JP-2026514382-A - Fuel storage rack system for underwater storage of spent nuclear fuel

Abstract

[Solution] 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. The 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. [Selection Diagram] Figure 2

Inventors

• シン、クリシュナ ピー
• アゲイス、スティーブン ジェイ

Assignees

• ホルテック インターナショナル

Dates

Publication Date

20260511

Application Date

20240328

Priority Date

20230328

Claims (20)

1. A fuel rack for wet storage of nuclear fuel in a fuel pool, wherein the fuel rack is A base plate; and a grid structure of linear plates extending perpendicularly 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 unidirectional flax strap configuration, the unidirectional flax strap configuration forming a unidirectional flax strap configuration, wherein (1) flax straps exist between adjacent cells of the 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 cells of the fuel storage cells arranged in a second orthogonal direction along the Z-axis of the orthogonal coordinate system.
2. The fuel rack according to claim 1, wherein the flax strap is sized such that when the fuel rack is fully loaded with the storage array of the plurality of nuclear fuel assemblies, the storage array has an effective K coefficient of less than 1.
3. The fuel rack according to claim 2, wherein each of the horizontal cross-sectional profiles of the fuel storage cells 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 vertically 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 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 weld; The fuel rack according to claim 7, comprising: an intermediate section of a second slotted plate stacked on top of the bottom section of the 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 the second slotted plate, wherein the third slotted plates are welded to each other to form an upper weld.
9. The fuel rack according to claim 8, further comprising: a plurality of vertically extending outer corner tension members, each corner tension member positioned at a 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, each strap member oriented perpendicularly to the corner tension members, and each strap member fixedly joined to one of the corner tension members by welding at a first end and to another of the corner tension members at a second end.
10. Furthermore, the fuel rack according to claim 9, comprising a centrally open upper girdle frame fixedly connected 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 its upper end connected to the upper weld and its bottom end connected to the base plate, with each of the internal tension members positioned on one of the flax straps.
12. The fuel rack according to claim 11, wherein each internal tensioning member comprises a vertically elongated tension rod detachably connected to the upper weld via a lateral restraining element positioned to engage with the upper part of the flak strap.
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 threaded nut, and the lower end of the tension rod is fixed to the base plate via a threaded 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 formed 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 each other.
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 and form a flow plenum between the base plate and the floor.
18. The fuel rack according to claim 17, wherein the undergirder 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 path holes, and the flow path holes are formed in the base plate at the bottom of each fuel storage cell and flax strap.

Description

This application, which cross-references related applications , claims priority to U.S. Provisional Patent Application No. 63/558,778, filed on 28 February 2024, and U.S. Provisional Patent Application No. 63/492,586, filed on 28 March 2023, the entire contents of which are incorporated herein by reference. Technical field This invention relates to a fuel storage rack system for underwater storage of spent nuclear fuel. This invention generally relates to a system for wet storage of spent nuclear fuel (SNF) in water, and more particularly to an improved nuclear fuel storage rack system for use in the fuel pools of nuclear power plants. In light water reactors, the standard practice is 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/lateral pitch, based on the reactivity limits permitted by nuclear regulatory guidelines. Conventional self-supporting, 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 these structures, defining the array of fuel storage cells, are welded to a common base plate installed on the fuel pool floor. This base plate acts as a support structure, bearing the weight of the cell structural members and the fuel assemblies stored within them, transferring the weight load to the reinforced concrete floor of the fuel pool. Each cell comprises a vertically elongated prismatic cavity, the cross-sectional area and height of which are sized to accommodate only a single nuclear fuel assembly containing multiple new or spent fuel rods. 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 region is the most radioactive (reactive) area within the fuel rack. The upper and lower ends of the rack are less reactive regions. Fuel racks used to store spent nuclear fuel assemblies hold the fuel assemblies upright in a water pool. This serves to dissipate the generated heat, 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. Fuel assemblies used in most Russian-origin reactors are elongated structures with a hexagonal cross-section. To store hexagonal 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 positioned higher than the pool liner (floor or bottom slab) so that a water-filled space (water plenum) is formed below the rack. The rack design must allow for the supply of chilled water to the space around the fuel and between the fuel rods by natural convection and thermal siphon action. Fuel assemblies used in Western-style reactors also have an elongated structure, but they have a linear (for example, square) cross-sectional shape. Storing this type of fuel assembly requires cells with a corresponding linear cross-sectional shape. Because the available floor space in the fuel pool 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 densely packed with multiple uranium fuel rods, are arranged vertically within the fuel storage cells of the fuel racks. By minimizing the lateral gaps between cells, as many fuel assemblies as possible can be accommodated in each rack, and simultaneously, as many fuel racks as possible can be accommodated in the fuel pool, high-density SNF storage is achieved. Conventional fuel rack designs have relied on stainless steel cell structures to provide 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, thereby controlling neutron transmission and, consequently, 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. The minimum permissible spacing between storage cells within each fuel rack is controlled by the reactivity of the fuel within the fuel assembly and the availability of B-10 (boron-10 isotope) content in the neutron absorber. T