JP4329076B2 - Radioactive waste disposal facility and its construction method - Google Patents

Description

  The present invention relates to a radioactive waste disposal facility and a construction method thereof.

Regarding the disposal of high-level radioactive waste, the solidified glass solidified by mixing high-level radioactive waste with glass and sealed with an overpack made of carbon steel, etc., is then formed on a stable bedrock in the depth of over 300m. It is planned to cover the mine with bentonite and contain it.
However, because there are fractures such as crush zones in the ground such as rock mass, it is expected that a large amount of spring water will be generated during excavation. There is. In addition, lowering the groundwater around the tunnel leads to the inflow of oxidizing groundwater near the ground surface, which may promote overpack corrosion. From this point as well, it is necessary to reduce the spring water into the tunnel. is there.
There is a grouting method using cement-based materials as a rock-water waterproofing method that is generally used in tunnel construction, but cement-based grouting materials have an adverse effect on bentonite, which is an important barrier in the disposal of radioactive waste, and its performance is reduced. It is known to deteriorate. For this reason, research is being conducted on the grout method using bentonite as an injection material.
On the other hand, Patent Document 1 discloses an invention of a radioactive waste disposal site that can prevent radioactive contamination due to groundwater flow even when radioactive waste is buried in a formation under a coastal seabed.
JP-A-5-203797 (page 2-3, FIG. 1)

However, since bentonite grout does not have sufficient strength, in excavation work under high water pressure such as deep tunnel construction, spring water flows into the tunnel and the bentonite grout material pushed back into the tunnel. There is a concern.
In addition, the method of depositing radioactive waste in the stratum beneath the coastal seabed as described in Patent Document 1 is considered difficult at this stage from the viewpoint of the relationship with the ocean dumping and the concreteness. The method of burying radioactive waste in the deep part is considered to be the most effective.

  The present invention has been made in view of the above-described problems, and provides a radioactive waste disposal facility capable of stopping water without adversely affecting bentonite or bentonite mixed soil filled in a tunnel, and a method for constructing the same. The purpose is to do.

In order to achieve the above object, the radioactive waste disposal facility according to the present invention is a radioactive waste disposal facility comprising a tunnel formed in the ground for storing radioactive waste, and is formed as a peripheral wall of the tunnel. The first improved ground layer made of bentonite grout or clay grout, and the second improved ground layer made of cement-based grout or silica-based grout formed on the outer periphery of the first improved ground layer. Features.
In the present invention, since the first improved ground layer made of bentonite grout or clay grout is formed as the peripheral wall of the tunnel, water can be stopped without adversely affecting the bentonite or bentonite mixed soil filled in the tunnel. Further, since the outer peripheral portion of the first ground improved layer to form a second ground improved layer high strength consisting of cementitious grout or silica-based grout, even under high water pressure, spring water flows into the gallery There is nothing.

Further, in the method for constructing the radioactive waste disposal facility according to the present invention, the second improved ground layer surrounding the excavation area as a tunnel ahead of the face is formed, and then the inner ground of the second improved ground layer The first improved ground layer is formed as a peripheral wall of a mine shaft, and then the excavation area is excavated.
In the present invention, a second improved ground layer made of cement grout or silica grout surrounding the excavation area in front of the face is formed, and further, bentonite grout or clay grout is formed inside the second improved ground layer. Since the tunnel is excavated after the first improved ground layer is formed, the inflow of spring water into the tunnel can be prevented even under high water pressure, and the construction can proceed smoothly.

According to the present invention, the first improved ground layer made of bentonite grout or clay grout is formed as the peripheral wall of the tunnel, and further the second improved ground layer made of cement-based grout or silica-based grout is formed on the outer periphery thereof. A radioactive waste disposal facility capable of stopping water can be realized without adversely affecting bentonite or bentonite mixed soil filled in the mine shaft.
The present according to the invention, surrounding the front of the excavation area from the working face to form a second improved ground layer made of cement grout or silica-based grout, further bentonite grout or inwardly of the second improved ground layer Since the tunnel is excavated after the first improved ground layer made of clay grout is formed, the inflow of spring water into the tunnel is prevented even under high water pressure, and the construction can proceed smoothly.

Hereinafter, the radioactive waste disposal facility according to the present invention will be described with reference to the drawings.
FIG. 1 is a side cross-sectional view and a cross-sectional view taken along line AA showing an example of a radioactive waste disposal facility according to the present invention.
As shown in FIG. 1, the radioactive waste disposal facility according to the present invention is formed as a cross-sectional circular tunnel 3 formed in the ground G for storing the radioactive waste 5 and a peripheral wall of the tunnel 3. First improvement layer 2 (first improvement ground layer) made of bentonite grout or clay grout, and second improvement layer 1 made of cement-type grout or silica-type grout formed on the outer periphery of the first improvement layer 2 (second Improved ground layer) .
Here, the first improvement layer 2 is mainly intended to stop water, and it is preferable to obtain a water permeability coefficient of about 10-5 to 10-6 cm / s or less. On the other hand, the 2nd improvement layer 1 aims at having intensity | strength with a certain amount of water stop, and the thing which has a function as what is called a poor water permeability whose water permeability coefficient is about 10 <-3> -10 <-5> cm / s is considered.

  The inside of the tunnel 3 is filled with bentonite 4, and radioactive waste 5 sealed with an overpack made of carbon steel or the like is stored in the bentonite 4. Here, the bentonite 4 serves as a cushioning material for relieving the pressure from the ground G. Further, when the overpack is broken, the permeability of the bentonite 4 is low, so that the transfer of the radioactive waste 5 is delayed, and the radioactive waste 5 is adsorbed on the bentonite 4 due to the ion exchange property.

  Cement grout or silica grout has high strength and can function even under high water pressure. A cement-type grout having a small amount of cement is desirable because a large amount of cement adversely affects bentonite. Further, silica-based grout is considered to be a near-neutral one that does not adversely affect bentonite, for example, a grout material in which silica fume and grout lime are mixed and the pH value is suppressed to a weak alkali while ensuring strength.

  On the other hand, bentonite grout is obtained by adding water to bentonite and may be diluted with ethanol or salt water in order to suppress viscosity. Kunigel V1 (registered trademark), Kunigel V0 (registered trademark), Volclay (registered trademark) Bentonite such as is preferred. The clay grout is obtained by adding water to general clay, and is preferably a fine-grained clay with low viscosity and high stability after sedimentation / deposition.

  In the radioactive waste disposal facility according to the present embodiment, the first improvement layer 2 made of bentonite grout or clay grout is formed as the peripheral wall of the tunnel 3, so that the bentonite 4 filled in the tunnel 3 is not adversely affected and is stopped. Can be water. Moreover, since the high strength 2nd improvement layer 1 which consists of cement-type grout or a silica-type grout is formed in the outer peripheral part of the 1st improvement layer 2, spring water flows in into the tunnel 3 under high water pressure. There is nothing.

Next, the construction method of the radioactive waste disposal facility according to the present invention will be described. Hereinafter, the excavation direction is “front”, and the reverse direction is “rear”.
FIG. 2 is a side sectional view showing a method for constructing a radioactive waste disposal facility according to the present invention.
First, a plurality of steel pipes 7 are radially radiated from the face 6 at the front end of the already formed mine shaft 3 toward the front excavation region R (about 20 to 30 m). Then, cement-based grout or silica-based grout is injected into the ground from the steel pipes 7 to form the cylindrical second improvement layer 1a around the excavation region R. In addition, a disc-shaped second improvement layer 1b is formed at the front end of the excavation region R in a state where a gap 8 corresponding to the thickness of the first improvement layer 2 is provided between the excavation region R and the second improvement layer 1a (see FIG. 2 (a)).
Next, the steel pipes 7 are pulled out, and a plurality of steel pipes 7 'are newly radiated from the face 6 toward the front excavation region R. Then, bentonite grout or clay grout is poured into the ground from the steel pipes 7 '... to form a cylindrical first improved layer 2a inside the second improved layer 1a. At this time, the first improved layer 2a is also formed in the gap 8 between the second improved layer 1b and the second improved layer 1a (see FIG. 2B).
Thereafter, the steel pipes 7 'are pulled out, and the mine shaft 3 is excavated forward from the face 6 (see FIG. 2C). At this time, the natural ground G ′ is partially left behind the second improved layer 1b without excavating to the second improved layer 1b. Thereby, it can prevent that the spring water which permeate | transmitted the 2nd improvement layer 1b penetrate | invades in the mine shaft 3. FIG.
Hereinafter, the radioactive waste disposal facility is constructed by repeating the above work at a predetermined pitch of about 20 to 30 m.

In addition, as shown in FIG.2 (d), while forming the 2nd improvement layer 1c in the edge part of the mine shaft 3 without providing a gap | interval between an edge part periphery and a surrounding wall, the inner side whole surface of the 2nd improvement layer 1c The first improved layer 2c is formed over the entire area.
In this way, a radioactive waste disposal facility is built, but after completion, as shown in FIG. 1, the radioactive waste 5 sealed with an overpack made of carbon steel or the like is carried into the mine shaft 3, Bentonite 4 is filled in the space between the radioactive waste 5 and the peripheral wall of the tunnel 3. As a result, the radioactive waste 5 is stored or disposed of semipermanently.

  In the construction method of the radioactive waste disposal facility according to the present embodiment, the second improvement layers 1a and 1b made of cement grout or silica grout surrounding the excavation region R in front of the face 6 are formed, and further the second improvement. After the first improved layer 2a made of bentonite grout or clay grout is formed inside the layer 1a, the tunnel 3 is excavated. Therefore, even under high water pressure, the inflow of spring water into the tunnel 3 can be prevented and smoothly Construction can proceed.

  As mentioned above, although embodiment of the radioactive waste disposal facility concerning this invention was described, this invention is not limited to said embodiment, In the range which does not deviate from the meaning, it can change suitably. For example, in the above embodiment, the cross section of the radioactive waste disposal facility is circular, but may be other shapes such as a rectangle. In short, it is only necessary to obtain the desired function in the present invention.

An example of the radioactive waste disposal facility which concerns on this invention is shown, (a) is the sectional side view, (b) is AA arrow sectional drawing. The construction method of the radioactive waste disposal facility which concerns on this invention is shown, (a) (b) (c) is a sectional side view of an intermediate part, (d) is a sectional side view of an edge part.

Explanation of symbols

1, 1a, 1b, 1c Second improvement layer (second improvement ground layer) 2, 2a, 2c First improvement layer ( first improvement ground layer) 3 Tunnel 4 Bentonite 5 Radioactive waste 6 Faces 7, 7 'Steel pipe G ground

Claims (2)

A radioactive waste disposal facility consisting of a tunnel formed in the ground for storing radioactive waste,
A first improved ground layer in which the ground formed as a peripheral wall of the mineway is bentonite grout or clay grout, and a second improved ground in which cement ground grout or silica grout is formed on the outer periphery of the first improved ground layer. A radioactive waste disposal facility characterized by comprising a layer. A method for constructing a radioactive waste disposal facility according to claim 1,
Forming the second improved ground layer surrounding the excavation area as a tunnel ahead of the face, and then forming the first improved ground layer on the inner ground of the second improved ground layer to form a peripheral wall of the tunnel Then, the construction method of the radioactive waste disposal facility, wherein the excavation area is excavated.

Images