KR20110004696A - Internal structure of wire spring type spacer grid - Google Patents

Abstract

PURPOSE: An internal structure of a wire spring type spacer grid is provided to firmly support a fuel rod by including first and second fuel rods. CONSTITUTION: A plurality of wires(110) are assembled together with to form a first fuel rod supporting part. A combiner(120) is inserted in the upper portion and lower portion of a plurality of wires. A wire support(130) is inserted inside the first fuel rod supporting part of a plurality of wires in horizontal direction. A second fuel rod supporting part has a recess shape corresponding to the outer circumference of the fuel rod. The first and second fuel rod supporting parts support the fuel rod in order to hold the location of the fuel rod.

Description

Internal structure of wire spring type support grid {INTERNAL STRUCTURE OF WIRE SPRING TYPE SPACER GRID}

The present invention relates to a fuel support lattice, and more particularly, to a support lattice for supporting a dual-cooled fuel rod compatible with a standard pressurized water reactor core.

The fuel support lattice is the main structural component constituting the nuclear fuel assembly used in the light-water reactor core, and stably supports the plurality of fuel rods constituting the fuel assembly by the end of the cycle under severe operating conditions inside the core, To be located.

Meanwhile, a coolant having a high flow rate flows around the fuel assembly, and the coolant may generate a flow induced vibration in the fuel rod, and the fuel support grid has a function of alleviating the flow induced vibration of the fuel rod. .

FIG. 1 is a front view schematically showing a conventional fuel assembly, FIG. 2 is a cross-sectional view schematically illustrating the fuel assembly of FIG. 1, and FIG. 3 is a schematic view of a support grid constituting the fuel assembly of FIG. 1. 4 is a plan view schematically illustrating the support grid of FIG. 3, and FIG. 5 is a perspective view schematically illustrating a unit grid of the support grid of FIG. 3.

1 to 5, the nuclear fuel rod assembly 10 includes a nuclear fuel rod 11, a guide tube 14, a support grid 15, an upper fixture 12, and a lower fixture 13. .

The nuclear fuel rod 11 includes a cylindrical uranium sintered body in the zirconium alloy cladding tube, and by the nuclear fission reaction of the uranium sintered body High temperature heat is generated.

The guide tube 14 is used as a passage of a control rod that moves up and down to regulate the output of the reactor core and stop the fission reaction.

The support grid 15 is usually made of a Zircaloy alloy to form a nuclear fuel rod cell into which a plurality of nuclear fuel rods are inserted, and a guide tube cell into which a plurality of guide tubes are inserted.

The support grids forming the nuclear fuel rod cell are located in two grid springs 28, one on each side and two on each of the upper and lower sides of the grid springs, and four dimples on each of the other two sides. (29) protrudes to support the fuel rods 11 at a total of six support points.

If the spring force of the spring 28 and the dimple 29 is too small, the nuclear fuel rod 11 may not be supported at a predetermined position, and thus the support integrity of the nuclear fuel rod 11 may be lost.

If the elastic force is too large, a flaw such as scratching may occur on the surface of the nuclear fuel rod 11 due to excessive frictional resistance when the nuclear fuel rod 11 is inserted into the support grid itself.

In addition, the longitudinal growth of the nuclear fuel rods 11 due to neutron irradiation during the operation of the reactor may not be adequately accommodated, which may cause the nuclear fuel rods 11 to bend, that is, to cause warpage of the nuclear fuel rods 11.

When the fuel rods 11 are bent, the fuel rods 11 are brought into close contact with or in contact with adjacent fuel rods 11 to narrow or block the cooling water channel between the fuel rods.

Here, the coolant flow path is enclosed by four nuclear fuel rods 11 or subaxially through the sub-channel 25 surrounded by three nuclear fuel rods 11 and one guide tube 14 in the lower core portion in the axial direction. Flows quickly to the top;

That is, the sub-channel 25 refers to a space surrounded by the nuclear fuel rods 11 and refers to a passage through which the side is open so that fluid can freely move to an adjacent flow path.

As described above, when the cooling water passage is narrowed or blocked, the heat generated from the fuel cannot be effectively transferred to the cooling water, which causes a temperature increase of the nuclear fuel rods, thereby resulting in the possibility of occurrence of nuclear boiling escape (DNB). It can be a major factor in reducing nuclear fuel output.

The upper fixture 12 and the lower fixture 13 serve to fix and support the nuclear fuel rod assembly 10 to the upper and lower structures of the core, and the lower fixture 13 floats the inside of the core. And a filtration device (foreign filter, not shown) for filtering foreign matter.

FIG. 6 is a schematic cross-sectional view of the dual cooling fuel rod, and FIG. 7 is a plan view schematically illustrating the nuclear fuel assembly in which the dual cooling fuel rod of FIG. 6 is inserted.

6 and 7, the dual cooled fuel rod has an annular structure instead of a cylindrical shape, which is disclosed in US Patent Nos. 3,928,132 and 6,909,765.

The dual-cooled nuclear fuel rod 20 having the annular structure is an sintered body 21 formed in an annular shape and an inner covering tube 22 provided on the inner circumference of the sintered body 21 and an outer covering tube 23 provided on the outer circumference. Is done.

In the case of the above structure, the coolant can flow not only to the outside of the dual cooling nuclear fuel rod 20 but also to the heat transfer is made by the dual, not only to maintain a low center temperature of the dual cooling nuclear fuel rod 20 The heat transfer area is also increased to achieve high combustion and high power.

As described above, when the central temperature of the dual-cooled fuel rod 20 is kept low, the possibility of fuel damage due to the increase in the central temperature of the nuclear fuel rod is lowered, thereby increasing the safety margin of the dual-cooled nuclear fuel rod 20.

However, in order to be structurally compatible with the existing pressurized PWR core, the dual-cooled fuel rods 20 are not able to change the position of the guide tube 14 in the fuel assembly 10, and the fuel rod outer diameter is dramatically increased. The gap between the fuel rods becomes extremely narrow. For example, when the fuel assembly is constructed by inserting dual-cooled fuel rods in a 12 × 12 array so as to be structurally compatible in existing LWR cores, the gap between the fuel rods is about 3.24 mm to about 1.24 mm. Will decrease.

Therefore, due to the narrow gap between the fuel rods, a problem arises in that the support grid developed so far cannot be used as the support grid of the dual cooling fuel rod 20 as it is.

That is, if the thickness of the unit grid of the existing support grid itself is subtracted from the gap between the fuel rods of 1.24 mm and subdivided in half, the distance between the unit grid and the fuel rod is only about 0.383 mm.

Within such a narrow gap, the spring design having the spring stiffness and hydraulic characteristics (mainly pressure loss) of the existing support grid is impossible by applying the same shape and support concept as the existing spring.

In addition, there is a problem in that the cooling water flow path is reduced by the narrow interval is reduced the cooling function.

The present invention has been made to solve the above problems, and structurally and stably supports the fuel rods even at intervals between the fuel rods narrowed with the increase in the outer diameter of the nuclear fuel rods, and the cover section of the flow path by the support grid body. Its aim is to provide an improved fuel support grid to minimize pressure losses.

The fuel support grid according to the present invention is spaced apart from each other so as to be in contact with each of the plurality of dual cooling nuclear fuel rods, and has a plurality of wires 110 having a convex portion 110a at the center, and having a groove or an insertion hole in the combiner 120. In this way, the wire 110 is bundled to include the wire support 130 and inserted and fixed at the intersection of the connecting grid plate at the upper and lower ends of the coupler 120 to form the entire supporting grid internal structure. In the bundled unit spring, one side of the wire 110 facing the rod forms a first fuel rod support 140a which is supported by direct point contact or line contact, wherein the wire support 130 of the wire 110 It prevents movement and promotes structural rigidity. In addition, the second fuel rod support portion 140b on the circumferential surface of the wire support 130 is formed by forming a second fuel rod support portion 140b on the wire support 130 in a conformal surface and rotating the bundle of unit wire springs by 90 degrees. Can also be supported by surface contact.

That is, in one embodiment of the present invention, the first fuel rod support 140a, which is the middle portion of the convex shape of the wire 110, may press the fuel rod 200 to support and fix the position of the fuel rod 200. In another embodiment, the second fuel rod support 140b, which is a portion between the wires 110 of the wire support 130, has a concave shape so as to correspond to an outer circumferential surface of the fuel rod 200. ) Can be fixed to position the fuel rod 200 by pressing and supporting.

Since the plurality of wires 110 have the curvature of the central portion convexly outward, the same curvature may be formed at a portion where the wire support 130 is positioned and connected.

The plurality of wires 110 are alternately repeated in a convex portion 110a which is convex outward and a plurality of concave portions 110b which are indented in an alternating sine wave and cosine wave, or a wave form of a combination of the two. Can be.

The wire support 130 positioned at the inner center of the convex portions 110a may support the rod on the outer circumferential surface of the wire support 130 in some cases while structurally connecting the plurality of wires 110.

The wire support 130 may have a constant groove so as to be mechanically assembled by receiving the back surface of the wire 110 in contact with the ring or ring.

The upper and lower ends of the coupler 120 may have an insertion structure such as a guide or a perpendicular processing so that the upper and lower ends of the coupler 120 may be mechanically fixed to the intersection point of the upper and lower gratings.

According to the fuel support lattice according to the invention, it is possible to support double cooled fuel rods by point or line contact at the convex portions of the wires, and also to support the rods at a support located on the circumferential surface of the wire support. .

The plurality of wires as described above may resist the force acting in the transverse direction of the wires by the wire support inserted into the convex portions of the wires, thereby preventing movement or deformation of the wires.

The ultimate reason for constructing the support grid as described above is to minimize the sectional area of the flow path in the narrow channel and contribute to the improvement of thermal and hydraulic performance as nuclear fuel, and to support the fuel rod structurally and stably. It is expected to have advantages such as reducing fretting wear damage and reducing fuel pressure loss.

Hereinafter, the nuclear fuel support grid according to the present invention will be described in detail with reference to the accompanying drawings.

First, the fuel support grid and the internal structure are constituent parts constituting a fuel rod assembly, and the fuel rods and the fuel rod cells are formed by forming a fuel rod cell into which a plurality of fuel rods are inserted and a guide tube cell into which a plurality of guide tubes are inserted. Guides may be supported.

Hereinafter, in the detailed description for the implementation of the present invention, except for the fuel support lattice of the specific content of the nuclear fuel rod assembly, the description is the same or similar to the prior art, and the description thereof will be replaced with the description of the background art described above.

8 to 10 are perspective views schematically showing a bundle of unit wire springs according to an embodiment of the present invention, and FIGS. 11A to 13 are inside a nuclear fuel support grid using unit wire spring bundles corresponding to FIGS. 8 to 10, respectively. A perspective view and a plan view schematically showing a structure, and a state in which a dual cooling fuel rod is inserted and supported.

8 to 10, the unit wire bundle spring of the nuclear fuel support grid internal structure 100 may include a wire bundle having a plurality of waveforms and a shape bundled radially by the coupler 120. The combiner 120 is a device for binding the plurality of wires 110 to each other, and the wire 110 may directly support the fuel rods. The wire support body 130 is provided with a groove or an insertion hole at a position supporting the wire 110 in a metal annular shape to insert a plurality of wires 110 into the groove or the insertion hole, and the bundle of the wire 110 is both ends. After joining, unit wire spring bundles are formed. In addition, the upper and lower coupler 120 of the unit spring may be processed into a right angle to facilitate insertion into the junction junction of the grid.

A plurality of wires 110 are provided to be spaced apart from each other, the outer surface of each of the plurality of wires 110 may be in contact with the outer surface of the fuel rod for supporting the fuel rod. The plurality of wires 110 may form convex portions 110a such that portions between both ends thereof are convex to the outside while both ends are in contact with each other.

For example, if the plurality of wires 110 is four, the four wires 110 may form a cosine wave shape in which the center is convex outward in a state where both ends thereof contact each other while having an angle of 90 degrees.

A coupler 120 having a ring shape having a penetrating inside thereof may be inserted into each of both ends to fix both ends of the plurality of wires 110.

Of course, the coupler 120 only needs to be configured in a structure capable of fixing both ends of the plurality of wires 110, and is not limited by the present invention and may take any shape and structure.

An inner space formed by the plurality of wires 110, that is, a ring-shaped wire support 130 for supporting the shape of the convex portion 110a may be interposed inside the convex portions 110a of the respective wires 110. Can be.

12A and 12B, the fuel rod 200 may be supported by a second fuel rod support 140b positioned in the plurality of wire supports 130 of the nuclear fuel support lattice internal structure 100. The fuel rod support 140b may be smaller than or equal to the outer curvature of the fuel rod to realize conformal contact.

10 and 13, the plurality of wires 110 of the fuel support grid 100 may be fixed by the coupler 120 in a state in which both ends thereof are in contact with each other as shown in FIG. 8. Portions between the end portions may have a form in which convex portions 110a convex outwardly and recesses 110b indented inward are alternately formed. That is, a constant waveform can be formed.

The wire support 130 may be inserted into the convex portions 110a of the wires 110, and the number of the wire supports 130 may depend on the number of the convex portions 110a.

11A to 13, when the fuel rod lattice support is interposed between the dual cooling fuel rods, each of the wires 110 of the fuel rod lattice support is supported in contact with the center of the dual cooling fuel rod. And, the wires 110 may be supported in contact with the upper and lower portions of the dual cooling fuel rods.

The nuclear fuel support lattice internal structure 100 having the above structure may support the dual-cooled fuel rods by point or line contact at the first fuel rod support 140a which is the convex portion 110a of the wires 110. In another embodiment, the rod may be supported by the second fuel rod support 140b positioned on the circumferential surface of the wire support 130.

Since the plurality of wires 110 having the above shape may resist the pressure applied to the wires 110 by the wire support 130 inserted into the convex portions 110a of the wires 110, It is possible to prevent arbitrary movement or shape deformation of the wires 110. In addition, since the wire support 130 uses a material having elastic force, the wire support 130 may be bent correspondingly even when the fuel rod is slightly bent, thereby improving stability of the internal structure of the wire spring type support grid.

Therefore, the dual cooling fuel rods are inserted into the nuclear fuel rod assembly, so that the dual cooling fuel rods can be stably supported by the fuel supporting lattice inner structure 100 even though the sub-channels, which are fluid movement paths, are narrowed.

In addition, the flow resistance due to the decrease in the contact area and the projected area of the fluid is smaller than that of the conventional plate-shaped support grid, which provided a relatively large friction surface, thereby improving the thermal and hydraulic performance according to the minimum support grid pressure loss. Can be.

In addition, since the convex portion 110a and the concave portion 110b are alternately formed in the wires 110 to support the dual-cooled fuel rods at a plurality of points, it is possible to support the nuclear fuel rods at a single point. It is possible to provide an effect of suppressing fretting wear damage due to vibration of the nuclear fuel rod caused by the flow of cooling water. In addition, the convex portion 110a and the concave portion 110b are alternately formed to support the dual cooling fuel rods at a plurality of points, so that the concave portion 110b has an inner coupler 120a in the structure of the wire support grid body. It is possible to further improve the stability of the internal structure (100).

Here, the inner structure 100 of the wire support grid itself of another embodiment provided with the inner coupler 120a also has the same shape and structure as the wire support grid internal structure 100 shown in FIG. Of course, it can be utilized.

On the other hand, the present invention can be applied to one of the shape of the support for supporting the pipe system and the support structure, when the long rods or pipes are arranged at a narrow interval in the general industrial equipment using a boiler or heat exchanger for transporting fluid. .

1 is a front view schematically showing a conventional fuel assembly.

FIG. 2 is a schematic cross-sectional view taken along line II ′ of FIG. 1.

Figure 3 is a perspective view schematically showing a support grid constituting the fuel assembly of Figure 1;

4 is a plan view schematically showing the support grid of FIG.

5 is a perspective view schematically showing a unit grid of the support grid of FIG.

6 is a schematic cross-sectional view of a dual cooled nuclear fuel rod.

FIG. 7 is a plan view schematically illustrating a fuel assembly in which the dual cooling fuel rod of FIG. 6 is inserted and the interval between the rods is significantly narrowed (except for the support grid).

8 to 10 is a perspective view schematically showing a support grid unit wire spring bundle according to an embodiment of the present invention.

11A to 13 are perspective views schematically illustrating a state in which a nuclear fuel support lattice internal structure is formed using unit wire spring bundles corresponding to 10 in FIGS. 8 and 10, and a double cooling fuel rod is inserted and supported.

<Description of Symbols for Main Parts of Drawings>

100: fuel support grid 110: wire

110a: convex portion 120: coupler

120a: internal coupler 130: wire support

140a: support 200: dual lattice fuel rods

Claims (9)

A plurality of wires 110 having a convex shape in the middle and having a top and bottom ends to form a radial shape; And Coupler 120 is fastened to the structure that is fitted to the upper and lower ends of the plurality of wires (110); Internal structure of the wire spring type support grid, characterized in that comprises a. The method of claim 1, A ring-shaped wire support 130 inserted in a horizontal direction in the convex portions of the plurality of wires 110 to support the wires 110; Wire spring-type support grid internal structure further comprising a. The method of claim 2, Internal structure of the wire spring type support grid, characterized in that the first fuel rod support part 140a, which is the middle portion of the convex shape of the wire 110, presses and supports the fuel rod 200 to fix the fuel rod 200. . The method of claim 2, The second fuel rod support part 140b, which is a portion between the wires 110 of the wire support 130, has a concave shape to correspond to an outer circumferential surface of the fuel rod 200 to press and support the fuel rod 200. Internal structure of the wire spring type support grid, characterized in that for fixing the position of the fuel rod (200). A plurality of wires 110 having a plurality of convex shapes and concave shapes alternately having upper and lower ends gathered to form a radial shape, Internal structure of the wire spring type support grid, characterized in that it comprises a coupler 120 is fastened to the structure fitted to the upper and lower ends of the plurality of wires (110). The method of claim 5, Wire spring-type support grid body characterized in that it further comprises a ring-shaped inner coupler (120a) is provided in a structure that is fastened to the concave portion of the plurality of wires 110 to bind the plurality of wires (110) Internal structure. The method of claim 5, Internal structure of the wire spring type support grid, characterized in that it further comprises a ring-shaped wire support 130 is inserted into the convex portion of the plurality of wires 110 to support the wire 110. . The method of claim 5, Internal structure of the wire spring type support grid, characterized in that the first fuel rod support part 140a, which is the middle portion of the convex shape of the wire 110, presses and supports the fuel rod 200 to fix the fuel rod 200. . The method of claim 7, wherein The second fuel rod support part 140b, which is a portion between the wires 110 of the wire support 130, has a concave shape to correspond to an outer circumferential surface of the fuel rod 200 to press and support the fuel rod 200. Internal structure of the wire spring type support grid, characterized in that for fixing the position of the fuel rod (200).

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