JPS60263890A - Fuel aggregate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a fuel assembly for a boiling water nuclear reactor or the like.

[Technical Background of the Invention] In general, a fuel assembly for a conventional boiling water nuclear reactor was constructed as shown in FIG. That is, 1 in the figure is a fuel bundle, and this fuel bundle 1 includes a plurality of fuel rods 2.
... and water rods (not shown) are arranged in a grid of, for example, 8 rows and 8 columns. The upper and lower ends of these fuel rods 2... and water rods are connected to the upper tie plate 3 and the lower tie plate 1.
-4 is maintained in a predetermined arrangement. The lower tie plate 4 is made of stainless steel and has a box shape, and a fuel support fitting (not shown) is fitted in the lower part of the tie plate 4 to support the fuel assembly and to supply coolant into the fuel assembly. A nozzle portion 4a for introducing the coolant is formed, and a lattice-shaped tie plate portion 4b is integrally formed on the upper surface to support the fuel rods 2 and water rods and allow the flow of the coolant. There is. Further, a handle 9 for lifting the fuel assembly is provided at the upper end of the fuel bundle 1.

The fuel bundle 1 thus configured is inserted into the channel box 5 from below. The channel box 5 is made of a material with a small neutron absorption cross section, such as a zirconium alloy, and has a cylindrical shape with a substantially square cross section. Clips 7.7 are provided at the corners of the upper end of the channel box 5, and these clips 7.7 are in contact with the upper tie brakes i to 3 of the fuel bundle 1. And these clips 7
．． 7 is fixed to the upper tie plate 3 by a channel fastener 8, and the upper end of the channel box 5 is configured to be attached to the upper end of the fuel bundle 1. Note that this channel fastener 8 is formed with a pair of leaf spring pieces, and when these fuel assemblies are loaded into the reactor core, the leaf spring pieces of this channel fastener 8 come into contact with each other, causing a gap between adjacent fuel assemblies. It is constructed to ensure the necessary clearance for the control rod to be inserted.

Further, the lower end of the channel box 5 is fitted to the outer peripheral surface of the lower tie plate 4 so as to be slidable in the axial direction, so as to reduce the difference in thermal expansion between the channel box 5 and the fuel handle 1. configured to absorb Also,
Finger springs 6 in the form of leaf springs are provided on the outer peripheral surface of the lower tie plate 4, and these finger springs 6 are arranged between the inner peripheral surface of the lower end of the channel box 5 and the outer peripheral surface of the lower tie plate 4. The fuel assembly is configured to close the gap and prevent coolant from leaking out of the fuel assembly through the gap.

[Problems with Background Art] Irradiated fuel assemblies are taken out of the reactor core using a fuel exchanger or the like by grasping their handles, and are transferred to a fuel pool for storage, inspection, and the like. During this inspection, the fuel bundle is removed from the channel box, and
The fuel rods, etc. of this fuel handle are inspected. However, in conventional fuel assemblies, the fuel handle is inserted into and removed from the channel box from below, so there is a problem in that the channel box cannot be removed while the handle of the fuel bundle is grasped by the manipulator of the fuel exchanger, etc. there were. For this reason, conventional fuel assemblies require special jigs to attach and detach channel boxes, and the work is also troublesome.

In addition, the channel box mentioned above is exposed to high temperatures and neutron irradiation during reactor operation, so it may cause creep.
Irradiation growth causes deformation such that the diameter increases. Such deformation is large at the lower end of the channel box, and as a result, the lower end of the channel box is deformed into a flared shape.

When the lower end of the channel box deforms in this way, a gap is formed between the lower end of the channel box and the lower tiebrae 1~, and coolant leaks out of the fuel assembly through this gap. occurs. Conventionally, as mentioned above, a finger spring in the form of a leaf spring is provided on the outer periphery of the lower tie brake 1, and even if the above-mentioned gap occurs, this finger spring closes this gap and prevents leakage of coolant from this gap. is configured to do so. However, when this gap becomes large, this finger spring becomes unable to follow the increase in the gap, resulting in a problem that the leakage of coolant exceeds an allowable amount.

For this reason, in the past, if the lower end of a channel box was deformed by a standard amount or more, the channel box was discarded.

Therefore, this channel box was discarded after a relatively short period of time, and its lifespan was short. Therefore, there was a problem that the cost required for operating the nuclear reactor increased.

To prevent such problems, the lower end of the channel box described above should be integrally connected to the lower tie plate.
This prevents the formation of a gap due to deformation of the lower end of this channel box, prolonging the life of this channel box, and allows cooling to be removed from the gap between the lower end of this channel box and the lower tie plate. It is possible to prevent the leakage of Possible means for connecting the channel box and the lower tie plate include welding, bolts, and the like. However, the above channel box is made of a zirconium alloy with a small neutron absorption cross section, and the above lower tie plate supports the weight of the fuel assembly and comes into contact with the fuel support fittings, so it has high mechanical strength and wear resistance. It is made of a material such as steel with high strength. For this reason, it has been difficult to join this channel box and the lower tie plate together by welding. In addition, when this channel box and the lower tie plate are connected using threaded parts such as bolts, excessive stress may be generated in the bolts and the material near them due to the difference in thermal expansion coefficient between the materials of this channel box and the lower tie plate. This causes fatigue in the material and also causes bolts and the like to loosen, resulting in problems with low reliability.

[Object of the Invention] The present invention has been made based on the above circumstances, and its purpose is to provide a channel box that can be easily attached and detached, and to reliably prevent leakage of coolant from the lower end of the channel box. An object of the present invention is to provide a fuel assembly that can extend the life of a channel box.

[Summary of the Invention] That is, the present invention includes a cylindrical channel box, a lower nozzle that is attached to the lower end of the channel box and introduces coolant into the channel box, a plurality of fuel rods, and the upper end of these fuel rods. a fuel bundle that is inserted from above into the channel box and supported on the lower nozzle; a handle provided at the upper end of the fuel handle; , a locking mechanism provided at the upper end of the fuel handle to releasably engage the fuel bundle and the channel box; and a locking mechanism interposed between the channel box and the lower nozzle and connected to the channel box or the lower nozzle. The intermediate member is welded and fitted into the lower nozzle or channel box.

Therefore, when the handle is grasped and pulled up, the channel box and the lower nozzle are lifted together with the fuel bundle via the locking mechanism. By disengaging this locking mechanism, the fuel bundle can be pulled upward from the channel box, and the channel box can be attached and detached while grasping the handle of the fuel bundle with the manipulator of the fuel exchanger. Easy to handle. In addition, since the lower end of this channel box is connected to the lower tie plate via the intermediate member, the lower end of this channel box will not be excessively deformed, and the coolant will not flow from the lower end of this channel box. leakage will be reduced. Furthermore, since this intermediate member is welded to either the channel pock member or the lower nozzle and is fitted to the other, the difference in thermal expansion between the two is absorbed at this fitting part, and excessive thermal stress is avoided. This is because it does not occur and does not loosen like screw parts do, so it is highly reliable.

[One embodiment of the invention] Hereinafter, the present invention will be described in detail with reference to the drawings.

1 and 2 show a first embodiment of the present invention. In the figure, 11 is a fuel bundle, and this fuel bundle 11
is constructed by arranging a plurality of fuel rods 12 and water rods (not shown) in a grid of 8 rows and 8 columns. The upper and lower end portions of these fuel rods 12, etc. are held in a predetermined arrangement by an upper tie plate 20 and a lower tie plate 14a, respectively.

The lower tie plate 14a has a flat lattice shape, and is configured to hold the lower ends of the fuel rods 12, etc., and allow coolant to flow therethrough.

Further, a lower nozzle 14b is provided at the lower end of this fuel assembly. The lower nozzle 14b is made of steel, has a box shape, and is configured to sit on a fuel support fitting (not shown) and support the weight of the fuel assembly. The structure is such that the coolant is introduced into the fuel assembly through the lower nozzle 14b.

The lower nozzle 14b is constructed separately from the lower tie plate 14a, and the upper surface of the lower nozzle 14b is open. And the above lower tie plate 1
4a is seated from above on the upper surface of this lower nozzle 14b,
The weight of the above fuel bundle 11 is the weight of this lower nozzle 14b.
It is configured to be supported by

Further, a channel box 15 is provided surrounding the fuel bundle 11 described above. This channel box 1
Reference numeral 5 is made of a material having a small neutron absorption cross section, such as a zirconium alloy, and has a substantially square cylindrical cross-sectional shape. The lower end of this channel box 15 fits into the outer peripheral surface of the lower nozzle 14b, and
The lower nozzle 14b is connected to the lower nozzle 14b via q. The intermediate member 16a is made of a material such as zirconium alloy or titanium alloy that can be welded to the channel box 15, and has a substantially square ring shape that fits around the outer periphery of the lower nozzle 14b. Fitting step portions 1 are provided at the upper and lower edges of this intermediate member 16a, respectively.
7a and 17b are formed. This intermediate member 1.6
The lower edge of the channel box 15 is welded to the outer peripheral surface of a. Further, a circumferentially continuous fitting step 17G is formed on the upper outer peripheral surface of the lower nozzle 14b, and this fitting step 17c has a fitting step 17G on the upper edge of the intermediate member 16a. 17a is fitted. Furthermore, a fixing member 16b is fitted to the lower outer periphery of the lower nozzle 14b. The fixing member 16b is made of a material such as steel that can be welded to the lower nozzle 14b. A fitting step 17d is formed on the upper edge of this fixing member 16b, and this fitting step 17Cl is connected to the intermediate member 16.
The fixing member 16'b is fitted into the fitting step 17b on the lower edge of the lower nozzle 14b, and the fixing member 16'b is welded to the outer peripheral surface of the lower nozzle 14b. Therefore, this intermediate member 16a is welded to the channel box 15 and is fitted to the outer periphery of this lower nozzle 14b in the axial and radial directions.

Note that a predetermined gap is formed between the intermediate member 16a and the outer peripheral surface of the lower nozzle 14b and between the fitting steps 17a, 17b, 17c, and 17d, so that heat between the intermediate member 16a and the lower nozzle 14b is It is configured to absorb the difference in thermal expansion due to the difference in expansion coefficient.

The upper tie plate 20 has a short, approximately square tube shape with both upper and lower ends open, and a lattice-shaped tie plate 1 (not shown) that holds the fuel rods 12, etc. therein. is formed. The upper end of the channel box 15 is slidably fitted to the lower part of the outer peripheral surface of the upper tie plate 20. The upper portion of the outer peripheral surface of the upper tie plate 20 projects upward from the upper edge of the channel box 15. A handle 21 protrudes from the upper end of this upper type 1 notebook 20.

It is. Further, a locking member 23 is attached to a corner of this upper tie plate 2o. This locking member 23 is provided with a pair of elastic hook-shaped portions 23a, 23a projecting downward. In addition, the above channel box 15
At the four corners of the upper end of the
A locking hole 25 shaped like the sulin 1 is formed at a position corresponding to a.

The hook-shaped portions 23a, 23a are elastically engaged in the locking holes 25 from the outside. The locking member 23 and the locking hole 25 form a locking mechanism. Therefore, when lifting the fuel assembly by grasping the handle 21 with a manipulator or the like of a fuel exchanger, the hook-shaped portions 23a, 2 of the locking member 23
3a is engaged with the locking hole 25 of the channel box 15, so the channel box 15 and the lower nozzle 1
4a is lifted together with this fuel bundle 11.

Furthermore, if the hook-shaped portions 23a, 23a of the locking member 23 are elastically deformed outward to release the engagement with the locking holes 25..., the engagement between the fuel bundle 11 and the channel box 15 is eliminated. The fuel bundle 11 is released and is configured to be able to be handled upwardly from within the channel box 15. The locking holes 25 have a predetermined length in the axial direction, and are configured to absorb the difference in thermal expansion between the channel box 15 and the fuel handle 11 in the axial direction.

Further, a spring spacer 24 is provided to overlap the locking member 23 described above. This spring spacer 2
Reference numeral 4 is composed of a curved leaf spring piece, and the above-mentioned locking member 2
3 and are fastened to the upper tie plate 20 by bolts 26 in several cases. Also, the spring fastener 2 is attached to the upper side of the upper tie plate 20 protruding from the upper edge of the channel box 15.
Spacer pads 27.27 are provided on both sides of 4. When this fuel assembly is loaded, this spring spacer 24 comes into contact with the spring spacer of an adjacent fuel assembly, thereby securing a gap for insertion of a control rod between these fuel assemblies. ing.

In addition, in the event that this spring spacer 24 is damaged, the above-mentioned spacer pads 27 and 27 will come into contact with each other, ensuring the minimum gap necessary for inserting the control rod between the fuel assemblies. has been done.

In the first embodiment of the present invention constructed as described above, when lifting the entire fuel assembly, the handle 21 is gripped by the manipulator of the fuel exchanger or the like and the fuel assembly is lifted. In this case, since the channel box 15 is locked to the fuel bundle 11 by a locking mechanism such as the locking member 23, the channel box 15 and the lower nozzle 14b are lifted up together with the fuel bundle 11. In addition, when removing this channel box 15, the hook-shaped portions 23a, 23a of the locking member 23 are
is deformed outward to release the engagement with the locking hole 25, and the fuel bundle 11 is pulled upward from the channel box 15. Therefore, the channel box 15 can be attached and detached while holding the handle 21 of the fuel bundle 11 with a manipulator or the like, and handling is easy.

In addition, since the lower end of the channel box 15 is axially and radially connected to the lower nozzle 14b via the intermediate member 16a, the lower end of the channel box 15 is deformed by neutron irradiation and growth. This will be prevented. Therefore, this channel box 15
There is no gap between the lower end of the nozzle 14b and the outer peripheral surface of the lower nostle 14b, and leakage of the coolant from between these is reliably prevented. Further, since the intermediate member 16a and the lower nozzle 14b are fitted together, the difference in thermal expansion due to the difference in coefficient of thermal expansion of the materials of the intermediate member 16a and the lower nozzle 14b is absorbed by the gap between the fitting parts. , no excessive thermal stress will occur.

Note that the present invention is not limited to the first embodiment described above. For example, FIG. 3 shows a second embodiment of the invention. In this second embodiment, a fitting groove 17' is formed on the circumferential surface of the lower nozzle 14b, and a ring-shaped intermediate member 16' is placed in the fitting groove 17-.
, and the lower edge of the channel box 15 is welded to the outer peripheral surface of the intermediate member 16-. Note that this intermediate member 16' is constructed by dividing a ring-shaped member into two in the radial direction. The lower edge of the channel box 15 is welded to the outer periphery of the divided pieces, and these divided pieces are integrated into a ring shape. Note that this second embodiment has the same configuration as the first embodiment described above except for the above-mentioned points, and in FIG. do.

In this second embodiment, the intermediate member 16' is divided in the radial direction and is movable in the radial direction with respect to the lower nozzle 14b, but this intermediate member 16' itself acts as a reinforcing material, and the channel box 15 is suppressed from deformation at the lower end. In addition, in this case, the intermediate member 16- is connected to the lower nozzle 1.
Since it is fitted in the fitting groove 17- of 4b in the radial direction,
Even if the lower end of the channel box 15 is slightly deformed, coolant will not leak from between the channel box 15 and the lower nozzle 14b unless the intermediate member 16' can be completely removed from the fitting groove 17-. do not have. That is, the fourth
As shown in the figure, in the conventional type, when the lower end of the channel box 5 expands in diameter in a flared manner, a gap is formed between the lower tie plates 4, and the coolant leaks from this gap. However, in the second embodiment, even if the lower end of the channel box 15 is deformed into a flare shape as shown in FIG. 5, the intermediate member 16' is fitted into the fitting groove 17'. Coolant does not leak from between the lower end of the channel box 15 and the lower nozzle 14b.

Incidentally, FIG. 6 shows the effect of this second embodiment.

That is, curves B and C in this figure show the conventional ones,
B is without finger spring installed, C
is equipped with a finger spring.

As is clear from this figure, in these conventional devices, the amount of leakage from the lower end exceeds the standard value in a relatively short period of time, making it necessary to replace the channel box. On the other hand, in the second embodiment shown by curve A in the figure, the leaker rises only slightly even after a long period of time, and the amount of leakage never reaches the reference value.

Further, FIG. 7 shows a third embodiment of the present invention.

That is, in this third embodiment, a plurality of w-fitting holes 32 . . . are formed at the lower end of the channel box 15 . These fitting holes 32 have a circular shape, and the inner surface thereof has a tapered shape whose diameter increases toward the outside. And, these fitting holes 32... have intermediate members 30...
・ are mated. These intermediate members 30... have a circular shape, and their outer circumferential surfaces are tapered so as to fit into the inner surfaces of the above-mentioned fitting holes 32.... In addition, a circular welding hole 31 is provided in the center of these intermediate members 30.
... is formed.

The intermediate member 30... is the lower nozzle 14b.
The edges of the welding holes 31 are fillet welded to the outer circumferential surface of the lower nozzle 14b.

Further, FIG. 8 shows a fourth embodiment of the present invention.

In this fourth embodiment, fitting holes 32-... formed at the lower end of the channel box 15, intermediate members 30'...
and welding holes 31'... are each formed into an oval shape, and the inner surfaces of the fitting holes 32-... and the intermediate member 3
Instead of tapering the outer peripheral surfaces of 0-..., a stepped portion 35 is formed on these.

In these third and fourth embodiments, the intermediate member 30
130-Although it cannot prevent leakage by itself, since the lower end of the channel box 15 is connected to the lower nozzle 14b by these intermediate members 30, 30'', the lower end of the channel box 15 is deformed. It is possible to prevent leakage.

FIG. 9 shows, for example, the effect of the third embodiment.

Curves B and C in the figure show conventional ones, with curve B not having a finger spring and curve C having a finger spring. Although the third embodiment shown by curve A' in the figure has a larger increase in leakage than the second embodiment, it is possible to maintain the leakage below the reference value over a long period of time.

Furthermore, the configuration of the locking mechanism described above is not limited to that of the first embodiment. For example, FIG. 10 shows a locking mechanism of a fifth embodiment. The fifth embodiment includes an upper tie plate 42 having the same structure as the conventional one, and the upper end of the channel box 15 extends above the upper tie plate 42.

A pair of hook-shaped portions 43a...
A locking member 43.43 having a diameter is attached. Further, the corner portions of the channel box 15 corresponding to these locking members 43, 43 are extended upward, and locking holes 44, 44 are formed in these extensions, respectively. The hook-shaped portions 43a of the locking members 43.43 are engaged with the locking holes 44.44 from the outside.

Furthermore, FIG. 11 shows a locking mechanism according to a sixth embodiment of the present invention. This is the hook-shaped part 43 of the locking member 43-143-.
The configuration is similar to that of the fifth embodiment described above, except that a'... are engaged with the locking holes 44 and 44 from the inside. In this sixth embodiment, the engagement can be released by pressing the tips of the hook-shaped portions 43a' from the outside toward the inside, so that handling is easier.

[Effects of the Invention] As described above, the present invention includes a cylindrical channel box, a lower nozzle attached to the lower end of the channel box for introducing coolant into the channel box, a plurality of fuel rods, and the fuel rods. The fuel bundle includes an upper tie plate and a lower tie plate that hold an upper end and a lower end, and is inserted into the channel box from above and supported on the lower nozzle; a locking mechanism provided at the upper end of the fuel bundle for removably engaging the fuel bundle with the channel box, and a locking mechanism interposed between the channel box and the lower nozzle, and a locking mechanism provided at the upper end of the fuel bundle, and a locking mechanism interposed between the channel box and the lower nozzle, The intermediate member is welded to the box or the lower nozzle and fitted into the lower nozzle or channel box.

Therefore, when the handle is grasped and pulled up, the channel box and the lower nozzle are lifted together with the fuel bundle via the locking mechanism. By disengaging this locking mechanism, the fuel bundle can be pulled upward from the channel box, and the channel box can be attached and detached while grasping the handle of the fuel bundle with the manipulator of the fuel exchanger. Easy to handle. In addition, since the lower end of this channel box is connected to the lower tie plate via the intermediate member, the lower end of this channel box will not be excessively deformed, and the coolant will not flow from the lower end of this channel box. leakage will be reduced. Furthermore, since this intermediate member is welded to either the channel box or the lower nozzle and is fitted to the other, the difference in thermal expansion between the two is absorbed at this fitting part, causing excessive thermal stress. It has great effects such as high reliability because it does not loosen and does not loosen like screw parts do.

[Brief explanation of drawings]

1 and 2 show a first embodiment of the present invention;
The figure is a perspective view, and FIG. 2 is a longitudinal sectional view of the lower part. FIG. 3 is a vertical sectional view of the lower part of the second embodiment. Figures 4 and 5
The figure is a longitudinal sectional view illustrating the operation of the conventional device and the second embodiment. FIG. 6 is a diagram showing the effects of the second embodiment. FIG. 7 is a vertical sectional view of the lower part of the third embodiment. FIG. 8 is a vertical sectional view of the lower part of the fourth embodiment. FIG. 9 is a diagram showing the effects of the third embodiment. Figure 10 is the fifth
It is a perspective view showing the locking mechanism of an example. Figure 11 is the 6th
It is a perspective view showing the locking mechanism of an example. Further, FIG. 12 is a partially cut away perspective view of the conventional example. 11...Fuel bundle, 14b...Lower nozzle, 1
5... Channel box, 16a, 16-. 32
゜32'... Intermediate member, 23.43.43'... Locking member, 25.44... Locking hole. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10

Claims (1)

[Claims] A cylindrical channel box, a lower nozzle attached to the lower end of the channel box for introducing coolant into the channel box, a plurality of fuel rods, and an upper tie plate holding the upper and lower ends of these fuel rods. and a lower tiebrae 1-, a fuel bundle inserted from above into the channel box and supported on the lower nozzle, a handle provided at the upper end of the fuel bundle, and a handle provided at the upper end of the fuel bundle. a locking mechanism for removably engaging the fuel bundle with the channel box; a locking mechanism interposed between the channel box and the lower nozzle and welded to the channel box or the lower nozzle; 1. A fuel assembly comprising: an intermediate member fitted into a box;