Backfilling material, and manufacturing method for backfilling material

Abstract

To provide a backfilling material and a manufacturing method for a backfilling material, capable of ensuring desired water shielding performance even when there is a place where crushed stone is concentrated.SOLUTION: A backfilling material 10 is used to backfill a tunnel 2, where excavated debris from the tunnel 2 is used as a base material (crushed stone B), and the surface of the crushed stone B is coated with water-swellable soil 11. A manufacturing method for a backfilling material comprises: a wetting process for using the excavated debris from the tunnel 2 as the base material (crushed stone B), and soaking the crushed stone B in binder liquid 4; a mixing process for mixing the crushed stone B with the surface soaked in the binder liquid 4 with the water-swellable soil 11, and coating the surface of the crushed stone B with the water-swellable soil 11; and a drying process for drying the crushed stone B coated with the water-swellable soil 11.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a backfill material for backfilling tunnels in a radioactive waste disposal facility for geological disposal of radioactive waste generated by nuclear power generation and the like, and to a method for manufacturing the backfill material. [Background technology]

[0002] The waste generated during the reprocessing of spent fuel from nuclear power plants is planned to be buried in deep, stable geological formations. Radioactive waste is buried in geological formations by melting it with glass raw materials to form a vitrified body, which is then stabilized and stored in an airtight container (overpack). The waste is placed in a disposal tunnel, and the radioactive materials are contained within an engineered barrier (buffer material) and a natural barrier (rock) constructed around the waste.

[0003] After that, the radioactive waste disposal facility will close the access tunnels, connecting tunnels, etc. that were excavated from the ground by backfilling them to their original state. The backfill material used to backfill the access tunnels, connecting tunnels, etc. must have the desired water-blocking performance, and the use of bentonite-mixed soil, which is made by mixing bentonite with tunnel excavation waste as a base material, has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-57746 Summary of the Invention [Problem to be solved by the invention]

[0005] Backfilling using bentonite mixed soil is carried out, for example, using a screw feeder A as shown in Figure 5. Screw feeder A can continuously transport large amounts of bentonite mixed soil.

[0006] It is desirable that the bentonite mixed soil discharged from the screw feeder A be deposited homogeneously with excavated debris and bentonite. However, since the excavated debris is from bedrock, it contains large-grained crushed stone B, and the crushed stone B separates from the small-grained granular material such as bentonite, preventing homogeneous filling.

[0007] When the bentonite mixed soil discharged from the screw feeder A is filled, crushed stone B and small-diameter granular material C are separated by classification on the slope. As shown in Figure 5, the separated crushed stone B rolls down the slope and collects at the tip of the slope (area X shown in Figure 5). The area where crushed stone B is concentrated becomes a water path, making it impossible to ensure the desired water-blocking performance.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a backfill material and a method for manufacturing the backfill material that can solve the above-mentioned problems and ensure the desired water-blocking performance even when there are areas where crushed stone is concentrated. [Means for solving the problem]

[0009] The backfill material of the present invention is a backfill material used for backfilling tunnels, and is made of the excavated waste from the tunnel as a base material, with the surface of the base material coated with water-swellable soil. Furthermore, in the backfill material of the present invention, the water-swellable soil is coated in multiple layers on the surface of the base material. Furthermore, the method for manufacturing backfill material of the present invention is a method for manufacturing backfill material used for backfilling tunnels, and comprises the following steps: a wetting step in which the excavated waste from the tunnel is used as a base material and the base material is immersed in a binder liquid; a mixing step in which the base material whose surface has been soaked in the binder liquid is mixed with water-swellable soil and the surface of the base material is coated with the water-swellable soil; and a drying step in which the base material coated with the water-swellable soil is dried. Furthermore, in the method for producing the backfill material, the wetting step, the mixing step, and the drying step are repeated multiple times. [Effects of the Invention]

[0010] According to the present invention, the backfill material 10 is formed by coating the surface of crushed stone B with water-swellable soil 11, and therefore has the effect of ensuring the desired water-proofing performance even if there are areas where the backfill material 10 is concentrated. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a radioactive waste disposal facility. [Figure 2] FIG. 2 is a cross-sectional view showing the configuration of a backfill material. [Figure 3] FIG. 3 is an explanatory diagram illustrating backfilling using the backfilling material shown in FIG. 2. [Figure 4] FIG. 10 is an explanatory diagram illustrating a method for manufacturing a backfill material. [Figure 5] FIG. 1 is an explanatory diagram illustrating backfilling using conventional bentonite mixed soil. DETAILED DESCRIPTION OF THE INVENTION

[0012] Next, a mode for carrying out the present invention (hereinafter simply referred to as an "embodiment") will be specifically described with reference to the drawings.

[0013] Referring to Fig. 1, a radioactive waste disposal facility is composed of a tunnel 3 constructed by excavation into stable bedrock 2 that functions as a natural barrier for containing radioactive materials. The tunnel 3 generally comprises a disposal tunnel 31, a working tunnel 32 for placing waste packages 1 in the disposal tunnel 31, and an access tunnel 33 from the surface to the working tunnel 32.

[0014] Radioactive waste materials are placed in the disposal tunnel 31 as waste bodies 1. After the waste bodies 1 are placed in the disposal tunnel 31, the disposal tunnel 31 is filled with buffer material that functions as an engineered barrier, and the buffer material and bedrock 2 (natural barrier) are configured to contain the radioactive materials.

[0015] The backfill material 10 of this embodiment is used to backfill a service tunnel 32 and an access tunnel 33. Referring to FIG. 2 , the backfill material 10 includes crushed stone B as a base material and water-swellable soil 11 coated (attached) to the surface of the crushed stone B.

[0016] The crushed stone B used as the base material is excavated debris from the disposal tunnel 31, the working tunnel 32, and the access tunnel 33. The excavated debris is stored in a temporary storage area and is used after being thoroughly dried. The excavated debris may be used as is for the crushed stone B, or it may be used after having its grain size adjusted.

[0017] The water-swellable soil 11 may be a water-swellable clay such as smectite clay (bentonite, hectorite, etc.) or swelling mica. The water-swellable clay may be natural or synthetic, but it is preferable to use natural bentonite. Bentonite is a naturally occurring inorganic clay and therefore safe. Bentonite is also inexpensive, yet is expected to have long-term stability and a high water-blocking effect.

[0018] The water-swellable soil 11 may be granulated to a particle size smaller than that of the crushed stone B. The water-swellable soil 11 can be granulated by a rolling granulation method in which the raw clay powder is rolled to aggregate, or by an extrusion granulation method in which the raw clay powder is mixed with a liquid and then extruded.

[0019] In the example shown in Figure 2, the crushed stone B is coated with three layers of water-swellable soil 11. By coating the water-swellable soil 11 in multiple layers, the thickness of the layer of water-swellable soil 11 can be increased, improving the water-stopping effect. As long as the desired layer thickness can be ensured, the coating layer of water-swellable soil 11 may be a single layer.

[0020] Backfilling of the tunnel 3 with the backfill material 10 can be carried out using a screw feeder A, as shown in Figure 3. The backfill material 10 can be used as a mixture with water-swellable soil 11. By using the screw feeder A, a large amount of backfill material 10 can be used for quick backfilling.

[0021] When backfilling using a mixture of backfill material 10 and water-swellable soil 11, the backfill material 10 and the water-swellable soil 11 will separate due to classification on the slope when filling is complete. As shown in Figure 3, the separated backfill material 10 rolls down the slope and concentrates at the tip (area Y shown in Figure 3). However, because the backfill material 10 is coated with water-swellable soil 11, it does not form a water path and the desired water-blocking performance can be ensured. Note that the backfill material 10 may be mixed with a water-blocking material other than the water-swellable soil 11 to backfill the tunnel 3, or the tunnel 3 may be backfilled with only the backfill material 10.

[0022] Next, a method for manufacturing the backfilling material 10 of this embodiment will be described in detail with reference to FIG. First, an infiltration process is carried out in which crushed stone B is soaked in binder liquid 4. In the infiltration process, crushed stone B is placed in a container 5 containing binder liquid 4 in an amount such that the entire surface is immersed in binder liquid 4, and the binder liquid 4 is infiltrated into crushed stone B.

[0023] The binder liquid 4 is an aqueous solution of an adhesive (for example, a vinyl acetate resin emulsion, a polystyrene resin solvent-based solution, a polyvinyl alcohol-based solution, etc.). The binder liquid 4 is adjusted to have a viscosity that allows it to infiltrate into the minute recesses on the surface of the crushed stone B.

[0024] Next, a mixing step is carried out to mix the crushed stone B with the water-swellable soil 11. In the mixing step, the crushed stone B is removed from the container 5, and excess binder liquid 4 is removed. The removed crushed stone B is then placed in a mixing device 6 such as a mixer together with the water-swellable soil 11, and the crushed stone B and the water-swellable soil 11 are mixed together. The surface of the crushed stone B is soaked in the binder liquid 4. Therefore, by mixing with the water-swellable soil 11, the surface of the crushed stone B is evenly coated with the water-swellable soil 11, and a backfill material 10 is obtained in which the surface of the crushed stone B is coated with the water-swellable soil 11.

[0025] Next, a drying step is carried out to dry the backfilling material 10. In the drying step, for example, the backfilling material 10 is transported by a belt conveyor, and hot air is blown onto the backfilling material 10 during transportation using a dryer or the like. The drying step may be natural drying.

[0026] After the drying step, it is determined whether the coating layer of water-swellable soil 11 formed on the backfill material 10 is sufficiently thick. If the coating layer of water-swellable soil 11 is not sufficiently thick, the above-described infiltration step, mixing step, and drying step are repeated until a sufficient thickness is achieved. If the coating layer of water-swellable soil 11 is sufficiently thick, the backfill material 10 is ready to be used for backfilling as a finished product.

[0027] As described above, this embodiment is a backfilling material 10 used to backfill a tunnel 3, in which the excavated waste from the tunnel 3 is used as the base material (crushed stone B), and the surface of the crushed stone B is coated with water-swellable soil 11. With this configuration, the backfilling material 10 has the surface of the crushed stone B coated with water-swellable soil 11, so that even if there are areas where the backfilling material 10 is concentrated, the desired water-blocking performance can be ensured.

[0028] Furthermore, in this embodiment, the surface of the crushed stone B is coated with multiple layers of water swelling soil 11. With this configuration, the backfill material 10 can have a thick coating layer of the water swelling soil 11, thereby improving the water-blocking performance.

[0029] This embodiment is a manufacturing method of backfill material 10 used to backfill a tunnel 3, and includes a wetting process, a mixing process, and a drying process. In the wetting process, excavated waste from the tunnel 3 is used as a base material (crushed stone B), and the crushed stone B is soaked in a binder liquid 4. In the mixing process, the crushed stone B, whose surface has been soaked in the binder liquid 4, is mixed with water-swellable soil 11, and the surface of the crushed stone B is coated with the water-swellable soil 11. In the drying process, the crushed stone B coated with the water-swellable soil 11 is dried. With this configuration, it is possible to produce a backfill material 10 in which the surface of the crushed stone B is evenly coated with the water swelling soil 11 by the binder liquid 4 that has been infiltrated into the surface of the crushed stone B.

[0030] Furthermore, in this embodiment, the wetting step, the mixing step, and the drying step are repeated multiple times. With this configuration, the backfill material 10 can coat the surface of the crushed stone B with multiple layers of water swelling soil 11, thereby improving the water-blocking performance.

[0031] The present invention has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in terms of the combination of the respective components, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0032] 1 Waste body 2. Bedrock 3 Mine shaft 10 Backfill material 11 Water-swelling soil 31 Disposal tunnel 32 Work Tunnel 33 Access Tunnel A Screw Feeder B Crushed stone C Small diameter granules

Claims

1. A backfill material used to backfill tunnels, A backfill material characterized in that the excavated waste from the tunnel is used as a base material, and the surface of the base material is coated with water-swellable soil.

2. 2. The backfill material according to claim 1, wherein the water swelling soil is coated on the surface of the base material in multiple layers.

3. A method for manufacturing a backfill material used to backfill a tunnel, comprising: a wetting step of immersing the excavated waste of the tunnel as a base material in a binder liquid; a mixing step of mixing the base material whose surface has been infiltrated with the binder liquid with water-swellable soil to coat the surface of the base material with the water-swellable soil; a drying step of drying the base material coated with the water-swellable soil.

4. The method for manufacturing a backfill material according to claim 3, wherein the wetting step, the mixing step, and the drying step are repeated a plurality of times.

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