airflow pathway to atmosphere through the lid from the riser ventilation shaft.

All drawings are schematic and not necessarily to scale. Parts given a reference numerical designation in one figure may be considered to be the same parts where they appear in other figures without a numerical designation for brevity unless specifically labeled with a different part number and described herein. References herein to a figure number (e.g.FIG. 1) shall be construed to be a reference to all subpart figures in the group (e.g.FIGS. 1A, 1B, etc.) unless otherwise indicated.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The features and benefits of the invention are illustrated and described herein by reference to exemplary embodiments. This description of exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. Accordingly, the disclosure expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features.

FIG. 1depicts an ISFSI facility forming a high-density subterranean Consolidated Interim Storage (CIS) system100comprising an array of underground vertical ventilated storage modules110. In one embodiment, each storage module110houses at least two sealed canisters containing spent nuclear fuel and/or radioactive waste materials. The storage modules110are arranged in a tightly packed configuration to minimize spatial site requirements. The storage modules110are spaced apart by a grid of orthogonally intersecting aisles102formed of concrete slabs104to provide access for commercially-available motorized wheeled equipment operable to move and lift (i.e. raise/lower) the canisters for insertion into and removal from the modules. Such equipment is well known to those skilled in the art without further elaboration. The low exposed vertical profile of the storage modules110(as further described herein) allows the equipment to move over modules in a single row to the desired module for inserting or removing canisters.

Each storage module110may include an associated concrete top pad112which is positioned and disposed between the aisles102of slabs104. The top pads112may form a contiguous structure with slabs104to provide radiation shielding. The top pads112may be square-shaped in top plan view in one non-limiting example; however, other suitable polygonal and non-polygonal configurations (e.g. circular) may be used.

FIG. 2is a cross-sectional view of a single storage module110fromFIG. 1. With additional reference toFIGS. 6 and 6A, storage module110is vertically elongated and includes a vertically-extending outer shell120defining an internal cavity122and an inner shell130. In one embodiment, outer and inner shells120,130are cylindrically and complementary shaped, albeit dimensionally different. The outer shell120provides an impermeable barrier against leakage of ground water through the earthen soil S fill into the storage module110. Outer shell has an open top121and a closed bottom formed by bottom plate123at the bottom end of the shell. Bottom plate123may be substantially flat and is preferably seal welded to outer shell120in one embodiment to hermetically seal the bottom of the shell thereby forming an impermeable barrier to ingress of external ground water. Accordingly, all portions of storage module110below grade are sealed against the ingress of moisture or water from the environment transmitted through the soil.

The bottom plate123of outer shell120may be positioned on and supported by a concrete base pad106. The area adjacent the outer shell120between the top pad112and base pad106is filled with fill or soil “S”, thereby forming a cross-sectional composite structure of upper and lower concrete caps with soil disposed therebetween. A majority of the height of the outer and inner shells120,130is disposed below grade as shown inFIGS. 2 and 6. The top portion of outer shell120is surrounded by the top pad112and embedded therein so that virtually none or only a small projection of the top end121of the outer shell protrudes above the concrete pad. Substantially the entire height of the outer shell120is therefore embedded in soil and/or concrete in the embodiment being described.

It will be appreciated that in some embodiments, a monolithic concrete base pad106may extend beneath a plurality or cluster of individual storage modules110in lieu of individually poured pads. Similarly, a monolithic top pad112may be used to surround and extend between a plurality or cluster of individual storage modules110in lieu of individually poured pads.

It will be appreciated that although the cross-sectional shape of the outer and inner shells120,130may be cylindrical in the illustrated embodiment, the shells can have other suitable polygonal and non-polygonal shapes, including without limitation rectangular, conical, hexagonal, or irregularly shaped. In some embodiments, the outer and inner shells120,130need not be concentrically aligned with each other.

Outer and inner shells120,130and bottom plate123are made of metal, such as steel in exemplary non-limiting embodiments. Outer shell120, which provides a barrier between the soil S in which the outer shell is embedded, is preferably made of a corrosion resistant metal such as without limitation coated steel, stainless steel, etc.

In one embodiment, inner shell130has an open top131and open bottom132(referenceFIGS. 6 and 6A). The open top131allow insertion of canisters140into the storage module110, as further described herein. Inner shell130may be coaxially and concentrically aligned with outer shell120about a vertical axis VA defined by storage module110. Outer and inner shell120,130have vertical heights that are substantially coextensive. The bottom132of inner shell130may rest on top of the bottom plate123of the outer shell120in one arrangement. The outer and inner shells120,130have a sufficient height or depth suitable to allow at least two canisters140to be stored in a vertically stacked configuration or relationship. In other embodiments, the outer and inner shells120,130may have heights or depths suitable for holding three or more vertically stacked canisters140.

Inner shell130has a smaller diameter than outer shell120. Inner shell130is radially spaced apart inwards from the outer shell120and acts to divide the cavity120into an outer annular space124and an inner portion configured and dimensioned to hold canisters140. The outer annular space124extends from the top121to bottom plate123of outer shell120.

The outer annular space124defines an annular-shaped vertical downcomer ventilation shaft125for introducing outside ambient cooling air into cavity122of storage module110to remove decay heat emitted from the spent nuclear fuel or radioactive waste material contained in canisters140. To complete a natural convection heat removal airflow circuit, a second inner annular space133is defined between the outer cylindrical shell sidewall141of canister140and inner shell130which is radially spaced apart outwards from the canister. The second inner annular space133extends from the bottom132to top131of inner shell130and defines an annular-shaped vertical riser ventilation shaft134for removing heated cooling air from storage module110. The inner shell130serves to separate the downcomer ventilation air from the up-flowing air heated by contact with the canister (see, e.g. airflow diagram ofFIG. 5).

The downcomer ventilation shaft125is fluidly (i.e. airflow) separated and isolated from riser ventilation shaft134by inner shell130for substantially the entire vertical height of storage module110along shells120,130except near the bottom of the storage module. The downcomer and riser ventilation shafts125,134respectively are in fluid communication through a plurality of circumferentially arranged and spaced apart airflow openings135formed at the bottom end of the inner shell130near the bottom132. The bottom end of shell130may have a castellated configuration in one embodiment with the openings135having a generally square or rectangular shaped configuration. Other suitable shaped airflow openings may be used however.

In one embodiment, the inner “divider” shell130is insulated being provided with an insulation layer150to minimize heat exchange between the incoming cooling (downcomer ventilation shaft125) and outgoing heated (riser ventilation shaft134) ventilation air in contact with the inner shells inner and outer surfaces, respectively (see, e.g.FIGS. 4 and 5, and best shown in detail inFIG. 4B). This keeps the ambient cooling air drawn into the storage module110by natural convention as cold as possible until it encounters the hotter outer shell sidewall141of the canisters140to maximize cooling efficiency. In one embodiment, the insulation layer150is disposed on the outer surface of inner shell130between the inner shell and outer shell120in the downcomer ventilation shaft125to prevent damage which could potentially occur from inserting and removing canisters from the storage module110. Any suitable type of insulating material may be used including without limitation separately formed and applied pliable, semi-rigid, and rigid insulating materials and sprayed on types (e.g. hardening foams). The insulation26is preferably chosen so that it is water and radiation resistant without substantial degradation. Some examples of suitable forms of insulation include, without limitation, blankets of alumina-silica fire clay (Kaowool Blanket), oxides of alumina and silica (Kaowool S Blanket), alumina-silica-zirconia fiber (Cerablanket), and alumina-silica-chromia (Cerachrome Blanket). The desired thickness of the of insulation layer150will be dictated by such considerations such as the heat load (e.g. temperature differential between ambient air and canister external temperatures), the thickness of the shells, and the type of insulation used (e.g. K factor). In some embodiments, the insulation may have a representative non-limiting thickness in a range of about ½ to 6 inches for example.

Canisters140stored in storage module110may be any type of canister, including without limitation Multi-Purpose Canisters (MPCs) available from Holtec International of Marlton, N.J. As shown inFIG. 5, canisters140have a generally hollow cylindrical shell sidewall141including a top142with removable and sealable lids144for inserting spent nuclear fuel and/or radioactive waste materials and an opposing bottom143. The interior of canisters140may include racks or grids to contain and support spent fuel rods and waste materials.

FIGS. 4 and 4Ashow the construction of the upper portion of storage module110and top pad112in greater detail. The tops121and131of outer and inner shells120,130respectively penetrate top pad112, thereby providing external above grade access to downcomer ventilation shaft125, riser ventilation shaft134, and cavity122of storage module110for inserting and removing canisters140. The top pad112, which may be formed of concrete in a one preferred embodiment, extends at least partially beyond the diameter of outer shell120as shown. In this non-limiting example, the top pad112may have a square shape (in top plan view) as previously described. The perimeter of the top pad112would be adjoined by the access aisles102formed between adjacent storage modules110.

With continuing reference toFIGS. 4 and 4A, top pad112includes one or more air inlets160which are in fluid communication with annular-shaped downcomer ventilation shaft125to introduce cooling ambient ventilation air into the storage module110. A common recessed air plenum161covered by a removable cover plate162may be formed in top pad112around outer shell120to fluidly connect the air inlets to the ventilation shaft125. Air plenum161further fluidly interconnects the air inlets160to each other. The air plenum161is formed by a recessed portion of top pad112and has a bottom surface166spaced vertically below the higher top surface113at peripheral portions of the pad112, as shown. Air plenum161may have a complementary shape to top pad112(e.g. square in this embodiment), or a different shape.

The air inlets160may be formed in one embodiment from short sections of pipe attached directly to and removable as a unit with the cover plate162(both of which preferably are formed of metal) by any suitable means (e.g. fasteners, welding, etc.). Cover plate162includes apertures167which fluidly communication with short pipe sections. The air inlet160pipe sections include lateral airflow openings164cut into the sides of the pipe and the open free end is covered by a weather cap163to prevent the direct ingress of rain and/or debris. The top end of shell120may include a plurality of circumferentially spaced apart airflow openings165which are in fluid communication with air plenum161to allow ambient ventilation air to flow through the air inlets160into the plenum and in turn down into the downcomer ventilation shaft125through the openings165.

The ambient ventilation cooling air is admitted through a plurality of air inlets160in the top pad112that are arranged to be non-preferential with respect to the horizontal direction of the wind to maximum cooling of the canisters in storage module110. In one non-limiting embodiment, four air inlets160may be provided with one inlet being positioned at each of the four corners of the top pad112to ensure each quadrant of the storage module110via the downcomer ventilation shaft125receives an equal amount of ambient cooling ventilation air. The air plenum161advantageously serves to further distribute the ventilation air uniformly to all portions of the downcomer ventilation shaft125.

It will be appreciated that other suitable configurations and numbers of air inlets160and configurations of air plenum161may be provided depending on the configuration of top pad112used and other factors.

The heated ventilation air exits riser ventilation shaft134from storage module110through a central airflow passageway201in the top lid200shown inFIGS. 4, 4A, and 5. Top lid200is a removable cover that closes storage module110and is positioned over the tops121and131of outer and inner shells120,130, respectively.

The top lid200is a massive stepped-shaped circular shielded structure in one embodiment equipped with a diametrically enlarged upper portion202and smaller cylindrical bottom protrusion203extending downwards therefrom. The upper portion202has a larger diameter than the diameter of the outer shell120forming an annular shaped peripheral portion (in top plan view) overhanging the outer shell. In some embodiments, upper portion202is configured and dimensioned to close off both the open tops121,131of the outer and inner shells120,130. This effectively seals off the top of vertical downcomer ventilation shaft125to prevent inlet cooling ventilation air entering from air plenum161via airflow openings165at the top of outer shell120from bypassing the shaft125and entering the riser ventilation shaft134at the top of the storage module110. In some embodiments, a top seal plate may be used to seal the top of vertical downcomer ventilation shaft125in addition to top lid200.

An annular gasket250formed of a suitable material may be provided between the underside of the upper portion202of top lid200and the inner top131of the inner shell130providing a sealed lid-to-inner shell interface (seeFIG. 4A).

The bottom protrusion203has a diameter smaller than the inner shell130and forms a plug that is inserted at least partially into the inner shell into cavity122to keep the lid200from sliding in a lateral direction excessively during a seismic event (e.g. earthquake). The annular gap G formed between the bottom protrusion203and inner surface of inner shell130forms a continuation of vertical riser ventilation shaft134as best shown inFIGS. 4A and 5.

In some embodiments, the top lid150may be a substantially hollow metal structure filled with a radiation absorbing material shielding such as concrete. The metal exoskeleton of top lid150can be constructed of a wide variety of materials, including without limitation various steel, stainless steel, aluminum, aluminum-alloys, and other metals. In some embodiments, the lid may be constructed of a single piece of material, such as concrete or steel for example.

With continuing reference toFIGS. 4, 4A, and 5, upper portion202of top lid200is annular shaped which defines the central airflow passageway201to eject heated ventilation air from vertical riser ventilation shaft134to the ambient environment. To complete this airflow circuit, the bottom protrusion203of lid200includes a plurality of radially extending air passages205which are in fluid communication with the annular-shaped riser ventilation shaft134and central airflow passageway201in the upper portion202of the lid. An air outlet210extending upwards from top lid200may be mechanically thereto and fluidly coupled to central airflow passageway201to help vent heated ventilation air away from storage module110. The air outlet210may be formed in one embodiment from a short section of pipe attached to the upper portion202of top lid200by any suitable means (e.g. fasteners, welding, etc.). The air outlet pipe sections include lateral airflow openings211cut into the sides of the pipe and the open free end is covered by a weather cap212to prevent the direct ingress of rain and/or debris.

In one embodiment, top lid200) may include four intersecting rigging plates204useable to raiser and lower the lid into position on storage module110(see, e.g.FIGS. 4 and 4A). The plates204may be welded to the metal exoskeleton plates of the lid200. The plates204may extend from the bottom of bottom protrusion203to the top of upper portion202, and in some embodiments have center extension sections206which extend radially inwards into central airflow passageway201and protrude upwards therefrom. Extension section of rigging plates204may therefore extend vertically upwards into and be covered by air outlet210when storage module110is in use. Extension sections206are configured for grappling by rigging and hoisting equipment (e.g. holes, clips, etc.) to facilitate manipulating and maneuvering the top lid200. Other suitable configurations and arrangements for rigging lid200are possible.

FIG. 5is an airflow diagram showing the cooling ventilation air path through storage module110created by the features described above. As shown by the directional airflow arrows in this figure, the cooling ventilation air will travel in a generally U-shaped airflow path through the storage module110to remove and dissipate decay heat emitted from the canisters140by the spent nuclear fuel and/or radioactive waste stored therein. Airflow circulation is created by natural convection induced by the decay heat liberated.

In operation, ambient cooling air is first drawn into air plenum161through each of the individual air inlets160and is mixed together. The inlet air circulates around and through the plenum. It should be noted that the air plenum161prevents ambient air flowing from the air inlets160directly into the annular vertical downcomer ventilation shaft125. Advantageously, this mitigates the effects of preferential wind direction which otherwise might adversely affect the amounts of cooling ventilating airflow reaching certain portions of the storage module110and canisters140therein. Without the plenum and its airflow balancing effects, certain areas of the canisters140may be starved of cooling air while other portions receive cooling resulting in differential cooling of the canisters shell sidewalls141. This would reduce the natural convection cooling efficiency.

With continuing reference toFIG. 5, the cooling ventilation air leaves the air plenum161through the airflow openings165and enters the vertical downcomer ventilation shaft125. The air flows downwards in the downcomer ventilation shaft125towards the bottom of the storage module110. The cooling ventilation air travels through the plurality of airflow openings135formed at the bottom end of the inner shell130near its bottom132(see alsoFIGS. 4 and 4C) and enters the bottom of cavity122and the annular vertical riser ventilation shaft134.

The cooling air reverses direction and flows upward through the riser ventilation shaft134contacting the exposed outer circumferential surfaces of the first the bottom and then the top canister140in storage module110to draw away decay heat via convection. As the ventilation air flows vertically upward along the canisters140in the riser ventilation shaft134, the air becomes progressively heated.

The now heated ventilation air flows to and eventually reaches the top of the storage module110at the top of cavity122in the vertical riser ventilation shaft134. The air flow changes direction and flows radially inwards through the radial air passages205in top lid200and is recombined in the central airflow passageway201in the upper portion202of the lid. The ventilation air then changes direction again and flows vertically upward entering air outlet210from which it is exhausted to atmosphere completing the ventilation airflow cycle.

The support and placement of the multiple canisters140in storage module110will now further described.

Referring toFIGS. 4 and 4C, the bottom or lower canister140(shown in, e.g.FIGS. 2 and 3) is horizontally supported and laterally restrained by a circumferentially spaced apart series of suitably shaped centering lugs300. Lugs300are oriented and extend in a radial direction from the vertical axis VA of the storage module110. When placed in the storage module110, the lower canister140rests on bottom plate123welded to the outer shell120and transfers dead load (weight) of both the lower and top or upper canisters140housed in the storage module110to the concrete base pad106. The canister140is positioned laterally adjacent to and inside the ring of radial lugs300as seen inFIG. 2. The lugs300are located proximate to the shell sidewall141of the canister140and positioned to fully engage the canister in the event of a lateral shift in position of the canister caused by a seismic event. This would stabilize the canister140and prevent excessive horizontal movement to protect the canister and its contents. Any suitable number of lugs300may be provided.

Lugs300may be formed from generally flat steel plate in one embodiment and extend both upwards and inwards from the outer shell120towards the vertical axis VA (see, e.g.FIG. 6A). As shown, the lugs300may have a substantially greater radial width and axial height than thickness T (thickness being measured perpendicular to the width and height in a circumferential direction along the outer shell120). At least a portion of the innermost axial edge301of lugs300is preferably straight or flat and arranged parallel to the shell sidewall141of canister140and vertical axis VA to prevent puncturing the canister in case of a seismic event. The lug300includes an angled edge302which adjoins the axial edge301that is angled downwards and inwards as shown inFIG. 6A. When the lower canister140is initially lowered into storage module110, this angled edge302helps blindly guide and center the bottom143of the canister towards the centerline or vertical axis VA so that the canister becomes properly seated on the bottom plate123or ring310if provided.

Centering and spacing lugs300may be attached to the outer shell120and/or inner shell130and are essentially not vertical load bearing structural members. In one exemplary arrangement, lugs300may be directly attached to the shell120(e.g. welded) through slots136formed through inner shell130at the location of each lug300. The slots may be closed at the top and open at the bottom adjacent bottom132of the inner shell130to allow the inner shell to slide over the lugs when initially inserted into the outer shell120during fabrication. The bottom ends of the inner shell130may then rest on the flat bottom plate123affixed to the outer shell120.

In one embodiment shown inFIGS. 6 and 6A, an interfacing centering and spacing bottom ring310may be provided for some specific canister designs to engage the bottom143of the canister. Ring310is disposed inside the lugs300and may be fixedly attached thereto (e.g. welded) or a separate element in various embodiments. In the latter separate or loose construction, the ring310may have peripheral notches configured to engage the lugs300for preventing the ring from rotating in relation to the lugs and outer shell120. On other embodiments, the ring300fits loosely inside lugs300without notches. The ring300rests on bottom plate123of outer shell120in abutting contact for transferring dead load (weight) of the canister140to the concrete base pad106. Ring310is preferably made of metal, such as a suitable steel.

In some embodiments, the top surface311of ring310may be castellated including a plurality of alternating arcuate raised segments312and arcuate recessed segments314having a complementary configuration to match and engage similarly configured features on the bottom143of a lower canister140. The segments312,314may extend radially from the inside to the outside of the ring300as best shown inFIG. 6A. Segments312,314have a circumferentially measured arc width greater than the corresponding width of the lugs300, and preferably may have a width at least coextensive with the radial depth of the segments (measured from the center of the ring outwards). The bottom surface313of ring310may be substantially flat.

Referring toFIGS. 2, 2A, and 5, the lower and upper canisters140) are horizontally supported and laterally restrained against the inner shell130by a centering and spacing middle ring320. Ring320may be configured and constructed similarly to bottom support ring310described above and shown inFIGS. 6 and 6A. In one embodiment, middle ring320may be a composite structure formed of an upper ring320A and lower ring320B each shaped similarly to bottom ring310. The two rings320A,320B may be attached together (e.g. welded) in back-to-back relationship with flat bottoms313in contact and exposed surfaces311with the raised and recessed segments312,314facing axially outwards as best shown inFIG. 2A.

It will be appreciated that in some embodiments, the upward and downward facing exposed top surfaces311of the middle ring310may be substantially flat without raised/recessed segments312,314depending on the canister design used. If different configuration lower and upper canisters140are to be accommodated in the storage module110, one of the rings310A or310B may be castellated (i.e. raised/recessed segments312,314) and the other may be flat on both surfaces. Accordingly, any combination may advantageously be used depending on the canister types to be stored in the storage module110.

Referring toFIGS. 2, 2A, and 5, centering and spacing middle ring320assembly further includes radially extending centering lugs322arranged in a circumferentially spaced pattern around the ring similarly to the bottom lugs300and ring310assembly already described. In one construction, the centering lugs322are welded around the perimeter of middle ring320and made integral therewith; both of which preferably are both made of suitable metal such as steel. The lugs322may not be fixedly attached to the inner shell130of storage module110such that the middle ring-lug assembly320/322is removable as a unit from the storage module with the canisters140. This allows the first lower canister140to be first positioned in the bottom half of the storage module110, the middle ring-lug assembly320/322then lowered and placed on top of the lower canister, and then the second upper canister140lowered and positioned into the top half of the storage module110to engage the middle ring-lug assembly320/322. The middle ring-lug assembly320/322may alternatively be lowered into the inner shell130with the lower canister simultaneously allowing the ring-lug assembly to be placed on top of the lower canister before being lowered into the inner shell together in one step.

FIG. 2shows the lower canister140in position within the storage module110and ready for receiving the upper canister140. The middle ring-lug assembly320/322is in position. The centering lugs322may have a similar side profile as lugs310already described including angled edges302to help guide and center the bottom143of the upper canister140when lowered into storage module110on top of the lower canister (see alsoFIG. 2A). Both the upper and lower portions of lugs322may include angled edges302as shown which helps center and properly position the middle ring-lug assembly320/322on the top142of the lower canister140when the assembly is lowered into place in the storage module110. Accordingly, in one embodiment the upper and lower portions of lugs322are mirror images.

It will be appreciated that middle ring-lug assembly320/322in conjunction with the lower canister140supports the upper canister140as shown inFIGS. 3 and 3A. Advantageously, from a structural standpoint, the middle ring320transfers and distributes the weight of the upper canister to the inherently stronger and stiffer cylindrical sidewalls of the shell sidewall141of the lower canister instead of onto the central portion of the structurally weaker canister lid. This enhances the load bearing capability of the lower canister for supporting the weight of the upper canister.

The middle ring-lug assembly320/322also laterally restrains the bottom end143of the upper canister140. Accordingly, the centering lugs322are configured, dimensioned, and positioned to engage both the top142of the lower canister140and the bottom143of the upper canister140. Significantly, the middle ring-lug assembly320/322further serves to maintain the inner annular space133and vertical riser ventilation shaft134formed between the canisters140and inner shell130by providing proper horizontal aligned of the canisters along the vertical axis VA of the storage module110. The middle ring-lug assembly320/322also provides some vertical spacing between the top142of the lower canister140and bottom of the upper canister140to permit cooling ventilation air to flow in the small space between the two canisters to enhance cooling the canisters.

Referring toFIGS. 3 and 3A, a top ring-lug assembly330/332is also provided to laterally support and restrain the top142of the upper canister140against the inner shell130. This assembly is comprised of a single support ring330having the arcuate raised/recessed segments312,314facing downwards towards the upper canister. The plurality of centering lugs332are welded to the perimeter of ring330in a similar manner to the middle ring320as already described. Preferably, the lugs332are not fixedly attached to the inner shell130like the middle centering lugs322to allow the top ring-lug assembly330/332to be removable in the same manner from the storage module110. In some embodiments, both the top and bottom surfaces311,313of the top ring330may be substantially flat instead of castellated. The centering lugs332may be configured similarly to lugs310or322already described.

It should be noted that the centering lugs300,322, and332laterally restrain and horizontally support the lower and upper canisters140inside storage module110during a seismic event (e.g. earthquake) against excessive movement. In addition, these lugs also maintain the inner annular space133along the entire height of the module to preserve the inner annular space133between the sidewalls of the canister shells140and inner shell130of the storage module110thereby protecting the integrity of the vertical riser ventilation shaft134for proper ventilated cooling of the canisters.

It should be noted that the support rings310,320, and330with undulating top surfaces311having raised and recessed segments312,314may be used with both canisters140having plain (i.e. flat) top and bottom ends, or with specially configured ends as described herein with complementary configured ends as the rings to provide an anti-rotation feature. In other possible embodiments, the rings310,320,330may be substantially flat on both the top surface311and opposing bottom surface313.

In some alternative constructions, the middle and top lugs322,332may be attached (welded) to the inner shell130of the storage module110and rings320,330may be separate and removable elements.

FIGS. 3 and 3Ashow storage module110with both lower and upper canisters140in position and top lid200) in place after insertion of the canisters. The lower and upper canisters140are concentrically aligned with the vertical axis VA of the storage module110. In one embodiment, the diameter of the inner shell130and diameter of the internal cavity122are only wide enough to accommodate a single canister140at each elevation of the storage module110so that two canisters will not fit in side-by-side relationship in the storage module. The canisters140undergo cooling by natural convection via the ventilated cooling air system described above and shown by the directional airflow arrows inFIG. 5. It stands noting that the upper canister140does not directly contact the lower canister, but instead bears on middle ring-lug assembly320/322which vertically separates and spaces the two canisters. The dead load or weight of the upper canister is transferred through the middle ring-lug assembly320/322to the lower canister which bears the weight of the upper canister.

It will be appreciated that the number of vertically stacked canisters in each storage module110may be limited by the load carrying capacity of the canisters themselves since each canister in the stack transmits and bears the weight of the canisters above; the lowermost canister140in the stack bearing the entire dead weight of the whole canister stack. Accordingly, a vertically deeper (higher) storage module110and internal cavity122with additional canisters can be deployed if the structural strength of the lowermost canister140and the support foundation were accordingly strengthened to support greater than two canisters.

According to the present invention, it bears noting that the top and bottom canisters140can be of different diameters and heights within a range of limits which fit within the storage module110. The centering and spacing rings310,320,330with lugs300,322,332as described herein can be customized to provide the necessary adaptation for varying canister diameters and different end type features. Accordingly, the storage modules110disclosed herein are highly customizable to accept numerous types and sizes of canisters from a number of different canister suppliers or sources.

While the foregoing description and drawings represent exemplary embodiments of the present disclosure, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope and range of equivalents of the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, sizes, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. In addition, numerous variations in the methods/processes described herein may be made within the scope of the present disclosure. One skilled in the art will further appreciate that the embodiments may be used with many modifications of structure, arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of the disclosure, which are particularly adapted to specific environments and operative requirements without departing from the principles described herein. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive. The appended claims should be construed broadly, to include other variants and embodiments of the disclosure, which may be made by those skilled in the art without departing from the scope and range of equivalents.