KR20220028262A - Bottom spacer grid of a nuclear fuel assembly - Google Patents

Abstract

The present invention relates to a bottom spacer grid of a nuclear fuel assembly with a foreign material filtering function, which can be manufactured by using three-dimensional printing with a high degree of design freedom while excluding sheet metal processing and welding processing. A bottom spacer grid (100) of a nuclear fuel assembly of the present invention allows square lattice cells (110) having an inner lattice surface to form a square lattice. The lattice cell (110) comprises: a spring (120) which is formed, to protrude in the longitudinal direction, on each of four inner lattice surfaces (111), to support a fuel rod (10); and a foreign material filtering unit (130) which is formed to protrude in at least one transverse direction within the range of a longitudinal section (h1) in which the spring (120) is formed.

Description

Bottom spacer grid of a nuclear fuel assembly

The present invention relates to a lower space grid of a nuclear fuel assembly having a foreign material filtering function that can be manufactured using 3D printing with a high degree of design freedom while excluding sheet metal processing and welding processing.

Nuclear fuel used in nuclear reactors is manufactured into fuel rods by charging enriched uranium into cylindrical pellets of a certain size, and then charging a number of sintered bodies in a cladding tube. It is then combusted through a nuclear reaction.

In general, a nuclear fuel assembly includes a plurality of fuel rods disposed in the axial direction, a plurality of spacer grids provided in the transverse direction of the fuel rods to support the fuel rods, a plurality of guide tubes fixed to the spacer grid to constitute the skeleton of the assembly; It consists of an upper fixture and a lower fixture that support the upper and lower ends of the guide tube, respectively.

The spacer grid is one of the important parts of the nuclear fuel assembly that maintains the arrangement of the fuel rods by restraining the lateral movement of the fuel rod and suppressing the axial movement by frictional force. These spacer grids have different shapes and numbers depending on the type and design of the reactor, but are divided into a protective spacer grid, a lower spacer grid, an upper spacer grid, and an intermediate spacer grid according to the assembly position with the fuel rod, and are assembled vertically crosswise. The structure to provide a grid cell in which the fuel rod is inserted is the same as that of a plurality of grid plates.

In particular, the lower spacer grid is located at the bottom of the spacer grids and is disposed immediately adjacent to the lower fixed body, and a function of filtering foreign substances introduced into the reactor together with the cooling water during the cooling water circulation process may be required.

Various kinds of foreign substances may be mixed in the coolant circulating in the nuclear reactor, and these foreign substances may pass through the flow path of the lower fixture to cause vibration between the fuel rod and the spacer grid and damage the fuel rod.

As a method of filtering foreign substances mixed in the cooling water, a function to filter foreign substances can be added to the lower space grid, or the size of the flow path of the lower fixture can be limited, Methods using a combination of lower space grids are being used.

In the method of limiting the size of the flow path of the lower fixture, the pressure drop of the coolant increases due to the reduction of the flow passage area. The pressing force must be increased, the vibration of the fuel rod can be intensified, the lateral flow of the coolant is induced, so fretting wear is promoted, and various problems can occur in that the heat of the fuel rod is not sufficiently absorbed.

The method of adding a filtering function capable of filtering foreign substances to the lower space grid itself has the advantage of increasing the foreign material filtering performance and relatively reducing the pressure drop, but the structure is complicated and manufacturing is difficult.

In general, a lower spacer grid having a filtering function includes a grid spring that elastically supports the fuel rod in the grid cell, a dimple for limiting horizontal movement of the fuel rod, and a foreign material filtering unit capable of filtering foreign substances mixed in the coolant.

In general, the grid spring, the dimple, and the foreign material filtering unit are formed by sheet metal processing of the spacer grid plate constituting each grid cell, and a grid spring is provided on two surfaces facing each other among the grid cells of four sides, respectively, and the remaining two A plurality of dimples are provided on the surface.

Specifically, in the manufacturing process of the spacer grid, after assembling and fixing each inner grid plate and the outer grid plate processed by sheet metal to a separately provided welding jig, the cross welding of the inner grid, the joint of the inner/outer grid, and the sleeve joint are laser welded (Laser Welding). ) or by brazing using filler metal, it is manufactured through a series of processes of grinding and processing the weld bead generated during the welding process of the external grid plate.

As described above, in the conventional manufacturing process of the spacer grid, there are many series of processes such as the sheet metal process and the welding process, and the shape design technology is quite difficult because the structure for filtering foreign substances is applied to the lower spacer grid, and there are many restrictions on the degree of design freedom. This happens.

In general, it has been reported that the impact strength of the space grid is very low at the end of life (EOL) condition. A technology for securing nuclear fuel seismic performance and mechanical soundness in the EOL condition is inevitably required. As described above, the conventional method for manufacturing the lower space grid has many restrictions on shape design, so it is sufficiently stable and high strength under the EOL condition. There is a limit to realizing a lower space grid with

Patent Document 1: US Patent No. 4,652,425 (Patent date: March 24, 1987) Patent Document 2: Korean Patent Publication No. 10-2010-0076465 (published date: 2010.07.06.)

The present invention is to improve the problems of the prior art, and the lower support of a nuclear fuel assembly having a foreign material filtering function that can be manufactured using 3D printing that can exclude sheet metal and welding processes, increase design freedom, and simplify the manufacturing process It is intended to provide a grid.

In particular, an object of the present invention is to provide a lower spacer grid of a nuclear fuel assembly in which a spring for elastically supporting a fuel rod and a foreign material filtering structure are disposed at the same height and a separate dimple is excluded, thereby reducing the height of the spacer grid.

In order to achieve this object, in the lower space lattice of the nuclear fuel assembly according to the present invention, square lattice cells having inner lattice surfaces form a square lattice, and the lattice cells are arranged on each of the four inner lattice surfaces. a spring protruding in the direction to support the fuel rod; It includes at least one foreign matter filtering unit protruding in the transverse direction within the range of the longitudinal section in which the spring is formed.

Preferably, the foreign material filtering unit comprises: a first foreign material filtering unit in the form of an arc disposed in the transverse direction at a height of 1/2 of the spring; A second foreign material filtering unit and a third foreign material filtering unit are formed to extend horizontally in the left and right directions, respectively, at the height of the upper end and the lower end of the first foreign material filtering unit 131 .

More preferably, the first foreign material filtering unit has a shape symmetrical left and right about the spring.

In the lower space lattice of the nuclear fuel assembly according to the present invention, square lattice cells having an inner lattice surface form a square lattice, and each lattice cell is formed to protrude longitudinally from each of the four inner lattice surfaces. Including a spring formed to support the fuel rod, and at least one foreign material filtering unit protruding in the transverse direction within the range of the longitudinal section where the spring is formed, sheet metal processing and welding processing are excluded and 3D printing with high design freedom is used. The fuel rod can be strongly and evenly maintained at the center of the grid cell until the end of the core life (EOL), and the height of the lower space grid can be reduced, thereby reducing pressure drop.

1 is a perspective configuration diagram of a lower space grid of a nuclear fuel assembly according to an embodiment of the present invention;
2 is a perspective configuration diagram of a unit grid cell of a lower space grid of a nuclear fuel assembly according to an embodiment of the present invention;
3 is a cross-sectional configuration view of the lower spacer grid of the nuclear fuel assembly cut along the line AA of FIG. 2;
4 is a cross-sectional perspective view of the lower spacer grid of the nuclear fuel assembly taken along line AA of FIG. 2;
5 is a plan view of a unit grid cell of a spacer grid for a nuclear fuel assembly according to an embodiment of the present invention.

Specific structural or functional descriptions presented in the embodiments of the present invention are only exemplified for the purpose of describing embodiments according to the concept of the present invention, and the embodiments according to the concept of the present invention may be implemented in various forms. In addition, it should not be construed as being limited to the embodiments described herein, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

On the other hand, the terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as "comprises" or "have" are intended to designate the existence of an embodied feature, number, step, operation, component, part, or combination thereof, one or more other features or numbers, It should be understood that the existence or addition of steps, operations, components, parts or combinations thereof is not precluded in advance.

The present invention is to provide a lower spacer grid that can be manufactured by metal 3D printing by excluding the sheet metal processing and welding process during the manufacturing process of the lower spacer grid, and the shape of the lower spacer grid produced by the conventional sheet metal processing and welding process It can eliminate design limitations and shorten the manufacturing process.

In general, various metal 3D printing devices are available, and for example, Germany's CONPCEPTLASER's 3D printing equipment has a maximum production size of 250 × 250 × 280 ㎣, making it difficult to manufacture a full-size spacer grid. PBF (Powder Bed) in which a product is manufactured in a way that a powder layer of several tens of μm is laid on a powder bed having a certain area in a powder supply device, a laser or electron beam is selectively irradiated according to the design drawing, and then melted layer by layer and laminated Fusion) method is used. On the other hand, the space grid of the present invention may be employed in a general metal additive manufacturing method employed in general metal 3D printing, and is not limited to a specific method.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a perspective configuration diagram of a lower space grid of a nuclear fuel assembly according to an embodiment of the present invention, FIG. 2 is a perspective configuration diagram of a unit grid cell of a lower space grid of a nuclear fuel assembly according to an embodiment of the present invention, and FIG. 3 is a cross-sectional configuration view of the lower space grid of the nuclear fuel assembly cut along line AA of FIG. 2 , FIG. 4 is a cross-sectional perspective view of the lower space grid of the nuclear fuel assembly cut along line AA of FIG. 2 , and FIG. 5 is the present invention It is a plan configuration diagram of a unit grid cell of a spacer grid for a nuclear fuel assembly according to an embodiment.

1 to 5 , in the lower space lattice 100 for a nuclear fuel assembly of this embodiment, the square lattice cells 110 having an inner lattice surface 111 are square lattice (n×n) have a structure Each grid cell 110 is formed to protrude in the longitudinal direction on each of the four inner grid surfaces 111, and a spring 120 formed to support the fuel rod 10; The spring 120 includes at least one foreign material filtering unit 130 protruding in the transverse direction within the section range (H) of the longitudinal direction (z-axis) is formed.

The lattice planes 111 of four sides constituting each lattice cell 110 are in the shape of a plate without slots or holes formed, and each inner lattice plane 111 of each lattice cell 110 has a longitudinal direction. A spring 120 formed to protrude is provided. For reference, the unit grid cell 110 in FIG. 2 shows a spring 120 and a foreign material filtering unit 130 on both the inner and outer surfaces of the four-sided grid surface 111, and each grid surface 111 It should be understood that the outer surface of ) corresponds to the inner grid surface of the grid cell immediately adjacent to the corresponding unit grid cell 110 . The four lattice planes constituting each lattice cell 110 are a solid plain plate that is entirely closed, so that it is possible to increase the impact strength and improve the seismic performance.

The spring 120 is formed to protrude in the longitudinal direction (z-axis) of each lattice plane 111 to elastically support the fuel rod 10 , and is preferably provided in the center of each lattice plane 111 . The spring 120 includes a contact portion having a curved surface to make surface contact with the surface of the fuel rod in the longitudinal direction (z-axis), and this contact portion includes a fuel rod lifting prevention groove 11 formed in the lower portion of the fuel rod 10 and An elastic protrusion 121 may be provided so that the fitting assembly is performed. As described above, the contact portion is in contact with the fuel rod lifting prevention groove 11 to prevent lifting of the fuel rod when the fuel rod is lifted by hydraulic power.

The foreign material filtering unit 130 is formed only within the range of the section h1 in the longitudinal direction (z-axis) in which the spring 120 is formed, and the upper and lower sections h2 in addition to the section h1 in the longitudinal direction are closed planes. It is a solid plain plate of

Preferably, the foreign material filtering unit 130 includes an arc-shaped first foreign material filtering unit 131 disposed in the transverse direction at a height of 1/2 of the spring 120 , and the upper end of the first foreign material filtering unit 131 , and It includes a second foreign material filtering unit 132 and a third foreign material filtering unit 133 formed to extend horizontally in the left and right directions, respectively, at the height of the lower end. In particular, the first foreign material filtering unit 131 has a shape symmetrical left and right about the spring 120 .

For reference, in the prior art, a separate structure (dimple) was required to regulate the position of the fuel rod other than the spring for elastically supporting the fuel rod. Springs are provided on both inner lattice planes of the dog. Therefore, according to the present invention, the fuel rod 10 can be firmly positioned in the center of the grid cell 110 until the end of the core life (EOL) because the spring can evenly and firmly support the fuel rod in four directions.

In addition, since the lower spacer grid of the present invention having such a structure can equally support the fuel rod in four directions, the dimple structure as in the prior art can be excluded, and the upper and lower sections h2 of the spring 120 ) can be reduced. In addition, there is an effect of reducing the pressure drop by reducing the height of the entire lower spacer grid (h1+2×h2), and it is possible to increase the internal length of the fuel rod, which greatly contributes to securing the margin of the rod inner pressure (RIP). can do.

The present invention described above is not limited by the above-described embodiments and the accompanying drawings, and it is common in the technical field to which the present invention pertains that various substitutions, modifications and changes are possible within the scope without departing from the technical spirit of the present invention. It will be clear to those who have the knowledge of

100: lower space grid 110: grid cell
111: grid surface 120: spring
130: foreign matter filtering unit 131: first foreign material filtering unit
132: second foreign matter filtering unit 133: third foreign material filtering unit

Claims (3)

In the lower spacer grid to support the fuel rod of the nuclear fuel assembly,
Square lattice cells with an inner lattice plane form a square lattice,
The grid cell is
a spring protruding from each of the four inner lattice surfaces in the longitudinal direction to support the fuel rod;
The lower spacer grid of the nuclear fuel assembly including at least one foreign material filtering part protruding in the transverse direction within the range of the longitudinal section in which the spring is formed. According to claim 1, wherein the foreign matter filtering unit,
a first foreign material filtering unit in the form of an arc disposed in the transverse direction at a height of 1/2 of the spring;
A lower space grid of a nuclear fuel assembly including a second foreign material filtering unit and a third foreign material filtering unit extending from the left and right in the transverse direction at the height of the upper end and the lower end of the first foreign material filtering unit, respectively. The lower spacer grid of claim 2, wherein the first foreign material filtering unit has a shape symmetrical about the spring.

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