JP2002040184A - Dummy shield plug of reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reusable dummy shield plug of a reactor by structuring it capable of exchanging the O-ring of a packing seal part in a dummy shield plug which is freely inserted in a spare hole drilled in a part of a shield plug of a reactor, such as fast reactor. SOLUTION: The dummy shield plug upper structure (22) contacting the inner wall of the spare hole (12) is separated into a top and a bottom, and the top first structure (22a) and the bottom second structure (22b) are detachably combined in one. Around the fist structure contacting the spare hole inner wall, the first packing seal part (28) is formed, and in the first structure connection surface connecting with the second structure, the second packing seal part (33) is formed. The first structure of the radioactivated dummy shield plug detached from the spare hole is separated from the second structure and two packing seals are exchanged. The first structure and the second structure are recombined so as to be reusable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a dummy shield plug which can be freely inserted into and removed from a preliminary hole formed in a part of a shield plug serving as a lid of a vessel top opening of a nuclear reactor such as a fast reactor. It is about.

[0002]

2. Description of the Related Art A conventional dummy shield plug will be described with reference to FIG. 3 which shows a schematic view of a longitudinal section of a fast experimental reactor "Joyo" in Japan. The reactor part in “Joyo” is a reactor vessel 5 having a coolant inlet nozzle 3 and a coolant outlet nozzle 4 by filling a reactor core 1 made of a fuel assembly or the like with liquid sodium 2 as a coolant, and a reactor vessel. Shield plug 6
It consists of.

Here, the shielding plug 6 is a conceptually formed lid formed by combining a plurality of devices and members having respective functions, and includes a large rotation plug 7, a small rotation plug 8, and a core upper mechanism. 9, a control rod drive mechanism 10 and the like. Naturally, the shielding plug 6 is required to have the functions of securing the boundary of the reactor vessel 5, radiation shielding, and heat shielding from the concept of a reactor lid.

A plurality of control rod driving mechanisms 10 for driving control rods 11 for adjusting the output of the nuclear reactor are disposed in the upper core mechanism 9, and a control rod is provided in the upper core mechanism 9. In addition to the installation holes of the rod drive mechanism 10, a plurality of spare installation holes are provided. These spare holes are used as loading holes for irradiation test equipment for performing irradiation tests in a nuclear reactor, but when no such use is made, they form a part of a shielding plug. Therefore, the dummy shielding plug 20 that satisfies the above-described function required for the shielding plug is inserted (loaded) into the preliminary hole.

[0007] As shown in FIG. 2, the dummy shielding plug 20 has a slender cylindrical shape as a whole, and is inserted into the preliminary hole 12 of the control rod driving mechanism 10 installed in the upper core mechanism 9. The dummy shielding plug 20 includes a cylindrical guide tube 21 and an upper structure 22 fixed to the upper portion of the guide tube 21 by welding.

In the example shown in FIG. 2, the upper structure 22 is provided as a solid cylindrical shielding member having a radiation shielding function and a heat shielding function, but may be a hollow pipe. . The inside of the guide tube 21 includes a lower shield 24 suspended from the upper structure 22 by a support rod 23.
And a pipe 26 in which a thermocouple 25 is provided. The lower shield 24 has a radiation shielding or heat shielding function. The thermocouple 25 is for measuring the temperature of the coolant outlet of the fuel assembly of the core (not shown).
The upper structure 22 extends upward through the through hole 27 formed in the upper structure 22, and hermetically connects the upper end of the pipe 26 to the lower end of the through hole 27 of the upper structure.
An airtight thermocouple communication line is formed. The pipe 26 containing the thermocouple is inserted through the through hole 27 of the upper structure, and a gap between the outer periphery of the pipe 26 and the inner periphery of the through hole 27 is welded to form a hermetic thermocouple communication line. Some have done it.

On the outer periphery of the upper structure 22 of the dummy shield plug 20, a packing seal portion 28 composed of a double O-ring (O-ring) is provided, and the dummy shield plug 20 is inserted into the preliminary hole 12. A check hole 29 for checking the soundness of the seal portion when inserted is also provided. The soundness of the seal portion 28 can be checked by appropriately applying gas pressure from the check hole 29 and monitoring the degree of gas pressure leakage between the double O-rings.

Further, an upper tube 30 for improving workability and a compensating lead wire 31 of a thermocouple are connected above the dummy shield plug 20, which are directly related to the original function of the dummy shield plug 20. It does not do.

The dummy shield plug 2 having the structure as described above
0 can perform the following functions as a part of the shielding plug 6. 1) The boundary of the reactor vessel 5 is a control rod drive mechanism 10
After the dummy shielding plug 20 is inserted into the preliminary hole 12, the gap between the preliminary hole and the dummy shielding plug is filled with the packing seal portion 28 and the thermocouple through hole 27 formed in the upper structure 22. By securing the pipes 26 in an airtight manner, they are secured.

2) The radiation shielding function is mainly ensured by the lower shield 24. However, when the upper structure 22 is formed of a solid cylindrical shielding member as shown in FIG. Both body 24 and superstructure 22 can provide a radiation shielding function. Further, by bending the thermocouple internal pipe 26 inside the guide pipe 21, streaming of radiation can be reduced.

3) The heat shielding function can shield radiant heat and convective heat by positioning the upper structure 22 and the lower shield 24 above the sodium level of the reactor vessel 5.

[0012]

However, the above-mentioned conventional dummy shield plug has the following problems. That is, when the irradiation test plan in the reactor using the preliminary holes 12 loaded with the dummy shielding plugs 20 is materialized, the dummy shielding plugs 20 are pulled out (unloaded),
An irradiation test device will be loaded instead. Although the dummy shielding plug 20 unloaded from the preliminary hole 12 has a low activation amount at the upper portion, the activation amount as a whole is extremely high, and the reactor vessel boundary component itself is activated at a high activity. Since the sodium coolant 2 is attached, it is handled in a large dedicated cask having a radiation shielding function. Unloaded dummy shielding plug 20
After being removed by a washing device, the attached sodium coolant is kept submerged in a water pool at the site until final disposal.

On the other hand, after the irradiation test using the preliminary holes 12 is completed, it is necessary to load the dummy shielding plugs 20 into the preliminary holes 12 again. I can't. This is because the soundness of the O-ring of the packing seal portion 28 cannot be guaranteed. In order to replace the O-ring, the worker must cut the old O-ring and remove it, then lift up a new O-ring from the lower end of the dummy shielding plug and fit it into the specified O-ring groove . At this time, since the upper part of the dummy shielding plug with the old O-ring has a low amount of activation, it is possible for an operator to access and remove the upper O-ring, but the lower part of the dummy shielding plug can be removed by the worker. Since the amount of activation is so high that it cannot be accessed, it is impossible to replace the O-ring.

[0014] Therefore, the conventional dummy shielding plug not only brings about an economic burden of having to manufacture a new dummy shielding plug every time the loading needs to be performed, but also increases large-sized radioactive waste. There was a problem that.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reusable dummy shielding plug of a nuclear reactor having a structure in which the O-ring of the packing seal portion can be exchanged.

[0016]

The most different point of the dummy shielding plug of the present invention from the conventional one is that the upper structure is divided. With such a divided structure, the O-ring of the packing seal portion can be replaced, and the dummy shielding plug unloaded from the preliminary hole can be reused.

That is, the dummy shielding plug of the nuclear reactor of the present invention divides the upper structure of the dummy shielding plug, which is in contact with the inner wall of the preliminary hole, into upper and lower parts, and separates the first structure above and the second structure below. And a first packing seal portion is formed on the outer periphery of the first structure in contact with the inner wall of the preliminary hole, and the first packing body is connected to the second structure. A second packing seal portion is formed.

According to the present invention as described above, the activated dummy shielding plug unloaded from the preliminary hole is installed in the shielding pit, the upper structure is separated into upper and lower parts, and the separated upper first structure is separated. Replace a seal member such as an O-ring of a packing seal portion attached to the body with a new seal member. This replacement of the seal member only requires handling the first structure above the dummy shielding plug, which has a low activation amount and is accessible to the operator, thereby making it easy and easy to manage under an acceptable dose control. The replacement operation of the seal member can be performed. The first structure after the replacement of the seal member can be reused as a dummy shielding plug by being combined again and integrated with the second structure below.

Since the first structure and the second structure are integrated with each other by a fastening bolt, they can be easily and reliably connected and separated.

Further, the bottom of the first structure or the top of the second structure has a shape such that a space is formed between the first structure and the second structure when the first structure and the second structure are combined. Thereby, this space can be used as a connector storage portion of a thermocouple.

[0021]

FIG. 1 shows an embodiment of a dummy shield plug according to the present invention. FIG. 1 shows only the vicinity of the top of the upper structure 22 of the conventional dummy shielding plug 20 shown in FIG. 2, and the upper structure 22 in FIG. The structure is basically the same as the conventional structure shown in FIG. 2 except that the structure is divided into a second structure 22b.

As shown in FIG. 1, the first structure 22
a and the second structure 22b are connected to a plurality of tightening bolts 32.
(Only one of them is shown in FIG. 1) makes it possible to easily perform the coupling and decoupling.

In the embodiment shown, the first structure 2
The coupling surface between 2a and the second structure 22b is a tapered surface, and a small-diameter portion formed at the bottom of the first structure 22a is formed in a concave portion formed at the top of the second structure 22b. It is structured to fit on the tapered surface.

In the outer periphery of the first structure 22a, the preliminary holes 12 are formed.
A first packing seal portion 28 made of a double O-ring and a check hole 29 for checking the soundness of the seal portion are formed in a portion in contact with the inner wall. Is the same as that of the conventional dummy shield plug shown in FIG. In the present invention,
A second packing seal portion 3 made of a double O-ring is provided on a joint surface between the first structure 22a and the second structure 22b.
3 and a check hole 34 for checking the soundness of the seal portion are further formed. By providing the second packing seal portion 33 and the check hole 34, it is possible to secure a reactor vessel boundary at a portion having a divided structure.

In the illustrated embodiment, the tapered connection surface is adjusted so that when the first structure 22a and the second structure 22b are connected, a space 35 is formed between them. It is. Such space is the thermocouple compensating lead 31
The connector 36 can be used as a storage space for a connection portion or the like.

The first structure 22a and the second structure 22b
The coupling surface is not limited to a fitting structure with a tapered surface as in the illustrated example, and may be a structure in which horizontal planes having both end surfaces are horizontally cut into a horizontal plane, or
A fitting structure (a structure like a tea caddy and its lid) on a vertical cylindrical surface in which the small-diameter cylindrical portion at the bottom of the first structure 22a is fitted into the cylindrical recess at the top of the second structure 22b. .

Alternatively, a space 35 is formed between the first structure 22a and the second structure 22b as in the illustrated embodiment, and the thermocouple compensating lead 31 is not connected with the connector 36. , The first structure 22a and the second structure 22
b, a thermocouple is inserted from above the through hole 37 formed in the first structure 22a, and the second structure 22
b may be inserted through the through hole 38 formed in the hole b.

The upper structure 22 in the illustrated embodiment is
Although the present invention has a solid cylindrical shape, the present invention can be applied to an upper structure having a hollow pipe shape.
In the case of a pipe shape, it is necessary to fix the walls at the bottom opening of the first structure and the top opening of the second structure, respectively, to form a sealed structure.

In reusing the dummy shielding plug of the present invention having the above-described structure, the unloaded activated dummy shielding plug is installed in an appropriate shielding pit, and the worker loosens the tightening bolt 32 to remove the second shielding plug. The first structure 22a is removed from the structure 22b. After replacing two seal members 28 and 33 such as double O-rings attached to the removed first structure 22 a with new seal members, the first structure 22 a is fixed to the second structure by a fastening bolt 32. Again with the structure 22b of FIG. Alternatively, a new seal member 2 previously manufactured for replacement without performing the replacement operation of the seal member may be used.
8, 33 may be replaced with the first structure 22a already mounted. Thus, the first structure 22a and the second structure 22b
After recombining, the integrity of the packing seal portion 33 between the two is checked by the check hole 34. The assembled dummy shielding plug, whose soundness has been confirmed, is stored in a dedicated cask, and is loaded into the spare hole in the reverse order of unloading. After loading in the preliminary hole 12, the packing seal portion 28
Is checked by the check holes 29, and the loading operation of the dummy shielding plug is completed.

[0030]

As described in detail above, according to the present invention, the upper structure of the dummy shielding plug is formed into a two-part structure that can be connected and detached, so that only the upper part of the dummy shielding plug with a low activation amount is operated. It is possible for a worker to access and perform the replacement work of the packing seal part under the control of the allowable dose.

As a result, it is possible to reuse the dummy shielding plug, which not only reduces the economical burden of having to create a new one every time the dummy shielding plug is required to be loaded, but also reduces the size of radioactive waste. Objects can be reduced.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional dummy shielding plug.

FIG. 3 is a schematic vertical sectional view of a fast reactor loaded with a dummy shielding plug.

[Explanation of symbols]

 6: shielding plug 9: core upper mechanism 10: control rod driving mechanism 12: preliminary hole 20: dummy shielding plug 22: upper structure 22a: first structure 22b: second structure 28: first packing seal Part 32: Tightening bolt 33: Second packing seal part 35: Space

Claims (6)

[Claims] 1. A dummy shielding plug, which is removably inserted into a preliminary hole provided in a part of a reactor shielding plug, and is divided into upper and lower parts of a dummy shielding plug upper structure that is in contact with an inner wall of the preliminary hole. The first structure above and the second structure below
With the structure of this product so that it can be connected and detached,
The first packing seal portion is formed on the outer periphery of the first structure in contact with the inner wall of the preliminary hole, and the second packing seal portion is formed on the coupling surface of the first structure coupled with the second structure. Characteristic reactor shielding plug. 2. The dummy shield plug according to claim 1, wherein a coupling surface between the first structure and the second structure is a horizontal surface. 3. The dummy shielding plug according to claim 1, wherein a coupling surface between the first structure and the second structure is a tapered surface. 4. The dummy shielding plug according to claim 1, wherein a connecting surface between the first structure and the second structure is a vertical cylindrical surface. 5. The dummy shield plug according to claim 1, wherein the first structure and the second structure are integrated by a fastening bolt. 6. The first structure bottom or the second structure top is shaped such that a space is formed between the first structure and the second structure when the first structure and the second structure are combined. The dummy shielding plug according to any one of claims 1 to 5, wherein: