JPH0772294A - Reactor shielding body - Google Patents

Abstract

PURPOSE:To provide a reactor shielding body which is prepared in advance as blocks separable for the activated part of the reactor shielding body, improves disassembling work efficiency by avoiding a cutting work with using a large and special cutting device, and reduces the exposure dose of workers. CONSTITUTION:In a reactor shielding body 8 placed around a reactor pressure vessel 2, a coupling reactor shield body 10 separated in a plurality of blocks structure of upper, middle and lower coupling reactor shield body is placed separably by using neutron shield material in the concave part 9 provided inside the region in the reactor shielding body 8 where radiation dose rate is strong.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear reactor shield body for a nuclear power plant, and more particularly to a nuclear reactor shield body which is easy to dismantle when a nuclear reactor is abolished and which is effective in reducing radioactive waste.

[0002]

2. Description of the Related Art Around a reactor pressure vessel in a nuclear power plant, for shielding the radiation emitted from the reactor fuel and the reactor internals constituting the reactor in the reactor pressure vessel, A reactor shield, which is a living body shield, is installed.

However, during the dismantling work of the reactor shield body accompanying the decommissioning of the nuclear reactor, the irradiation of radiation from the reactor during operation of the nuclear power plant confronts the area where the reactor fuel is arranged, Since the reactor shield of the adjacent part is activated and contains residual radioactivity (mainly activated radioactivity by neutrons), from the viewpoint of reducing radioactive waste, that part of the shield It is necessary to separate it from the non-radioactive part, remove it, and dispose of it as radioactive waste.

In the dismantling work of the nuclear reactor shield, a mechanical cutting method using a dedicated machine is performed on the activated portion of the nuclear reactor shield. Conventionally, as shown in the sectional view of FIG. 8, a reactor pressure vessel 2 accommodating a core in which a reactor fuel 1 is arranged is surrounded by a reactor shield 3 which is a living body shield. The shield 3 is made of steel and concrete.

The thickness is relatively thick in the A portion of the reactor shield 3a, which is relatively thin in the general portion, and in the region adjacent to the region of the reactor fuel 1 and where the radiation dose is large. Part B of the reactor shield 3b, the part B reactor shield 3b is close to the reactor fuel 1 and has a high neutron irradiation dose. is doing.

At the time of dismantling due to the decommissioning of the nuclear power plant, the part B reactor shield 3b, which is the activation part of the reactor shield 3, is handled as radioactive waste. As shown in the perspective view of FIG. 1, a cutting device 4 is installed inside the reactor shield 3 for mechanical cutting. The demolition work by the dedicated cutting device 4 is performed by cutting the B part reactor shield 3b with the attached blade 5 first in the vertical direction and then in the horizontal direction. The cut pieces 6 are collected by the gripping machine 7.

The cutting device 4 and the gripping machine 7 are operated by a control panel (not shown) at a place distant from the reactor shield 3, and radioactive dust generated during cutting work is installed in the reactor building. A cutting local dust collector (not shown) prevents the dust from being collected and scattered around.

[0008]

The dismantling work for the part B reactor shield 3b of the activation part of the reactor shield 3 is carried out after the large-scale cutting device 4 is installed in the reactor shield 3. Since a large number of cut pieces 6 are cut and collected in a shape convenient for handling, many steps and a long working period are required for all the steps. As for the residual radioactivity in the reactor shield 3, as shown in the characteristic diagram of FIG. 10, the attenuation ratio of neutron rays to the thickness of concrete, which is the main constituent material of the reactor shield 3, is Attenuation rate of up to 30 cm later is as high as 1/10 or more.

Therefore, the worker approaches the inner wall surface of the reactor shield 3 during the installation and adjustment of the cutting device 4 and the replacement of the blade 5 during the cutting work, so that the worker is forced to be exposed to radiation. Therefore, when performing work,
It is difficult to improve work efficiency because workers are frequently replaced for reasons of strict adherence to the planned line equivalent.

The object of the present invention is to make the activation part of the reactor shield a separable block in advance, which improves the dismantling work efficiency by eliminating the need for cutting work by a large-scale dedicated cutting device, (EN) Provided is a nuclear reactor shield body with reduced exposure to radiation.

[0011]

In order to achieve the above object, the present invention uses a neutron shielding material in a region of a nuclear reactor shield which is provided around a reactor pressure vessel and has a large radiation dose. It is characterized in that the shield body having a block structure divided into a plurality of pieces is detachably attached.

[0012]

[Function] The inlaid reactor shield during operation of the reactor is
Radiation is shielded and activated in the region where the radiation dose is high on the inner wall surface of the reactor shield. The dismantling work of the reactor shield body accompanying the reactor decommissioning is performed by cutting a part of the reactor shield body and inserting it and removing the joint surface with the reactor shield body. The shield can be taken out as a block with dimensions and weight that are easy to handle.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. It should be noted that the same components as those in the above-described conventional technique are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in the cross-sectional view of FIG. 1, a reactor pressure vessel 2 accommodating a reactor core in which a reactor fuel 1 is disposed is installed inside a reactor shield 8.

The reactor shield 8 is usually made of steel or concrete, and the thickness of the reactor shield 8a is relatively thin in the general part and the radiation dose in the vicinity of the reactor fuel 1 is large. A relatively thick B part reactor shield 8 that shields this high radiation in many areas.
and b.

Further, as shown in the enlarged cross-sectional view of FIG. 2, the inner surface of the B part reactor shield 8b faces the reactor fuel 1 and has an annular concave portion 9 in a region where the radiation dose is large. Is formed. The recessed portion 9 is divided into blocks each having a size, weight and the like that are easy to handle, and a fitted reactor shield body 10 formed by stacking a plurality of the recessed portions 9 is mounted to form the reactor shield body 8. .

The inlaid reactor shield 10 is shown in FIG.
An upper-stage inlaid reactor shield 10a shown in a perspective view of FIG.
Intermediate-fitting reactor shield 10 shown in perspective view in FIG.
b, and the lower-stage fitting reactor shield 10c shown in the perspective view of FIG. This inlaid reactor shield
10 is formed by using a material having a large absorption effect of thermal neutron energy, which is a constituent having a high neutron effect, and a substance consisting of an element having a large total absorption cross section of thermal neutrons, and an element having a small neutron activation product. ing.

That is, as an example, a material having a large effect of absorbing thermal neutron energy, consisting of a graphite plate having a plurality of holes so as to have a large thermal absorption area, and an element having a large total absorption cross section of thermal neutrons In the concrete of the material, the graphite plates are arranged so that the positions of the holes do not overlap with each other, and the graphite plates are alternately laminated with the concrete to form blocks.

As shown in FIG. 3, the upper fitting nuclear reactor shielding body 10a has a convex portion 11a fitted to the upper portion of the concave portion 9 of the nuclear reactor shielding body 8 on the inside of the upper surface and an intermediate fitting nuclear reactor on the lower surface center. A recess 12 for combination with which the shield body 10b is fitted is formed, and both side surfaces thereof are flat, and are arranged at the uppermost step of the embedded reactor shield body 10.

Also, the intermediate fitting reactor shield 10b.
As shown in FIG. 4, a convex portion 11 for combination that fits with a concave portion 12 of the reactor shielding body 10a fitted in the upper stage at the center of the upper surface is shown.
b to the center of the lower surface, and insert it in the middle
10b, or a concave portion 12 for combination to be fitted with the convex portion 11b of the lower-stage fitted reactor shield body 10c is formed, and both side surfaces are flat, and are arranged in the middle portion of the fitted reactor shield body 10. Then, a plurality of layers are stacked corresponding to the height of the concave portion 9.

Furthermore, the lower-stage fitting reactor shield 10
As for c, as shown in FIG. 5, a convex portion 11b for combination, which fits into the concave portion 12 of the nuclear reactor shield 10b, is fitted in the center of the upper surface, and a lower step portion of the concave portion 9 fits inside the lower surface. A convex portion 11c is formed, and both side surfaces thereof are flat, and are arranged at the lowest step of the embedded nuclear reactor shield 10. It should be noted that the upper, middle, and lower fitted nuclear reactor shields 10a, 10
Both side surfaces of b and 10c are formed at an angle so as to form an annular shape if a required number of adjacent surfaces are arranged.

The recessed portion 9 of the reactor shield 8 is closed by mounting the fitted reactor shield 10. The recessed portion 9 and the upper, middle and lower fitted reactor shields 10a mounted on the reactor shield 10a, A minute slit is formed between the 10b and 10c.

In order to prevent the streaming phenomenon caused by these minute slits and to make the inventory distribution range of activation fit within the reactor shield body 10, the recessed portion 9 and the upper, middle and lower stages of the fitted reactor shield body 10a, Ten
The protrusions 11a, 11b, 11 are provided between the contact points b, 10c.
A maze is formed in the slit as a shape having a step formed by c and the concave portion 12.

Further, the upper, middle, and lower fitted nuclear reactor shields 10a, 10b, which serve as slits between the above, are inserted.
In order to block neutrons and firmly fix each other to the adhesive portion 13 of each block of 10c, an adhesive agent is appropriately applied and assembled.

The cross-sectional view of FIG. 6 is a cross-sectional view taken along the line A--A of FIG. 1, showing the arrangement of the embedded reactor shield 10 and the B-section reactor shield 8, and showing a plurality of embedded reactor shields.
The blocks 10 adjacent to each other are bonded at a bonding portion 13 between adjacent blocks, and a bonding portion 14 is formed with the B portion reactor shield 8b.

Further, the partially cut perspective view of FIG. 7 shows the assembled state of the fitted reactor shield 10 in the concave portion 9 of the B part reactor shield 8b, below the upper fitted reactor shield 10a. The intermediate fitting reactor shields 10b are stacked in three stages, and the lower fitting reactor shields 10c are arranged at the lowermost stage and are bonded to blocks adjacent to each other.

To mount the inlaid reactor shield 10 in the concave portion 9 provided in the reactor shield 8, first, apply an adhesive between the lower-stage inlaid reactor shields 10c of several blocks. Place it. Next, the intermediate fitting nuclear reactor shielding body 10b is fitted on the concave portion 12 with the convex portion 11b of the lower fitting nuclear reactor shielding body 10c, and an adhesive is applied and stacked. The number of stacking steps of the intermediate fitting reactor shield 10b is determined according to the height of the concave portion 9.

Further, at the uppermost stage, the upper fitting nuclear reactor shield 10a is installed so that the concave portion 12 fits into the convex portion 11b of the lower intermediate fitting nuclear reactor shielding body 10b. The furnace shield 10a is inserted from the side.

The above work is repeated in sequence to fit into the concave portion 9 of the B part reactor shield body 8b, and the reactor shield body 10 is inserted.
Is attached in a ring shape. In addition, since each block of the fitted nuclear reactor shield 10 that is sequentially fitted into the concave portion 9 has a fan-shaped plane surface and has a convex portion 11b and a concave portion 12 on the upper and lower sides, the fitting in the annular final row is particularly important. The process becomes complicated.

However, for example, the upper row of the upper fitting reactor shield 10a in the last row has a special shape in which the recess 12 is filled in advance, and the convex portion 11b of the intermediate fitting reactor shield 10b immediately below is deleted, By fitting the upper fitting nuclear reactor shield 10a with a filler, an adhesive or the like, the fitting nuclear reactor shield 10 can be easily constructed.

Further, when the nuclear reactor shield 10 fitted into the concave portion 9 is mounted, the reactor shield 10 fitted intermediately is inserted.
There is a method of stacking the b and the upper-stage inlaid reactor shield 10a by shifting them by 1/2 in the circumferential direction with respect to the lower block.

According to this, the man-hours for fitting and dismantling increase, but the convex portion 11b or the concave portion 12 of one block is increased.
In contrast, the concave portion 12 or the convex portion 11b of the two blocks
Since they are in a fitted state, there is an effect that the strength of the completed inlaid reactor shield body 10 is increased. Furthermore, the upper, middle, and lower stages of the fitted reactor shield 10
By forming recesses and protrusions (not shown) on both side surfaces of a, 10b, and 10c and fitting them together at the bonding portion 13, the strength of the inlaid reactor shield 10 is further increased.

Next, the operation of the above configuration will be described. During operation of the reactor, as shown in FIG. 1, the inlaid reactor shield 10 is attached and fixed to the inner surface of the B part reactor shield 8b.
Upper, middle, and lower-stage inlaid reactor shields that form the
As shown in FIG. 6 and FIG. 7, the blocks 10a, 10b, and 10c are fitted with convex portions 11b and concave portions 12 on the upper and lower sides of each block, with the bonding portions 13 on the left and right, and the B portion reactor shield. It is joined to the body 8b at the joint portion 14.

At the time of dismantling due to decommissioning of the reactor, first, the upper portion of the concave portion 9 of the B-section reactor shield 8b protruding inward in the reactor shield 8 shown in FIG. To disconnect.

Next, the upper, middle and lower stages of the fitted reactor shield 10 which is annularly mounted in the concave portion 9 on the inner surface of the B part reactor shield 8b.
For each block, a, 10b and 10c are sequentially taken out from the upper shielded reactor shield 10a and disassembled.

If necessary, an intermediate fitting reactor shield body 10b and a lower fitting reactor shield body 10c.
Even the adhesive portion 13 at the lowermost step can be disassembled more easily by separating it with a separating jig. In addition,
The dust generated during the separating operation is prevented from being collected by the cutting local dust collector and diffused to the surroundings as in the conventional case, but the generated amount is extremely smaller than that in the conventional cutting operation by the cutting apparatus 4.

As a result, in the reactor shield body 8, the reactor shield body 8 is disassembled because the reactor shield body 10 is fitted in the high radiation area where the radioactive waste treatment is required. At any time, the in-fit reactor shield body 10 can be easily separated into a plurality of blocks of the upper, middle, and lower-stage inlaid reactor shield bodies 10a, 10b, 10c simply by separating the adhesive portion 13 for each block and separating with a jig. Can be taken out.

Therefore, the steps and man-hours of the dismantling work can be reduced, and since the activation site can be fitted to the reactor shield 10 or its vicinity, the radioactive waste can be reduced. Further, since work such as installation adjustment of the cutting device 4 in the nuclear reactor shield 3 and replacement of the blades 5 at the time of disassembling is unnecessary, the radiation exposure of workers is greatly reduced.

[0038]

As described above, according to the present invention, since a large-scale cutting device is not required for the dismantling work of the activation part of the reactor shield, it is possible to reduce the working process, the number of man-hours and the radioactive waste, and the working period. Can also be shortened. Further, prior to cutting, there is no need for a worker to install, adjust, or replace the blade inside the shielded body of the nuclear reactor, which has the effect of reducing the exposure of the worker.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a nuclear reactor shield according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a concave portion of a B-section nuclear reactor shield according to an embodiment of the present invention.

FIG. 3 is a perspective view of an upper fitting nuclear reactor shield body according to an embodiment of the present invention.

FIG. 4 is a perspective view of an intermediate fitting nuclear reactor shield according to an embodiment of the present invention.

FIG. 5 is a perspective view of a lower-stage inlaid reactor shield body according to an embodiment of the present invention.

FIG. 6 is a cross-sectional view taken along the line AA of FIG. 1 showing a B-section nuclear reactor shield according to an embodiment of the present invention.

FIG. 7 is a partially cutaway perspective view of an embedded nuclear reactor shield according to an embodiment of the present invention.

FIG. 8 is a sectional view of a conventional nuclear reactor shield.

FIG. 9 is an installation perspective view of a conventional cutting device.

FIG. 10 is a neutron beam attenuation rate characteristic diagram with respect to concrete thickness.

[Explanation of symbols]

1 ... Reactor fuel, 2 ... Reactor pressure vessel, 3, 8 ... Reactor shield, 3a, 8a ... A part reactor shield, 3
b, 8b ... B part reactor shield, 4 ... cutting device, 5 ...
Blade, 6 ... Cutting piece, 7 ... Gripping machine, 9 ... Recessed portion, 10 ...
Fitting reactor shield, 10a ... Upper fitting reactor shield, 10b ... Intermediate fitting reactor shield, 10
c ... Lower-stage fitted reactor shield body, 11a to 11c ... Convex portion, 12 ... Recessed portion, 13 ... Adhesive portion, 14 ... Joined portion.

Claims (1)

[Claims] 1. A shielded body having a block structure divided into a plurality of parts using a neutron shield material in a region of the reactor shielded body having a large radiation dose in a reactor shielded body provided around a reactor pressure vessel. Reactor shield body characterized by being installed as much as possible.