JPH01227991A - Fuel assembly - Google Patents

Abstract

PURPOSE:To prolong the life of a channel box by increasing the thickness in the corner parts of the channel box with respect to the thickness in the lateral center parts. CONSTITUTION:The angle parts (corner parts) in the cross section of the channel box 1 is formed to the thickness larger than the thickness in the lateral center parts. The bottom end regions l to be fitted to a lower tie plate are formed to the thickness uniform in the cross section and is the same thickness as the thickness of the thick angle parts. The angle parts are formed to such thickness at which said parts is thicker 1.4-1.7 times the lateral center parts in such a manner that guide rollers 10 of a control rod 9 faces the thin lateral center parts if the diameter of the guide rollers 10 is relatively large and that the guide rollers face the thick angle parts if said diameter is relatively small. The stresses and deformation of the channel box are thereby decreased without increasing the volume thereof and the life of the channel box is improved without degrading the economy of neutrons.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a channel box for a fuel assembly, and particularly to a structure of a channel box suitable for improving its life.

[Conventional technology]

FIG. 2 shows a conventional fuel assembly 2. As shown in FIG. The fuel assembly 2 includes a plurality of fuel rods 3 and water rods 4 bundled together using a plurality of spacers 5, and the fuel bundle in which the upper and lower ends of the fuel rods 3 are supported by an upper tie plate 6 and a lower tie plate 7 is placed in a channel box 1. It has a housed structure.

The channel box 1 is a long rectangular tube made of Zircaloy and has the following functions.

(1) By forming isolated coolant flow paths for each fuel assembly, the flow rate of the coolant flowing within the fuel assembly is ensured, and the cold electrode material flows uniformly.

(2) Form a guide surface when inserting and withdrawing control rods between fuel assemblies.

(3) Ensure the rigidity of the fuel assembly and facilitate handling.

During nuclear reactor operation, a pressure difference is created between the inner and outer surfaces of the channel box 1 due to the flow pressure of the coolant flowing through the fuel assembly 2, and the channel box 1 is exposed to neutron irradiation, causing the channel box 1 to be deformed to bulge outward. . Such deformation may reduce the gap between the control rod and the control rod, which may impede the insertion and withdrawal operations of the control rod, and increase the gap between the channel box 1 and the lower tie plate 7, reducing the leakage flow rate. may increase, and the necessary supply of coolant to the inside of the fuel assembly 2 may be inhibited.

For this reason, in the past, the wall thickness of the channel box 1 was made sufficiently thick to suppress deformation, and a leaf spring 8 as shown in FIG. 1 was interposed between the channel box 1 and the lower tie plate 7 to prevent leakage. Controls the flow rate. Furthermore, the period of use of the channel box 1 is limited, and, for example, reuse of the channel box 1 dismantled from spent fuel is avoided.

However, from the perspective of neutron economy, it is desirable to reduce the wall thickness of channel box 1 as much as possible to reduce the volume ratio of structural materials in the reactor core. It is desirable to reduce the amount of waste to be disposed of by, for example, extending the period of use of the channel box 1 as long as possible and reusing the used channel box 1.

Furthermore, in recent years, fuel burn-up has been increasing from the viewpoint of improving fuel economy, so the channel box 1 will also be used for a longer period of time than in the past. For this reason, the deformation during use increases compared to the conventional one, reducing the design margin, and the spring force of the plate spring 8 that controls the leakage flow rate decreases as the period of use becomes longer, so that the original function is not sufficient. There is a possibility that it will not be able to perform effectively.

Based on the above background, as a method of creating a structure that can withstand long-term use by not increasing the volume of the channel box 1 much and suppressing deformation to a small value to improve the lifespan and endure long-term use, for example, Japanese Patent Publication No. 57-1752
As described in No. 36, the stress is reduced by making the corner wall thickness relatively thicker in the cross section of the channel box 1, where the stress due to the pressure difference between the inside and outside of the channel box 1 is highest,
For regions with relatively low stress, a thinner structure may be considered as an option.

In addition, as a method for controlling the coolant leakage flow rate at the lower end of the channel box 1, for example,
As described in No. 33, it is possible to suppress the deformation of the lower end of the channel box 1 by increasing the rigidity by increasing the thickness of only the lower end of the channel box 1, for example, without using the leaf spring 8.

[Problem to be solved by the invention]

Said Japanese Unexamined Patent Publication No. 57-175286 and Japanese Patent Publication No. 51-42
Although the method described in No. 33 eliminates the drawbacks of the prior art, it does not take into account the relationship between the channel box and the control rods facing each other, and unless the control rods currently in use are replaced by changing the design. However, there was a problem that the channel box of these methods could not be introduced as is, and these methods that involved replacing the control rods were not realistic from an economic point of view.

As described above, the channel box 1 has the function of guiding the control rod. A guide roller is attached to the tip of the control rod in order to smoothly perform insertion and withdrawal operations, and the control rod moves up and down while the guide roller is in contact with the channel box.

The channel box described in JP-A No. 57-175286 is characterized by thick walls at the corners of the cross section and thin walls at the center of the sides, but the amount of guide roller protrusion from the control rod blade is is smaller than the difference in wall thickness between the thick part at the corner and the thin part at the center of the side.

The control rod blade and the thick corner part come into contact, and the guide roller cannot come into contact with the channel box. As a result, the frictional force on the control rod increases, which may impede control rod operation.

Similarly, in the case of the example in Japanese Patent Publication No. 51-4233, if the difference in thickness between the thick wall part at the lower end and the other parts is greater than the amount of protrusion of the guide roller, the control rod blade and the thick wall part at the lower end is in contact with the channel box, and the guide roller cannot come into contact with the channel box. As a result, the frictional force of the control rods increases, potentially causing the same problem as described above.

An object of the present invention is to provide a fuel assembly equipped with a channel box that can extend the service life without increasing the volume and can be introduced without replacing the control rods currently in use. .

[Means to solve the problem]

The above purpose is to increase the thickness of the corner part in the cross section of the channel box by 1.4 to 1.7 compared to the thickness of the center part of the side.
The thickness is about twice as thick, and the thin area at the center of the side is 35 to 45% or 60 to 70% of the inner width of the channel box, and at the lower end that fits with the lower tie plate,
This is achieved by making the wall thickness uniform and having a structure that has the same wall thickness as the inner corner portion.

[Effect]

The channel box of the present invention is made thicker only at the corners where the stress generated by the pressure difference between the inside and outside is maximum, and the central part of the side is made thinner to suppress volume increase, and the amount of deformation in the cross section is reduced. Widen the gap between the control rod and the control rod at the position where it is maximum.

When applying such a channel box to a core in which control rods with guide rollers having a relatively small diameter are used, the thick corner regions are extended in the direction in which the guide rollers are located to accommodate manufacturing tolerances and The thick region is defined so that the thick portion and the guide roller always face each other even if play between the guide roller and the channel box is taken into consideration. On the other hand, when applying the channel box to a core in which control rods with guide rollers with relatively large diameters are used, even if manufacturing tolerances and play between the guide rollers and the channel box are taken into consideration, Define the thick area so that the guide rollers never face each other.

To obtain such a channel box, the thick-walled region may be set to occupy 55 to 65% of the inner width in the former case, and 30 to 4% of the inner width in the latter case.
It may be set so that it occupies 0%. (Therefore, the proportion of the thin area at the center of the side is 35 to 45% of the inner width.
% and 60-70%. ) By setting the above-mentioned limits on the thick-walled corners of the channel box (assuming, of course, that the range that can reduce stress and deformation is satisfied), the thick-walled corners and control rod blades can be It can prevent contact and prevent unnecessary frictional force from occurring.

As a result, the service life can be improved without replacing the control rod or increasing the volume of the channel box.

In addition, by making the wall thickness of the bottom end of the channel box uniform and the same as that of the corners, even when applied to a core where control rods with guide rollers with relatively small diameters are used,
Since the lower end thick portion and the control rod blade do not come into contact with each other, the conventional problem of making the lower end portion thicker can be solved. Moreover, since it is possible to thicken the lower end without changing the design of the control rod, the problem of increased leakage flow rate due to increased deformation of the lower end can be solved simply by applying the channel box of the present invention. The leaf spring used conventionally to control the leakage flow rate is no longer required.

Note that since the lower end thick portion is located below the fuel effective portion, there is no effect on the neutron economy due to thickening of the region.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1, 3, and 4.

Figure 1 shows a channel box 1 which is an embodiment of the present invention.
FIG. 3 and FIG. 4 are diagrams showing the cross section of section A in FIG. 1 and the engagement of the guide roller 10 of the control rod 9.

The corner wall thickness in the cross section of the channel box 1 of the embodiment shown in FIG. In the region shown in ), the wall thickness is uniform in the cross section and is the same thickness as the thick corner portion.

The channel box 1 of the embodiment shown in FIG. The cross section of the channel box 1 in the case where it is applied to a so-called one-lattice structure core with a narrow
As shown in the figure, the areas of the thick interior and the thin portion are distributed so that the guide roller 10 of the control rod 9 faces the thickness of the central portion of the side.

On the other hand, the control rod 9 whose guide roller 10 has a relatively small diameter
The cross section of the channel box 1 is applied to a core in which control rods are used (for example, a core with a so-called C-lattice structure in which the water gaps on the control rod side and non-control frame side are equal), as shown in Fig. 4. The thick corner region of the rod 9 is extended to a position facing the guide roller 10.

From the viewpoint of reducing the volume of the channel box 1 while keeping the stress generated in the channel box 1 almost the same,
It is preferable to make the corner wall thickness as thick as possible and the wall thickness at the center of one side to be thinner.

However, in the case of application to a reactor core in which control rods 9 with guide rollers 1o having a relatively large diameter are used,
The difference in wall thickness between the thick part at the corner and the thin part at the center of the side is less than half the difference between the diameter of the guide roller 10 and the thickness of the control rod blade (actually, considering manufacturing tolerances and play of the guide roller 10) (becomes a small value). In addition, in the case where the guide roller 10 is applied to a core where the diameter is relatively small and the control rod 9 is used, extremely thickening of the corners will increase the volume of the channel box 1, resulting in neutron economy. Therefore, the relative ratio between the corner wall thickness and the side center wall thickness depends on the relationship between the control rod 9 and the guide roller 10, the amount of stress/deformation and the volume (or cross-sectional area) of the channel box 1. ), as will be described later, the corner wall thickness is approximately 1.4 to the side center wall thickness.
A wall thickness combination of 1.7 times is desirable.

Next, the distribution of the thick-walled corner areas and the thin-walled areas at the center of the sides in Figures 3 and 4 is determined from the viewpoint of preventing contact between the control rod blade and the thick-walled corner areas, as described above. Thus, in the case of FIG. 3, the guide roller 10 always faces the thin part at the center of the side, and in the case of FIG. 4, the guide roller 10 always faces the thick part at the corner.

The guide roller 10 of the control rod 9 is located at a position closer to the corner from the center of the channel box 1 by about 25% of the inner width of the channel box 1.

The position of the guide roller 10 of the control rod 9 may vary by approximately ±5% of the inner width of the channel box 1 due to the gap between the channel box 1 and the control rod 9, the backlash of the guide roller 10, and manufacturing tolerances, so take this into account. However, the guide roller 10 of the control rod 9 must not deviate from the thick corner portion or the thin center portion of the side.

Therefore, in the case shown in FIG. 3, since the guide roller 10 should not face the thick corner part as described above, the area of the thin part at the center of the side should be at least 2X ( 25+5)=6Q% or more. In addition, in the case shown in FIG. 4, contrary to the front case, the guide roller 10 and the thin part at the center of the side must not face each other, so the area of the thin part at the center of the side is 2 times the inner width.
×(25-5)=40% It should be about 40%.

(Since the variation in the position of the guide roller 10 depends on the wall thickness of the corner, the area of the thin wall part at the center of the side in practical use is 35 to 35 mm of the inner width.
The range is 45%. ) The specific effects of the embodiments described above are shown in Figures 5 to 8.
This will be explained with reference to the figures.

FIG. 5 shows the ratio of the width a of the thick corner region to the inner width of the channel box 1 and the cross-sectional area 9 of the channel box 1 in the embodiment shown in FIG.

This figure shows the relationship between stress and deformation compared to conventional methods. The shaded area in FIG. 5 is the guide roller 1 of the control rod 9.
0 corresponds to a region that does not face the corner thick portion. (a/b
≦0.4, that is, the thin-walled area at the center of the side is 60% of the inner width.
% or more) As is clear from Figure 5, in order to reduce the stress and deformation compared to the conventional method, a/b must be secured to be approximately 0.3 or more (in other words, the area in which the thin wall at the center of the side is (70% or less of the width) is required.

Therefore, together with the above results, it can be seen that in the embodiment shown in FIG. 3, it is desirable that the thin region at the center of the side be 60 to 70% of the inner width.

(Thickness at the center of the side)/(thickness at the corner) and cross-sectional area 9 in the embodiment shown in FIGS. 3 and 4.

The relationship between the stress and the amount of deformation compared to the conventional method is shown in FIGS. 6 and 7, respectively.

In Fig. 6, a/b = 0.4 (that is, the thin area at the center of the side is 60% of the inner width), and in Fig. 7, a/b = 0.
6 (In other words, the thin area at the center of the side is 40% of the inner width.
) shows the results for the case.

Assuming that the cross-sectional area of the channel box 1 is the same or smaller than the conventional one, the bending rigidity is the same as the conventional one, and the amount of stress and deformation is the same or smaller than the conventional one, (thickness at the center of the side)/( It can be seen from FIG. 6 that the corner wall thickness is 0.6 to 0.7, and from FIG. 7 to 0.6.

Therefore, in the embodiment shown in FIG. 3, the corner wall thickness is about 1.4 to 1.7 times the side center wall thickness, and in the embodiment shown in FIG. It can be said that the thickness should be approximately 1.7 times the thickness.

In the embodiments shown in FIGS. 3 and 4, the interference position with the control rod 9 when the channel box 1 is deformed is different due to the diameter of the guide roller 10 and the thickness of the control rod blade. The guide roller 1o position and the latter are the center positions of the sides of the channel box 1.

In the embodiment shown in FIG. 3, the amount of deformation at the center of the side is approximately 95% of the conventional amount (FIG. 6), but the guide roller 1
The amount of deformation at the position facing 0 is approximately 84% of the conventional amount due to the thickening of the corners.

Channel box 1 at the position of guide roller 10
Due to the thinner center of the side, the gap between the
The gap will widen by about %. As a result, the lifespan of Channel Box 1 has been extended by more than 30% (1,1
310,84=1.35).

On the other hand, in the embodiment shown in FIG. 4, as shown in FIG. 7, the amount of deformation at the center of the side is the same as the conventional one. In addition, due to the thinning of the central part of one side, the gap between the channel box 1 and the control rod 9 will be about 23% wider than before, so the life of the channel box will be increased by more than 20% ('1
．． 23/1.00=1.23).

Next, in the embodiment shown in FIG. 1, the lower end area (the area indicated by Ω in FIG. 1) that fits with the lower tie plate 7 is -
The effect of making the thickness within the same thickness as the corner portion will be explained with reference to FIG.

FIG. 8 shows the relationship between the fuel residence period in the reactor and the leakage flow rate in the case where the leaf spring 8 for controlling the leakage flow rate is not interposed between the channel box 1 and the lower tie plate 7, and the broken line indicates the conventional example and the solid line represents an embodiment of the present invention.

From FIG. 8, it can be seen that in the example of the present invention, the leakage flow rate is lower than the leakage flow rate at the beginning of the life of the conventional example throughout the life of the fuel. Since the leaf spring 8 for controlling the leakage flow rate is not required if the leakage flow rate is around the initial level of the conventional example, the leaf spring can be removed by applying the channel box 1 of the embodiment of the present invention. It becomes possible to do so.

Another embodiment of the present invention will be described with reference to FIGS. 9 to 12.

FIG. 9 shows a bird's-eye view of one embodiment of the present invention, and FIGS. 10 and 11 show parts A and B, respectively, of the embodiment shown in FIG. Further, FIG. 12 shows a cross section of the channel box 1 and the engagement with the control rod 9 in another embodiment.

In the embodiment shown in FIG. 9, similarly to the embodiment shown in FIG. 1, the corner wall thickness /1,1 of the channel box 1 is thickened, and the center wall thickness of the side is relatively thick (see FIG. 10). , the region of the lower end that fits with the lower tie plate 7 (see Q in Figure 9).
In the region shown in ), the thickness 1 is uniform in the cross section and the same thickness Pi as the thick corner portion (see Fig. 11),
This embodiment differs from the embodiment shown in FIG. 1 in that the corner portions are built up inside the channel box 1 to make them thicker.

The ratio of the corner wall thickness to the side center wall thickness and the ratio of the corner thick wall area to the side center thin wall area of the channel box 1 in this embodiment are basically the same as in the embodiment shown in FIG. , the ratio of the thick corner area to the thin area at the center of the side is in the range of 3=7 to 4:6 (i.e., from the viewpoint of reducing the cross-sectional area of the channel box 1 and improving neutron economy). It is desirable that the thin area at the center of the side be 60 to 70% of the inner width.

Next, in another embodiment shown in FIG. 12, the ratio of the corner wall thickness to the center wall thickness of the side is the same as that of the embodiment shown in FIG. By interposing a region having a thickness between the two, the region and the control rod 9 are interposed.
The structure is such that the guide rollers 1o of the two face each other. In this embodiment, the thin area at the center of the side is 35 to 45% of the inner width, and the thick area at the corner is 30 to 40% (two locations) of the inner width.

Therefore, each region of intermediate thickness facing the guide roller 10 is approximately 10% of the inner width. This embodiment has the advantage that the cross-sectional area of the channel box 1 is smaller than that of the embodiment shown in FIG. 4, and the volume can be reduced.

In the case of this embodiment as well, in the region where the lower tie plate 7 is fitted, the thickness is uniform over the entire cross section, as in the embodiment shown in FIG. 1, and has the same thickness as the thick corner portion.

Even when the embodiments shown in FIGS. 9 and 12 are applied, effects substantially equivalent to those of the embodiment shown in FIG. 1 can be obtained.

A method of manufacturing the channel box 1 of the embodiment described above will be explained with reference to FIGS. 13 to 15.

The plate material 11 forming the channel box 1 has an uneven cross section and is uniform in shape and size over its entire length, as shown in FIG. 13(a), for example.

Such a plate material 11 is made up of a plurality of rolls 12 and 12' having different diameters as shown in FIG. Rolling is carried out by a group of separated rolling rolls 13.

The plate material 11 manufactured by the method described below is shown in FIG.
As shown in b), the convex portion, that is, the thick inside, is bent to form a U-shape. The member 1 is attached to the end of the elongated U-shaped member 14.
A short U-shaped member 1 having the same thickness fq as the corner wall thickness of 4.
5 are joined by welding, for example, as shown in FIG. 13(c), and then the two members 16 are faced and joined by welding or the like,
A long rectangular cylindrical tube is finished as in the embodiment shown in FIG.

Note that the short U that is joined to the end of the long IJ-shaped member 14
In the U-shaped member 15, the end of the U-shaped cross section is, for example, the first
As shown in FIG. 5(a), the thickness may be the same as that of the thin portion of the elongated U-shaped member 14. By doing this, after joining the long U-shaped member 14 and the short IJ-shaped member 15, the member 2
When joining books together to make a long rectangular tube, the thickness of the joint is constant over the entire length (see Figure 15 (b)), which has the advantage of making it easier to set conditions for welding, etc. be.

On the other hand, in the embodiments shown in FIGS. 1, 9, and 12, long U-shaped members 14 are joined together to form a long rectangular cylindrical tube, and then short U-shaped members 15 are joined together. The rectangular tube may be finished by joining the long rectangular tube by welding or the like, or
A similar structure can be obtained by making the long rectangular cylindrical tube to the final length in advance and attaching a plate material of a predetermined thickness to the thin area at the center of the lower end.

In the detailed explanation of the present invention described above, only the case of a rectangular long pipe is typically mentioned, but the present invention is also applicable to polygonal long pipes such as a hexagonal long pipe. It goes without saying that it is possible.

〔Effect of the invention〕

According to the invention, the volume (cross-sectional area) of the channel box
Stress and deformation can be reduced without increasing the neutron economy, and the gap between the control rod and the control rod can be widened.
~30% improvement.

Moreover, it has the advantage of being able to be introduced without replacing the control rods currently in use.

In addition, the leakage flow rate can be controlled without intervening a leaf spring between the channel box and the lower tie plate, eliminating the need for a leaf spring, making it easier to attach the channel box to the fuel bundle than before, improving work efficiency. It has the effect of

[Brief explanation of the drawing]

Fig. 1 is a detailed view of a channel box according to an embodiment of the present invention, Fig. 2 is a vertical sectional view of a conventional fuel assembly, and Figs. 3 and 4 are a diagram of a channel box according to an embodiment of the present invention. Cross-sectional views, FIGS. 5 to 8 are diagrams illustrating the present invention in detail,
The figure is a detailed diagram of a channel box according to another embodiment of the present invention, FIGS. 10 and 11 are sectional views of parts A and B, respectively, of FIG. 9, and FIG. 12 is a detailed diagram of a channel box according to another embodiment of the present invention. A cross-sectional view of the channel box, FIG. 13 is a diagram explaining the method of manufacturing the channel box of the present invention, FIG. 14 is a diagram showing an example of a rolling roll for plate material, and FIG. 15 is a diagram of the lower end parts of the channel box, and It is an assembly diagram. 1... Channel box, 2... Fuel assembly, 3
... fuel rod, 4 ... water rod, 5 ... spacer,
6... Upper tie plate, 7... Lower tie plate, 8... Leaf spring, 9... Control rod, 10... Guide roller, 11... Plate material, 12.12'... Rolling roll, 13... Rolling roll, 14... Long U-shaped member, 15... Short U-shaped member, 16... U-shaped member,
17...Ponchi, 18...Da 1st Exit Z Ward 3 Figure Iυ Figure 4 Figure 5 Rikake 1 6 Figure (Kyuchu Kyuu Iwa P Toro Sono/Hiba Department Printing Rod Figure 7 (jezz Nakazushima fr/V)/ (7M5rl) 1st
20 Zo 13 (Kuno 14/Z Gua 5)

Claims (1)

[Scope of Claims] 1. In a fuel assembly in which a fuel bundle in which a plurality of fuel rods and water rods are bundled with a plurality of spacers and whose upper and lower ends are supported by upper and lower tie plates is housed in a channel box, The corner wall thickness in the cross section of the channel box is made 1.4 to 1.7 times thicker than the side center wall thickness,
In addition, the thin wall region at the center of the side is 35 to 45% or 60 to 70% of the inner width of the channel box, and the wall thickness is the same in the cross section in the region where the channel box and the lower tie plate fit together. What is claimed is: 1. A fuel assembly comprising a channel box having the same wall thickness as the thick corner portion. 2. The fuel assembly according to claim 1, further comprising the channel box in which the corner and lower end portions of the channel box are raised outward. 3. The fuel assembly according to claim 1, wherein the corner and lower end of the channel box are raised inwardly, and the central region of the side that is concave inwardly is 60 to 70% of the inner width of the channel box. body. 4. The corner thick region of the channel box is 15 to 20% of the inner width of the channel box per location, and the thin center region of the side is 35 to 45% of the inner width of the channel box, 3. The fuel according to claim 1, wherein the remaining region of the channel box is between the thick walled corner portion and the thin walled portion at the center of the side, and the wall thickness is approximately intermediate between the corner and the center of the side. Aggregation. 5. In the channel box according to claim 1, 2, 3, or 4, the vicinity of the center of the side of two opposing surfaces of the surfaces constituting the lower end thick portion is A channel box whose wall thickness is the same as the thin wall at the center of the sides other than the bottom edge. 6. The channel box according to claim 5, wherein the cross section is polygonal. 7. A plate material having thick and thin parts in its cross section, which is uneven, and whose shape and dimensions in cross section are uniform over the entire length, is formed by bending the convex parts, that is, the thick parts. A method for manufacturing a structural material, characterized in that a polygonal long tube is formed by a plurality of the members. 8. A method for manufacturing a channel box, which comprises joining a short tubular member having the same wall thickness as the corner wall thickness of the structural member to the end of the structural member according to claim 7. 9. Consisting of a plurality of rolls with different diameters, the rolls are coaxially arranged in series and separated so that they can rotate independently, and the rolls are rolled so that the cross section is uneven. The method for manufacturing a plate material according to claim 7.