JP7615582B2 - Spraying Method - Google Patents

Description

The present invention relates to a spraying method.

As a method of disposing of radioactive waste, it is planned to use dedicated tunnels to transport the radioactive waste to an underground facility. When closing such an underground facility, it will be necessary to backfill the tunnels that were used. Here, when backfilling, it is being considered to form a low-permeability layer inside the tunnels in order to prevent the radioactive waste from flowing out due to groundwater.

In order to form such a low-permeability layer, a spraying method using a material containing bentonite is being considered. There are two types of spraying methods: wet and dry. The wet method involves adding a certain amount of moisture to bentonite to give it adhesiveness, which is then air-pressurized through a spraying hose. The dry method involves air-pressurizing dry bentonite through a spraying hose, and then supplying moisture just before spraying.

Patent Document 1 discloses a wet spraying method that uses bentonite.

JP 2008-223359 A

By the way, bentonite swells when it absorbs moisture. When using a wet spraying method, the swollen bentonite gradually adheres to the inner surface of the spraying hose or nozzle, which can result in the hose or nozzle becoming clogged.

The present invention aims to provide a method for preventing pipe clogging in a spraying method using bentonite.

The inventors have discovered that when a dispersant is added to a material containing bentonite, the viscosity of the material decreases, making it possible to spray the material without clogging the hose or nozzle used for spraying. The present invention is based on this discovery.

Specifically, one embodiment of the present invention is a spraying method in which a material containing a bentonite mixture and a dispersant is sprayed onto a spraying location through a piping of a spraying device.

According to the present invention, the clogging of pipes can be suppressed in the spraying method using bentonite.

FIG. 1 is a diagram showing a spraying device according to an embodiment. FIG. 13 is a diagram showing material adhered to the inside of a pipe in an embodiment. FIG. 2 is a diagram showing the spraying state (without dispersant) in an example. FIG. 1 is a diagram showing the spraying state (with dispersant) in an example.

The objectives, features, advantages, and ideas of the present invention will be clear to those skilled in the art from the description in this specification, and those skilled in the art will be able to easily reproduce the present invention from the description in this specification. The embodiments and specific examples of the invention described below show preferred embodiments of the present invention, and are shown for illustrative or explanatory purposes, and do not limit the present invention thereto. It will be clear to those skilled in the art that various changes and modifications can be made based on the description in this specification within the intent and scope of the present invention disclosed in this specification.

The materials used in the spraying method according to this embodiment include a bentonite mixture and a dispersant.

==Bentonite Mixture==
The bentonite mixture includes at least bentonite and water.

Bentonite is a powdered or granular material produced from bentonite ore. Bentonite has high viscosity and water absorption properties. Bentonite swells when it absorbs water and has low permeability in the solid state.

Specifically, sodium bentonite or calcium bentonite can be used as the bentonite. For example, Kunigel V1 ("Kunigel" is a registered trademark, manufactured by Kunimine Kogyo Co., Ltd.) can be used as powdered sodium bentonite.

The water content of the bentonite mixture is preferably about ±2% of the optimal water content specified in JIS A 1210. By setting the water content of the bentonite mixture in this way, the density of the low-permeability layer (described below) can be increased.

The bentonite mixture may contain other solids besides bentonite, such as sand (e.g., silica sand), gravel, soil, etc.

==Dispersant==
The dispersant is used to reduce the viscosity of the bentonite mixture. The dispersant is preferably one whose main component is a sulfonate, more preferably one whose main component is a polycarboxylate or a polyphosphate. The dispersant contains water.

The proportion of dispersant used in the spraying method according to this embodiment is preferably 0.1 to 0.5 mass% by weight of the bentonite mixture. If the proportion of dispersant is lower than 0.1 mass%, it will not be mixed sufficiently throughout the material. If the proportion of dispersant is higher than 0.5 weight%, the bentonite mixture may clump.

In addition, the moisture content of the entire material (bentonite mixture and dispersant) used in the spraying method according to this embodiment is preferably within ±2% of the optimal moisture content defined in JIS A 1210.

==Other Additives==
The material used in the spraying method according to this embodiment may contain appropriate additives within the range that does not affect the performance of the bentonite mixture and the dispersant.

==Spraying method==
In the spraying method according to the present embodiment, a material containing a bentonite mixture and a dispersant is sprayed onto a spraying position via a piping of a spraying device.

The spraying location is the area where the material is sprayed. For example, when filling a tunnel to transport radioactive waste to an underground facility, the spraying location is the inside of the tunnel. In this case, the material is used as backfill for the tunnel.

The spraying device sprays the material onto the target location. The spraying device may be used alone or attached to other equipment such as heavy machinery.

Figure 1 shows the spraying device 1 according to this embodiment. The spraying device 1 has a main body 10, a hose 20, and a nozzle 30.

The main body 10 includes a storage section for storing the material and a compressor for pneumatically feeding the material (neither shown). The material may be premixed in an external mixer device and then supplied to the storage section of the main body 10, or a mixer may be provided in the main body 10 and the materials may be mixed within the main body 10.

The hose 20 is a long tube connected at one end to the main body 10 and for guiding the pneumatically pumped material to the nozzle 30. The hose 20 may be flexible or rigid. The nozzle 30 is a tube provided at the other end of the hose 20 (the end opposite to the end connected to the main body 10) for discharging the material. In the case of a spraying device used for filling a tunnel, the length of the hose 20 and the nozzle 30 is preferably about 15 m to 30 m. In addition, the inner diameter of the hose 20 is preferably about 60 to 80 mm, and the inner diameter of the nozzle 30 is preferably about 30 to 60 mm. The inner diameters of the hose 20 and the nozzle 30 may be the same or different. As a specific example, the diameter of the tip of the nozzle 30 may be smaller than the diameter of the tip of the hose 20. The hose 20 and the nozzle 30 are examples of "piping".

The spraying device is not limited to the configuration shown in FIG. 1, so long as it has a pipe for spraying the material to the spraying position. On the other hand, since the tunnel for transporting the radioactive waste to the underground facility is narrow (for example, about 4 m in diameter), it is preferable that the spraying device used to fill the tunnel is smaller than a general spraying device.

By adding a dispersant to the bentonite mixture, the viscosity of the bentonite mixture is reduced, making the material less likely to adhere as it passes through the piping of the spraying device. In other words, the bentonite mixture and material containing a dispersant can be sprayed at the spraying location without clogging the piping.

The material sprayed onto the spraying position solidifies to form a low-permeability layer. The low-permeability layer is a layer for suppressing the outflow of groundwater, etc. The low-permeability layer has a permeability coefficient of, for example, 1.0×10 ⁻⁸ m/s or less.

Example
Spraying experiments were carried out using materials with and without dispersants.

(Materials used)
The materials used are as follows:
Bentonite: Kunigel V1 (Na-type bentonite, manufactured by Kunimine Kogyo Co., Ltd.)
Silica sand: Mixture of No. 3 and No. 5 (dry weight ratio 50:50. Kashima-produced)
Dispersant: Polycarboxylate-based dispersant

(Method of preparing materials for spraying)
Silica sand No. 3 (wet mass 125.3 kg) and silica sand No. 5 (wet mass 125.6 kg) were charged into a mixer and stirred for 30 seconds. Then, bentonite (wet mass 276.8 kg) was charged and stirred for 30 seconds. The mixer used was a twin-shaft forced mixing mixer (volume 0.5 m ³ ).

Then, the aqueous solution of the dispersant was added to the mixer and stirred for 300 seconds to prepare the material for spraying. On the other hand, when no dispersant was included, only water was added. The amount of water was adjusted so that the water content of the entire material was 15.8%.

(Spraying of materials)
The material produced by the above-mentioned production method that passed through a 50 mm sieve was put into the spraying device, and spraying was started. The spraying device used had a material pumping distance (pipe length) of 20 m, a hose with an inner diameter of 75 mm, and a spray nozzle with an inner diameter of 40 mm. In addition, in the spraying device, the amount of spraying air was set to 12 ^m3 /h, and the rotor rotation speed was set to 5 rpm. The discharge amount of the material was determined by the amount of spraying air and the rotor rotation speed.

(Experimental Results)
When a material without dispersant was used, the discharge rate dropped significantly one minute after spraying began, and the spraying device was stopped. When the inside of the pipe was checked, lumps of material were formed as shown in Figures 2(a) and (b). It is believed that these lumps were material containing bentonite that had swelled with moisture and adhered to the inside of the pipe, causing the pipe to become clogged. When a material without dispersant was used, dust from the bentonite mixture was generated during operation, as shown in Figure 3.

On the other hand, when a material containing a dispersant was used, all of the material (500 kg for one patch) could be dispensed without stopping the operation of the spraying device. Also, as shown in Figure 4, almost no dust was generated by the bentonite mixture during operation.

This result can be attributed to the following reasons, for example. In the case of materials that do not contain dispersants, bentonite that is swollen due to moisture and non-swollen bentonite are mixed in the material. The presence of additional moisture between the particles of swollen bentonite increases the viscosity of the bentonite, making it more likely to adhere to the inside of the pipe. Non-swollen bentonite is in a dry state and is therefore more likely to scatter when sprayed. On the other hand, by adding a dispersant, the moisture in the material becomes uniform, and most of the bentonite becomes in a swollen state. In other words, there is almost no dry bentonite, so it does not scatter when sprayed. In addition, the swollen bentonite electrostatically repels each other, reducing the viscosity, which makes it possible to discharge the bentonite without adhering to the inside of the pipe.

Claims (2)

A spraying method in which a material containing a bentonite mixture , water, and a dispersant mainly composed of a polycarboxylate is sprayed onto a spraying position through a piping of a spraying device,
A spraying method characterized in that the moisture content of the material is within ±2% of the optimum moisture content specified in JIS A 1210 . The method of claim 1 , wherein said material further comprises silica sand .

Images