JP3491014B2 - Reactor dummy shield plug - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a core forming a part of a shield plug which serves as a lid for a top opening of a reactor of a fast reactor or the like.
The present invention relates to an improvement of a dummy shield plug which is removably inserted into a preliminary hole of a control rod drive mechanism formed in an upper mechanism .

[0002]

2. Description of the Related Art A conventional dummy shield plug will be described with reference to FIG. 3, which is a schematic view of a vertical cross section of a fast experimental reactor "JOYO" in Japan. The reactor part in "Joyo" fills a reactor core 1 made of a fuel assembly or the like with liquid sodium 2 as a coolant, and a reactor vessel 5 having a coolant inlet nozzle 3 and a coolant outlet nozzle 4, and a reactor vessel. Shield plug 6 that is the lid of
Composed of.

Here, the shielding plug 6 conceptually forms a lid by combining a plurality of devices and members each having an individual function. The large rotation plug 7, the small rotation plug 8 and the core upper part mechanism. 9, a control rod drive mechanism 10 and the like. Naturally, the shield plug 6 is required to have the functions of ensuring the boundary of the reactor vessel 5, radiation shielding, and heat shielding from the concept of the reactor lid.

By the way, a plurality of control rod drive mechanisms 10 for driving the control rods 11 for adjusting the output of the nuclear reactor are arranged in the upper core mechanism 9, and the permanent control 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 preliminary holes are used as a loading hole for an irradiation test device for performing an irradiation test in a nuclear reactor, but when they are not used, they form a part of a shielding plug. Therefore, the dummy shield plug 20 satisfying the above-mentioned functions required for the shield plug is inserted (loaded) in the preliminary hole.

As shown in FIG. 2, the dummy shield plug 20 has an elongated cylindrical shape as a whole in appearance, and is inserted into the preliminary hole 12 of the control rod drive mechanism 10 installed in the core upper mechanism 9. The dummy shielding plug 20 is composed of a cylindrical guide tube 21 and an upper structure 22 fixed to the upper portion of the guide tube 21 by welding connection.

In the example shown in FIG. 2, the upper structure 22 is made as a solid cylindrical shield member to have a function of shielding radiation and heat, but there is also a hollow pipe shape. . The inside of the guide tube 21 has a lower shield 24 suspended from the upper structure 22 by a support rod 23.
And a pipe 26 in which the thermocouple 25 is installed. The lower shield 24 has a function of shielding radiation and heat. The thermocouple 25 is for measuring the temperature of the fuel assembly outlet coolant of the core (not shown),
By extending through the through hole 27 formed inside the upper structure 22 to the upper part of the upper structure 22, the upper end of the pipe 26 and the lower end of the through hole 27 of the upper structure are air-tightly connected,
An airtight thermocouple line is formed. The pipe 26 having the thermocouple installed therein is inserted into the through hole 27 of the upper structure, and the gap between the outer circumference of the pipe 26 and the inner circumference of the through hole 27 is welded to form an airtight thermocouple passage. Some have been done.

A packing seal portion 28 composed of a double O-ring (O-ring) is provided on the outer periphery of the upper structure 22 of the dummy shield plug 20 so that the dummy shield plug 20 can be inserted into the preliminary hole 12. A check hole 29 is also provided for checking the soundness of the seal portion when inserted. 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.

Furthermore, an upper tube 30 and a compensating lead wire 31 of a thermocouple are connected above the dummy shield plug 20 for improving workability, but these are directly related to the original function of the dummy shield plug 20. Not something to 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 the control rod drive mechanism 10
After the dummy shield plug 20 is inserted into the spare hole 12, the packing seal portion 28 is provided for the gap between the spare hole and the dummy shield plug, and the through hole 27 for the thermocouple is formed in the upper structure 22. On the other hand, by connecting the pipes 26 in an airtight manner, they are secured respectively.

2) The radiation shielding function is mainly secured by the lower shield 24. However, when the upper structure 22 is made of a solid cylindrical shielding member as in the example of FIG. Both the body 24 and the superstructure 22 can provide a radiation shielding function. Further, by bending the thermocouple-equipped pipe 26 inside the guide tube 21, the streaming of radiation can be alleviated.

3) The heat shield function can shield radiant heat and convective heat by positioning the upper structure 22 and the lower shield 24 above the sodium liquid 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 hole 12 loaded with the dummy shield plug 20 is embodied, the dummy shield plug 20 is pulled out (unloaded),
The irradiation test device will be loaded instead. Although the dummy shield plug 20 unloaded from the preliminary hole 12 has a low activation amount in the upper part, the activation amount as a whole is extremely high, and the reactor vessel boundary component itself is activated and has high activity. Since the sodium coolant 2 is attached, it is handled by a large dedicated cask having a radiation shielding function. Unloaded dummy shield plug 20
Will be stored in the on-site water pool until it is finally disposed of, after the adhering sodium coolant has been removed by a cleaning device.

On the other hand, after the irradiation test using the spare hole 12 is completed, it is necessary to load the dummy shield plug 20 into the spare hole 12 again. At this time, the dummy shield plug previously unloaded is reused. You cannot do it. 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, it is necessary for the worker to remove the old O-ring by removing it, and then tuck up the new O-ring from the lower end of the dummy shield plug and fit it into the specified O-ring groove. . At this time, since the upper part of the dummy shield plug with the old O-ring has a low activation amount, it is possible for the worker to access and remove the upper O-ring, but the lower part of the dummy shield plug is Since the amount of activation is so high that it cannot be accessed, it is impossible to replace the O-ring.

Therefore, the conventional dummy shield plug not only brings an economical burden due to the fact that a new dummy shield plug must be manufactured each time it is necessary to load the dummy shield plug, but also increases large radioactive waste. Had the problem.

Therefore, the present invention has been made for the purpose of providing a dummy shield plug for a nuclear reactor, which has a structure in which the O-ring of the packing seal portion can be exchanged and is thus reusable.

[0016]

The most different point of the dummy shield plug of the present invention from the conventional one is that the upper structure has a divided structure. With such a divided structure, the O-ring of the packing seal portion can be exchanged, and the dummy shield plug unloading from the spare hole can be reused.

[0017] That is, the present onset Ming, of the reactor shielding plug one
Rod installed in the core upper part mechanism (9) which constitutes the
Can be freely inserted into and removed from the spare hole (12) of the drive mechanism (10).
Dummy shield plug to be inserted, which is a cylindrical guide tube
(21) is fixed to the upper part of this guide tube and contacts the inner wall of the preliminary hole
A thermocouple (25)
The pipe (26) containing the
Installed and penetrated inside the upper structure for thermocouple penetration
The upper structure is formed by airtightly connecting to the hole (27) and penetrating.
An airtight thermocouple wire passage extending above the structure is formed.
In the dummy shield plug, the upper structure is divided into upper and lower parts, and the first structure (22a) above and the second structure below.
The structure (22b) of (1) is detachably combined with the structure (22b), and the first structure is formed on the outer periphery of the first structure that contacts the inner wall of the preliminary hole.
Forming a packing seal part (28), and forming a second packing seal part (33) on the coupling surface of the first structure which is combined with the second structure, and the first structure and the second structure. Structure
Through holes (37, 38) for thermocouples are drilled inside
It is characterized by having done.

According to the present invention as described above, the activated dummy shield plug unloaded from the preliminary hole is installed in the shield pit, the upper structure is separated into two upper and lower parts, and the upper first structure is separated. Replace the seal member such as the O-ring of the packing seal part attached to the body with a new seal member. This replacement of the sealing member only needs to deal with the first structure above the dummy shield plug, which has a low activation level and is accessible to the operator, which makes it easy and easy under the control of an acceptable radiation dose. The seal member can be replaced. The first structure after exchanging the seal member can be reused as a dummy shield plug by recombining and integrating with the second structure below.

With the structure in which the first structure and the second structure are integrated with each other by the tightening bolts, they can be connected / disconnected easily and reliably.

Further, the first structure bottom portion or the second structure top portion has a shape such that a space is formed between the first structure body and the second structure body when the first structure body and the second structure body are joined together. As a result, this space can be used as a connector housing portion for the thermocouple.

[0021]

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 shield plug 20 shown in FIG. 2, and the upper structure 22 in FIG. It is basically the same as the conventional structure of FIG. 2 except that it is divided into the second structure 22b.

As shown in FIG. 1, the first structure 22
a and the second structure 22b include a plurality of tightening bolts 32
(Only one of which is shown in FIG. 1) allows easy connection and disconnection.

In the illustrated embodiment, the first structure 2
The coupling surface between 2a and the second structure 22b is a tapered surface, and the small-diameter portion formed at the bottom of the first structure 22a is formed in the recess formed at the top of the second structure 22b. It has a structure that fits on the tapered surface.

A preliminary hole 12 is formed on the outer periphery of the first structure 22a.
A first packing seal portion 28 made of a double O-ring and a check hole 29 for checking the soundness of this seal portion are formed in a portion in contact with the inner wall. Such a packing seal portion and a check hole are shown in FIG. It is similar to that of the conventional dummy shield plug shown in FIG. In the present invention,
The second packing seal portion 3 formed of a double O-ring is provided on the coupling 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, the reactor vessel boundary can be secured in the portion having the divided structure.

In the illustrated embodiment, the taper coupling surface is adjusted so that a space 35 is formed between the first structure 22a and the second structure 22b when they are combined. There is. In such a space, the thermocouple compensation lead wire 31
It can be used as a storage space for a connecting portion by the connector 36 of FIG.

The first structure 22a and the second structure 22b
The coupling surface with and is not limited to the fitting structure with the tapered surface as shown in the example, and may have a structure in which the horizontal surfaces are butt-jointed such that both end surfaces are horizontally sliced, or,
It is also possible to adopt a fitting structure (a structure such as a tea barrel and its lid) with a vertical cylindrical surface in which the small-diameter cylindrical portion at the bottom of the first structure 22a is fitted in the cylindrical recess at the top of the second structure 22b. .

Alternatively, instead of forming the space 35 between the first structure 22a and the second structure 22b and connecting the thermocouple compensating conductor 31 with the connector 36 as in the illustrated embodiment, , The first structure 22a and the second structure 22
After connecting b, the thermocouple is inserted from above the through-hole 37 formed in the first structure 22a to form the second structure 22a.
You may make it penetrate in the through-hole 38 provided in b.

The upper structure 22 of the illustrated embodiment is
Although it has a solid cylindrical shape, the present invention can also be applied to a hollow pipe-shaped upper structure.
In the case of a pipe shape, it is necessary to fix wall bodies to the bottom opening of the first structure body and the top opening of the second structure body, which are divided into two parts, to form a sealed structure.

In reusing the dummy shield plug of the present invention having the above-mentioned structure, the unloading activated dummy dummy shield plug is installed in an appropriate shield pit, and the worker loosens the tightening bolt 32, and the second The first structure 22a is removed from the structure 22b. After the two seal members 28 and 33 such as double O-rings attached to the removed first structure 22a are replaced with new seal members, the first structure 22a is tightened with the fastening bolts 32 The structure 22b is re-bonded to the original bonded state. Alternatively, a new seal member 2 that is manufactured for replacement in advance without performing the replacement work of the seal member 2
It may be replaced with the first structural body 22a that has been mounted on the first and second structures 8 and 33. Thus, the first structure 22a and the second structure 22b
After reconnecting, the integrity of the packing seal portion 33 between them is checked by the check hole 34. The assembled dummy shield plug whose soundness has been confirmed is stored in a special cask and loaded in the spare hole in the reverse order of unloading. After loading the spare hole 12, the packing seal portion 28
Is checked through the check hole 29, and the work of loading the dummy shielding plug is completed.

[0030]

As described in detail above, according to the present invention, the upper structure of the dummy shield plug has a two-part structure that can be connected / disconnected, so that the work can be performed only on the upper portion of the dummy shield plug having a low activation amount. It becomes possible for a worker to access and carry out the replacement work of the packing seal portion under the allowable radiation dose management.

As a result, the dummy shield plug can be reused, which not only reduces the economic burden of having to make a new one each time the dummy shield plug needs to be loaded, but also causes a large radioactive waste. It is possible to reduce the amount of goods.

[Brief description of 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 shield plug.

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

[Explanation of symbols]

6: Shield plug 9: Upper core mechanism 10: Control rod drive mechanism 12: spare hole 20: Dummy shield plug 22: Upper structure 22a: first structure 22b: second structure 28: First packing seal portion 32: Tightening bolt 33: Second packing seal portion 35: space

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Claims (6)

(57) [Claims] 1. A reactor core forming a part of a reactor shield plug.
A dummy shield plug which is inserted into and removed from the spare hole (12) of the control rod drive mechanism (10) installed in the mechanism (9) and which is a cylindrical guide tube (21). And this guide tube
Upper structure fixed to the upper part and in contact with the inner wall of the preliminary hole (22)
And a pipe (2 with a thermocouple (25) inside)
6) is arranged in the longitudinal direction inside the guide tube and the upper structure is
Airtight connection to the thermocouple through hole (27) drilled inside the structure
Airtightness that extends above the upper structure by
For dummy shield plugs that have different thermocouple wire passages
The upper structure is divided into upper and lower parts and the first
The structure (22a) and the second structure (22b) below are integrated so that they can be joined and separated, and the first packing seal portion (28) is provided on the outer periphery of the first structure that is in contact with the inner wall of the preliminary hole. And forming a second packing seal part (33) on the coupling surface of the first structure that is coupled to the second structure, and inside the first structure and the second structure, respectively.
A dummy shield plug for a nuclear reactor, wherein a thermocouple through hole (37, 38) is formed . 2. The dummy shield plug according to claim 1, wherein the coupling surface between the first structure and the second structure is a horizontal plane. 3. The dummy shield plug according to claim 1, wherein the coupling surface between the first structure and the second structure is a tapered surface. 4. The dummy shield plug according to claim 1, wherein a coupling 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 body and the second structure body are integrated by fastening bolts. 6. The first structure bottom portion or the second structure top portion is shaped so that a space is formed between the first structure body and the second structure body when the first structure body and the second structure body are coupled to each other , Heat this space
Dummy shielding plug according to any one of claims 1-5, wherein characterized to have access as a thermocouple connector receiving portion.