JP2000121767A - Sealing device utilizing thimble plug assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thimble plug assembly for making sealing secure by eliminating the need for remodeling a conventional thimble plug assembly and a fuel assembly when transporting and storing the fuel assembly and preventing access to the fuel assembly. SOLUTION: A thimble plug assembly 10 is provided with a hollow part 32 that is extended in upper and lower directions while an upper end 30 is open, and a hole 36 that faces the hollow part on a side surface, and is also provided with a hollow thimble plug 28 for inserting into a guide pipe 14 from a guide pipe mounting hole 16, and an insertion bar 38 that has length in upper and lower directions exceeding distance from the upper end of the hollow thimble plug to the hole 36 and is inserted into a hollow part from the upper end of the hollow thimble plug. In this case, the insertion bar 38 is provided with an insertion bar traveling means for moving the insertion bar at the upper portion of an upper nozzle 22 at the upper part and at the same time an enlargement connection part reinforcing means for reinforcing a pipe-spreading connection part 49 from the inside of the hollow part at the lower part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a sealing device using a thimble plug assembly.

[0002]

2. Description of the Related Art Conventionally, a pressurized water reactor (hereinafter abbreviated as PWR) has been widely used as a commercial reactor as one of nuclear power generation facilities. The PWR generates heat by heating pressurized cooling water by utilizing heat generated by a fission reaction. For this purpose, a PWR reactor vessel is loaded with a fuel assembly called a so-called core. As shown in FIG. 3, the fuel assembly includes a plurality of long fuel rods 12 containing fissile material such as uranium oxide fuel.
And a plurality of guide tubes 14 interposed between the plurality of combustion rods 12 and projecting vertically from the fuel rods 12.
5 and an upper nozzle 22 and a lower nozzle 25 connected to the respective guide tubes via the protrusions. Usually, a control rod (not shown) is inserted into the guide tube 14 from above to control the fission reaction. As shown in FIG. 4, the upper nozzle 22 is provided with a gripper 21 at an upper portion, and an instrumentation guide tube mounting hole and a cooling water flow furnace hole are formed at a lower portion in addition to the same number of guide tube mounting holes 16 as the number of guide tubes. Adapter plate 18.

The upper nozzle 22 and the guide tube 1
4 is usually connected to a so-called bulge (expanded tube) via a sleeve extending downward from the guide tube mounting hole 16 of the upper nozzle 22, and as a result, the following problem occurs. That is, when transporting and / or storing such a fuel assembly, there is no possibility that the upper nozzle can be removed from the guide tube, and there is a risk of access to the fuel rod. And after accessing the fuel rods,
If the upper nozzle is reconnected to the guide tube, no trace of the access to the fuel rods remains from outside. In particular, this problem
This is remarkable in the case of a so-called MOX fuel in which the supply of fuel depends on foreign countries and long-term transportation and / or storage is indispensable. The possibility of access to such fuel rods is a serious problem that can ultimately be a problem of nuclear proliferation.

In order to solve such a problem, MOX of PWR is used.
For example, a sealing method using ultrasonic sealing technology for fuel is described in BCd'Agraives, et.al: "Ultrasonic Sea
ling Technique Developed by JRC-ISPLA and their Ap
plication to the Safeguradsof Nuclear Fuel "(No. 15
Japan Society of Nuclear Materials Management Annual Meeting, 1994). In this sealing method, the upper end opening of the guide tube is closed using a plate, and this plate is fastened to the guide tube by a nut having an ultrasonic sealing function. The nut having the ultrasonic sealing function is a special nut whose internal defect pattern changes when loosened with a predetermined torque after being once fastened to the plate. The nut is provided with a sealing function by detecting this defect pattern by ultrasonic waves. According to this technique, during transport / storage of the fuel assembly, access to the fuel assembly is prevented by preventing the plate from being removed from the guide tube unless the nut is loosened, and even if the access is made, the fuel assembly is not removed. By making the trace detectable, it is possible to seal the burning aggregate.

[0005]

However, particularly when the thimble plug assembly is mounted on the upper nozzle from above, such a technique cannot be applied as it is. The thimble plug assembly is used not only at the time of transportation / storage but also at the time of operation to insert the control rod or the BP rod into the guide tube which is not loaded in order to suppress the bypass flow of the coolant. is there. As shown in FIG. 5, the thimble plug assembly 10
And a base plate 33 to which a plurality of thimble plugs 28 each extending downward are attached, and a spring 35 interposed between the hold-down bar 31 and the base plate 33. When the thimble plug assembly is mounted on the fuel assembly, each thimble plug 28 is inserted into the guide tube mounting hole of the upper nozzle while pushing down the hold down bar 31, so that the base plate 33 is biased by the spring 35. By pressing against the adapter plate 18, each thimble plug 28 can be inserted and held in the corresponding guide tube.

[0006] On the other hand, without the need for such thimble plug assembly and fuel assembly modifications, not only closing the guide tube opening, but also expanding the tube between the upper nozzle and the guide tube. It is also necessary to reduce the possibility of access to the fuel assembly by reinforcing the connection itself. In view of the above problems, an object of the present invention is to provide access to a fuel assembly during transportation / storage of the fuel assembly without requiring modification to a conventional thimble plug assembly and fuel assembly. It is an object of the present invention to provide a sealing device using a thimble plug assembly which prevents the fuel assembly from being detected and makes it possible to detect the trace even if the access is made. Another object of the present invention is to provide a fuel assembly with improved access to the fuel assembly during transport / storage without requiring modifications to the conventional thimble plug assembly and fuel assembly. It is an object of the present invention to provide a thimble plug assembly which prevents the fuel assembly from being damaged and makes it possible to detect the trace even if the access is made.

[0007]

Means for Solving the Problems In order to solve the above problems,
A sealing device using a thimble plug assembly according to the present invention includes a plurality of fuel rods extending in a vertical direction, a plurality of guide tubes extending in a vertical direction, the same number of guide tube mounting holes as these guide tubes, and these guide tubes. A fuel assembly of a nuclear reactor having a lower nozzle fitted into the mounting hole and having a downwardly extending sleeve, and an upper nozzle expanded and coupled to the respective guide tube via the sleeve, and is mounted from above the upper nozzle. A thimble plug assembly, wherein the thimble plug assembly is provided with a hollow portion having an open upper end and extending in the vertical direction, and a hole facing the hollow portion on a side surface. A hollow thimble plug for insertion, and a vertical length not less than a distance from the upper end of the hollow thimble plug to the hole; And an insertion bar that is inserted into the hollow portion from above, and the insertion bar has an insertion bar moving means for moving the insertion bar up and down above the upper nozzle at an upper portion thereof, and an insertion bar moving portion at a lower portion thereof. There is an enlarged connecting portion reinforcing means for reinforcing the expanded connecting portion from inside the hollow portion, and the enlarged connecting portion reinforcing means is interposed between the inner wall of the hollow thimble plug and the insertion bar and protrudes from the hole. Pressing means for pressing the guide tube or the sleeve against the sleeve or the guide tube, and for moving the pressing means in the hollow portion radially outward of the hollow thimble plug. And a seal detecting means of the insertion bar moving means.

The insertion bar moving means includes a screw portion provided on an upper portion of the insertion bar, a fastening device screwed to the screw portion, and a movement preventing member for preventing the fastening device from moving in the vertical direction. Means. Further, it is preferable that the radially outward moving means comprises a tapered portion whose diameter increases toward a lower end. Furthermore, it is preferable that the pressing means is formed of a spherical body which is held in the hollow portion by the tapered portion and which can press the guide tube or the sleeve against the sleeve or the guide tube. . In addition, the spherical body has a size that fits in an annular groove formed in the pipe joint so that the guide tube or the sleeve can be pressed against the sleeve or the guide pipe at the pipe joint. There should be.

In order to solve the above problems, a thimble plug assembly according to the present invention comprises a plurality of vertically extending guide tubes, the same number of guide tube mounting holes as these guide tubes, and the fitting of these guide tube mounting holes. A thimble plug assembly mounted from above the upper nozzle to a fuel assembly of a reactor having a downwardly extending sleeve and an upper nozzle which is expandedly coupled to the respective guide tube via the sleeve. The thimble plug assembly has a hollow portion having an open upper end and extending vertically, and a hollow thimble plug for inserting the guide tube from the guide tube mounting hole into the guide tube, the hole having a hole facing the hollow portion on a side surface. ,
An insertion bar inserted into the hollow portion from the upper end of the hollow thimble plug, the insertion bar having a vertical length equal to or greater than the distance from the upper end of the hollow thimble plug to the hole. It has insertion bar moving means for moving the insertion bar in the vertical direction above the upper nozzle, and has expanded connecting portion reinforcing means for reinforcing the expanded connecting portion from inside the hollow portion below the insertion bar moving means, and The connecting portion reinforcing means is interposed between the inner wall of the hollow thimble plug and the insertion bar and protrudes from the hole to press the guide tube or the sleeve against the sleeve or the guide tube. Means, while holding the pressing means in the hollow portion, having a radially outward means for moving radially outward of the hollow thimble plug,
Further, a seal detecting means of the insertion bar moving means is provided.

[0010]

The sealing device using the thimble plug assembly according to the present invention reinforces the expansion connection between the upper nozzle and the guide tube while having the function of the conventional thimble plug assembly, and detaches the expansion connection. By making it possible to detect the presence or absence of the fuel assembly, the sealing of the fuel assembly is ensured. More specifically, when the insertion bar is moved upward in the hollow portion of the hollow thimble plug using the insertion bar moving means above the upper nozzle, the pressing means interposed between the inner wall of the hollow thimble plug and the insertion bar is moved. At the lower part of the insertion bar, while being held in the hollow portion by the radially outward moving means, the hollow thimble plug is moved radially outward, thereby pressing the guide tube or sleeve against the sleeve or guide tube, In this way, it is possible to reinforce the expansion connection from the inside of the hollow portion, and at the same time, it is possible to remove the expansion connection unless the insertion bar moving means is tampered, thereby making it impossible to access the fuel assembly. In addition, if the insertion bar moving means is tampered with, the trace can be detected by the seal detecting means, so that the fuel assembly can be reliably sealed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 2 by taking as an example a case where the present invention is applied to a fuel assembly of a PWR type light water reactor. In addition,
Since the fuel assembly of the PWR type light water reactor is the same as that of the prior art, the same components are denoted by the same reference numerals and detailed description thereof will be omitted. The thimble plug assembly 10 is mounted on the fuel assembly 12 from above the adapter plate 18 through the guide tube mounting hole 16. Therefore, the same components are denoted by the same reference numerals, and the detailed description thereof will be omitted.

As shown in FIG. 1, the hollow thimble plug 28 has a hollow portion 32 whose upper end 30 is open.
A hole 36 facing the hollow portion 32 is provided. Upper end 30
Is provided with a flange 39. By supporting the flange 39 on the upper surface of the base plate 26, the hollow thimble plug 28 is inserted and held in the guide tube 14 through the guide tube mounting hole 16. . The hollow thimble plug 28 is located at the upper end 3 of the hollow thimble plug 28.
It has an insertion bar 38 that is inserted from 0 into the hollow portion 32.
The insertion bar 38 has a tapered portion 40 whose diameter increases toward the lower end at the lower end, and a threaded portion 44 extending vertically, at the upper end, and is longer than the distance from the upper end 30 of the hollow thimble plug 28 to the hole 36. Vertical length.
Thereby, the ultrasonic sealing nut 50 described later is screwed into the screw portion 44 above the upper nozzle 22. Thread 4
As shown in FIG. 2A, two key grooves 45 extending in the vertical direction are cut at opposite positions in the diameter direction. Further, inside the hollow portion 32, a metal ball which is held by the inclined surface of the tapered portion 40, is a spherical body having a size protruding from the hole 36 and having a size capable of pressing the guide tube 14 against the sleeve 20. 48 are provided. The metal ball 48 is also large enough to fit in an annular groove 51 formed on the inner wall surface of the guide tube 14 so that the guide tube 14 can be pressed against the sleeve 20 at the expanded joint portion 49. In addition, three pipe expansion joints 49 are provided at appropriate intervals in the vertical direction.

Above the upper nozzle 22, a nut 5 is provided.
0a and a lower flange portion 50b (FIG. 2B).
), And an ultrasonic sealing nut 50 screwed to the screw portion 44 is provided. This ultrasonic sealing nut 50 is described in the aforementioned paper.
BCd'Agraives, et.al: "Ultrasonic Sealing Techniq
ue Developed by JRC-ISPLA and their Applicationto
It has an ultrasonic sealing function similar to, for example, a "sealing bolt" disclosed in "The Safegurads of Nuclear Fuel".
This is a special nut capable of detecting a change in an internal defect pattern generated in the ultrasonic sealing nut 50. As the seal detecting means of the ultrasonic sealing nut 50 for that purpose, an ultrasonic emitting device that emits ultrasonic waves toward the ultrasonic sealing nut 50 and a data processing device for processing the ultrasonic wave reflected by the ultrasonic sealing nut 50 It is roughly composed of

The ultrasonic sealing nut 50 is provided with a nut stopper 52 for preventing its vertical movement. The nut stopper 52 is provided with a keyed bearing 54 supported on the upper surface of the flange 39 of the hollow thimble plug 28.
And a nut retainer 56 attached to the outside of the ultrasonic sealing nut 50. As shown in FIG. 2 (C), the bearing 54 includes a cylindrical portion 58 and a flange portion 60 which are fitted inside the inner wall surface of the hollow thimble plug 28, and the insertion bar 3 is provided at the center.
A bore 62 through which 8 passes is formed. This bore 62
The key 6 that fits into the key groove 45 of the insertion bar 38
4 are provided. The ultrasonic sealing nut 50 is prevented from moving downward by the lower flange portion 50b abutting against the flange portion 60, and idling is prevented by the relationship between the key groove and the key. On the other hand, the nut retainer 56 has a stepped bore 66 as shown in FIG. 2D, and a shoulder 68 formed by the stepped bore 66 prevents the ultrasonic sealing nut 50 from moving upward. It has become.

Next, the operation of the thimble plug assembly having the above configuration, that is, a method of sealing the fuel assembly 12 using the thimble plug assembly will be described below. After the sleeve 20 of the upper nozzle 22 is externally fitted to the guide tube 14 and expanded and connected, the fuel assembly 12
The upper plug 22 is mounted in advance. When attaching the thimble plug assembly 10 to the combustion assembly 12, first, each hollow thimble plug 28 is inserted into the guide tube 14 from the guide tube attachment hole 16 of the adapter plate 18,
By depressing the hold down bar, the base plate 26 is pressed against the adapter plate 18 and each hollow thimble plug 28 is stably held. Next, when the ultrasonic sealing nut 50 is turned, the bearing 54 and the nut holder 5
6 prevents the ultrasonic sealing nut 50 from moving in the vertical direction. As a result, the insertion bar 38 rotates together with the assist of the key action, and the insertion bar 38 moves upward as shown in FIG. 1B. Further, the upward movement of the tapered portion 40 at the lower end causes the hollow portion 32 held on the slope of the tapered portion 40 to move.
The inner metal ball 48 is gradually pushed outward in the radial direction, and protrudes from the thimble plug hole 36 toward the inner wall surface of the guide tube 14.
, Whereby the guide tube 14 is pressed against the sleeve 20 at the expansion joint 49. As a result, the sleeve 20 is pulled out of the guide tube 14 and the upper plug 22 cannot be removed from the guide tube 14 unless the expansion joint 49 is reinforced and the ultrasonic sealing nut 50 is loosened. Access to is blocked. Further, when the ultrasonic sealing nut 50 is loosened, it can be detected by the same inspection method as the ultrasonic inspection disclosed in the above-mentioned paper, so that sealing of the fuel assembly 12 can be reliably achieved. Can be.

Although the embodiments of the present invention have been described in detail, various changes and modifications can be made within the scope of the present invention described in the claims. For example, of the thimble plugs of the conventional thimble assembly, necessary ones may be replaced with the hollow thimble plug of the present invention. The number of metal balls 48 arranged in the hollow portion 32 may be appropriately selected according to the diameter of the insertion bar 38 and the like. Further, the guide tube 14 may be fitted over the sleeve 20. Furthermore, the number of installations of the enlarged connecting portion may be appropriately selected.

[0017]

As described above in detail, according to the sealing device using the thimble plug assembly of the present invention, when the fuel assembly is transported / stored, the thimble assembly or the fuel assembly can be modified. It is possible to prevent the access to the fuel assembly and to detect the trace even if the access is made, thereby making it possible to securely seal the fuel assembly.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing the vicinity of one hollow thimble plug of a thimble plug assembly according to an embodiment of the present invention and a sealing method using the thimble plug assembly.

FIG. 2 is a schematic perspective view showing main parts of the thimble plug assembly of FIG. 1;

FIG. 3 is an elevation view of a fuel assembly of a conventional PWR reactor.

FIG. 4 is a perspective view of a thimble plug assembly used for a fuel assembly of a conventional PWR reactor.

FIG. 5 is a perspective view of an upper nozzle of a fuel assembly of a conventional PWR reactor.

[Explanation of symbols]

 Reference Signs List 10 thimble plug assembly 12 fuel assembly 14 guide tube 16 guide tube mounting hole 18 adapter plate 20 sleeve 22 upper nozzle 26 base plate 28 thimble plug 30 upper end 32 hollow portion 34 side surface 36 hole 38 insertion bar 40 taper portion 44 screw portion 48 metal Ball 49 Expansion joint 50 Ultrasonic sealing nut 51 Annular groove 52 Nut stop 54 Bearing 56 Nut restraint

Claims (6)

[Claims] 1. A plurality of vertically extending fuel rods, a plurality of vertically extending guide tubes, the same number of guide tube mounting holes as the number of these guide tubes, and fittings in these guide tube mounting holes and downward. A reactor fuel assembly having an upper nozzle having an extending sleeve and expandingly coupled to each guide tube via the sleeve; and a thimble plug assembly mounted from above the upper nozzle. The thimble plug assembly includes a hollow portion having an open upper end and extending in a vertical direction, and a hole facing the hollow portion on a side surface, and a hollow thimble plug for inserting the guide tube from the guide tube mounting hole into the guide tube; An insertion bar inserted into the hollow portion from the upper end of the hollow thimble plug and having a length in the vertical direction at least equal to the distance from the upper end of the hollow thimble plug to the hole. The insertion bar has an insertion bar moving means for moving the insertion bar in a vertical direction above the upper nozzle at an upper portion thereof, and a reinforcing bar for reinforcing a pipe joint from the hollow portion at a lower portion thereof. The enlarged connecting portion reinforcing means is interposed between the inner wall of the hollow thimble plug and the insertion bar, and projects from the hole to guide the guide tube or the sleeve to the sleeve or the sleeve. Pressing means for pressing against the guide tube,
A radially outward moving means for moving the hollow thimble plug radially outward while holding the pressing means in the hollow portion, wherein the thimble plug assembly further comprises: A sealing device comprising: a sealing detection unit. 2. The insertion bar moving means includes a screw portion provided on an upper portion of the insertion bar, a fastening device screwed to the screw portion, and a movement preventing member for preventing the fastening device from moving in a vertical direction. 2. The sealing device according to claim 1, comprising means. 3. The method according to claim 1, wherein the radially outward moving means comprises a tapered portion whose diameter increases toward a lower end.
The sealing device according to item 1. 4. The pressing means comprises a spherical body held in the hollow portion by the tapered portion and having a size capable of pressing the guide tube or the sleeve against the sleeve or the guide tube. Item 4. The sealing device according to Item 3. 5. The spherical body fits in an annular groove formed in the pipe joint so that the guide pipe or the sleeve can be pressed against the sleeve or the guide pipe at the pipe joint. The sealing device according to claim 4, wherein 6. A plurality of guide tubes extending in the vertical direction, a guide tube mounting hole having the same number as the guide tubes, and a sleeve which is fitted in the guide tube mounting hole and extends downward. A fuel assembly of the reactor having an upper nozzle that is expanded and coupled to each guide tube via
In the thimble plug assembly attached from above the upper nozzle, the thimble plug assembly has a hollow portion having an open upper end and extending in a vertical direction, and a guide tube mounting hole provided with a hole facing the hollow portion on a side surface. A hollow thimble plug for insertion into the guide tube from above, a vertical length greater than the distance from the upper end of the hollow thimble plug to the hole, and an insertion inserted into the hollow portion from the upper end of the hollow thimble plug The insertion bar has an insertion bar moving means for moving the insertion bar in the vertical direction above the upper nozzle at an upper portion thereof, and a pipe connecting portion from within the hollow portion at a lower portion thereof. An enlarged connecting portion reinforcing means for reinforcing, wherein the expanding connecting portion reinforcing means is provided between the inner wall of the hollow thimble plug and the insertion bar. Pressing means for projecting from the hole to press the guide tube or the sleeve against the sleeve or the guide tube; and a radius of the hollow thimble plug while holding the pressing means in the hollow portion. A thimble plug assembly comprising: a radially outward means for moving outward in the direction; and a seal detecting means for the insertion bar moving means.