JP2503652Y2 - Geological disposal structure for radioactive waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial application field" The present invention relates to a geological disposal structure for radioactive waste.

“Prior Art” High-level radioactive waste (waste liquid, etc.) generated in facilities related to a nuclear power plant can be handled easily by vitrification treatment, for example.

The solidified package (canister) with the glass solidified material stored in the container is stored in an artificially constructed radioactive waste storage facility for a long time until the emission of radiation is significantly reduced in order to prevent radiation contamination. In addition to the storage plan, it is planned to be stored in a deep geological formation and isolated from the living area.

In this plan for deep geological disposal, it is possible to suppress the migration and diffusion of radionuclides by utilizing the nature of natural rocks, but based on the fact that the state of the rocks in the deep ground cannot be fully understood, It is considered practical to control the leakage of radionuclides using artificial artifacts. In the nuclear program, it is said that it is effective to use borosilicate glass as a solidified body and a solidified package (canister) using a stainless steel alloy as a storage container.

FIG. 3 shows a structural example of a geological disposal plan for radioactive waste, in which rock (host rock) 1 is excavated to open a disposal hole 2, and bentonite is formed at the bottom of the disposal hole 2. A suitable amount of cushioning material is laid, and the canister 4 is placed in a state in which the canister 4 is hermetically sealed with an overpack 3 made of an appropriate metal material such as carbon steel. After forming 5, the cover 6 is covered with the cover 6, and the cover 6 is fixed to the bedrock 1 with anchor bolts 7. Reference numeral 8 in the drawing is a tunnel.

Further, with such a disposal structure, when a water infiltration phenomenon occurs from the crack X of the bedrock 1, a part of the buffer layer 5 swells and the internal pressure of the buffer layer 5 increases, so that the intrusion of water can be prevented. Thus, it is possible to ensure the hermeticity.

[Problems to be solved by the invention] However, since the swelling phenomenon of the buffer layer 5 occurs concentratedly in the vicinity of the crack X, as indicated by the hatched portion Y in FIG.
In addition to attempting to shift the overpack 3 and the canister 4 to one side by the local force of the swelling portion Y, when the amount of water flowing from the crack X is extremely large, the buffer material near the crack X is caused to flow out and the groundwater is discharged. Is likely to reach the overpack 3, and the hermeticity due to uniform swelling may be impaired.

The present invention has been made in view of such circumstances, and it is an object of the present invention to swell the buffer layer evenly when groundwater enters the disposal hole to ensure excellent water stopping performance.

[Means for Solving the Problem] In order to achieve such an object, in the present invention, a canister containing radioactive waste is loaded into a disposal hole opened in a bedrock, and the canister and an inner wall of the disposal hole are connected to each other. Between the buffer layer formed by processing the bentonite into a block shape and surrounding the canister, and the buffer layer and the inner wall surface of the disposal hole, and in a state of covering the entire surface of the buffer layer. A geological disposal structure for radioactive waste is provided, which comprises a water diffusion layer made of a porous material for diffusing water into the disposal hole along the entire surface of the buffer layer.

"Operation" When water enters the disposal hole from a crack in the rock for some reason, the water is generated at each bottom of the disposal hole based on the porosity and gravity of the water diffusion layer. Diffuse in the direction.

Therefore, the occurrence of the phenomenon in which only a part of the buffer layer near the crack swells is delayed, and water is diffused by the capillary action of the moisture diffusion layer, and the buffer that forms a block shape in the entire moisture diffusion layer. Even if water runs over the entire surface of the layer and there are breaks or seams, these effects are less affected, and the average swelling of the buffer layer occurs, and the pressure of the entire buffer layer is increased. As a result, the water is prevented from entering and the hermeticity is secured.

"Embodiment" FIGS. 1 and 2 show an embodiment of a geological disposal structure for radioactive waste according to the present invention.

In FIGS. 1 and 2, reference numerals 5A to 5E are disk-shaped cushioning materials formed by forming bentonite or the like into a disk shape, 5a is a storage hole for loading the overpack 3, and 9a.
Is a moisture diffusion layer made of, for example, a ceramic-based porous material.

[Formation of Disposal Hole] As shown in FIG. 1, the bedrock 1 is excavated to form the disposal hole 2 in a cylindrical vertical hole shape. The depth to the position of the disposal hole 2 is, for example, about 500 to 800 m.

[Formation of Water Diffusion Layer] Most of the water diffusion layer 9 is formed in a cylindrical shape with a bottom by, for example, attaching a thin plate-shaped porous material to the inner wall surface (and inner bottom surface) of the disposal hole 2 in a cylindrical shape. To do.

[Molding of cushioning material] Disc-shaped cushioning materials 5A and 5E and cushioning material 5B having storage holes 5a are taken into consideration in consideration of the shape of the disposal hole 2 and the shape of the water diffusion layer 9.
・ Mold and process 5C and 5D.

The bentonite is a clay rock produced by tuff or glassy rhyolite originating from volcanic products under geochemical alteration such as diagenesis and hydrothermal alteration in a weak alkaline environment. Its main component is montmorillonite, a clay mineral, which has a large swelling property due to the property of montmorillonite by taking in a large amount of water between layers, and is molded and processed by an appropriate method to improve its handleability. .

[Partial installation of disc-shaped cushioning material] The disc-shaped cushioning material is provided on the inner bottom of the disposal hole 2 and the water diffusion layer 9.
5E is placed and the disk-shaped cushioning material 5D, 5C
The buffer layer 5 is constructed by stacking 5B and leaving the disc-shaped buffer material 5A.

[Canister loading] A canister 5 obtained by vitrifying the above-mentioned high-level radioactive waste (waste liquid, etc.) in an overpack 3 in a hermetically sealed state is placed on a disc-shaped cushioning material 5E.
The disk-shaped cushioning material 5B, 5C, 5D is loaded into the storage hole 5a in an inserted state.

[Formation of Buffer Layer] Stacking the disk-shaped buffer material 5A on the disk-shaped buffer material 5B and the overpack 3 to complete the buffer layer 5, and placing the disk-shaped porous material on the buffer layer 5. The buffer layer 5
The entire surface of is covered with the moisture diffusion layer 9.

[Fixing of Lid] The lid 6 is placed and covered on the buffer layer 5 and fixed with the anchor bolts 7 to obtain the structure shown in FIGS. 1 and 2.

With such a geological disposal structure for radioactive waste, when water enters the disposal hole 2 through the crack X in the bedrock 1, the water is caused by the porous capillarity of the water diffusion layer 9. Dispersion hole 2 due to gravity and
A phenomenon occurs in which the water flows down and is stored at the bottom.

Therefore, as shown by the hatched lines in FIGS. 1 and 2, even if the flooded portion Z occurs in the vicinity of the crack X, the water does not reach the buffer layer 5 and only a part of the buffer layer 5 is present. The occurrence of the swelling phenomenon is suppressed, and as shown by WL in FIG.
A phenomenon that swelling starts from the lower part of the buffer layer 5 appears due to the water level inside the container gradually increasing. Since the swelling phenomenon in this case occurs in the entire circumference of the buffer layer 5, the expansion force is dispersed and the inner wall surface of the disposal hole 2 is pressed uniformly.

Then, the water level WL reaches above the position of the crack X,
When the swelling phenomenon of the buffer layer 5 averaged over the entire area of the water diffusion layer 9 occurs, the pressure of the entire buffer layer 5 increases,
This balances with the water invasion pressure and hinders subsequent water invasion, so that the overpack 3 and the canister 4 are secured and fixed.

It should be noted that the buffer layer 5 is formed by stacking the molded disk-shaped buffer materials instead of by stacking them on the water diffusion layer 9 and the overpack 3.
It can be constructed by filling anytime between and.

"Effect of the device" As described above, according to the geological disposal structure for radioactive waste according to the present invention, (1) since the water diffusion layer is formed on the inner wall surface of the disposal hole, it is possible to prevent rock cracks. When water enters the disposal hole, the water is guided to the entire surface of the buffer layer by the water diffusion layer and gradually and evenly swells the buffer layer, and excellent water stopping performance can be obtained. it can.

(2) Even if there are cuts or joints in the buffer layer having a block shape in order to diffuse the water to the entire inner wall surface of the disposal hole by the water diffusion layer, the entire surface of the buffer layer can be covered. The water is less likely to be affected by breaks and joints by turning, the average swelling of the buffer layer does not occur, and the waterproofness does not depend on the position of the crack, and the stability can be improved.

(3) Since it has a simple structure in which the water diffusion layer is interposed between the disposal hole and the buffer layer, it is easy to understand the phenomenon when water invades by an experimental model on the ground, The soundness of geological disposal of radioactive waste can be secured in advance.

And so on.

[Brief description of drawings]

Fig. 1 is a front sectional view showing an embodiment of the geological disposal structure for radioactive waste according to the present invention, Fig. 2 is a view taken along the line II-II in Fig. 1, and Fig. 3 is a stratum for radioactive waste. It is a right sectional view showing an example of structure of a disposal plan. 1 ... Bedrock, 2 ... Disposal hole, 3 ... Overpack, 4
...... Canister (solidified package), 5 ... Buffer layer, 5A
・ 5B ・ 5C ・ 5D …… Disk-shaped cushioning material, 5a …… Storage hole, 6 ……
Lid, 7 ... anchor bolt, 8 ... tunnel, 9 ... water diffusion layer, X ... crack, Y ... swelling part, Z ... flooded part, WL ... water level.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 62-282684 (JP, A) JP 61-201200 (JP, A) JP 60-33097 (JP, A) JP 61- 97600 (JP, A) JP 63-174000 (JP, A)

Claims (1)

(57) [Scope of utility model registration request] 1. A disposal hole (2) opened in a bedrock (1) is loaded with a canister (4) containing radioactive waste, and the canister is surrounded and bentonite is provided between the canister and the inner wall of the disposal hole. A buffer layer (5) formed by processing the buffer into a block shape, and the buffer layer and the inner wall surface of the disposal hole are interposed and the entire surface of the buffer layer is covered. A geological disposal structure for radioactive waste, comprising: a water diffusion layer (9) made of a porous material that diffuses inundation along the entire surface of the buffer layer.