Fuel storage rack system for underwater storage of spent nuclear fuel

Abstract

A fuel rack for wet storage of nuclear fuel in a fuel pool comprises, in one embodiment, a base plate and a cellular body formed from slotted plates bonded to each other and stacked, coupled to the base plate. This cellular body comprises densely packed, upward-opening cells, each holding a nuclear fuel assembly. When the rack is submerged in water, open flax straps are formed between at least some of the water-filled cells, acting as neutron moderators to control the reactivity within the rack. In one embodiment, flax straps are interspersed between adjacent cells in a first direction along a first horizontal axis of the rack. However, flax straps are not interspersed between adjacent cells in a second direction perpendicular to a second horizontal axis. Other flax strap and cell arrangements are also provided. Tension elements penetrate some of the flax straps, and these tension elements compress the stack of plates to ensure stability.

Description

Technical Field

[0001] Cross-reference of related applications This application claims priority to U.S. Provisional Patent Application No. 63 / 558,778, filed Feb. 28, 2024, and U.S. Provisional Patent Application No. 63 / 492,586, filed Mar. 28, 2023, the entire contents of which are incorporated herein by reference. Technical field The present invention relates to a fuel storage rack system for underwater storage of spent nuclear fuel.

Background Art

[0002] The present invention generally relates to a system for wet storage of spent nuclear fuel (SNF) underwater, and more particularly to an improved nuclear fuel storage rack system for use in a fuel pool of a nuclear power plant.

[0003] In light water reactors, it is standard practice to store spent nuclear fuel (SNF) discharged from the reactor in a deep pool of water called a “fuel pool.” The physical embodiment of this nuclear fuel storage device is simply referred to in the art as a “fuel rack.” The fuel rack is designed to be installed on the floor of the nuclear fuel pool. The fuel rack includes means for holding fuel assemblies at a predetermined horizontal / transverse pitch based on reactivity limits acceptable in nuclear regulatory guidelines.

[0004] Conventional freestanding high-density nuclear fuel storage racks (simply referred to as "fuel racks") are typically multi-cell structures supported on a series of pedestals from the floor or bottom slab of a water-filled spent fuel pool. The lower ends of this structure, which define the array of fuel storage cells, are welded to a common base plate installed on the floor of the fuel pool. This base plate acts as a support structure, bearing the weight of the cell structural members and the fuel assemblies stored within the cells, and transferring that weight load to the reinforced concrete floor of the fuel pool. Each cell has a vertically elongated prismatic cavity, and the cross-sectional area and height of each cavity are set to accommodate only a single nuclear fuel assembly containing multiple new or spent nuclear fuel rods.

[0005] The term "active fuel region" refers to the vertical space on the base plate in the intermediate portion between the upper and lower ends of the fuel rack, where enriched uranium is positioned according to the fuel assembly design. This is the most radioactive (reactive) region within the fuel rack. The upper and lower ends of the rack are less reactive regions.

[0006] Fuel racks, used to store spent nuclear fuel assemblies, hold the fuel assemblies upright in a water pool. This serves to dissipate the heat generated, protect the fuel assemblies from damage during earthquakes, and control their reactivity. There are currently two forms of fuel racks and corresponding fuel assemblies in use. The fuel assemblies used in most Russian-origin reactors are elongated structures with a hexagonal cross-section. To store hexagonal cross-section fuel assemblies, it is desirable to have rack modules with hexagonal cross-section cells so that the amount of water in and around the storage cavity is precisely controlled. This is necessary to achieve the desired subcritical state of the stored fuel array. The fuel also needs to be installed higher than the pool liner (floor or bottom slab) so that a water-filled space (water plenum) is formed below the rack, and the rack design configuration must allow for the supply of chilled water to the space around the fuel and between the fuel rods by natural convection thermal siphon action.

[0007] Fuel assemblies used in Western-style reactors are similarly elongated, but they have a linear (for example, square) cross-sectional shape. Storing this type of fuel assembly requires a cell with a corresponding linear cross-sectional shape.

[0008] Because the available floor space in fuel pools is limited, the guiding principle in the design of fuel storage devices such as fuel racks is to maximize nuclear fuel storage density. Therefore, fuel assemblies, which are vertically elongated structures in which multiple uranium fuel rods are densely packed together, are arranged vertically within the fuel storage cells of fuel racks. By minimizing the lateral gaps between cells as much as possible, each rack can accommodate as many fuel assemblies as possible, and at the same time, as many fuel racks as possible can be accommodated in the fuel pool, thereby achieving high-density SNF storage.

[0009] Conventional fuel rack designs have relied on stainless steel cell structures to provide the structural strength for fuel storage. However, the reactivity between cells and fuel assemblies within the fuel rack is controlled by unstructured boron-containing or retaining / absorbing materials, which in turn controls neutron transmission and consequently the criticality control of the nuclear fuel stored in the rack. These materials are less strong and relatively brittle to impact compared to steel cell structures.

[0010] The minimum permissible spacing between storage cells within each fuel rack is controlled by the reactivity of the fuel within the fuel assemblies and the availability of B-10 (boron-10 isotope) content in the neutron absorber, which is typically manufactured in the form of boron carbide powder-impregnated aluminum alloy plates, known as aluminum boride. A widely used type of aluminum boride is sold under the trade name Mctamic® by Holtec International in Camden, New Jersey, USA, and is an aluminum boron carbide metal matrix composite material. In fuel racks formed entirely of stainless steel to form fuel storage cells, neutron absorber panels are inserted into the various spaces or pockets formed between each metal cell. Fuel storage systems must also meet other requirements, such as keeping the fuel cool (spent fuel rods release thermal energy when nuclides undergo radioactive decay) and having sufficient structural strength to withstand natural environmental phenomena such as earthquakes and impacts from falling objects transported onto the pool by cranes.

[0011] Conventional all-metal cell fuel rack designs have several drawbacks. Although stainless steel has excellent weldability, welded structures are prone to significant distortion due to welding. This necessitates making the nominal cell openings larger than necessary to absorb the losses caused by welding distortion in the prismatic fuel assembly storage openings (i.e., cells) within the fuel rack. This directly negatively impacts storage density. As a fully welded structure, conventional fuel racks have low structural damping, a crucial factor that dampens the rack's structural response (high structural damping is a desirable characteristic).

[0012] An alternative fuel rack design minimizes the amount of welding (and therefore the strain within the storage cells induced by welding) and creates a true "egg crate" structure. This is disclosed in U.S. Patent No. 10,650,933, owned by Holtec International, which is incorporated herein by reference. This fuel rack is formed by mechanically connecting multiple slotted panels or plates, and the fuel storage cells consist of rows of plates stacked vertically upward from a base plate. The vertically elongated spaces created within the fuel rack by the intersecting of the slotted plates form the array of fuel storage cells.

[0013] Additional design requirements for fuel racks include: (a) the hexagonal cavities must provide smooth fuel interfaces so as not to hinder fuel insertion and removal operations; (b) the side walls of the storage cavities must be able to withstand lateral loads caused by rattling of fuel assemblies during an earthquake; and (c) in the case of freestanding modules (i.e., not fixed to the floor slab of the spent fuel pool), the racks must have sufficient bending stiffness to withstand the design basis earthquake of the nuclear power plant without excessive movement.

[0014] Improvements are desired to the fuel rack, which is formed of slotted plates connected together to create fuel storage cells for wet storage of SNF within the fuel pool. [Overview of the project]

[0015] This application discloses several design variations of fuel racks suitable for wet storage of spent nuclear fuel (SNF) in spent fuel pools of nuclear power plants. Improvements are provided over conventional designs that enhance both the structural strength of the fuel racks to withstand shock and seismic loads and the fuel storage density. In one embodiment, each rack comprises a base plate configured to be installed on the floor of the fuel pool and a cellular body supported on the upper surface of the base plate and rising upward. The body comprises a plurality of interconnected slotted panels or plates, which, when assembled, define an array of fuel storage cells, each with cross-sectional dimensions and area capable of accommodating only a single fuel assembly. Each fuel rack comprises a combination of stainless steel slotted plates to ensure structural strength and boron-containing neutron-absorbing slotted plates for reactivity control in the active fuel storage area of ​​the rack.

[0016] The fuel racks disclosed herein include hexagonal and linear (e.g., square) cells for storing Russian-type and Western-type fuel assemblies, respectively. Flax-strap and non-flax-strap fuel racks are provided and are described in further detail herein.

[0017] Depending on the reactivity of the stored fuel, if the energy of the fuel assembly is low, it is possible to place the fuel storage cells in the "active fuel region" in the center of the fuel rack, with a single layer wall of neutron absorber (e.g., Metamic®) interposed between them. This is called a "non-flux-trap" rack in the art. Flux is the amount of radiation (e.g., neutrons, alpha particles, etc.) or energy emitted from the nuclear fuel contained in the fuel assembly. In the case of fuel assemblies with a large cross-sectional area, such as those found in PWRs (Pressurized Water Reactors), a large amount of nuclear fuel and the resulting high flux may require small vertical spaces or gaps (called "flux traps") between the storage cells. This is called a "flux-trap" rack in the art. While the fuel rack is immersed in the fuel pool, these gaps or flux traps are filled with water to reduce the radiation flux between fuel assemblies in adjacent cells within the rack. Neutron particles emitted from the fuel assemblies are slowed down by the water-filled traps. While the design structures of both flax-strap and non-flax-strap racks are similar, they are not identical. The similarities and differences between these two types of racks are further described herein.

[0018] To increase the number of fuel assemblies that can be stored in the fuel rack and, at the same time, the number of fuel assemblies that can be stored in the entire fuel pool, a linear cell fuel rack having a unidirectional flax-strap configuration is disclosed. In this configuration, (1) flax-straps exist between adjacent fuel storage cells in a first direction along the X-axis of the Cartesian coordinate system, and (2) flax-straps do not exist between adjacent fuel storage cells in a second direction along the Z-axis of the Cartesian coordinate system. The flax-straps are sized such that the K effective coefficient of the fuel rack is less than 1, preferably 0.95 or less as further described herein, in order to maintain the subcritical state of the fuel rack when the fuel rack is filled with an array of stored nuclear fuel assemblies. The expression "the fuel rack is filled with an array of stored nuclear fuel assemblies" means that spent nuclear fuel assemblies are placed in all fuel storage cells of the rack. [Brief explanation of the drawing]

[0019] Features of exemplary embodiments will be described with reference to the following drawings, in which similar elements are given similar numbering.

[0020] [Figure 1] Figure 1 is a side view of a spent fuel pool showing a fuel rack representative of several embodiments of fuel racks for wet storage of nuclear fuel assemblies disclosed herein.

[0021] [Figure 2] Figure 2 is a top perspective view of a first embodiment of a fuel rack according to the present disclosure having a unidirectional flax strap arrangement and linear cells.

[0022] [Figure 3] Figure 3 is a bottom perspective view of the first embodiment.

[0023] [Figure 4] Figure 4 is a top exploded perspective view of the first embodiment showing three sections of the slotted plate of the rack.

[0024] [Figure 5] Figure 5 is a bottom exploded perspective view of the first embodiment.

[0025] [Figure 6] Figure 6 is a first side view of the first embodiment.

[0026] [Figure 7] Figure 7 is a second side view of the first embodiment.

[0027] [Figure 8] Figure 8 is a top view of the first embodiment.

[0028] [Figure 9] Figure 9 is a bottom view of the first embodiment showing the base plate.

[0029] [Figure 10] Figure 10 is a perspective view of the first slotted plate of the fuel rack.

[0030] [Figure 11] Figure 11 is a perspective view of the second slotted plate of the fuel rack.

[0031] [Figure 12] Figure 12 is a perspective view of the third slotted plate of the fuel rack.

[0032] [Figure 13] Figure 13 is a perspective view of the fourth slotted plate of the fuel rack.

[0033] [Figure 14] Figure 14 is a first perspective view in the assembly procedure of the fuel rack of FIG. 1, showing the bottommost part of the fuel rack including the base plate and the first layer of the structural slotted plate.

[0034] [Figure 15] Figure 15 is a second perspective view of the assembly procedure of the fuel rack in Figure 1, showing a second layer of slotted plates, which includes neutron-absorbing slotted plates stacked and connected on top of a first layer of structural slotted plates.

[0035] [Figure 16] Figure 16 is a third perspective view of the assembly procedure of the fuel rack in Figure 1, showing the third layer which includes neutron-absorbing slotted plates stacked and connected on top of the second layer of neutron-absorbing slotted plates.

[0036] [Figure 17] Figure 17 is a fourth perspective view of the fuel rack assembly procedure in Figure 1, showing all layers of neutron-absorbing slotted plates that form the intermediate section of the fuel rack.

[0037] [Figure 18] Figure 18 is a fifth perspective view of the assembly procedure for the fuel rack in Figure 1, showing the addition of a structural slotted plate that forms the upper section of the fuel rack to the top of the stack of neutron-absorbing slotted plates in Figure 17.

[0038] [Figure 19] Figure 19 is a sixth perspective view of the assembly procedure for the fuel rack in Figure 1, showing the addition of the open girdle frame that extends around the slotted plate in the upper section of the rack in Figure 18.

[0039] [Figure 20] Figures 20 and 21 are top and bottom perspective views, respectively, showing the fuel rack assembly procedure in Figure 1 with the addition of corner tension members extending perpendicularly to the fuel rack. [Figure 21]Figures 20 and 21 are top and bottom perspective views, respectively, showing the fuel rack assembly procedure in Figure 1 with the addition of corner tension members extending perpendicularly to the fuel rack.

[0040] [Figure 22] Figure 22 is a perspective view showing the assembly procedure of the fuel rack in Figure 1, with the addition of horizontally extending strap members to the fuel rack.

[0041] [Figure 23] Figure 23 is a detailed, enlarged view of a portion of the upper section of the fuel rack in Figure 1, showing an array of unidirectional flak straps, which will be further described herein.

[0042] [Figure 24] Figure 24 is a perspective view showing a portion of the upper section of the fuel rack in Figure 1, illustrating an internal tensioning member and associated lateral restraint elements coupled to one of the flak straps.

[0043] [Figure 25] Figure 25 is a perspective view of the bottom of the fuel rack in Figure 1, showing the base plate with an under girder beam.

[0044] [Figure 26] Figure 26 is a perspective view of a Western-type nuclear fuel assembly with a square cross-section.

[0045] [Figure 27] Figure 27 is a first partial vertical cross-sectional view of the fuel rack in Figure 1, showing the internal tensioning member connected to the upper section of the rack and the base plate.

[0046] [Figure 28] Figure 28 is a second partial vertical cross-sectional view of the fuel rack in Figure 1, showing the internal tensioning member connected to the upper section of the rack and the base plate.

[0047] [Figure 29] Figure 29 is a top perspective view showing a portion of the upper section of the fuel rack in Figure 1, with the upper end of the internal tension member, the lateral restraint element, and the lock nut shown in exploded view.

[0048] [Figure 30] Figure 30 is a top perspective view of a lateral constraint element.

[0049] [Figure 31] Figure 31 is a bottom perspective view of the lateral constraint element.

[0050] [Figure 32] Figure 32 is a first cross-sectional view taken along the length of the lateral constraint element.

[0051] [Figure 33] Figure 33 is a second cross-sectional perspective view that spans the width of the lateral constraint element.

[0052] [Figure 34] Figure 34 is a top perspective view of a second embodiment of a fuel rack according to the present disclosure, which has linear cells and does not have flax straps.

[0053] [Figure 35] Figure 35 is a bottom perspective view of the second embodiment.

[0054] [Figure 36] Figure 36 is a top view of the second embodiment.

[0055] [Figure 37] Figure 37 is a bottom view of the second embodiment.

[0056] [Figure 38] Figure 38 is a top perspective view of a third embodiment of a fuel rack according to this disclosure, which has a bidirectional arrangement of linear cells and flax straps.

[0057] [Figure 39] Figure 39 is a bottom perspective view of the third embodiment.

[0058] [Figure 40] Figure 40 is a top view of the third embodiment.

[0059] [Figure 41] Figure 41 is a bottom view of the third embodiment.

[0060] [Figure 42] Figure 42 is a top perspective view of a fourth embodiment of a fuel rack according to this disclosure, which has hexagonal cells and triangular flax straps.

[0061] [Figure 43] Figure 43 is a bottom perspective view of the fourth embodiment.

[0062] [Figure 44] Figure 44 is a first side view of the fourth embodiment.

[0063] [Figure 45] Figure 45 is a second side view of the fourth embodiment.

[0064] [Figure 46] Figure 46 is a top view of the fourth embodiment.

[0065] [Figure 47] Figure 47 is a bottom view of the fourth embodiment.

[0066] [Figure 48] Figure 48 is a partial top perspective view of the fuel rack in Figure 42, showing a Russian-type hexagonal fuel assembly located in one of the hexagonal cells of the rack.

[0067] [Figure 49]Figure 49 is a partial perspective view of the fuel rack in Figure 42, showing the first layer of structural slotted plates attached to the base plate.

[0068] [Figure 50] Figure 50 is a partial top perspective view of the fuel rack in Figure 42, showing an internal tensioning member positioned in one of the triangular flax straps and an associated triangular lateral constraint element.

[0069] [Figure 51] Figure 51 is a top perspective view of a triangular lateral constraint element.

[0070] [Figure 52] Figure 52 is a bottom perspective view of a triangular lateral constraint element.

[0071] [Figure 53] Figure 53 is a perspective view of the slotted plate used to construct the fuel rack in Figure 42.

[0072] [Figure 54] Figure 54 is a top perspective view of a Russian-type hexagonal fuel assembly.

[0073] [Figure 55] Figure 55 is a bottom perspective view of a Russian-type hexagonal fuel assembly.

[0074] All drawings are schematic and not necessarily to scale. A part shown and / or numbered in one drawing may be considered the same part as a part that is not numbered in other drawings for simplification purposes, unless otherwise assigned a different part number herein. [Modes for carrying out the invention]

[0075] The features and advantages of the present invention are illustrated and described herein by reference to exemplary embodiments. The description of these exemplary embodiments is intended to be read in conjunction with the accompanying drawings, which are considered to be part of the entire specification. Therefore, this disclosure should not be expressly limited to exemplary embodiments showing combinations of features that may exist individually or in combination with other features, and which may not be limiting. Furthermore, all features and designs disclosed herein can be used in combination, even if not expressly stated otherwise.

[0076] In the descriptions of the embodiments disclosed herein, references to direction or orientation are intended solely for illustrative purposes and are not intended to limit the scope of the invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top,” “bottom,” and their derivatives (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be interpreted as referring to the orientation described or shown in the drawings discussed therein. These relative terms are for illustrative purposes only and do not require the apparatus to be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar terms, unless expressly otherwise stated, refer to both movable and fixed connections or links, as well as relationships in which structures are directly or indirectly fixed or attached to one another through intervening structures. Any numerical range described herein is understood to include closing values ​​or limits of the lower and upper numerical values ​​of the cited range, and any numerical value included in the cited range can function as a closing value.

[0077] Referring first to Figure 1, a nuclear facility such as a nuclear power plant is provided with a water-storage spent fuel pool 40 according to this disclosure, which is configured for wet storage of nuclear fuel in individual nuclear fuel racks, etc. The illustrated fuel racks represent any of the fuel racks 100, 200, 300, and 400 disclosed herein. The fuel pool 40 comprises a plurality of vertical side walls 41 rising upward from an adjacent substantially horizontal bottom floor wall or slab 42 (note that some inclination may be intentionally provided on the top surface of the floor slab for drainage to lower points, taking into account installation tolerances, or when it is necessary to empty the pool for cleaning / decontamination at some point). The floor slab 42 and side walls 41 may be formed of reinforced concrete in one embodiment, not limited to this. The floor slab 42 of the fuel pool may be formed in soil or an artificial embankment and rested thereon. The floor slab 42 may be installed on the ground surface, below the ground surface, or above the ground surface. In some embodiments, the floor slab 42 and side walls 41 are at least partially embedded in the soil, and / or artificial embankments are installed to surround the outer surfaces of the side walls. The above arrangements, or other arrangements, are available depending on the layout of the nuclear facility and do not limit the invention.

[0078] In one embodiment, the fuel pool 40 may have a linear shape in a plan view. With four side walls 41, the pool may have an elongated rectangular shape (in a plan view) with two long opposing side walls and two short opposing side walls (e.g., end walls). Other shapes of the fuel pool 40 are also possible, such as squares, other polygons, non-polygons, and combinations thereof, which may vary from nuclear facility to nuclear facility.

[0079] The side walls 41 and floor slab 42 of the fuel pool 40 define the pool water W and an upwardly opening well or cavity 43 configured to hold multiple underwater nuclear fuel racks. Depending on the selected rack, these racks may be fuel racks 100, 200, 300, or 400, each holding multiple nuclear fuel assemblies, such as fuel assembly 30A (Western-style square cross-sectional shape) shown in Figure 26 or fuel assembly 30B (Russian-style hexagonal cross-sectional shape) shown in Figures 54-55. Each fuel assembly individually houses multiple spent uranium fuel rods. In various embodiments, the fuel racks housing the fuel assemblies are installed on the floor slab 42 in a high-density arrangement, either horizontally adjacent or with minimal spacing between racks.

[0080] Referring to Figure 26, the conventional Western-type fuel assembly 30A has an elongated body 34A with a square cross-section, and an upper flow nozzle 32A and a bottom flow nozzle 33A are provided at its tip. This assembly contains multiple fuel rods 31A filled with uranium.

[0081] Referring to Figures 54 and 55, the conventional Russian-type fuel assembly 30B has an elongated body 34B, which has a hexagonal cross-section and is terminated by an upper flow nozzle 32B and a bottom flow nozzle 33B. This assembly contains multiple fuel rods 31B filled with uranium.

[0082] Figures 2-25 illustrate a first embodiment of the fuel rack 100 according to this disclosure and various features / details of the first embodiment for use with the Western-style fuel assembly 30A described above. The fuel rack 100 is a cellular upright module or unit comprising a vertically extending cellular body 101 and an array of vertically extending fuel storage cells 110. In this embodiment, the cellular body has a linear cross-sectional shape. The cells 110 of the fuel rack 100 define an opening that extends across the entire height of the cellular body rack, from the top 102 of the cellular body rack to the bottom 103 on the upper surface of the base plate 140. This is referred to as the cellular region of the fuel rack.

[0083] The fuel rack 100 comprises four sides 104 that extend vertically from the top 102 to the bottom 103 of the cellular body 101. The fuel rack defines a vertical centerline VC that passes through the geometric center of the rack from left to right. The cellular body 101 rises upward from the base plate 140 and is supported by the base plate 140. The base plate 140 is configured to be installed on the floor slab 42 of the fuel pool 40, as will be further described herein. The weight of the fuel rack body 101 and the fuel assemblies housed in the cells 110 is supported by the base plate 140 and transferred to the floor of the fuel pool. Therefore, the base plate is preferably made of a ductile and corrosion-resistant metal such as stainless steel.

[0084] In this embodiment, the structure of the cellular body 101 and the array of fuel storage cells 110 of the fuel rack 100 is formed by a plurality of interconnected and orthogonal slotted plates 120. The rack consists of four different plates shown in Figures 10-13, which will be described later. Each elongated slotted plate 120 defines a longitudinal axis LA extending along the length L1 of the plate. The slotted plates 120 are elongated horizontally, and each length L1 is substantially greater than the height H1 as shown (for example, at least four times the height). When installed, the plates 120 are positioned horizontally and laterally with respect to the vertical centerline VC of the fuel rack 100. The side surface 104 of the fuel rack is defined overall by the outermost circumferentially extending slotted plate 120 that defines the outward-facing outer peripheral side surface 105 of the rack. The plate 120 is a continuous monolithic structure extending from one corner 106 to the opposite corner of the fuel rack 200. The corners of the rack are defined by the orthogonal intersections of the plates.

[0085] Each slotted plate 120 comprises a flat, parallel, opposing vertical main surface 124, an upper longitudinal edge 122, a lower longitudinal edge 123, and opposing ends 125 defining the periphery of the plate. To connect the plates, depending on the position and configuration of the plates in the rack, a number of vertical slots 121 are formed on the upper longitudinal edge, the lower longitudinal edge, or both, spaced longitudinally and perpendicular to the longitudinal axis LA. The height of the slots is lower than the total height H1 of the slotted plate. Any suitable number, height (i.e., vertical depth), and arrangement of the slots 121 may be provided to form the illustrated fuel rack structure and, at the same time, the intended size of the cells 110 of the fuel rack 100 for storing fuel assemblies containing spent nuclear fuel (SNF).

[0086] The plates of the slotted plate 120 are oriented horizontally / laterally and connected to one another via slots 121, forming a stacked structure consisting of multiple horizontal levels or layers of plates rising from the base plate 140 and stacked up to the desired height of the fuel rack. The bottom layer plate 120 of the fuel rack has its bottom end 123 connected to the base plate, so only the slots formed at its top end 122 connect to the next level / layer plate above. The top layer slotted plate 120 of the upper layer of the fuel rack may consist of a slotted plate 120 having only downward-opening slots 216 necessary for finishing the top of the rack, a slotted plate 120 having downward-opening and upward-opening slots 121, or a combination thereof. The intermediate layer slotted plates between the top and bottom layers of the fuel rack have slots 121 on both the top and bottom surfaces to form a connection with both the top and bottom plates. As shown in the figure, some of the slots 120 extend only partially across the entire height H1 of the slotted plate, and in some embodiments, they are less than or equal to about 50% of the height H1. Not all slots are of the same height. Depending on their position in the plate stack of the fuel rack structure, the plates 120 may have the same height and length, or different heights and lengths.

[0087] The fuel storage cells 110 of the fuel rack 100 have a grid-like arrangement of densely packed, vertically extending cells inside. Each cell is configured to accommodate only one Western-type fuel assembly 28 (containing a number of spent nuclear fuel rods 28a), and its cross-sectional area, height, and shape are dimensioned. An example of this type of fuel assembly, having a conventional linear cross-sectional shape, is shown in Figure 26. Such fuel assemblies are well known in the industry. Thus, the cells 120 of the fuel rack, partitioned by orthogonal slotted plates 120, also have a linear cross-sectional shape (e.g., a square).

[0088] The base plate 140 is composed of a broad, flat horizontal plane and, in the illustrated embodiment, has a linear (i.e., square or rectangular) shape. The base plate defines four peripheral sides 140a that define the entire perimeter of the base plate. The peripheral sides 140a may be linear. The base plate 140 is preferably made of a corrosion-resistant metal plate, such as stainless steel, so that it can withstand corrosion when immersed in the fuel pool. The base plate has a thickness appropriate to support the total weight when the fuel rack 100 (i.e., slotted plate 120) and fuel assemblies are housed in it. A typical thickness is about ±4 inches (10.2 cm).

[0089] In some embodiments, the base plate 140 of the fuel rack 100 may include a number of legs or pedestals 141 that support the rack from the floor slab 42 of the fuel pool 40 (see, for example, Figures 1 and 35). Each pedestal 141 may have a flat lower end that engages with the floor slab 42 of the pool and an upper end that is fixed to the bottom of the base plate 140 by welding or bolting, etc. The pedestals 141 project downward from the flat body of the base plate 140, are spaced laterally apart from each other, and are positioned appropriately on the base plate to properly support the fuel rack 100. The pedestals 141 are provided at all of the four lower corners of the base plate, and in the case of large racks, they may also be provided between the corner pedestals.

[0090] The base plate 141 lifts the rack's base plate 140 from the floor slab 42 of the fuel pool 40, separating it vertically and thereby creating a gap between them, forming a bottom flow plenum P directly beneath the rack 100 (see, for example, Figure 1). More specifically, when the heat-induced fuel assembly 30A is placed in the cell 110, which is submerged in the fuel pool 40, the water in the cell surrounding the fuel assembly is heated and rises due to a decrease in density and an increase in buoyancy, forming a natural upward flow pattern. As this heated water rises and is discharged from the open end of the cell 110, the cooler water W in the fuel pool 40 is drawn into the bottom of the cell through the flow holes 142 of the base plate 140 at the bottom of the cell, and flows upward through the cell and fuel assembly, cooling the nuclear fuel. This heat-induced water flow and circulation pattern along the fuel assembly continue to naturally dissipate the heat generated by the fuel assembly. Therefore, the height of the base 141 is selected to form a bottom flow plenum P of approximately appropriate height to ensure sufficient thermally induced natural circulation to adequately cool the fuel assemblies and thereby protect the spent fuel (SNF) contained therein. In one non-limiting example, the height of the plenum P may be approximately 2 to 2.5 inches (5.1 to 6.4 cm) (including the values ​​described within this range and values ​​in between). However, other appropriate heights may be used depending on the installation requirements of the fuel rack and the reactivity of the fuel assemblies.

[0091] The flow path holes 142 in the base plate 140 form inlet passages from the plenum P below the base plate 140 to the cells 110 formed by the stacked slotted plates 120 of the rack 100. In the case of a fuel rack with flax straps, such as the fuel rack 100, the base plate 140 is provided with flow path holes for each flax strap, allowing cooling pool water to be introduced through the traps. Each cell 110 and trap is provided with corresponding flow path holes 142 in the base plate 140. The flow path holes 142 may be circular in some embodiments, but holes of other shapes may be used. For example, some flow path holes 143 associated with cells 110 are configured differently from the majority of the normal flow path holes in the base plate 140 and also provide rigging mounting points for raising and lowering empty fuel racks from the fuel pool 40. However, the flow path holes associated with these rigging function in the same way as introducing pool water W to the bottom of the cells to cool the fuel assemblies 30 stored within the cells.

[0092] Preferably, each cell 110 is provided with at least one flow path hole 142, but additional holes may be used as needed to create sufficient flow through the tube to cool the fuel assembly 30A therein.

[0093] Referring particularly to Figures 4-5, the fuel rack 100 includes an upper section 100A, a bottom section 100B, and an intermediate section 100C of slotted plates 120, the intermediate section being positioned between the upper and bottom sections. All slotted plates in each section are slidably connected and assembled to form the cellular body 101 of the fuel rack 100, collectively defining the fuel storage cells 110 from top to bottom. However, multiple slotted plates 120 are formed from two different materials for different purposes and have multiple configurations as shown in Figures 10-13, occupying different positions within the fuel rack 100. The plates assembled as shown in Figures 2-3 form the cellular body 101 of the rack.

[0094] As a first type of plate, the fuel rack 100 includes corrosion-resistant structural metal slotted plates 120A, preferably formed of a strong, corrosion-resistant, weldable metal such as stainless steel, to ensure structural support and rigidity (these may also be referred to simply as “structural plates” in this specification for brevity). Plates 120A are used in the upper section 100A and bottom section 100B of the cellular body 101 of the rack, as will be further described herein. For example, Figure 14 shows half-height starter plates 120A welded directly to a base plate 140 that forms the starter layer of slotted plates. These lower structural slotted plates, together with the base plate 140, form a stable lower weld 100B-1 in the bottom section 100B of the slotted plates of the rack. At the top of the rack, Figures 10-11 show how half-height and full-height slotted plates 120A are combined to form the upper section 100A of the rack. These uppermost structural slotted plates are mechanically and slidably connected and then preferably welded to form a stable upper weld 100A-1 for the upper section 100A. Thus, the slotted plate 120A is considered a structural slotted plate.

[0095] A second type of slotted plate is required for reactivity control of the fuel rack 100. Therefore, the fuel rack also includes an unstructured boron-containing metal neutron-absorbing slotted plate 120B in the middle section 100C of the rack, which is the “active fuel region” from the perspective of radiation emission (for brevity, this may also be referred to simply as the “neutron-absorbing plate” in this specification). For clarity, the neutron-absorbing plate 120B is shown with a dot pattern in some figures showing the complete stacking of these plates (or parts thereof) and is visually distinguishable from the structural plate 120A, which is not dotted for clarity. In other figures, the neutron-absorbing plate may not be dotted for clarity of depiction. The neutron-absorbing plate 120B reduces intercellular neutron radiation transmission from the fuel assemblies 30A within the cell 110, ensuring that the fuel rack maintains negative reactivity, i.e., a subcritical state (criticality being a state in which a sufficient number of neutrons are emitted by the fission of the nuclear fuel, resulting in an autonomous chain reaction). Figures 11 and 12 show two different configurations of neutron-absorbing plates 120B used to form the intermediate section 100C of the fuel rack cell body 101. In one embodiment, the neutron-absorbing plate 120B may be, but is not limited to, an aluminum boride plate sold under the trademark Metamic® by Holtec International, Inc. of Camden, New Jersey, USA. However, in other embodiments, other metallic neutron-absorbing plate materials may be used.

[0096] The reactivity between the rack cells 110 and the fuel assemblies 30A within them is controlled by an unstructured boron-containing absorbent. This unstructured boron-containing absorbent controls neutron radiation and enables criticality control of the nuclear fuel stored in the rack. However, these boron-containing metal plates 120B are less strong than the stainless steel structural slot plates 120A, and, as mentioned above, are relatively brittle compared to steel slot plates in terms of impact due to their boron 10 (B-10) content. Furthermore, the boron-containing neutron-absorbing slot plates 120B are not particularly easy to weld to one another. Therefore, these slotted plates are held together only by sliding mechanical connections formed between the plates via slots 121. In particular, the neutron-absorbing slotted plates 120B are metallurgically incompatible with welding to the boron-free stainless steel slotted plates 120A.

[0097] It should be noted that the pairs of adjacent slots in both slotted plates 120A and 120B in Figures 11-13 are related to the formation of the flax strap 150, which will be further described herein.

[0098] The structural slotted plates 120A of the upper section 100A and bottom section 100B, formed of stainless steel, are firmly bonded together with the stainless steel base plate 140 and other structural support members described herein to form the structural framework of the fuel rack 100. This structural framework supports, holds, and protects the intermediate neutron absorber slotted plate 120B in the active fuel area of ​​the fuel rack 100. In addition to the structural slotted plate 120A and base plate 140, other structural members of the fuel rack structural framework include a number of vertically extending tension members that serve to join and pull the upper and lower welds together to compress the neutron absorber plate 120B of the intermediate section 120. In some embodiments, the tension members include an internal tension member 130 and / or a vertically extending external corner tension member 131. Other structural members provided to reinforce and structurally strengthen the fuel rack include a lateral / horizontally extending strap member 132 and an upper girdle frame 133. These structural members may be formed from stainless steel, as well as the structural slotted plate 120A and the base plate 140, as will be further described below.

[0099] The internal tension members 130 may be used in a fuel rack including a flax strap. Each internal tension member is coupled to the upper section 100A of the slotted plate 120A (upper weld 100A-1) and the base plate 140 at multiple locations between the fuel storage cells 110 in the flax strap within the internal cell region of the fuel rack 100, and extends vertically between them. The tension members may be of any suitable type, shape, and structure, as long as they can be fixed to the rack by mechanical or welding processes. Examples of suitable tension members 130 include tension rods 130-1, hollow tubes, steel cables, etc., as shown in the figure. In one preferred but non-limiting embodiment, the internal tension member 130 may be threaded at its upper and lower ends and detachably connected to a slotted plate 120A of the upper section 100A (upper weld 100A-1) of the rack via a lateral restraint element 130A and a threaded nut 134, and to a bottom base plate 140 via a threaded lock nut 134. Thus, the lock nuts screw-in connect each tension member to the lateral restraint element and the base plate. The tension member 130 is located within the internal cell region of the fuel rack 100 and penetrates vertically through the opening gap between specific selected cells 110 within the fuel rack 100. This opening gap is referred to in the art as the flax strap 150 and will be further described herein. By being located within the flax strap, interference with the space for inserting and removing fuel assemblies within the cells is avoided. The tension member 130 provides a tensioning function that pulls the slotted plate 120A of the upper section 100A downward toward the base plate 140, thereby compressing the laminate of the unstructured neutron-absorbing slotted plate 120B of the intermediate section 100C and stabilizing the engagement between these plates. These plates are not welded to each other but are only mechanically connected. Thus, essentially, the tension member serves to prevent the upper weld 100A-1 and the lower weld 100B-1 from separating and to fix the laminate of the intermediate slotted neutron-absorbing plate 120B in place within the rack. The tension member 130 has the advantage of further improving the axial load-bearing capacity of the rack structure.To achieve this function, any appropriate number of tension members can be provided and arranged. The number selected is determined in part based on the horizontal dimensions / size of the rack. When used with tension member 130, tension rod 130-1 may be cylindrical with a circular cross-section in one embodiment, but tension rods of other shapes, including linear, hexagonal, or other cross-sections, may be used.

[0100] The vertically extending outer corner tension members 131 are positioned at the corners 106 of the fuel rack, with one at each corner (four in total). In one embodiment, the tension members 131 may be elongated, linear, rod-shaped structural members having a straight cross-sectional shape. The upper end of the corner tension member 131 may be welded to the structural slotted plate 120A of the upper section 100A of the fuel rack 100 (i.e., upper weld 100A-1), or to the upper girdle frame 133, or both. If welded to the girdle frame 133, the girdle frame protrudes laterally beyond the outer periphery of the rack, so in some embodiments, the corner tension member 131 may be welded to the underside of the girdle frame 133 (see, for example, Figure 20). The lower end of the outer corner tension member 131 is preferably welded to a thick base plate 140, and in one embodiment, to its side. These upper and lower fixing points are the only points of attachment of the corner tension member to the fuel rack. The intermediate section 100C of the neutron-absorbing plate 120B is not bonded to it.

[0101] It should be noted that the corner tension member 131 is not simply attached to the corner of the rack, but is a tension element installed to apply tension to the slotted structural plate 120A within the rack. This tension simultaneously applies tension to the laminate of slotted neutron-absorbing plates 120B in the intermediate section 100C of the rack 100, and because the neutron-absorbing plates are not welded, it pulls them together and holds them in place. Thus, the corner tension member 131 is configured and capable of operating in such a way as to compress the laminate of neutron-absorbing plates 120B together.

[0102] In one embodiment, which is not limited to this, multiple lateral / horizontally extending strap members 132 are formed from linear rod-shaped structural members having a straight cross-section, and their ends are fixed to the outer corner tension members 131 by welding or other means, as shown in the figure. In other embodiments, mechanical connections other than welding (e.g., screw fasteners such as bolts) may be used to fix the strap members to the corner tension members. Each strap member extends horizontally and vertically from one corner tension member to another so as to cross the vertical centerline VC of the rack 100. The strap members are arranged at vertical intervals, as shown in the figure. Any appropriate number of strap members 132 may be provided as needed to laterally stabilize and fix the intermediate neutron absorber slotted plate 120B to each other. Since the fuel rack 100 is transported laterally to the nuclear power plant site by flatbed truck or railcar after assembly, the strap members 132 also have the advantage of mechanically connecting the unwelded intermediate sections 100B of the neutron absorber plates 120B until the rack is upright for movement and unloading into the fuel pool. The strap members also help prevent the neutron absorber plates 120B from shifting laterally in the event of an earthquake while the rack is submerged in the fuel pool during operation.

[0103] The upper girdle frame 133 is an open frame (i.e., a body that is open in the center and continuous in the circumferential direction) that extends circumferentially over the top of the fuel rack 100. This frame is welded to the side of the uppermost slotted structural plate 120A of the upper section 100A of the rack (upper weld 100A-1) to form a fixed, rigid joint (see, for example, Figure 20). The frame 133 is positioned slightly below the upper end of the circumferentially extending uppermost slotted plate 120A that defines the four outer sides of the fuel rack 100. In one embodiment, this frame may be formed from four steel structural bars arranged orthogonally and welded to each other at their ends, forming a straight frame that conforms to the shape and dimensions of the top of the fuel rack. The structural rods may be pre-assembled and welded before being welded to the rack, or the structural rods may be welded directly to the fuel rack one by one to form the completed girdle frame.

[0104] The steel structural framework, including the upper / lower welds 100A-1, 100B-1, internal tension members 130, corner tension members 131, strap members 132, and girdle frame 133, forms a cage or exoskeleton that surrounds and protects the more brittle neutron-absorbing slotted plate 120B, which is mechanically connected only in the intermediate section 100C of the fuel rack 100. In the event of an earthquake, the slotted plate 120B is prevented from moving or displacing laterally by the structural members, and this lateral movement or displacement could adversely affect the structural integrity of the fuel rack and the storage of spent nuclear fuel (SNF) contained within the rack's cells. From a general standpoint, the steel structural framework provides strength and protection to the rack as a whole during transport, lifting, handling, installation in the fuel pool, and in the event of an earthquake. When the rack is lifted and handled by an overhead crane, the strong structural framework withstands the weight load, and the weight load is not transferred to the lamination of more brittle neutron-absorbing slotted plates 120B located in the middle section 100C of the rack.

[0105] Here, we will briefly describe the general process or method for assembling the fuel rack 100.

[0106] First, the lower weld is formed by welding the structural slotted plate 120A of the bottom section 100B of the fuel rack 100 to the upper main surface 140B of the base plate 140 (see, for example, Figure 14). The multiple slotted plates are arranged parallel to each other and spaced horizontally, as shown in the figure. The slotted plates extend in a first direction perpendicular to a pair of opposing peripheral edges 140a of the base plate 140. As shown in the figure, the lower edges of these slotted plates 120A abut the base plate, so it is not necessary to provide slots on the lower edges. The spacing between the steel structural plates may be precisely controlled during the installation of the bottom layer of slotted plates, where an orthogonal array of partial-depth grooves 136 is machined into the upper surface of the base plate to form a foundation for housing the first layer or level of neutron-absorbing slotted plate 120B.

[0107] In one embodiment, the base plate 140 may be further structurally reinforced and made more rigid by a plurality of undergirder beams 144 fixed to the bottom main surface 140C of the base plate by welding or bolting (see, for example, Figures 3, 9, and 14). These beams, together with a slotted plate 120A welded to the upper surface opposite the base plate, form a single structural portion of the lower weld 100B-1. Because the undergirder beams structurally reinforce and support the base plate from the bottom of the fuel pool, the base plate itself can be made thinner (thickness from the top to the bottom of the base plate) while still supporting the weight load of the entire fuel rack loaded with fuel assemblies. A typical unreinforced base plate may have a thickness of approximately 4 inches (10.2 cm) to support the weight load of the fuel rack. However, the thickness of the base plate reinforced with undergirder beams may be thinner.

[0108] The beams 144 are spaced horizontally and parallel to one another. In one embodiment, the undergirder beam extends continuously from one side 140A of the base plate to the opposite side of the base plate, as shown in the figure. In other embodiments, the undergirder beam may have a length that does not extend continuously from one side to the opposite side of the base plate (i.e., a length shorter than the width from one side to the opposite side of the base plate). The undergirder beam is preferably oriented and positioned perpendicular to the starter layer of the structural slotted plate 120A welded to the upper surface of the base plate described above. Increased rigidity of the base plate is advantageously achieved by the starter slotted plate 120A extending in one direction, the array of undergirder beams 144 extending in a second orthogonal direction, and each starter plate being supported by multiple beams. The undergirder beam is configured to engage with the bottom 42 of the fuel pool 40, and its height allows the base plate to be raised without the use of a pedestal 141 to form only the flow plenum P. Therefore, in some embodiments, flow channels may be provided in the beam 144 to promote the circulation of pool water W below the base plate (see, for example, Figure 1).

[0109] In various embodiments and arrangements, the base plate 140 may include a pedestal only, a beam only, or a combination of both (see, for example, Figure 35), depending on the configuration of the fuel storage pool. If both are included, the beam 144 preferably has the same height as the pedestal 141 and protrudes downward by the same distance from the bottom surface of the base plate 140. This allows the beam and pedestal to contact the floor of the fuel pool, distributing the weight of the fuel racks and the fuel assemblies contained therein across the entire floor. The beam has a greater contact length and contact area with the underside of the base plate than a generally cylindrical pedestal, thus increasing rigidity and reducing the likelihood of the base plate flexing in a given area due to the weight of the racks and fuel assemblies. The under girder beam 144 also helps prevent the base plate 140 from flexing when lifting or lowering the fuel racks 100, suspended from the fuel pool crane, into or out of the fuel pool.

[0110] Referring to Figure 15, the bottom layer of neutron-absorbing slotted plate 120B is stacked on top of the starter layer of structural slotted plate 120A, which is welded to the base plate 140 as described above, and mechanically connected. The neutron-absorbing slotted plate 120B is positioned orthogonal / perpendicular to the structural slotted plate 120A as shown in the figure. The neutron-absorbing plate is held on the structural plate only through connecting slots. The boron-containing neutron-absorbing plate 120B is metallurgically unsuitable for welding to the stainless steel structural slotted plate 120A. Figure 16 shows the second layer of neutron-absorbing slotted plate 120B being stacked on top of the first layer of neutron-absorbing plate and mechanically connected. The plate 120B of the second layer of neutron-absorbing plate is positioned orthogonal to the plate 120B of the first layer of neutron-absorbing plate. Next, in a similar manner, neutron-absorbing plate slots 120B are added to the lamination, gradually constructing the neutron-absorbing intermediate section 100C of the fuel rack 100 to the height required to completely cover the active fuel area of ​​the rack. This allows for control of the reactivity between the cells within and the fuel assemblies 30A. This process gradually increases the height of the fuel storage cells 110 layer by layer. Once all the neutron-absorbing plates 120B are in place, the intermediate section of the rack is completed (see, for example, Figure 17).

[0111] After all the necessary neutron-absorbing slotted plates 120B have been added to the rack, the structural slotted plates 120A of the upper section 100A of the fuel rack (e.g., upper weld 100A-1) are stacked on top of the uppermost neutron-absorbing slotted plates and mechanically joined (see, for example, Figure 18). Unlike the single starter layer of structural slotted plates 120A extending in only one direction, welded to the base plate 140 as described above, the final upper weld consists of two layers of structural slotted plates 120A that extend in two different orthogonal directions and intersect orthogonally. The plates 120A shown in Figures 10 and 11 are used to form the upper weld. The half-height plate 120A in Figure 10, with downward-opening slots, forms the horizontal upper end of the cellular body 100 of the fuel rack. These stainless steel slotted plates 120A are mechanically joined via slots 121 and then welded to each other to complete the upper weld structure. The upper welded section 100A-1 may be formed by placing two slotted plates 120A on top of the uppermost neutron-absorbing plate 120B and then welding them together. Alternatively, the slotted plates 120A may be welded first to complete the weld, and then attached to the neutron-absorbing plate stack. Both methods are possible, and neither of these structural slotted plates 120A is welded to the uppermost neutron-absorbing plate 120B.

[0112] As shown in the diagram, it should be noted that the slotted plates 120A and 120B at each level or layer within the fuel rack 100 are intentionally offset vertically from the slotted plates of the layers above and below them and are connected to eliminate a continuous horizontal shear failure path through the slotted plates. This prevents the slotted plates of one or more layers from shifting or being displaced horizontally from the slotted plates of other layers, although this could impair the linearity of the storage cells 110 within the rack during an earthquake and negatively affect the structural integrity of the fuel rack for protecting the fuel assemblies. In other words, a pair of slotted plates in a layer is vertically offset by approximately half the height of the plate from the connected slotted plates of the adjacent upper and / or lower layers.

[0113] Referring to Figure 19, an upper girdle frame 133 may then be welded around the outward-facing side of the structural slotted plate 120A located in the upper section 100A of the fuel rack 100. The girdle frame acts as a bumper protecting the slotted plate at the top of the fuel rack 100 from damage when used in the fuel pool or when laid on its side during transport and handling. The girdle frame 133 may be prefabricated and then mounted on the stack of slotted plates, or it may be prepared as four separate straight components, each welded to the fuel rack. Either mounting method may be used.

[0114] Next, the vertically extending corner tension members 131 can be positioned at the corners 106 of the rack, with each end welded to the upper girdle frame 133 and the bottom welded to the base plate 140 (see, for example, Figures 20 and 21). In one embodiment, the upper end of the corner tension member 131 may be welded to the underside of the girdle frame. Alternatively, the bottom end of the member 131 may be welded to the side of the base plate. In another embodiment, the corner tension member 131 may be bolted to the girdle frame and base plate.

[0115] Next, a strap member 132 extending in the lateral / horizontal direction is added, and each end is welded to one of the corner tension members 131 (see, for example, Figure 22). The strap member 132 is positioned perpendicular to the corner tension member 131 extending in the vertical direction. Note that the order in which the strap members and corner tension members are attached may be reversed, and this is left to the assembler's discretion. In some embodiments, fillet welds and groove welds may be used to connect the strap members and corner tension members.

[0116] As shown in Figures 2, 8, 23, and 24, the fuel rack 100 comprises a plurality of flax straps 150. The flax straps are intentionally formed open spaces or gaps between fuel storage cells 110 within the rack, controlling the reactivity between the cells and the fuel assemblies stored therein. While the rack is immersed in the fuel pool 40, the flax straps 150 are filled with water, which acts as a radiation (e.g., neutron) moderator, reducing the reactivity between the cells. The flax straps extend from the top 102 to the bottom 103 across the entire height of the cellular body 101 of the fuel rack, defining openings that end on the top surface of the base plate 140. The cross-sectional area and volume of the flax straps are preset to provide the required level of reactivity control between the cells 110 (when filled with water), depending on the energy level of the fuel in the fuel assemblies housed in the rack. The cross-sectional area of ​​the flax straps 150 is too small to hold the fuel assemblies.

[0117] Referring to Figure 19, each flax strap 150 has a horizontally elongated configuration defined by length L2 and width W2, each dimension measured horizontally and in plane. Length L2 is greater than width W2. Width W2 defines the water-filled gap between adjacent cells separated by the flax strap (for example, between cells 110 in each row extending along the horizontal X-axis shown in Figure 8). Length L2 has the same spread as the dimensions of the cell 110 measured along the length of the flax strap. Thus, width W2 determines the horizontal spacing and gap between cells separated by the flax strap.

[0118] Referring to Figures 24-25 and 27-29, the assembly of the fuel rack 100 is then completed by installing vertically elongated internal tension members 130, such as tension rods 130-1, in illustrated but not limited embodiments. The tension rods 130-1 are installed through at least several flack straps 150 from top to bottom, preferably spaced horizontally along the interior of the cellular body or region of the rack. Each tension rod passes through each of the flack straps 150 at a selected position and extends from the upper weld 100A-1 of the rack through the open trap to the base plate 140.

[0119] A lateral restraint element 130A, located at the top of each tension rod 130-1, is configured to engage with a selected flak strap and engages with the upper end 120A-1 of the uppermost slot structure plate 120A that surrounds and defines the top of each linear flak strap at the top of the rack, as shown in Figure 24. The threaded upper end of the tension rod 130-1 passes through the mounting hole 135F of the restraint element and is secured there by a threaded lock nut 134. The threaded lower end of the tension rod 130-1 passes through each through hole in the base plate 140 located within the flak strap 150 and is secured there by another threaded lock nut 134 on the back of the base plate (see, for example, Figure 25).

[0120] When at least one of the opposing nuts 134 on the tension rod 130-1 is tightened, tension is generated in the tension rod, compressing the vertical stack of slotted plates 120A and 120B and pulling them towards each other. This ensures that the plates fit together securely through the connecting slots 121 of the plates and are fixed in place. Importantly, the compressive force acting on the intermediate section 100C of the neutron-absorbing plate 120B, sandwiched between the upper weld 100A-1 and the lower weld 100B-1, prevents these unwelded intermediate plates from shifting laterally relative to each other during transport or due to vibrations transmitted to the fuel racks submerged in the fuel pool and placed at the bottom during an earthquake.

[0121] Figures 30-33 individually detail one non-limiting embodiment of the lateral restraint element 130A. Each restraint element is configured to reliably engage with its respective flak strap 150, preventing relative lateral / horizontal movement between the restraint element, the tension rod 130-1, and the flak strap 150. In one embodiment, the restraint element 130A may be a rectangular, generally elongated flat bar that matches the shape of the flak strap 150. The restraint element 130 includes a top surface 135A, an opposing bottom surface 135B, opposing ends 135C, and opposing sides 135D. In one embodiment, the bottom surface 135B has a stepped structure and defines a circumferentially extending downward lip 135E and a downwardly extending anti-rotation projection 135G. The lip 135E forms a downward-facing support surface 135H, which abuts and engages with the upper end 120A-1 of four orthogonally arranged structural slotted plates 120A that constitute the flak strap 150. These structural slotted plates 120A constitute the flak strap 150 to which the restraint element is attached. When the tension rod 130-1 is tightened by the nut 134, the tension rod 130-1 pulls the lateral restraint element 130A downward, applying a compressive force to the laminate of slotted plates 120A, 120B. Thus, the lateral restraint element 130A not only prevents lateral movement of the restraint element but also functions as a compression plate.

[0122] The anti-rotation projection 135G is configured complementary to the flak strap opening and extends downward around the flak strap 150 to below the upper edge 120A-1 (see, for example, Figures 27-28). The horizontal dimensions of the projection 135G (e.g., width W3 and length L3) are such that it fits inside the flak strap 150 while remaining in close contact with it. This locking projection prevents the lateral restraint element 130A from twisting relative to the flak strap when the lock nut is rotatably tightened. The lateral restraint element further prevents horizontal / lateral movement between the restraint element and the tension rod 130-1 relative to the flak strap 150 and the slotted plate 120A in the upper section 100A of the upper weld 100A-1. This keeps the tension rod centrally located within the flak strap.

[0123] It should be noted that other configurations and types of lateral restraint elements may be provided, as long as horizontal / lateral movement between the lateral restraint element 130A and the tension rod 130-1 is prevented from occurring between the lateral restraint element 130A and the slotted plate 120A in the upper section 100A of the flax strap 150 and the upper weld 100A.

[0124] One-way flax strap placement

[0125] To increase the number of fuel assemblies that can be stored in each fuel rack 100, the inventors discovered that the flax straps 150 can be arranged in one direction (i.e., a single direction) while still favorably maintaining the subcritical state of the rack with respect to satisfying the required K effective coefficient (described later) as defined by the Nuclear Regulatory Commission (NRC). This means that flax straps can be placed between adjacent fuel storage cells 110 in the rack in only one orthogonal direction (see, for example, Figures 2, 8, 23, and 24). The XYZ orthogonal coordinate system shown in Figures 2 and 8 is used for illustrative purposes (the Y axis is vertical, and the X and Z axes are horizontal). In the one-directional flax strap arrangement, the flax straps 150 are scattered only between each pair of adjacent cells in the cell rows arranged along the horizontal X axis in the first orthogonal direction (X direction) within the rack. However, in the cell rows arranged along the orthogonal horizontal Z axis in the second orthogonal direction (Z direction) perpendicular to the first direction, no flax straps are provided between each pair of adjacent cells. This means that, when a flax strap must be provided due to the reactivity of the nuclear fuel, more cells can be packed into the cell rows along the Z axis, in contrast to the conventional method of providing flax straps aligned along both the X and Z axes, thereby increasing the total number of cells and fuel assemblies housed in the fuel rack. The stacking between fuel storage cells 110 in the two orthogonal directions is variable, and in the extreme, the flax strap in one orthogonal direction (e.g., the Z direction along the Z axis) becomes zero (i.e., no flax strap), resulting in a unidirectional flax strap configuration where flax straps are provided only between cells along the X axis.

[0126] As background, the amount of U-235 "burned" and "integrated combustible toxins" consumed by spent nuclear fuel (SNF) removed from the reactor and stored in the fuel pool varies depending on the reactor's operating method. The reactivity of each removed fuel is a complex function of burnup and decay time after fission cessation in the core. The primary function of the fuel racks in the pool is to ensure that the number of neutrons generated by ongoing fuel decay in the pool is less than the number absorbed by the neutron-absorbing plates. The neutron-absorbing plates can capture neutrons slowed down by collisions with hydrogen atoms in the water. Neutrons traveling at low speeds are also called thermal neutrons. The amount of thermal neutrons relative to the total number of neutrons is controlled by adjusting the amount of water surrounding the fuel (determined by the cross-sectional area of ​​the storage cell). By installing a "flax trap" around the cell, the first absorbent plate captures thermal neutrons generated by the water inside the cell, the remaining neutrons are thermally neutronized in a water-filled flax trap, and then captured by a second plate made of boron-containing neutron-absorbing plate material (e.g., Metamic™). Therefore, if the number of fast neutrons is too large to be thermally neutronized and captured by a single wall of neutron-absorbing plate, a flax trap design is necessary.

[0127] The goal of rack design is to extinguish a sufficiently large number of neutrons so that the neutron count does not increase over time (so that the storage array does not become critical). Therefore, designers choose to provide an appropriate amount of flax trapping in both the X and Y directions to satisfy the subcriticality target. Since neutron capture is a volume effect rather than a directional one, making the storage cells rectangular allows for wider water gaps in the orthogonal directions than in other directions. Similarly, flax trapping may or may not be necessary, and if necessary, it can be of different sizes in the two orthogonal directions. In one extreme example, there may be no flax trapping in one direction and not in the other. For some fuels that produce small amounts of fast (high-energy) neutrons, flax trapping may not be necessary at all (e.g., fuel racks without flax trapping). Optimization is required to maximize the number of storage cells in each rack, and collectively the number of storage cells in the entire fuel pool with fixed-bed slab areas.

[0128] According to NRC regulations, the effective K coefficient of a spent fuel storage rack must be 0.95 or less. An effective K coefficient of less than 1.0 means that the number of neutrons released from the decaying spent nuclear fuel in the fuel rack is less than the number of neutrons absorbed (annihilated) by the neutron-absorbing plates. This ensures that the nuclear fuel in the fuel rack remains in a subcritical state where it cannot sustain a nuclear fission chain reaction. Therefore, to meet the NRC requirements, the effective K coefficient of fuel rack 100 is preferably less than 1.0, and more preferably 0.95 or less.

[0129] By using the unidirectional flax-strap array described above, the number of fuel assemblies that can be housed in a fuel rack equipped with sufficiently sized flax-straps can be increased. If the flax-strap size is sufficient, the K effective coefficient will be less than 1.0 due to the volume effect of neutron capture in each cell via the neutron-absorbing plates and water within the flax-straps. The ability of the unidirectional flax-strap configuration to meet the NRC's K effective coefficient criterion has been verified by the inventors using the K effective coefficient calculation code (algorithm) MCNP (A General Monte Carlo N-Particle Transport Code, Version 5, LA-UR-03-1987) from Los Alamos National Laboratory in the United States. Other commercially available codes for modeling the K effective coefficient are also available.

[0130] As an illustrative but non-limiting example shown in Figure 8, each row of cells 110 in the fuel rack 100 houses eight fuel assemblies along the X-axis direction (flax strap direction), while each row houses eleven fuel assemblies along the Z-axis direction (non-flax strap direction). Thus, compared to a conventional flax-strapped rack where flax straps are provided in both orthogonal directions, rack 100 can house 24 additional fuel assemblies. In other cases, other numbers of fuel assemblies may be packed into the fuel rack depending on the total horizontal dimensions of the rack in the X and Y directions, and this is not limiting to the present invention.

[0131] It should be noted that, depending on the reactivity of the fuel assemblies housed in the rack, it may not be necessary to have flax straps 150 for unidirectional flax strap arrangement between all pairs of cells 110 in a column extending along the X-axis in order to keep the K effective coefficient below 1.0. Therefore, in some embodiments, some pairs of cells in one or more columns extending along the X-axis may not require flax straps between them. Furthermore, in other embodiments, the widths W2 of at least two flax straps in one or more columns extending along the X-axis may differ from each other. Thus, considering the reactivity of the particular fuel assemblies housed in the fuel rack 100, numerous variations are possible in the arrangement and sizing of flax straps in unidirectional flax strap arrangement.

[0132] Figures 34-37 show a second embodiment of the linear cell fuel rack 200. This rack 200 is superficially similar to the fuel rack 100 and shares many common features, but in comparison, the rack 200 does not have flax straps. The rack design without flax straps can be used for wet storage of low-energy fuel assemblies, as previously described herein. The linear cells 110 are separated only by a single neutron-absorbing plate, not by two neutron-absorbing plates and a flax strap filled with water between them. Therefore, the fuel rack 200 does not have flax straps for inserting these members into the cell region of the rack, and thus does not have internal tension members 130. The fuel rack 200, like the rack 100 described herein, includes structural members of the fuel rack structural framework, including vertically extending outer corner tension members 131, lateral / horizontally extending strap members 132, and an upper girdle frame 133. The fuel rack is tensioned using corner tension members 131, applying compressive force to the plate stack. When the rack is assembled and tension is applied to the corner tension members, the stack of structural slotted plates 120A and neutron-absorbing plates 120B can be temporarily compressed by mechanical clamping means such as cables, hydraulic jacks, or large vise mechanisms. The corner tension members 131 can then be welded to the corners of the rack in the same manner as described above. Once the clamping means are released after welding, the slotted plate stack loosens and attempts to return to its original height, causing tension to be applied to the corner tension members. However, the corner tension members maintain compression in the intermediate section of the neutron-absorbing plate 120B between the upper and lower welds.

[0133] The fuel rack 200 also includes a combination of both a pedestal 141 and an undergirder beam 144. In other embodiments, only one type of these fuel rack support elements (e.g., a pedestal or a beam) may be provided, as shown for the fuel rack 100. The beam 144 in this embodiment omits the flow path holes 144A.

[0134] Figures 38-41 show a third embodiment of the linear cell fuel rack 300. This rack is superficially similar to the fuel rack 100 and shares many common features. In contrast, the fuel rack 300 is equipped with bidirectional flax straps 150, and each linear cell 110 is separated from adjacent cells by flax straps. The flax straps extend in two orthogonal directions along two horizontal axes (X-axis and Z-axis). The cells are separated by two neutron-absorbing plates and a water-filled flax strap placed between them.

[0135] The fuel rack 300 includes an internal tension member 130 and a flak strap 150 for passing the tension member through the cell area of ​​the rack. The fuel rack 300 also includes structural members of the fuel rack structural framework, the vertically extending external corner tension members 131, the laterally extending strap members 132, and the upper girdle frame 133 are configured in the same manner as the rack 100 described herein. The fuel rack 300 can be assembled in the same manner as the rack 100 described herein.

[0136] The fuel rack 300 uses only an undergirder beam 144 to raise the rack's base plate 140 from the floor of the fuel pool. However, a pedestal may be used in addition to, or instead of, the beam.

[0137] Figures 42-53 show a fourth embodiment of a fuel rack 400 having hexagonal cross-sectional cells 410 configured to accommodate Russian-type hexagonal fuel assemblies 30B shown in Figures 54-55. The rack 400 is formed by a plurality of diagonally arranged, connected, and slotted plates, including a structural slotted plate 420A and a neutron-absorbing slotted plate 420B shown in Figure 53. This single slotted plate configuration can be used for both types of these plates 420A and 420B. Plate 420A is similar to the slotted plate 120A described herein and can be made of stainless steel. Plate 420B is similar to the slotted plate 120B and can be made of boron-containing aluminum such as Metamic® or other boron-containing metal plates. Therefore, for brevity, slotted plates 420A and 420B will not be described further.

[0138] The structural slotted plate 420A and the neutron-absorbing slotted plate 420B are connected via slot 121 (see, for example, Figure 53) and stacked vertically in a connected arrangement and layered manner, similar to the plates 120A and 120B of the fuel rack 100 described herein. This similarly forms the upper section 100A, bottom section 100B, and middle section 100C of the slotted plate of the hexagonal fuel rack 400. The assembly process is the same, but instead of linear cells like those in fuel racks 100, 200, and 300, three rows of plates oriented in different directions are required to form the hexagonal cross-section cell 410.

[0139] Accordingly, two sets of horizontally elongated slotted plates 400A and 400B are arranged in a classic harlequin (diamond) grid pattern, with the first set of parallel plates diagonally intersecting the second set of parallel plates to first form elongated diamond-shaped cells (see, for example, Figure 46). To generate the final hexagonal cells 410, a third set of horizontally elongated parallel plates 400C is arranged to diagonally connect and intersect the first and second sets of plates 400A and 400B, with the third set of parallel plates penetrating the previously formed diamond-shaped cell openings in two places. The final result is an array of hexagonal cells 410 shown in Figure 46. Each slotted plate may contain a suitable number of slots formed on the top and bottom sides of the plate to form an interconnected plate structure. The set of plates will be either a structural slotted plate 420A or a neutron-absorbing slotted plate 420B, depending on which part of section 100A, 100B, or 100C of the fuel rack the plates are located within vanes similar to those of the fuel rack 100 described herein.

[0140] As shown in Figure 46, each slotted plate in sets 420A and 420B may have a width that extends from one peripheral edge 140a of the base plate 140 to the opposite side. Thus, the slotted plates are elongated horizontally, and their width is greater than their height (see, for example, Figure 53). The maximum height is achieved by stacking and connecting the plates vertically, as disclosed in the two patents above.

[0141] Similar to the linear cell fuel rack 100, the hexagonal cell fuel rack 400 has a top surface 402, an opposite bottom surface 403, and a number of sides 404 extending vertically between them. The fuel rack defines the geometric center of the rack as a vertical centerline VC passing from side to side. The cell-shaped body 401 rises upward from the base plate 140 and is supported by the base plate 140. The base plate 140 is configured to be installed on the floor slab 42 of the fuel pool 40 and may include a pedestal 141 and / or an under girder beam 144 as shown.

[0142] The slotted plates 420A and 420B define a number of triangular flax straps 450 around each cell 410. The flax straps define a space for inserting tension rods 130-1, similar to the flax straps 150 of the fuel rack 100 described herein. A triangular version of the lateral restraint element 130A described herein is used to connect the upper end of the tension rod 130-1 to the slotted plate 420A of the upper section 100A of the fuel rack 400. Specifically, a triangular lateral restraint element 430A is provided for insertion into the triangular flax straps 450.

[0143] The lateral restraint element 430A has a similar function to element 130A, securely engaging with each flak strap 450 and preventing relative lateral / horizontal movement between the restraint element, tension rod 130-1, and flak strap. However, the triangular lateral restraint element 430A employs a different configuration and mounting method than element 130A described herein. In fuel exchange machines for fuel racks holding Russian-type hexagonal fuel assemblies 30B, it is required that there are no protrusions that extend above the upper surface (horizontal plane) of the fuel rack to avoid interference. Therefore, the lateral restraint element 430A is configured to fit completely within the triangular flak strap 450, and three sides are directly welded to a slotted plate so that they do not protrude above the rack surface.

[0144] Each lateral restraint element 430A comprises a flat top surface 435A, an opposing flat bottom surface 435B, a mounting hole 435F extending between them, and an obliquely oriented peripheral side surface 435D. The corner portions 435M formed between the side surfaces can be chamfered as shown to improve fit into the flak strap 450. When mounted in a triangular flak strap 450, the top surface 435A may be at most flush with the upper edge 420A-1 of the three-slotted plate 420A defining the top or plane of the trap and rack, or slightly recessed downward (see, for example, Figure 50). The upper part of the lateral restraint element 430A or tension rod 130-1 does not protrude above the upper edge 420A-1 of the plate. To prevent the upper end of the threaded nut of the tension rod from protruding from the top surface of the rack, the upper end of the rod and the threaded nut 134 are recessed into the upper part of the rod mounting hole 435F, as shown in the figure. The hole 435F has a stepped cross-sectional shape in which the upper diameter is larger than the lower diameter. The lower diameter is smaller than the diameter of the nut but larger than the diameter of the rod, so that the lateral restraint element 430A can pass through (see also Figures 51 and 52). When the tension rod 130-1 is tightened and the stack of slotted plates 420A, 420B is compressed, the nut 134 cannot pass through the lower diameter and is pressed against the annular seating surface 435K formed within the hole 435F. Of course, the upper diameter of the hole 435F is larger than the rod and nut so that they fit completely inside the hole as described above.

[0145] Exemplary Claims

[0146] The following are exemplary claims relating to the aforementioned invention and its embodiments.

[0147] Exemplary Claim 1: A fuel rack for wet storage of nuclear fuel in a fuel pool, wherein the fuel rack comprises: Base plate; and A grid structure of linear plates extending vertically from the base plate along the Y-axis of a Cartesian coordinate system; The grid structure of the linear plate is provided, A plurality of vertically extending fuel storage cells, each of which has a horizontal cross-sectional profile configured to accommodate nuclear fuel assemblies within each of the plurality of vertically extending fuel storage cells; and A one-way flax strap configuration, wherein (1) flax straps exist between adjacent fuel storage cells in a first orthogonal direction along the X-axis of the orthogonal coordinate system, and (2) flax straps do not exist between adjacent fuel storage cells arranged in a second orthogonal direction along the Z-axis of the orthogonal coordinate system. A fuel rack that forms part of the structure.

[0148] Exemplary Claim 2: The fuel rack according to Claim 1, wherein the flax strap is sized such that the storage array has an effective K coefficient of less than 1 when the fuel rack is fully loaded with the storage array of the plurality of nuclear fuel assemblies.

[0149] Exemplary claim 3: The fuel rack according to claim 2, wherein each of the horizontal cross-sectional profiles of the fuel storage cell is configured to hold only a single nuclear fuel assembly.

[0150] Exemplary claim 4: The fuel rack according to claim 3, wherein a single plate separates adjacent cells of the fuel storage cells arranged in a second direction along the Z axis.

[0151] Exemplary claim 5: The fuel rack according to claim 2, wherein the horizontal cross-sectional profile of each cell is linear in shape, and each flak strap has a linear cross-sectional shape.

[0152] Exemplary claim 6: The fuel rack according to claim 2, wherein the cells and the flax straps are each elongated vertically and extend over the entire height of the cellular body.

[0153] Exemplary claim 7: The fuel rack according to any one of claims 2 to 6, wherein the grid structure of the plates comprises a plurality of slotted plates that are slidably connected and intersect orthogonally.

[0154] Exemplary claim 8: The slotted plate is A bottom section of a first slotted plate fixedly attached to the upper surface of the base plate, wherein the first slotted plate is welded to the base plate to form a lower welded portion; An intermediate section of a second slotted plate stacked on top of the bottom section of the aforementioned slotted plate, wherein the second slotted plate of the intermediate section is formed of a neutron-absorbing material containing boron; and An upper section of a third slotted plate stacked on top of the intermediate section of a second slotted plate, wherein the third slotted plates are welded together to form an upper weld. A fuel rack according to claim 7, comprising:

[0155] Exemplary claim 9: Furthermore Multiple vertically extending outer corner tension members, each corner tension member positioned at the corner of the fuel rack, and each corner tension member fixedly joined to the base plate by welding at its bottom end; and A plurality of horizontally extending and vertically spaced strap members, wherein the strap members are oriented perpendicular to the corner tension members, and each strap member is fixedly joined by welding at a first end to one of the corner tension members and at a second end to another of the corner tension members. A fuel rack according to claim 8, comprising:

[0156] Exemplary claim 10: The fuel rack according to claim 9, further comprising a centrally open upper girdle frame fixedly coupled to the upper girdle along the periphery of the upper weld, wherein the upper ends of the corner tension members are each welded to the upper girdle frame.

[0157] Exemplary claim 11: The fuel rack according to claim 9, further comprising a plurality of vertically extending internal tension members, each having an upper end connected to the upper weld and a bottom end connected to the base plate, wherein each of the internal tension members is positioned in one of the flax straps.

[0158] Exemplary claim 12: The fuel rack according to claim 11, wherein each internal tensioning member comprises a vertically elongated tensioning rod detachably connected to the upper weld via a lateral restraining element positioned to engage with the upper part of one of the flak straps.

[0159] Exemplary claim 13: The fuel rack according to claim 12, wherein the opposing upper and lower ends of each tension rod are threaded, the upper end of the tension rod is secured to the lateral restraint element via a threaded nut, and the lower end of the tension rod is secured to the base plate via a threaded nut.

[0160] Exemplary claim 14: The fuel rack according to any one of claims 8 to 13, wherein the second slotted plate is formed from an aluminum boron carbide metal matrix composite material that is metallurgically unsuitable for welding.

[0161] Exemplary claim 15: The fuel rack according to claim 14, wherein the second slotted plate of the intermediate section is made of aluminum boride and the first and third slotted plates are made of stainless steel.

[0162] Exemplary claim 16: The fuel rack according to any one of claims 8 to 14, wherein the lower weld comprises a single layer of horizontally spaced third slotted plates welded to the upper surface of the base plate, the single layer of slotted plates being oriented parallel to one another.

[0163] Exemplary claim 17: The fuel rack according to claim 16, wherein the base plate further comprises a plurality of horizontally spaced undergirder beams fixedly mounted to the bottom surface of the base plate, the undergirder beams being positioned on the floor of the fuel pool and configured to lift the base plate to form a flow plenum between the base plate and the floor.

[0164] Exemplary claim 18: The fuel rack according to claim 17, wherein the under girder beams are oriented parallel to each other and extend from one side of the base plate to the opposite side of the base plate.

[0165] Exemplary claim 19: The fuel rack according to claim 18, wherein the under girder beam is arranged orthogonally to the third slotted plate in the single layer on the upper surface of the base plate.

[0166] Exemplary claim 20: The fuel rack according to any one of claims 17 to 19, wherein each under girder beam comprises a plurality of flow holes, the flow holes being formed in the base plate at the bottom of each fuel storage cell and flax strap.

[0167] Exemplary claim 21: The fuel rack according to claim 17, wherein the under girder beam is made of a stainless steel bar having a straight cross-sectional shape, and the under girder beam is welded to the bottom surface of the base plate.

[0168] Exemplary claim 22: The fuel rack according to any one of claims 1 to 21, wherein each of the flak straps has a length and width that defines a gap between adjacent cells in a first direction along a first horizontal axis, and at least two of the flak straps have different widths from each other.

[0169] Exemplary claim 23: A fuel rack according to any one of claims 17 to 22, further comprising a plurality of pedestals hanging downward from the bottom surface of the base plate, each of which is configured to engage with the floor of the fuel pool and to lift the base plate above the floor.

[0170] Exemplary claim 24: The fuel rack according to claim 1, wherein the axial pitch between the fuel storage cells in two orthogonal X and Z directions is variable, and the flax strap in the second orthogonal direction is zero, resulting in a unidirectional flax strap configuration.

[0171] Exemplary claim 25: A fuel rack for wet storage of nuclear fuel in a fuel pool, wherein the fuel rack comprises: A base plate made of metal; A cell-shaped body extending from the base plate, the cell-shaped body comprising a plurality of fuel storage cells configured to accommodate fuel assemblies, the cell-shaped body comprising a vertical stack, the vertical stack, The bottom section of the first slotted plate, which is welded onto the base plate to form a bottom weld; An intermediate section, laminated on the bottom section and comprising a second slotted plate, wherein the second slotted plate is formed of a boron-containing material that functions as a neutron absorber, and the second slotted plate is mechanically bonded; The upper sections of the third slotted plate welded to each other to form an upper weld; and Multiple flax straps formed between at least some of the fuel storage cells A cellular body comprising; and Multiple tension members, each of the multiple tension members having an upper end connected to the upper weld and a lower end connected to the lower weld, and each of the tension members extending through one of the flax straps, A fuel rack equipped with a fuel rack.

[0172] Exemplary claim 26: The fuel rack according to claim 25, wherein each internal tensioning member comprises a vertically elongated tensioning rod detachably connected to the upper weld via a lateral restraining element configured to engage with the upper part of one of the flak straps.

[0173] Exemplary claim 27: The fuel rack according to claim 26, wherein the opposing upper and lower ends of each tension rod are threaded, the upper end of each tension rod is removably coupled to one of the lateral restraint elements via a threaded nut, and the lower end of each tension rod is removably coupled to the base plate via a threaded nut.

[0174] Exemplary claim 28: The fuel rack according to claim 27, wherein each of the internal tensioning members can be tightened by rotating a threaded nut to pull together the vertical stack of slotted plates and compressing the intermediate section of the second slotted plate between the lower weld and the upper weld.

[0175] Exemplary claim 29: The fuel rack according to claim 26, wherein each lateral restraint element is provided with a mounting hole for receiving the threaded upper end of the tension rod and for coupling to one of the threaded nuts on the upper surface of the lateral restraint element.

[0176] Exemplary claim 30: A fuel rack, The first, second, and third slotted plates form an orthogonal grid defining the fuel storage cells and the flax straps, and the fuel storage cells and the flax straps each have a linear cross-sectional shape. Each of the lateral restraint elements has a stepped bottom surface configured to lock-engage with one of the flak straps, thereby preventing relative lateral movement between the lateral restraint element, the tension rod, and the flak strap. The fuel rack according to claim 26.

[0177] Exemplary claim 31: The fuel rack according to claim 30, wherein the bottom surface of the lateral restraint element includes a circumferentially extending downward lip that engages with the upper end of a third slotted plate of the upper weld surrounding the upper part of each flak strap, and a downwardly extending locking projection that is receptively received within the flak strap.

[0178] Exemplary claim 32: Furthermore, A plurality of vertically extending outer corner tension members, each corner tension member positioned at the corner of the fuel rack, and each corner tension member having a bottom end fixedly connected to the base plate; and A plurality of strap members extending horizontally and spaced apart vertically, wherein the strap members are oriented perpendicular to the corner tension members, and each strap member has a first end fixedly attached to one of the corner tension members and a second end fixedly attached to another of the corner tension members. A fuel rack according to any one of claims 25 to 31, comprising:

[0179] Exemplary claim 33: The fuel rack according to claim 32, further comprising an upper girdle frame with a central opening, wherein the upper girdle frame is fixedly coupled to the upper weld along the periphery of the upper girdle frame, and the upper ends of the corner tension members are each fixedly coupled to the upper girdle frame.

[0180] Exemplary claim 34: A fuel rack, The first, second, and third slotted plates form a hexagonal grid defining the fuel storage cells and the flax straps, the fuel storage cells having a hexagonal cross-sectional shape, and each of the flax straps having a triangular cross-sectional shape. The fuel rack according to claim 26, wherein each of the lateral restraint elements is triangular in shape and is welded to a third slotted plate in the upper weld on the inside of the flak strap, so that the lateral restraint elements do not protrude above the upper plate of the upper weld.

[0181] Exemplary claim 35: A method for assembling a fuel rack for underwater storage of nuclear fuel in a fuel pool, comprising the following steps: A step of forming a lower weld and an upper weld, wherein the lower weld comprises a base plate and a plurality of first slotted plates welded to the base plate, and the upper weld comprises a plurality of third slotted plates welded to each other; A process of stacking multiple second slotted plates on top of a first slotted plate, wherein the second slotted plates are mechanically joined together; A step of stacking the aforementioned upper welded portion on top of the second slotted plate; A process of collectively defining a plurality of fuel storage cells, each configured to hold a nuclear fuel assembly, and a plurality of flax straps positioned between at least some of the cells, using first, second, and third slotted plates; A step of inserting elongated tension members into at least some of the aforementioned flax straps; A step of joining the upper end of each tension member to the upper welded portion; A step of joining the bottom end of each tension member to the lower welded portion; A step of generating tension in the tension member; A step of pulling the upper weld and the lower weld towards each other via the tension member; and A step of compressing the second slotted plate between the upper weld and the lower weld.

[0182] Exemplary claim 36: The method of claim 35, wherein the step of connecting the upper end of each tension member to the upper weld comprises screwing the threaded upper end of the tension member to the lateral restraint element engaged with the upper weld.

[0183] Exemplary claim 37: The method according to claim 36, wherein the step of connecting the bottom end of each tension member to the lower weld includes screwing the threaded bottom end of the tension member to the lower weld.

[0184] Exemplary claim 38: The method according to claim 37, wherein each tension member has a lock nut screwed into the upper part of the tension member and a lock nut engaged into the bottom end of the tension member.

[0185] Exemplary claim 39: The method of claim 38, wherein the step of generating tension in the tension members includes the step of tightening one or both of the lock nuts on each tension member.

[0186] Exemplary claim 40: The method according to any one of claims 38 to 39, wherein the tension member is a tension rod, the lateral restraint element is a plate with mounting holes, and the threaded upper end of each tension rod is inserted into the mounting holes and engages with one of the lock nuts.

[0187] Exemplary claim 41: A fuel rack for wet storage of nuclear fuel in a fuel pool, wherein the fuel rack comprises: Base plate; A grid structure of plates extending from the base plate, wherein the grid structure of plates is Multiple fuel storage cells, each of which has a horizontal cross-sectional profile configured to accept a single nuclear fuel assembly. A grid structure of plates that forms; and A flax strap configuration, wherein (1) flax straps exist between some adjacent cells of the fuel storage cell, and (2) flax straps do not exist between other adjacent cells of the fuel storage cell, and the flax straps are sized such that when the fuel rack is filled with an array of stored nuclear fuel assemblies, the K effective coefficient of the stored array is less than 1. A fuel rack equipped with a fuel rack.

[0188] Exemplary claim 42: A method for manufacturing a fuel rack for wet storage of nuclear fuel in a fuel pool, A step of preparing a base plate having an upper main surface, a bottom main surface, and a side edge extending between the upper main surface and the bottom main surface; A step of welding a plurality of first slotted plates to the upper surface of a base plate in a substantially parallel arrangement to one another, wherein each of the plurality of first slotted plates comprises a first main side surface and a second main side surface, and each of the first and second main side surfaces is perpendicular to the upper main surface of the base plate; and A process of welding multiple undergirder beams to the bottom surface of the base plate in a substantially parallel arrangement to each other, thereby forming a lower welded portion. A method that includes this.

[0189] Exemplary claim 43: The method according to claim 42, wherein each of the plurality of slotted plates extends along the plate axis, and each of the plurality of under-girder beams extends along the beam axis, the beam axis being perpendicular to the plate axis.

[0190] Exemplary claim 44: The method according to claim 43, wherein each of the undergirder beams has a continuum extending from one side of the base plate to the opposite side of the base plate.

[0191] Exemplary claim 45: The method according to claim 43, wherein the under girder beam protrudes downward from the bottom surface of the base plate to form a plenum beneath the base plate.

[0192] Exemplary claim 46: The method according to any one of claims 42 to 45, wherein the under-girder beam comprises a plurality of flow holes.

[0193] Exemplary claim 47: The method according to claim 43, wherein the slotted plate is welded to the upper surface of the base plate and the under girder beam is welded to the bottom surface of the base plate.

[0194] Exemplary claim 48: The method according to claim 47, wherein the base plate, the slotted plate, and the under girder beam are formed of stainless steel.

[0195] Exemplary claim 49: The method according to any one of claims 42 to 48, further comprising the step of joining a plurality of bases to the bottom surface of the base plate.

[0196] Exemplary claim 50: Furthermore A step of stacking a grid array of second slotted plates formed from a boron-containing metal matrix composite material on the lower weld, wherein the second slotted plates are metallurgically incompatible for welding to the first slotted plates of the lower weld; and A process of stacking a grid array of third slotted plates on top of a second slotted plate, wherein the third slotted plates are welded together. The method according to any one of claims 42 to 49, wherein the first, second, and third slotted plates collectively define a plurality of fuel storage cells, each configured to hold a nuclear fuel assembly.

[0197] Exemplary claim 51: The method according to claim 50, further comprising the steps of forming a plurality of flax straps between at least some cells in a first orthogonal direction, and not forming a plurality of flax straps between the cells in a second orthogonal direction.

[0198] Exemplary claim 52: A method for manufacturing a fuel rack for wet storage of an array of nuclear fuel assemblies in a fuel pool, wherein each nuclear fuel assembly in the array is stored in a fuel storage cell, the method a) A step of varying the axial pitch between adjacent fuel storage cells in two orthogonal directions, wherein the dimensions of the flax strap in one of the orthogonal directions are adjusted until the K effective coefficient of the array is less than 1, thereby determining a unidirectional flax strap configuration; and b) Steps to construct the fuel rack having the unidirectional flax strap configuration. Methods that include...

[0199] Exemplary claim 53: The method of claim 52, wherein the dimension of the flax strap in the other of the orthogonal directions is kept at zero during step a).

[0200] Exemplary claim 54: A fuel rack for wet storage of nuclear fuel in a fuel pool, wherein the fuel rack is A lower weld comprising a base plate, a plurality of first slotted plates welded to the upper surface of the base plate, and a plurality of under girder beams fixedly bonded to the bottom surface of the base plate; An intermediate section comprising a grid structure of a second slotted plate, wherein the second slotted plate is formed of a boron-containing metal matrix composite; Upper weld section including the grid structure of the third slotted plate; The intermediate section sandwiched between the upper weld and the lower weld, the first slotted plate, the grid structure of the second slotted plate, and the grid structure of the third slotted plate, which collectively define a plurality of fuel storage cells, each configured to hold a nuclear fuel assembly; and Multiple vertically elongated tension members, each including an upper end connected to the upper weld and a lower end connected to the lower weld. A fuel rack equipped with a fuel rack.

[0201] Exemplary claim 55: The fuel rack according to claim 54, wherein the tension members include corner tension members, one of each corner tension members being positioned at a corner of the fuel rack.

[0202] Exemplary claim 56: The fuel rack according to claim 55, further comprising a plurality of strap members extending horizontally and spaced apart vertically, wherein the strap members are oriented perpendicular to the corner tension members, and each strap member is fixedly coupled at a first end to one of the corner tension members and at a second end to another of the corner tension members.

[0203] Exemplary claim 57: The fuel rack according to claim 56, further comprising a centrally open upper girdle frame fixedly coupled to the upper girdle along the periphery of the upper weld, wherein the upper ends of the corner tension members are each fixedly coupled to the upper girdle frame.

[0204] Exemplary claim 58: The fuel rack according to claim 55 or 56, wherein the tension member further comprises a plurality of internal tension members extending vertically between the fuel storage cells, each internal tension member being positioned in one of a plurality of vertically extending flax straps formed between at least some of the fuel storage cells of the fuel rack.

[0205] Exemplary claim 59: The fuel rack according to claim 58, wherein each internal tensioning member comprises a vertically elongated tensioning rod having an upper end detachably coupled to the upper weld via a lateral restraining element that engages with the upper part of one of the flak straps, and a lower end detachably coupled to the base plate.

[0206] Exemplary claim 60: The fuel rack according to any one of claims 54 to 59, wherein the first slotted plate and the third slotted plate are made of stainless steel.

[0207] Although the above description and drawings represent embodiments of the present invention, 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 equivalents. In particular, it will be apparent to those skilled in the art that the present invention can be embodied in materials and components, along with other forms, structures, arrangements, proportions, sizes, and other elements, without departing from its spirit or essential features. Furthermore, many variations of the applicable methods / processes described herein can be made without departing from the spirit of the present invention. Those skilled in the art will further understand that the present invention can be used with many modifications to adapt the structures, arrangements, proportions, sizes, materials, and components used in the implementation of the present invention to particularly specific environmental and operational requirements, without departing from the principles of the present invention. Accordingly, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive, and the scope of the present invention is defined by the appended claims and equivalents and is not limited to the above description or embodiments. Rather, the appended claims should be interpreted broadly to include other variations of the present invention that can be made by those skilled in the art without departing from the scope of the equivalents of the present invention.

Claims

1. A fuel rack for wet storage of nuclear fuel in a fuel pool, wherein the fuel rack is Base plate; and A grid structure of linear plates extending vertically from the base plate along the Y-axis of the Cartesian coordinate system; The grid structure of the linear plate is provided, A plurality of vertically extending fuel storage cells, each of which has a horizontal cross-sectional profile configured to accommodate nuclear fuel assemblies within each of the plurality of vertically extending fuel storage cells; and A one-way flax strap configuration, wherein (1) flax straps exist between adjacent fuel storage cells in a first orthogonal direction along the X-axis of the orthogonal coordinate system, and (2) flax straps do not exist between adjacent fuel storage cells arranged in a second orthogonal direction along the Z-axis of the orthogonal coordinate system. A fuel rack that forms part of the structure.

2. The fuel rack according to claim 1, wherein the flax strap is sized such that the storage array has an effective K coefficient of less than 1 when the fuel rack is fully loaded with the storage array of the plurality of nuclear fuel assemblies.

3. The fuel rack according to claim 2, wherein each of the horizontal cross-sectional profiles of the fuel storage cell is configured to hold only a single nuclear fuel assembly.

4. The fuel rack according to claim 3, wherein a single plate separates adjacent cells of the fuel storage cells arranged in a second direction along the Z-axis.

5. The fuel rack according to claim 2, wherein the horizontal cross-sectional profile of each cell is linear in shape, and each flax strap has a linear cross-sectional shape.

6. The fuel rack according to claim 2, wherein the cells and flax straps are each elongated in the vertical direction and extend across the entire height of the cell-shaped body.

7. The fuel rack according to any one of claims 2 to 6, wherein the grid structure of the plate comprises a plurality of slotted plates that are slidably connected and intersect orthogonally.

8. The aforementioned slotted plate A bottom section of a first slotted plate fixedly attached to the upper surface of the base plate, wherein the first slotted plate is welded to the base plate to form a lower welded portion; An intermediate section of a second slotted plate stacked on top of the bottom section of the aforementioned slotted plate, wherein the second slotted plate of the intermediate section is formed of a neutron-absorbing material containing boron; and An upper section of a third slotted plate stacked on top of the intermediate section of a second slotted plate, wherein the third slotted plates are welded together to form an upper weld. A fuel rack according to claim 7, comprising:

9. moreover A plurality of vertically extending outer corner tension members, each corner tension member positioned at the corner of the fuel rack, and each corner tension member fixedly joined to the base plate by welding at its bottom end; and A plurality of horizontally extending and vertically spaced strap members, wherein the strap members are oriented perpendicular to the corner tension members, and each strap member is fixedly joined by welding at a first end to one of the corner tension members and at a second end to another of the corner tension members. A fuel rack according to claim 8, comprising:

10. Furthermore, the fuel rack according to claim 9, further comprising a centrally open upper girdle frame fixedly coupled to the upper weld along the periphery of the upper weld, and the upper ends of the corner tension members each welded to the upper girdle frame.

11. Furthermore, the fuel rack according to claim 9 comprises a plurality of vertically extending internal tension members, each having an upper end connected to the upper weld and a bottom end connected to the base plate, wherein each of the internal tension members is positioned on one of the flax straps.

12. The fuel rack according to claim 11, wherein each internal tensioning member comprises a vertically elongated tensioning rod detachably connected to the upper weld via a lateral restraining element positioned to engage with the upper part of one of the flak straps.

13. The fuel rack according to claim 12, wherein the opposing upper and lower ends of each tension rod are threaded, the upper end of the tension rod is fixed to the lateral restraint element via a screw nut, and the lower end of the tension rod is fixed to the base plate via a screw nut.

14. The fuel rack according to any one of claims 8 to 13, wherein the second slotted plate is formed from an aluminum boron carbide metal matrix composite material that is metallurgically unsuitable for welding.

15. The fuel rack according to claim 14, wherein the second slotted plate of the intermediate section is made of aluminum boride, and the first and third slotted plates are made of stainless steel.

16. The fuel rack according to any one of claims 8 to 14, wherein the lower welded portion comprises a single layer of third slotted plates welded to the upper surface of the base plate and arranged at horizontal intervals, the single layer of slotted plates being oriented parallel to one another.

17. The fuel rack according to claim 16, wherein the base plate further comprises a plurality of horizontally spaced undergirder beams fixedly attached to the bottom surface of the base plate, the undergirder beams being positioned on the floor of the fuel pool and configured to lift the base plate to form a flow plenum between the base plate and the floor.

18. The fuel rack according to claim 17, wherein the under girder beams are oriented parallel to each other and extend from one side of the base plate to the opposite side of the base plate.

19. The fuel rack according to claim 18, wherein the under girder beam is arranged perpendicular to the third slotted plate in the single layer on the upper surface of the base plate.

20. The fuel rack according to any one of claims 17 to 19, wherein each under girder beam is provided with a plurality of flow holes, and the flow holes are formed in the base plate at the bottom of each fuel storage cell and flax strap.

21. The fuel rack according to claim 17, wherein the under girder beam is made of a stainless steel bar having a straight cross-sectional shape, and the under girder beam is welded to the bottom surface of the base plate.

22. The fuel rack according to any one of claims 1 to 21, wherein each of the flak straps has a length and width that defines a gap between adjacent cells in a first direction along a first horizontal axis, and at least two of the flak straps have different widths from each other.

23. The fuel rack according to any one of claims 17 to 22, further comprising a plurality of pedestals hanging downward from the bottom surface of the base plate, each pedestal engaging with the floor of the fuel pool and configured to lift the base plate above the floor.

24. The fuel rack according to claim 1, wherein the axial pitch between the fuel storage cells in two orthogonal X and Z directions is variable, and the flax strap in the second orthogonal direction becomes zero, resulting in a unidirectional flax strap configuration.

25. A fuel rack for wet storage of nuclear fuel in a fuel pool, wherein the fuel rack is A base plate made of metal; A cell-shaped body extending from the base plate, the cell-shaped body comprising a plurality of fuel storage cells configured to accommodate fuel assemblies, the cell-shaped body comprising a vertical stack, the vertical stack, The bottom section of the first slotted plate, which is welded onto the base plate to form a bottom weld; An intermediate section laminated on the bottom section and comprising a second slotted plate, wherein the second slotted plate is formed of a boron-containing material that functions as a neutron absorber, and the second slotted plate is mechanically bonded; Upper sections of third slotted plates welded to each other to form an upper weld; and Multiple flax straps formed between at least some of the fuel storage cells A cellular body comprising; and Multiple tension members, each of the multiple tension members having an upper end connected to the upper weld and a lower end connected to the lower weld, and each of the tension members extending through one of the flax straps, A fuel rack equipped with a fuel rack.

26. The fuel rack according to claim 25, wherein each internal tensioning member comprises a vertically elongated tensioning rod detachably connected to the upper weld via a lateral restraining element configured to engage with the upper part of the flak strap.

27. The fuel rack according to claim 26, wherein the opposing upper and lower ends of each tension rod are threaded, the upper end of each tension rod is detachably connected to one of the lateral restraint elements via a threaded nut, and the lower end of each tension rod is detachably connected to the base plate via a threaded nut.

28. The fuel rack according to claim 27, wherein each of the internal tension members can be tightened by rotating a threaded nut to pull together the vertical stack of slotted plates and compressing the intermediate section of the second slotted plate between the lower weld and the upper weld.

29. The fuel rack according to claim 26, wherein each lateral restraint element is provided with a mounting hole for receiving the threaded upper end of the tension rod and for coupling to one of the threaded nuts on the upper surface of the lateral restraint element.

30. It is a fuel rack. The first, second, and third slotted plates form an orthogonal grid defining the fuel storage cells and the flax straps, and the fuel storage cells and the flax straps each have a linear cross-sectional shape. Each of the lateral restraint elements has a stepped bottom surface configured to lock-engage with one of the flak straps, thereby preventing relative lateral movement between the lateral restraint element, the tension rod, and the flak strap. The fuel rack according to claim 26.

31. The fuel rack according to claim 30, wherein the bottom surface of the lateral restraint element includes a circumferentially extending downward lip that engages with the upper end of a third slotted plate of the upper weld surrounding the upper part of each flak strap, and a downwardly extending locking projection that is receptively received within the flak strap.

32. moreover, A plurality of vertically extending outer corner tension members, each corner tension member positioned at the corner of the fuel rack, and each corner tension member having a bottom end fixedly connected to the base plate; and A plurality of strap members extending horizontally and spaced apart vertically, wherein the strap members are oriented perpendicular to the corner tension members, and each strap member has a first end fixedly attached to one of the corner tension members and a second end fixedly attached to another of the corner tension members. A fuel rack according to any one of claims 25 to 31, comprising:

33. Furthermore, the fuel rack according to claim 32, comprising an upper girdle frame with an open center, wherein the upper girdle frame is fixedly connected to the upper welded portion along the periphery of the upper girdle frame, and the upper ends of the corner tension members are each fixedly connected to the upper girdle frame.

34. It is a fuel rack, The first, second, and third slotted plates form a hexagonal grid defining the fuel storage cells and the flax straps, the fuel storage cells having a hexagonal cross-sectional shape, and each of the flax straps having a triangular cross-sectional shape. The fuel rack according to claim 26, wherein each of the lateral restraint elements is triangular in shape and is welded to a third slotted plate in the upper weld on the inside of the flak strap, so that the lateral restraint elements do not protrude above the upper plate of the upper weld.

35. A method for assembling fuel racks for underwater storage of nuclear fuel in a fuel pool, comprising the following steps: A step of forming a lower weld and an upper weld, wherein the lower weld comprises a base plate and a plurality of first slotted plates welded to the base plate, and the upper weld comprises a plurality of third slotted plates welded to each other; A step of stacking multiple second slotted plates on top of a first slotted plate, wherein the second slotted plates are mechanically joined together; A step of stacking the upper welded portion on top of the second slotted plate; The process of collectively defining a plurality of fuel storage cells, each configured to hold a nuclear fuel assembly, and a plurality of flax straps positioned between at least some of the cells, using first, second, and third slotted plates; A step of inserting elongated tension members into at least some of the aforementioned flax straps; A step of joining the upper end of each tension member to the upper welded portion; A step of joining the bottom end of each tension member to the lower welded portion; A step of generating tension in the tension member; A step of pulling the upper weld and the lower weld towards each other via the tension member; and A step of compressing the second slotted plate between the upper weld and the lower weld.

36. The method according to claim 35, wherein the step of connecting the upper end of each tension member to the upper weld portion includes screwing the threaded upper end of the tension member to the lateral restraint element engaged with the upper weld portion.

37. The method according to claim 36, wherein the step of connecting the bottom end of each tension member to the lower welded portion includes screwing the threaded bottom end of the tension member to the lower welded portion.

38. The method according to claim 37, wherein each tension member has a lock nut screwed into the upper part of the tension member and a lock nut screwed into the lower end of the tension member.

39. The method according to claim 38, wherein the step of generating tension in the tension member includes the step of tightening one or both of the lock nuts on each tension member.

40. The method according to any one of claims 38 to 39, wherein the tensioning member is a tension rod, the lateral restraining element is a plate with mounting holes, and the threaded upper end of each tension rod is inserted into the mounting holes and engages with one of the lock nuts.

41. A fuel rack for wet storage of nuclear fuel in a fuel pool, wherein the fuel rack is Base plate; A grid structure of plates extending from the base plate, wherein the grid structure of plates is Multiple fuel storage cells, each of which has a horizontal cross-sectional profile configured to accept a single nuclear fuel assembly. A grid structure of plates that forms; and A flax strap configuration, wherein (1) flax straps exist between some adjacent cells of the fuel storage cell, and (2) flax straps do not exist between other adjacent cells of the fuel storage cell, and the flax straps are sized such that when the fuel rack is filled with an array of stored nuclear fuel assemblies, the K effective coefficient of the stored array is less than 1. A fuel rack equipped with a fuel rack.

42. A method for manufacturing a fuel rack for wet storage of nuclear fuel in a fuel pool, A step of preparing a base plate having an upper main surface, a bottom main surface, and a side edge extending between the upper main surface and the bottom main surface; A step of welding a plurality of first slotted plates to the upper surface of a base plate in a substantially parallel arrangement to one another, wherein each of the plurality of first slotted plates comprises a first main side surface and a second main side surface, and each of the first and second main side surfaces is perpendicular to the upper main surface of the base plate; and A process of welding multiple undergirder beams to the bottom surface of the base plate in a substantially parallel arrangement to each other, thereby forming a lower welded portion. A method that includes this.

43. The method according to claim 42, wherein each of the plurality of slotted plates extends along the plate axis, and each of the plurality of under-girder beams extends along the beam axis, the beam axis being perpendicular to the plate axis.

44. The method according to claim 43, wherein each of the under girder beams has a continuum extending from one side of the base plate to the opposite side of the base plate.

45. The method according to claim 43, wherein the under girder beam protrudes downward from the bottom surface of the base plate and forms a plenum below the base plate.

46. The method according to any one of claims 42 to 45, wherein the under-girder beam is provided with a plurality of flow path holes.

47. The method according to claim 43, wherein the slotted plate is welded to the upper surface of the base plate, and the under girder beam is welded to the bottom surface of the base plate.

48. The method according to claim 47, wherein the base plate, the slotted plate, and the under girder beam are made of stainless steel.

49. The method according to any one of claims 42 to 48, further comprising the step of joining a plurality of bases to the bottom surface of the base plate.

50. moreover A step of stacking a grid array of second slotted plates formed from a boron-containing metal matrix composite material on the lower weld, wherein the second slotted plates are metallurgically incompatible for welding to the first slotted plates of the lower weld; and A process of stacking a grid array of third slotted plates on top of a second slotted plate, wherein the third slotted plates are welded together. The method according to any one of claims 42 to 49, wherein the first, second, and third slotted plates collectively define a plurality of fuel storage cells, each configured to hold a nuclear fuel assembly.

51. The method according to claim 50, further comprising the steps of forming a plurality of flax straps between at least some cells in a first orthogonal direction, and not forming a plurality of flax straps between the cells in a second orthogonal direction.

52. A method for manufacturing a fuel rack for wet storage of an array of nuclear fuel assemblies in a fuel pool, wherein each nuclear fuel assembly in the array is stored in a fuel storage cell, and the method a) A step of varying the axial pitch between adjacent fuel storage cells in two orthogonal directions, wherein the dimensions of the flax strap in one of the orthogonal directions are adjusted until the K effective coefficient of the array is less than 1, thereby determining a unidirectional flax strap configuration; and b) Steps to construct the fuel rack having the one-way flax strap configuration. Methods that include...

53. The method according to claim 52, wherein during step a), the dimension of the flax strap in the other of the orthogonal directions is kept at zero.

54. A fuel rack for wet storage of nuclear fuel in a fuel pool, wherein the fuel rack is A lower weld comprising a base plate, a plurality of first slotted plates welded to the upper surface of the base plate, and a plurality of under girder beams fixedly bonded to the bottom surface of the base plate; An intermediate section comprising a grid structure of a second slotted plate, wherein the second slotted plate is formed of a boron-containing metal matrix composite; Upper weld including the grid structure of the third slotted plate; The intermediate section sandwiched between the upper weld and the lower weld, the first slotted plate, the grid structure of the second slotted plate, and the grid structure of the third slotted plate, which collectively define a plurality of fuel storage cells, each configured to hold a nuclear fuel assembly; and Multiple vertically elongated tension members, each including an upper end connected to the upper weld and a lower end connected to the lower weld. A fuel rack equipped with a fuel rack.

55. The fuel rack according to claim 54, wherein the tension member includes a corner tension member, and one of the corner tension members is positioned at each corner of the fuel rack.

56. The fuel rack according to claim 55, further comprising a plurality of strap members extending horizontally and spaced apart vertically, wherein the strap members are oriented perpendicular to the corner tension members, and each strap member is fixedly coupled at a first end to one of the corner tension members and at a second end to another of the corner tension members.

57. The fuel rack according to claim 56, further comprising a centrally open upper girdle frame fixedly connected to the upper weld along the periphery of the upper weld, wherein the upper ends of the corner tension members are each fixedly connected to the upper girdle frame.

58. The fuel rack according to claim 55 or 56, wherein the tension member further comprises a plurality of internal tension members extending vertically between the fuel storage cells, each internal tension member being positioned in one of a plurality of vertically extending flax straps formed between at least some of the fuel storage cells of the fuel rack.

59. The fuel rack according to claim 58, wherein each internal tensioning member comprises a vertically elongated tension rod having an upper end detachably coupled to the upper weld via a lateral restraining element that engages with the upper part of one of the flak straps, and a lower end detachably coupled to the base plate.

60. The fuel rack according to any one of claims 54 to 59, wherein the first slotted plate and the third slotted plate are made of stainless steel.

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