KR810000037B1 - Peripheral pin alignment system for fuel assemblies - Google Patents

Abstract

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Description

Pin alignment device around fuel assembly

1 is a partial front view of a reactor according to the present invention.

2 is a perspective view of a lower core support structure in a preferred embodiment of the present invention.

3 is a partial side view of the core and supporting structures for supporting and aligning the core fuel assemblies.

3A is a partial side view of an upper end of a nuclear fuel assembly as another embodiment.

4, 4a, 4b, 4c are plan and schematic plan views of other embodiments taken along line 4-4 of FIG.

5 and 6 are cross-sectional views of FIG. 4 taken along lines 5-5 and 6-6, respectively, showing the corner support structure and the alignment pins of the two lower end assemblies being snapped.

The present invention relates to an apparatus for laterally aligning the lower end and the upper end of a nuclear fuel assembly within the core of a nuclear reactor.

Nuclear fuel assemblies that form the nuclear core of a reactor consist of a plurality of elongated fuel rods containing fuel or fissile material that are joined together into rectangular fuel assemblies to form a group.

Each of these rectangular fuel assemblies must be aligned exactly within the core within a predetermined tolerance.

Therefore, a device must be provided within the reactor to support the respective fuel assemblies forming the reactor core and core and to align each of these fuel assemblies in place. Recently, structural support of nuclear fuel assemblies in nuclear reactors has been made to be provided by hollow tubes extending vertically inside the fuel rod bundles.

These hollow tubes act as guides for the adjusting rod components and are attached to the top and bottom plates or assemblies. The fuel rods are aligned and supported in the structural aggregate formed by the induction tubes and the top and bottom plates by spacer grit attached to the induction tubes to provide lateral inhibition and some axial inhibition with respect to the fuel rods.

One of the devices already developed to support and align nuclear fuel assemblies in the core was to provide a lower core scaffold with pins slid into the extension of the downward adjustment rod guide tubes and facing upwards.

As a solid, the already known arrangement has been to provide holes in the lower core support plate to accommodate the downwardly directed fin-like extensions at the lower ends of the adjusting rod guide tubes. The contact surfaces between the top assembly of the fuel assemblies and the top guide plate typically include a plurality of holes in the top guide plate to accommodate the fuel assembly top assemblies or the adjustment rod guide tubes and the upwardly extending extensions.

In addition to the holes formed in the upper and lower support plates or the pins supported by the upper and lower support plates, these plates also have outlet holes through which the coolant flows to form a flow path for the coolant so that the coolant enters the core from the bottom to the core to the core. You can let go.

One of the difficulties in this conventional design is that these top and bottom core alignments and support plates are difficult to manufacture and costly.

In addition, installing a plurality of fins extending upwards or downwards around the cross section of the nuclear fuel reactor assembly creates a local area where the coolant is prevented from flowing through the core support plates and the fuel assembly.

Therefore, there is a need for core supports and fuel assemblies that avoid these difficulties and are easy to manufacture and low in cost.

According to the present invention, stronger and smaller tolerances provide better alignment compared to the prior art, lower coolant flow disturbances, thereby lowering pressure drop, improving the thermal margin of the core and Core support structures and nuclear fuel assemblies are provided that improve the ability of the fuel assemblies to induce during fuel loading. The new design of the present invention provides a lower core support structure consisting essentially of beams forming a grid network.

Small pads and alignment pins are welded or otherwise secured on top of the beams to provide support and heat transfer of the fuel assemblies.

The fuel assemblies themselves are provided with circumferential recesses in the lower end assemblies to receive a portion of the upwardly aligned alignment pins.

In a preferred embodiment, the alignment pins are arranged in a square matrix and the fuel assemblies have recesses located around the corners of the bottom assemblies.

In this arrangement, the respective corners of each fuel assembly bite with one quarter of one alignment pin.

Thus, only one alignment pin is required for each fuel assembly located inside the core.

The same one pin per fuel assembly has been adopted for use in the top fuel assembly assembly and the top core support plate.

Thus, the upper end assembly of the fuel assemblies will be provided with a perimeter recess adapted to bite with a quarter of the alignment pins protruding downward from the upper core alignment plate.

As one possible modification, springs may be provided on the alignment pins facing down the upper core alignment plate such that the compression of the springs of the heating fins may be used to provide fuel assembly pressing.

In another arrangement, a portion of the top assembly of the fuel assembly may be provided with a spring rather than an alignment pin to provide a pressing force against the fuel assembly.

FIG. 1 shows a reactor 10 including a furnace 12 having an active core or fuel zone 14 therein. The core 14 includes a vertical fuel assembly 16 at equal intervals in the longitudinal direction supported in place by the lower support structure 18 for flowing the fluid coolant to the core 14. The core support shroud 20 surrounds the core 14 and extends upwardly from the lower support structure 18. The lower support structure 18 and the entire core fuel assembly 14 are vertically supported by the support bridge 31 and the core support barrier 24. By the way, the core support barrier 24 is suspended from the container flange 26 by the lip 28 biting with the flange.

In general, as can be seen in FIG. 3, nuclear fuel assembly 16 includes a plurality of nuclear fuel components 30 extending in the longitudinal direction and a plurality of hollow induction tubes interspersed between components 30 in an array of fuel components 30. 32, 34.

In the arrangement shown, nuclear fuel assembly 16 includes four outer guide tubes 32 extending vertically, which are disposed adjacent to four corners of nuclear fuel assembly 16 and attached to upper and lower assembly 36, 38. Fifth guide tube 34 is centrally located within each fuel assembly 16 and is also attached to upper and lower assembly 36, 38. The top of the induction tubes 32, 34 may all extend above the top assembly 36 but the bottom should end at the bottom assembly 38. Induction tubes 32 and 34 and the upper and lower end assemblies 36 and 38 form a structural framework for fuel device 16.

A plurality of spacer grids 40, usually arranged in a rectangular shape, are properly secured to the induction tubes at intervals along the induction tubes 32,34. The spacer grit 40 acts to support the shooter's nuclear fuel components 30 parallel in a vertical position. The grit 40 are constructed in a conventional design and consist of an array of openings with the fuel component 30 extending therethrough and having a mutually aligned rectangular arrangement.

Located above core area 14 is an guiding structure 42, which aligns the upper ends of the nuclear fuel assembly assemblies 16 and also acts to guide adjustment components (not shown) from the core region 14 and into the core region 14. .

Induction structure device 42 is described in US Pat. No. 3,849,357, generally entitled “Induction Structure for Adjustment Components,” filed June 28, 1972, a detailed description of which is not necessary for this application. Inductive structure device 42 generally comprises a pair of tube plates 46, 48 spaced vertically, with intermediate tubes 47. Plate 48 is generally located above the entire cores 14 and serves as an upper core alignment and support plate. As best shown in FIG. 2, the lower core support structure 18 includes a plurality of support members or beams 19 extending in one direction and a plurality of second support members or beams 21 extending across the direction. .

The grooves are gripped or notched so that the beams 19 and 21 can be assembled into the grit net work of the intersecting support members as shown.

The cores 19 and 21 are supported by a band 29 which is in contact with the core support barrier 24. In addition, a selected number of beams 19, 21 extend downward to support the coolant flow distribution plate 27 having the coolant flow distribution holes 25.

On top surfaces of beams 19 and 21 are placed metal pads 22 welded or otherwise secured, and alignment pins 23 that are longitudinally aligned.

The pads 22 and the pins 23 are arranged in a square matrix with a spacing or reference dimension equal to the width of the fuel assemblies 16. With this arrangement, fuel assemblies 16 in core 14 will be placed on core support structure 18 and supported by core support structure 18 in such a way that the intersection of four adjacent fuel assemblies 16 is located on one of the pins 23. Thus, the pins 23 support and align the bottom of the fuel assembly 16 and the pads 22 act as a support member to seat the fuel assemblies 16.

During normal operation of reactor 10, fluid coolant, typically water, enters reactor 10 through inlet nozzle 66 and flows downward around the outside of the core support barrier 24. The coolant then flows inwards and upwards through the holes 25 of the coolant flow distribution plates 27. Because of the open structure of the grit formed by the beams 19, 21, a very evenly distributed coolant flow is present across the core support structure 18. As the coolant flows upward through the reactor core 14, the coolant takes away the heat generated by the nuclear fission of the fuel assembly 16.

The heated coolant then flows through the holes 68 of the lower tube tube 48 to an outlet region 56 located between the two tube plates 46, 48.

This fluid is conveyed from the outlet zone 56 through an outlet nozzle 70 to a steam generator or similar device, acting as a working medium for heating the evaporating fluid to be supplied thereto.

The bottom assembly 38 consists essentially of the bottom plate 54, which extends downward from the plate 54 and has an alignment post bound to the plate.

In an exemplary embodiment, the alignment posts 60 are located in the corners of the bottom assembly of the square fuel assembly and include inwardly facing recesses 62.

The inwardly facing recesses 62 generally consist of a cone having a quarter size of cylindrical space. The cylindrical recesses 62 are adapted to receive at least a portion of the cylindrical alignment pin 23 extending upwardly in the recess. Thus, each of the alignment posts 60 is adapted to slide into place after partially accommodating one alignment pin 23 in the post 60, so that the four corner alignment posts 60 interlock with each other for one of the four corner alignment pins 23. Is located.

Four corner alignment posts 60 are also seated on one of the pads 22, respectively.

Lower plate 54 includes a plurality of openings (shown in FIG. 4) of various sizes and shapes, which coolants through the openings to cool and remove heat generated by the nuclear fuel during normal operation of the reactor. Allow free flow of

Alignment pins 23 are shown to be constructed in a cylindrical shape with a conical portion 23 'facing upwards.

However, it should be recognized that the figures show only good practice, and it is conceivable that the alignment pins 23 may have other shapes than cylindrical ones. In addition, the downwardly aligned postposts 60 may have various forms that make up spaces 62 including planes and angles, such as the corner of a square space.

Therefore, it is conceivable that the alignment posts 62 may consist of a cylindrical pin that snaps together with a cylindrical pin along only two contact lines.

Another feature to be appreciated is that the upwardly facing cone 23 'of pin 23 acts as a cone to guide the fuel assembly to a suitable position during the refuel loading process.

In this regard, the design of the present invention allows the alignment pins 23 to be positioned on the periphery of the fuel assemblies, with fewer alignment pins per fuel assembly, and more conical 23 'laterally than in conventionally known designs. It is advantageous over the prior art in that larger alignment pins 23 can be merged so that they can be accessed. This cone 23 'is of considerable importance where the core is designed to withstand large seismic forces. In this core, the spacer grit is more important and protrudes outward from the outer wall of the fuel assembly to reduce the separation between adjacent fuel assemblies in the core. In this arrangement, during the refuel loading process, the spacer grit is likely to be caught in the spacer grit of the adjacent fuel assembly.

Thus, the cone 23 'with increased dimensions keeps the fuel assemblies in place by keeping the spacing between the fuel assemblies larger than previously possible.

4 shows a core arrangement made possible by the present invention and which is a preferred embodiment of the present invention. In this preferred embodiment, the alignment pins 23 are arranged to have a rectangular or square arrangement with the same spacing or reference dimensions as the lateral dimensions of the rectangular or square fuel assemblies 16.

As already mentioned above, the lower end assemblies 38 of the fuel assemblies 16 have alignment posts 60 in the corners and comprise side recesses 62 shaped to have a quarter size of the cylindrical space.

In this arrangement, the fuel assembly 16 will be disposed in the core in such a way that the corners of the fuel assembly 16 and the downwardly aligned alignment posts 60 are located above the alignment pins 23 and adjacent the alignment pins 23, respectively.

Since each of the alignment posts receives only one quarter of the alignment pins 23, it can be seen that the fuel assemblies located inside the core need only one fin per fuel assembly.

The need for one fin per fuel assembly represents a significant reduction in the number of fins required in the prior art, which significantly reduces material and production costs.

4B shows an alternative embodiment in which the pins are located along the sides of the fuel assemblies rather than in the corners of the fuel assemblies.

In this arrangement, the alignment coasts will be located on the sides, not the corners, of the fuel assemblies and will be adapted to accommodate 1/2 but not 1/4 of the fin.

4C shows a modified preferred embodiment where the fuel assemblies 16C have hexagons rather than squares. In this arrangement with the fuel assemblies shown at 16C, the pins will be located in the corners of the fuel assemblies. In the arrangement shown in FIG. 4C, one fin is provided for each fuel assembly because each corner of the hexagonal fuel assemblies receives one third of the fin.

Many other modifications to this form are possible within the scope of the invention.

For example, alignment pins may be placed in two opposite corners.

Thus, each of the alignment pins will bite with only two alignment pins so that four fuel assemblies are used with half pins per fuel assembly.

Looking at the top of the nuclear fuel assembly in FIG. 3, essentially the top assembly 36 is a transversely extending top plate 44 of guide tubes 32, 34 extending vertically, and transversely extending the guide tubes from the top plate 44. A press spring 50, spaced parallel to the upper plate 44 at intervals, and a coil spring device, such as a coil spring 52, which is compressed and supported between the press plate 50 and the upper plate 44.

When the core of the reactor is assembled, a form is provided in which the spring 52 is pressed against the pressing plate 50 so that a downward force on the top plate 44 can be provided.

This downward force prevents the support pad 22 from being lifted by the outflow of coolant through the fuel assembly 16.

In the embodiment shown in FIG. 3, the device provided against the upper press plate 50 comprises an upper core alignment support plate 45 and an upper alignment pin 58.

The upper alignment pins 58 consist of a cylindrical portion and a conical portion 58 'facing downward in the longitudinal direction.

Press tube 50 of the nuclear fuel assembly is provided with a recess having a conical tapered downward and outward. In a similar manner to the bottom assembly, these side portions of the top assembly will be located at the corners or sides.

Another embodiment is shown in FIG. 3A, in which the top assembly 36a is simplified by including a core presser plate and a plate 50a that acts as the top tube of the fuel assembly 16.

In this embodiment, the alignment pin 58a depends on the upper core alignment plate 48a and has a spring to provide the core pressing force and to counter fuel assembly 163.

Claims (1)

A reactor having a longitudinal axis, a core support structure positioned within the container, and an alignment pin protruding from the core support structure along a direction parallel to the longitudinal axis, the nuclear fuel part and the fuel part being supported and positioned. 10. An improved fuel assembly having at least one end assembly for the purpose of claim 1, wherein the fuel assembly comprises a device for providing side recesses to receive at least a portion of the alignment pins.

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