JPH11118970A - Support lattice of reactor fuel assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damage of adjacent fuel assemblies due to mutual contact interaction of support lattices in refueling of a reactor and the like. SOLUTION: This support lattice 3 consists of a plurality of inner straps 35 arranged extending in parallel and perpendicular directions and assembled, and 4 sides outer straps 31 and 33 surrounding the inner strap 35 groups. The outer straps 31 and 33 in this case have at the both ends connection end parts and slope parts 31a and 33a next to the connection end parts so that the bent connection parts of the adjacent outer straps 31 and 33 overlap on each other and form welding connection parts and the upper and lower fringes of this welding connection parts are finished by grinding with larger slope angle than the slope parts 31a and 33a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a fuel assembly of a nuclear reactor, and more particularly to a structure of a fuel rod support grid of a fuel assembly of a pressurized water reactor.

[0002]

2. Description of the Related Art An example of a fuel assembly for a pressurized water reactor is shown in FIG. In general, the structure of the upper nozzle 1, the lower nozzle 3, a plurality of control rod guide tubes 5 connecting these two nozzles, and the upper part of the upper part fixed to the control rod guide tubes 5 at intervals in the longitudinal direction. The support grid 7, a plurality of intermediate support grids 9 and a lower support grid 11, a plurality of fuel rods 13 inserted and supported in the grid spaces of the support grids 7, 9, 11, and the support grid 11 and the lower nozzle 3. The fuel assembly 10 is constituted by the foreign matter filter 15 provided therebetween.

The above-described upper support grid 7, middle support grid 9 and lower support grid 11 are structurally substantially the same in shape, and FIG. Show. In FIG. 17, the inner straps 17 made of thin metal strips forming the support grid 9 are combined in parallel at equal intervals and perpendicular to each other to define a number of grid spaces 19 between each other. Further, the outer strap 2 interconnects the ends of the adjacent inner straps 17 to each other.
1 are provided on four sides to form a support grid 9 having a square outer shape as a whole. The control rod guide tubes 5 described above are inserted and fixed in some of the lattice spaces 19 in a predetermined arrangement, and the fuel rods 13 are inserted and supported one by one in the empty lattice space 19 in FIG.

FIGS. 18 and 19 show the structure of the corners of the support grid 9 on an enlarged scale.
A projection (also referred to as a dimple) 17a and a spring 17b are integrally formed by molding in correspondence with the center of the lattice space 19. Although not shown, dimple 17
a and the spring 17b are displaced in the width direction of the inner strap 17 and are formed separately on the front and the back. The dimples 17a and the springs 17b of the two opposing inner straps 17 defining one lattice space 19 form three support points for the fuel rods 13, and the fuel rods 13 inserted into the lattice space 19 are separated. Support elastically. On the other hand, as shown in FIG. 19, the outer strap 21 has a slope 21 on both sides adjacent to the end.
a, which terminates in a flat end 21b.
The adjacent outer straps 21 and 21 are fixed by welding by bending and overlapping the flat end portions 21b as shown conceptually in an enlarged manner in particular in FIG. The flat end 21b is flat without upper and lower side edges being inclined.

[0005]

The fuel assembly 10 having the intermediate support grid 9 and the other support grids 7 and 11 as described above may be lifted or hung by a crane during refueling of the reactor. I do. At this time, the support grid 7 above the fuel assembly 10 to be transferred and the intermediate support grid 9
And the lower support grid 11 may interfere with the support grids 7, 9, 11 of the adjacent fuel assembly 10 at rest,
The upper and lower portions of the inclined portion and the overlapping portion of the outer strap 21 at the corners (four places) where the risk is high are finished in a sharp and smooth state by grinding or grinding and polishing as conceptually shown in FIG. . The finishing of the corners by such grinding and polishing is performed by the upper support grid 7 and the intermediate support grid 9.
When both the lower support grid 11 and the lower support grid 11 are made of a nickel-based alloy material, the intended purpose is achieved.

However, if the intermediate support grid is formed of a zirconium-based alloy material in consideration of the neutron absorption of the core, the following problems occur. 1) Since the zirconium-based alloy material is about half as soft as the nickel-based alloy material, the intermediate support grid made of the zirconium-based alloy material has another support made of the nickel-based alloy material. Upon contact interference with the grid, the intermediate support grid may be scraped off by the softer material, and in some cases (depending on the compatibility at the time), although small, but slipping. 2) When the inclined portion adjacent to the end of the outer strap is slightly dug while slipping as shown in FIG. 22, the last slip-through position, that is, the welded portion of the overlapped portion is more rigid than the inclined portion. Is large and strong, there is a risk that it will be caught here and the shaft generated load will increase, causing damage to the support grid.

[0007]

According to the present invention, there is provided, in accordance with the present invention, a plurality of thin metal strip inner straps which extend in parallel and orthogonal directions and which are combined with one another. And a four-sided thin metal band outer strap surrounding the group of inner straps, the outer straps each having a joint end and a joint end at each end. And an inclined portion having a reduced width adjacent to the outer strap, wherein the bent joint ends of the adjacent outer straps overlap each other to form a weld joint, and upper and lower edges of the weld joint are formed by the upper and lower edges. It is configured by grinding and finishing at an inclination angle larger than the inclination part. Further in accordance with the present invention, in a support grid for a reactor fuel assembly having a basic structure as described above, said outer straps each have an end with a uniform slope that decreases in width and are adjacent to each other. The bent front ends of the ends of the outer strap are superimposed on each other to form a welded joint, and the upper and lower edges of the welded joint are smoothly ground. Further, according to the present invention, in the support lattice of the reactor fuel assembly having the basic structure as described above, one of the outer straps adjacent to the outer end has a joint end at both ends and a width adjacent to the joint end. Has an inclined portion that narrows,
The other of the adjacent outer straps has an outer overlapping end with a uniform slope that decreases in width, and the tip of the outer overlapping end is bent and welded to the outer surface of the joining end. It is composed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an end shape of a blank (before bending) of the outer straps 31 and 33 constituting the support grid according to the present invention. The outer straps 31 and 33 are integrally punched from a zirconium-based alloy thin strip, and have inclined portions 31a and 33a that are inclined in the direction of decreasing the width in the vicinity of the ends. The upper and lower side edges have not inclined joining end portions 31b and 33b. As is clear from the figure,
The joining ends 31b and 33b have the same width in the vertical direction (in the drawing), but the amount of projection of the joining end 33b is equal to the joining end 31b.
These are bent at bending positions 31c and 33c shown by two-dot chain lines in FIG. 1, and are temporarily assembled and welded as shown in FIG. In FIG. 2, the inner strap 35 is also made of the same material, and is arranged so as to extend in directions parallel and perpendicular to each other and is combined with each other as in the conventional case. Together with the support grid 30.

FIG. 3 shows the shape of the end of the support grid 30 as viewed from the direction of arrow III in FIG. 2, and FIG. 4 is a perspective view of the end. Welded. And after welding, the inclined portion 31
As shown in FIG. 5, a corner is chamfered in a range A of a and 33b, and further, in a range B above and below a joint end, the ground is finished with a larger inclination than the inclination of the inclined portions 31a and 33a. Although FIG. 4 shows a state before welding, it should be understood that these outlines are melted and changed by welding.

The support grid 30 having such four corner shapes
If the fuel assembly in which the fuel assembly is incorporated is lifted or hung during refueling, the fuel assembly may come into contact with and interfere with the adjacent fuel assembly that is stationary.
Is located on the outermost side of the fuel assembly, so that the support grids 30 often interfere with each other in a state as shown in FIGS. 6 and 7, for example. FIGS. 6A and 6B show a contact interference state generally called diagonal contact, in which FIG. 6A is a plan view and FIG. 6B is a side view. In this case, the outer straps 31 and 33 of the two supporting grids 30 that interfere with each other are formed by the inclined portions 3.
1a and 33a come into contact with each other, and even if the inclined portions 31a and 33a are cut down to a small extent in the range A (see FIGS. 3 and 4) as the fuel assembly moves up and down, the strong folded portions overlap. In the range B (see FIGS. 3 and 4), which is a welded portion, the inclination is further steep, so that the contact points are separated from each other, and no snagging occurs. FIG. 7 shows a contact interference state generally called irregular diagonal contact, and FIGS. 7A and 7B show similar states. In this state, one support grid 30
The outer strap 31 of the other support lattice 30 and the outer strap 33 of the other support lattice 30 are mainly in contact with each other, but a similar sliding state is obtained.

Next, a second embodiment of the present invention will be described.
FIG. 8 shows end shapes of blanks (before bending) of the outer straps 41 and 43 constituting the support grid of the present embodiment. The outer straps 41 and 43 are integrally punched from a zirconium-based alloy thin strip plate, and have inclined portions 31a and 33a that are uniformly inclined in the direction of decreasing the width in the vicinity of the ends, respectively. It continues to the edge tip. Then, it is bent at bending positions 41c and 43c shown by a two-dot chain line in FIG. 8, and is temporarily assembled as a support grid 40 and welded as shown in FIG.
Note that the inner strap 35 shown in FIG. 9 is also made of the same material, and is arranged so as to extend in directions parallel and perpendicular to each other and is combined with each other as in the conventional case. End is outer strap 4
1 and 43 to form a support grid 40.

FIG. 10 shows the shape of the end of the support grid 40 as viewed from the direction of arrow X in FIG. 97. FIG. 11 is a perspective view of the end, but the bent portions at the tips of the inclined portions 41a and 43a. Are overlapped and welded. This way,
As shown in FIG. 10, the vertical inclination of the tip end 41aa of the inclined portion 41a becomes large. Although not shown, the outer corners of the inclined portions 41a and 43a of the outer straps 41 and 43 are chamfered by grinding in the same manner as shown in FIG. FIG. 9 shows a state before welding, and it should be understood that these projections are melted and changed into a smooth shape by welding. In such an embodiment, as described above, the foremost end 41aa of the inclined portion 41a of the outer strap 41
Has an inclination greater than that of the other parts, so that the same effect of prevention of catching as in the first embodiment can be obtained. I have a slight dislike.

Further, as a compromise between the first embodiment and the second embodiment, further modified embodiments can be made as described below. That is, FIG. 12 shows the end shapes of the blanks (before bending) of the outer straps 41 and 33 constituting the support grid of the present embodiment.
Details of these outer straps 41 and 33 are as described above. Then, a bending position 41 indicated by a two-dot chain line in FIG.
It is bent at c and 33c, temporarily assembled as a support grid 50 as shown in FIG. The inner strap 35 is the same as described above, and the shape and the arrangement are the same.

FIG. 14 shows the shape of the end of the support grid 50 as viewed from the direction of arrow XIV in FIG. 13. FIG. 15 is a perspective view of the end, and is joined to the bent portion at the tip of the inclined portion 41a. The ends 33b are overlapped and welded. In this manner, as shown in FIG. 14, the tip 4 of the inclined portion 41a
The vertical inclination of 1aa increases. Although not shown, the outer corners of the inclined portions 41a and 33a of the outer straps 41 and 33 are chamfered by grinding in the same manner as shown in FIG. FIG. 15 shows a state before welding, and it should be understood that the protrusion of the welded portion is melted by welding and changes to a smooth shape. In such an embodiment, as described above, since the foremost end 41aa of the inclined portion 41a of the outer strap 41 has an inclination greater than the inclination of the other portions, even in the diagonal contact, in the irregular diagonal contact, Also, the same effect of prevention of catching as in the first embodiment can be obtained.

[0015]

As described above, according to the present invention,
The end shape of the outer straps forming the four corners of the support grid of the fuel assembly is formed as an inclined portion in which the width at the upper and lower sides adjacent to the overlap welding portion in the shape at the time of completion of production decreases toward the welding portion, The upper and lower side edges of the overlap welding portion are inclined more than the inclined portion. For this reason, at the time of refueling or the like, in the adjacent fuel assembly, the two support grids that were in contact with each other at the inclined portion follow the relative vertical movement, and are separated from each other due to the steep inclination at the overlap welding portion. The catch is properly prevented.

[Brief description of the drawings]

FIG. 1 is a partial elevational view showing a main part of a blank of an outer strap used in the configuration of a support grid according to a first embodiment of the present invention.

FIG. 2 is a partial top view showing a corner portion of the support lattice of the first embodiment at the time of temporary assembly.

FIG. 3 is a partial side view as viewed from the direction of arrow III in FIG. 2;

FIG. 4 is a partial perspective view showing a corner of the support grid of the first embodiment.

FIG. 5 is a partial sectional view taken along line VV of FIG. 4;

FIG. 6 is a diagram illustrating the operation of the embodiment.

FIG. 7 is a view for explaining the operation of the embodiment.

FIG. 8 is a partial elevational view showing a main part of a blank of an outer strap used in the configuration of the support grid of the second embodiment of the present invention.

FIG. 9 is a partial top view showing a corner portion during temporary assembly of the support grid of the second embodiment.

FIG. 10 is a partial side view as seen from the direction of arrow X in FIG. 9;

FIG. 11 is a partial perspective view showing a corner of a support grid of the second embodiment.

FIG. 12 is a partial elevational view showing a main part of a blank of an outer strap used in the configuration of the support grid of the third embodiment of the present invention.

FIG. 13 is a partial top view showing a corner portion during temporary assembly of the support grid of the third embodiment.

FIG. 14 is a partial side view as viewed from the direction of arrow XIV in FIG. 13;

FIG. 15 is a partial perspective view showing a corner of a support grid of the third embodiment.

FIG. 16 is a partially omitted elevation view of a fuel assembly in which the support grid according to the present invention is used.

FIG. 17 is a top view of a conventional support grid.

FIG. 18 is an enlarged partial top view showing a corner of the support grid of FIG. 17;

FIG. 19 is a partial elevational view showing a corner of the support grid of FIG. 17 in an enlarged manner.

FIG. 20 is a conceptual partial top view showing a corner portion of a conventional support grid in an enlarged manner.

FIG. 21 is a conceptual partial top view showing a corner portion of a conventional support grid in an enlarged manner.

FIG. 22 is a partial side view seen from the direction of the arrow in FIG.

[Explanation of symbols]

 Reference Signs List 30 Support lattice 31, 33 Outer strap 31a, 33a Inclined part 31b, 33b Joint end 31c, 33c Bend position 35 Inner strap 40 Support lattice 41, 43 Outer strap 41a, 43a Inclined part 41c, 43c Bend position 50 Support lattice

Claims (3)

[Claims] 1. A plurality of thin metal strip inner straps extending in parallel and orthogonal directions and combined with each other, and a four-sided thin metal strip surrounding a group of the inner straps. In a support grid for a reactor fuel assembly comprising outer straps, each of the outer straps has a joint end at each end and an inclined portion having a reduced width adjacent to the joint end. The bent joint ends of the strap are overlapped with each other to form a weld joint, and upper and lower edges of the weld joint are ground and finished at an inclination angle larger than the inclined portion. Support grid for reactor fuel assemblies. 2. A plurality of thin metal strip inner straps extending in parallel and orthogonal directions and combined with each other, and four thin metal strips surrounding the group of inner straps. In a support grid of a reactor fuel assembly comprising outer straps, the outer straps each have an end with a uniform inclined portion having a reduced width,
A reactor fuel characterized in that the bent extremes of the ends of adjacent outer straps are superimposed on one another to form a welded joint, the upper and lower edges of which are smoothly ground. Aggregate support grid. 3. A plurality of thin metal strip inner straps extending in parallel and orthogonal directions and combined with each other, and a four-sided thin metal strip surrounding the group of inner straps. In a support grid of a reactor fuel assembly comprising an outer strap, one of the outer straps adjacent to the outer strap has a joint end at both ends and an inclined portion having a narrow width adjacent to the joint end, The other of the adjacent outer straps has an outer overlapping end with a uniform slope that decreases in width, the tip of the outer overlapping end being bent and welded to the outer surface of the joining end. A support grid for a reactor fuel assembly.