KR20080060742A - Spacer grid with unsymmetric dimple for the debris filtering - Google Patents

Abstract

A spacer grid with an unsymmetrical dimple for filtering a debris is provided to minimize a cross section in a horizontal direction and to reduce a maximum diameter for inflow of the debris through an effective cross section structure of the dimple. A spacer grid with an unsymmetrical dimple for filtering a debris(D) includes a spacer grid(20) and a dimple(21). The spacer grid divides a plurality of unit grid cells by crossing strips with slots horizontally and vertically and reciprocally inserting the slots. The dimple is formed by asymmetrically bending the strips to be divided into a short piece(212) and a long piece(211), projected from centers of grid surfaces of the spacer grids in a perpendicular direction, and installed on the grid surface in a direction to have a minimum cross section for an axial direction of the spacer grid to support a lower rod short stopper(14) of a fuel rod through a line contact between the long piece of the dimple and the lower rod short stopper.

Description

Spacer grid with unsymmetric dimple for the debris filtering}

1 is a schematic representation of a typical fuel assembly

2 is a plan view showing a general support grid

3 is a cutaway perspective view showing a general support grid

4 is a perspective view showing a lower end fixing body restricting the size of a conventional flow path hole;

5 is a plan view showing a support grid for filtering foreign matter in the prior art

Figure 6a is a plan view showing a support grid for filtering foreign matter of Example 1 of the present invention

Figure 6b is a perspective view showing a support grid for filtering foreign matter of Example 1 of the present invention

Figure 7a is a plan view showing a support grid for filtering foreign matter of Example 2 of the present invention

Figure 7b is a perspective view showing a support grid for filtering foreign matter of Example 2 of the present invention

<Description of the symbols for the main parts of the drawings>

21: asymmetric dimple 22: arch

The present invention relates to a foreign matter filtration device of a nuclear fuel assembly, and specifically, to filter foreign substances introduced through the lower stationary passage hole along with the cooling water on the lower stationary body of the nuclear fuel assembly, and at the same time, a minimum flow rate in the flow direction of the cooling water. It relates to a filtration device having a resistance cross section to minimize the pressure drop.

A nuclear reactor is a device made to be used for various purposes such as generating heat by producing artificial fission reaction of fissile material, producing radioisotopes and plutonium, or forming a radiation field.

In general, light water reactors use enriched uranium with an increased ratio of uranium-235 to 2-5%. In order to process the nuclear fuel used in nuclear reactors, uranium is molded into cylindrical pellets weighing about 5g. Hundreds of these pellets are bundled in bundles, charged in a vacuum in a zircaloy cladding tube, spring and helium gas are placed therein, and the upper rod stopper is welded to produce fuel rods. The fuel rods finally form a fuel assembly and are burned through a nuclear reaction in the reactor.

The fuel assembly and its components are shown in [FIG. 1] to [FIG. 3]. FIG. 1 is a schematic view showing a general fuel assembly, FIG. 2 is a plan view of a support grid from above, and FIG. 3 is a cutaway perspective view showing the support grid in detail.

Referring to FIG. 1, the nuclear fuel assembly includes a top body 4, a bottom body 5, a support grid 2, a guide tube 3, and a support grid 2. Supported by a spring 6 (see [FIG. 2] and [FIG. 3)) and dimples 7 (see [FIG. 2] and [FIG. 3]), which are inserted into the support grid 2 and formed in the support grid 2 It consists of the fuel rod (1). In order to prevent scratches on the surface of the fuel rod (1) and to prevent damage to the spring (6) in the support grid, the locker is applied to the surface of the fuel rod, charged into the skeletal body, and then fixed by attaching the upper and lower fixing bodies. After the assembly of the nuclear fuel assembly is completed, the assembly manufacturing process is completed by removing the lockers of the completed assembly and inspecting the spacing, warpage, electrical length, and dimensions between the fuel rods.

Referring to FIGS. 2 and 3, the support grid 2 includes slots 21 each having a strip (thin metal plate) formed at regular intervals so as to partition a space in which a plurality of fuel rods 1 can be charged. (Refer to ;;) to form a lattice. The support grids are arranged up to about 10 to 13 up and down and welded with a guide tube 3 of 4m length. Springs 6 and dimples 7 are regularly formed in each space portion partitioned by the support grid 2, and the springs 6 and dimples 7 are fuel rods 1 (see Fig. 1). By maintaining contact with the fuel rods 1 (see FIG. 1), the fuel rods 1 are secured by the elasticity of the springs 6 and arranged at a predetermined position.

The fuel assembly thus completed emits heat by nuclear fission in the reactor, and the heat generated from the fuel assembly is absorbed by the coolant. Cooling water circulates the reactor and reactor piping by a reactor cooling pump and promotes heat transfer from the nuclear fuel assembly to the cooling water.

On the other hand, foreign matter introduced into the reactor along with the cooling water during the circulation of the cooling water, including fragments and debris such as metal particles, chips, and shavings during the production, installation, and repair of piping and cooling facilities. Various kinds of foreign matters may be mixed in the cooling water, and these foreign matters pass through the passage holes of the lower fixing body, causing micro vibration between the fuel rods and the support lattice and damaging the cladding of the fuel rods.

In order to solve the above problems, as shown in [FIG. 4], the method of restricting the size of the passage hole 12 of the lower fixing body 11 and the foreign material filter lattice for debris filtration as shown in [FIG. 5] The method of using (13) or the method of using a combination of the lower fixing channel hole and the support grid for filtering foreign substances is used.

The method of limiting the passage hole size of the lower fixing body in the foreign matter filtration device has the advantage of being easy to apply in a relatively simple method, but has a disadvantage of increasing the pressure drop due to the reduction of the passage area compared to the improvement of the foreign matter filtration performance. When the pressure of the coolant drops, the hydraulic uplift force must increase to increase the pressing force of the spring of the upper fixture, and increase the vibration of the nuclear fuel rod or cause the lateral flow of the coolant to fretting wear. Disadvantages are that they do not absorb enough heat from the fuel rods.

In the case of using a support grid for filtering foreign substances with the lower fixing body, there is an advantage that the pressure drop is relatively small while increasing the foreign matter filtration performance, but the number of parts is increased.

An example of using the above-described support grid for filtering foreign substances is 'US Patent US4652425' `` Bottom grid mounted debris trap for a fuel assembly '' filed on August 8, 1985 (hereinafter referred to as prior art).

Referring to FIG. 5, the prior art has four lattice cells forming a unit lattice cell with dimples 15 supporting the lower end caps 14 of the nuclear fuel rods on the lower support lattice 13 of the support lattice. It is configured on each side to prevent foreign matter from entering the effective section in the fuel assembly with the support of the nuclear fuel rods 14.

In order to prevent the inflow of foreign matter, a more complicated dimple structure or a larger cross-sectional area can be used to reduce the cross-sectional area through which foreign matter can pass. However, since the pressure drop of the cooling water is proportional to the cross-sectional area of the grid as viewed in the axial direction, the structure of the dimple cannot be unconditionally complicated or the area of the cross-sectional area can be increased.

From the object or need for solving the above problems,

It is an object of the present invention to provide dimples and foreign matter inflow preventing means that minimize the transverse cross-sectional area and minimize the maximum inflow of foreign matters while providing a means to sufficiently ensure the bearing capacity of the fuel rods.

In order to achieve the above technical problem,

The support grid for filtering foreign matters according to the present invention includes a support grid and dimples formed on the support grid. Furthermore, an arch may be further provided.

The support grid partitions the plurality of unit grid cells by interposing the slots formed with slots at regular intervals in the longitudinal and transverse directions to insert the slots.

In addition, the dimple is formed by bending the strip asymmetrically so as to be divided into a piece and a long piece, protrudes in both normal directions at the center of each lattice plane of the support grid, and supports the support in a direction having a minimum cross-sectional area with respect to the axial direction of the support grid. By being provided on the lattice surface of the lattice, the long piece of the dimple and the lower end cap of the fuel rod make linear contact to support the lower end cap of the fuel rod.

In addition, the arch is formed by bending a strip on the upper part or the lower part of each part where the long piece of the dimple and the support lattice are connected, and protrude in the same direction as the dimple.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Unless otherwise defined or mentioned, terms indicating directions such as 'up, down, left and right' used in the present description are based on the states indicated in the drawings. In addition, the same reference numerals throughout the embodiments indicate the same member.

On the other hand, each space part divided by the lattice structure of the support grid is called a unit lattice cell, and one surface inside the lattice cell is defined as a lattice plane. If one lattice plane is defined as the longitudinal direction, all lattice planes parallel to the lattice plane become longitudinal lattice planes, and the lattice plane perpendicular to the longitudinal lattice plane is referred to as a transverse lattice plane. The axial direction refers to the direction in which the nuclear fuel rod is charged as the longitudinal direction of the unit cell.

Hereinafter, Embodiment 1 of the present invention will be described in detail with reference to FIGS. 6A and 6B. 6A is a plan view showing a support grid for foreign matter filtration according to the first embodiment, and FIG. 6B is a perspective view showing a support grid for foreign matter filtration according to the first embodiment.

In Embodiment 1 of the present invention, the support grid 20 and the dimples 21 formed on the support grid are main components thereof.

The support grid 20 is formed in a lattice shape by inserting the slots to cross each other in the longitudinal direction and cross the strip formed slots at regular intervals as is known. The inside of each lattice of the support grid 20 is called a unit lattice cell, and the four surfaces inside the unit lattice cell are called lattice planes, respectively.

The asymmetrical dimples 21 are formed asymmetrically with the long pieces 211 and the fragments 212 on each side by bending the strips to one side rather than the center. In addition, the asymmetrical dimples 21 are provided to protrude in both normal directions at the center of each of the lattice planes 20 of the support grid. As shown in FIG. 6B, the asymmetrical dimples 20 protruding in both normal directions may be formed above and below, respectively, or may be formed at the same height. In addition, the asymmetrical dimple 21 is fixed to the lattice surface 20 by standing a portion having a wide width in the transverse direction so as to have a minimum cross-sectional area with respect to the axial direction of the support grid, but a portion having a narrow width in the axial direction. do.

The operation of the first embodiment will be described with reference to FIG. 6A.

The dimple 21 is in line contact with the lower end cap 14 on the long piece 211 to support the lower end cap 14. At this time, the maximum size of the foreign matter that can pass in the axial direction of the unit lattice cell is the diameter of the foreign matter D that can pass through the space between the adjacent pieces from the connecting portion of the long piece 211 and the support grid. According to the present invention, the support lattice for filtering foreign matters was found to reduce the minimum diameter of foreign matter passing through the measurement to about 60% compared to the conventional method.

Hereinafter, Embodiment 2 of the present invention will be described with reference to FIGS. 7A and 7B.

7A is a plan view showing a support grid for foreign matter filtration according to the second embodiment, and FIG. 7B is a perspective view showing a support grid for foreign matter filtration according to the second embodiment.

In Embodiment 2 of the present invention, the support grid 20, the dimples 21 and the arch 22 formed on the support grid are the main components thereof.

The support grid for foreign material filtration according to the second embodiment has an additional configuration of the arch 22 as compared to the support grid for foreign material filtration according to the first embodiment.

The arch 22 has an arch 22 formed by bending a strip at an upper portion or a lower portion of the connecting portion at each portion where the long piece 211 of the dimple 21 and the support grid 20 are connected to the same as the dimple 21. It is formed on the support grid 20 to protrude in the direction.

As described above, the portion through which the largest foreign matter can pass in the first embodiment is the fuel rod 14, the long piece 211 of the dimple 21 and the neighboring dimple 21 as shown in FIG. 6A. The space portion formed by the fragment 212 and the foreign matter of the maximum size that can pass at this time is D. Therefore, the arch 22 is formed to reduce the size of the foreign matter that can pass in the axial direction.

Although the preferred embodiments of the present invention have been described above, the technical idea of the present invention is not limited to the above-described preferred embodiments, and various foreign matter filtration supports within the scope not departing from the technical idea of the present invention specified in the claims. It can be implemented in a grid.

From the structural features of the present invention described above,

The support grid for foreign material filtration according to the present invention minimizes the lateral cross-sectional area through the cross-sectional structure of the effective dimple while sufficiently securing the fuel rod through the two line contacts, and significantly reduces the maximum inflow diameter of the foreign material compared to the prior art. Can be.

Claims (2)

In the support grid provided on the lower fixed body to filter foreign matter, A support grid for partitioning a plurality of unit grid cells by intersecting the strips in which slots are formed at regular intervals in the longitudinal and transverse directions to insert the slots; And The strip is formed asymmetrically bent to be divided into a piece and a long piece, protrudes in both normal directions at the center of each of the grid grating plane, the grid of the support grid in a direction having a minimum cross-sectional area with respect to the axis direction of the support grid A dimple supporting the lower rod end of the fuel rod by being in contact with the long piece of the dimple and the lower rod end of the fuel rod by line contact; Support grid for foreign material filtration having an asymmetric dimple composed of. The method of claim 1, The support grid for filtering foreign matter having an asymmetrical dimple further comprising an arch formed by bending a strip at an upper portion or a lower portion of each portion of the dimple to be connected to the support grid.

Images