JP2017142263A - Radioactive contaminant storage method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radioactive contaminant storage method that can reduce the leak of radiation, can prevent the leak of a radioactive material, and enables mass production at a low cost.SOLUTION: In a bottomed cylindrical member 2 made of concrete porous molded body that includes reinforcement fiber and air bubbles in a dispersion state and has a specific gravity in a range of 0.8-1.5, a radioactive contaminant is stored directly or in an accommodated state in a flexible container bag without using a metal drum. In the state in which an opening in the upper end of the bottomed cylindrical member is closed by a lid member 3 made of a concrete porous molded body, the radioactive contaminant is statically stored in a temporary yard or an intermediate storage facility.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radioactive contaminant storage method for storing radioactive contaminants contaminated with radioactive materials diffused into the atmosphere due to a nuclear power plant accident.

  After an accident at a nuclear power plant in Fukushima, contaminated soil and contaminated sludge containing radioactive materials are stored in a flexible container bag (hereinafter abbreviated as FIBC) made up of sheets woven from yarn such as polyethylene and polypropylene. Packed and transported to a temporary storage site in Fukushima Prefecture.

  However, when the air dose from the flexible container is measured, high values of radiation of 0.15 to 2.5 μSV / h are detected from the contaminated sludge and 0.20 to 2.5 μSV / h from the contaminated soil. Yes.

  As a container capable of reducing radiation leakage, for example, a radioactive waste filling container in which a concrete container is lined on an iron drum can is known. This type of concrete container is composed of cement, fine aggregate, coarse aggregate, and nuclide adsorption reinforcement, and fibrous activated carbon capable of adsorbing radionuclides is used as the nuclide adsorbent (for example, Patent Document 1).

JP-A-10-153690

  However, the conventional radioactive waste filling container in which a concrete container is lined on the drum can is heavy and not easily transported. Also, drums are not suitable for mass production, and it is not possible to procure early enough containers to store contaminated sludge and soil generated in large quantities in Fukushima, etc., or incinerated ash containing radioactive materials. There is a problem.

  The Ministry of the Environment envisioned placing a flexible container filled with contaminated soil, contaminated sludge, etc. in a temporary storage area, embanking it, covering the embankment with a cover, and loading a sandbag on the cover. ing. The Ministry of the Environment is considering storing the flexible container in a temporary storage area for about three years and then moving it to an intermediate storage facility for about 30 years.

  However, in reality, flexible containers filled with contaminated soil and the like are placed in the temporary storage site as they are. Since FIBC is not durable and is sensitive to ultraviolet rays, it may deteriorate and break in just a few months. Therefore, the contaminated soil leaks from the broken flexible container, and the surrounding soil is secondarily contaminated. Therefore, there is a problem that the contaminated soil increases on the contrary. Moreover, even if the flexible container does not break, secondary soil contamination cannot be prevented by infiltration and leaching of rainwater or the like.

  In addition, the temporary storage site needs to be restored to the initial state and returned to the local government. However, since the amount of contaminated soil increases as described above, it is difficult to return the temporary storage site to the initial state. Furthermore, according to surveys by the Chernobyl municipality in Ukraine and the Nevada Nuclear Test Site in the United States, most of the radioactive cesium deposited on the soil surface remains within 10-30 cm from the ground surface even after a long period of time. It is reported that the amount of contaminated soil that must be excavated has increased in large quantities. Under such circumstances, there is an urgent need to develop a radioactive contaminant storage method for storing radioactive contaminants such as contaminated soil and contaminated sludge.

  The present invention has been made in consideration of the problems in the conventional method for storing radioactive contaminants as described above, and can reduce the leakage of radiation, prevent the leakage of radioactive material, and can be mass-produced at low cost. It is possible to provide a method for storing radioactive contaminants that is light, lightweight, and easy to handle.

  A radioactive contaminant storage method according to the present invention is a radioactive contaminant storage method for storing radioactive contaminants contaminated with radioactive materials released into the atmosphere in the event of a nuclear power plant accident. In addition, the bottomed cylindrical member made of a concrete porous molded body containing a reinforcing fiber and air bubbles in a dispersed state and having a specific gravity in the range of 0.8 to 1.5, directly or without a drum can, or a flexible container The bottomed cylindrical member is stored in a bag, and the bottomed cylindrical member is closed in a temporary storage site or an intermediate storage facility in a state where the opening at the upper end of the bottomed cylindrical member is closed by a lid member made of the concrete porous molded body. The gist is to store the radioactive contaminants by standing still.

  In this invention, it is preferable that the thickness of a bottomed cylinder member is 30-70 mm.

  According to the method for storing radioactive contaminants according to the present invention, contaminated sludge, contaminated soil, or incinerated ash containing radioactive substances can be stored in a storage container. Leakage of radioactive material from the container can be reduced by the adsorption / shielding action of the radioactive material by the bottomed cylindrical member and the lid member.

  Moreover, by adopting cement hardened material as the container main body of the radioactive contaminant storage container, the container main body can be reduced in weight and cost as compared with the conventional storage container in which the container main body is a drum can and a concrete container, and transportation is facilitated.

  In addition, unlike a conventional containment container in which a concrete container is lined on a drum can, the container of the radioactive contaminant storage method according to the present invention is easy to manufacture and suitable for mass production.

  Furthermore, according to the concept of the Ministry of the Environment, if a container storing contaminated soil is stored in a temporary storage area for about 3 years and further in an intermediate storage facility for about 30 years, the radiation dose value after about 33 years is sufficient. If it has decayed, this soil can be returned to nature. At that time, it is difficult to destroy the conventional barbed containment container with a heavy machine or the like, and even if it can be destroyed, a large amount of metal waste is generated. On the other hand, since the storage container of the radioactive contaminant storage method according to the present invention is made of hardened cement, it can be easily pulverized with a heavy machine or the like while storing the soil, and metal waste is not generated. Accordingly, it is possible to prevent the containment vessel itself from becoming a large radioactive waste without being pulverized.

It is a perspective view which shows the structure of the radioactive contaminant storage container which concerns on embodiment of this invention. It is a longitudinal cross-sectional view of a radioactive contaminant storage container. It is explanatory drawing which shows the state which loaded the radioactive contaminant storage container in multiple stages. It is a perspective view which shows the other structure of a radioactive contaminant storage container. It is a perspective view which shows the radioactive contaminant storage container which concerns on other embodiment. It is a perspective view which shows a cover member partially. It is a figure which shows the detailed structure of a conveyance auxiliary member. (A), (b) is a figure which shows the rotation direction of the conveyance auxiliary member of FIG. It is the graph which showed the relationship between the distance from a container, and a dose. It is the graph which showed the relationship between the distance from a container, and a shielding rate.

Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.
1. Configuration of Radioactive Containment Container In FIGS. 1 and 2, the radioactive contaminant storage container 1 (hereinafter simply abbreviated as a container) 1 of the radioactive contaminant storage method according to the present invention is made of cement hardened material. A bottom cylinder member 2 and a lid member 3 made of a hardened cement material capable of closing the upper end opening of the bottomed cylinder member 2 are provided.

  After the bottomed cylindrical member 2 stores radioactive waste or radioactive material-containing soil, sludge or other radioactive contaminants, or incinerated ash containing radioactive material, the lid member 3 opens the upper end of the bottomed cylindrical member 2. Is configured to close.

  A plurality of metal transportation aids (hooks) 4 can be attached to the lid member 3. Alternatively, a plurality of transportation aids 4 can be attached to one side surface of the bottomed tubular member 2 and the opposite side surface thereof. Of course, the transport aid 4 can be attached to both of them. The container 1 can be easily transported by attaching a wire or the like to these transport aids 4 and lifting the wire with a heavy machine such as a crane. In addition to the hook as shown in FIG. 1, a plurality of long members having an L-shaped cross section can be provided on the lower surface of the bottomed tubular member 2 at intervals as the transport aid. In this case, since the fork of the forklift can be inserted and transported between the long members, the transportability is improved.

As an example of design values, the radioactive contaminant storage container 1 has an internal size of 1.2 m × 1.2 m × 0.91 m, a weight of about 800 kg (bottomed tubular member: 650 kg, lid member: 150 kg), and an internal volume of 1.2 m. ³ can be used. Moreover, the thickness of the radioactive contaminant storage container 1 can be 30 mm-70 mm, for example. In addition, the thickness of the cover member 3 can be 80 mm, for example.

  A plurality of recesses 2 a can be provided on the four side surfaces of the bottomed cylindrical member 2. Thereby, weight reduction of the bottomed cylindrical member 2 can be achieved. Moreover, the vent hole for discharging | emitting methane gas generated from the sludge etc. in the container 1 can be provided.

2. Production Method of Radioactive Containment Container In the present invention, the manufacturing method of the bottomed cylindrical member 2 of the radioactive contaminant storage container 1 is as follows.

  The radioactive contaminant storage container 1 has a porous structure in which reinforcing fibers and a large number of air bubbles are dispersed therein. First, cement, water, a water reducing agent (if necessary), and reinforcing fibers are mixed to form a cement. A mixture is obtained.

  Next, air from the compressor is introduced into the foaming agent to create bubbles foamed at a predetermined magnification, for example, about 10 to 30 times. The bubbles are added to the cement mixture and stirred to obtain a foamed cement. In addition, air bubbles can be further added so that the specific gravity of the cement mixture is appropriately measured in the middle of stirring and approaches the target value. The foaming agent is not particularly limited, and various foaming agents known in the art, such as cement and concrete foaming agents, such as protein-based, surfactant-based, and resin-based foaming agents can be used. Furthermore, a bubble can also be efficiently produced | generated using metallic foaming agents, such as aluminum powder, with the said foaming agent. Although the addition amount and addition method of a foaming agent are not specifically limited, Usually, it is the range of 0.1-12 weight part with respect to 100 weight part of cement, and the specific gravity of the radioactive contaminant storage container 1 is 0.8-1. Adjust to .5. Thereby, the strength of the container 1 can be ensured while avoiding an extreme weight increase, and the balance between the avoidance of weight increase and the strength guarantee can be maintained.

  Next, the foamed cement is filled in a mold and cured and solidified. The curing may be normal curing, steam curing, or a combination of both.

  The type of cement is not particularly limited, and various cements such as ordinary Portland cement, early-strength Portland cement, and ultra-early-strength Portland cement can be used.

  The blending ratio of cement and water is preferably 20 to 100 parts by weight of water with respect to 100 parts by weight of cement, but the more preferable blending ratio of water is in the range of 20 to 50 parts by weight. This is because if the water content is too high, the strength of the radioactive contaminant storage container 1 tends to decrease, and if the water content is too low, the fluidity of the foamed cement tends to decrease during molding.

  Examples of reinforcing fibers include polyvinyl alcohol fibers (vinylon fibers), polyolefin fibers such as polypropylene fibers and polyethylene fibers, aramid fibers, carbon fibers, steel fibers, and glass fibers.

  The fiber length of the reinforcing fiber is not particularly limited, but is preferably in the range of 4 to 35 mm. If the fiber length of the reinforcing fiber is less than 4 mm, the reinforcing effect tends to be insufficient. The longer the fiber length of the reinforcing fiber is advantageous in terms of the reinforcing effect. On the other hand, the longer the fiber length is, the lower the dispersibility becomes, and the reinforcing fiber is unevenly distributed inside the radioactive contaminant storage container 1. The strength of the container 1 may be reduced. The thickness of the reinforcing fiber is not particularly limited, but a fiber in the range of 10 μm to 100 μm can be used. It should be noted that a reinforcing structure in which reinforcing fibers are entangled with each other can be obtained simply by stirring the reinforcing fibers uniformly during cement kneading, and strength without variation can be obtained.

  The compounding amount of the reinforcing fiber is preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of cement. When the amount of the reinforcing fiber is small, the reinforcing effect is low and the strength of the radioactive contaminant storage container 1 is also low. The larger the amount of the reinforcing fiber, the more advantageous in terms of reinforcing effect. However, when the amount is excessive, the dispersibility deteriorates, the reinforcing fibers are unevenly distributed, and the strength of the container 1 is locally reduced. There is a risk of lowering the strength. From such a viewpoint, the more preferable range of the compounding amount of the reinforcing fiber is 0.5 to 3 parts by weight with respect to 100 parts by weight of cement.

  According to the radioactive contaminant storage method of the present invention, the stored contaminated sludge, contaminated soil, or incinerated ash by the shielding action of the radioactive material by the bottomed cylindrical member 2 and the lid member 3 made of hardened cement containing reinforcing fibers. Leakage of radionuclides from can be reduced.

  Further, by adopting a cement hardened material as the container main body of the radioactive contaminant storage container, the container main body can be lighter than the conventional storage container which is a drum can and a concrete container, and can be easily transported.

  Further, unlike a conventional containment container in which a concrete container is lined on a drum can, the container 1 of the radioactive contaminant storage method according to the present invention is inexpensive and easy to manufacture and suitable for mass production.

  Furthermore, according to the concept of the Ministry of the Environment, if a container storing contaminated soil is stored in a temporary storage area for about 3 years and further in an intermediate storage facility for about 30 years, the radiation dose value after about 33 years is sufficient. If it has decayed, this soil can be returned to nature. At that time, it is difficult to destroy the conventional barbed containment container with a heavy machine or the like, and even if it can be destroyed, a large amount of metal waste is generated. On the other hand, since the container 1 of the radioactive contaminant storage method according to the present invention is made of cement hardened material, it can be easily pulverized with a heavy machine or the like while storing the soil, and metal waste is not generated. Accordingly, it is possible to prevent the containment vessel itself from becoming a large radioactive waste without being pulverized.

  In addition, in FIG. 1, although the cross section of the radioactive contaminant storage container 1 was made into the rectangle, it is not limited to this, It is good also as other shapes, such as a square, an ellipse, a circle, a hexagon, or an octagon. If the shape of the cross section of the container 1 is unified with a rectangle or a square, there is an advantage that the container 1 can be easily arranged and arranged regularly in a storage space. For example, the Ministry of the Environment contemplates a temporary storage place as shown in FIG. 3, and the containers 1 of the radioactive contaminant storage method according to the present invention can be loaded in multiple stages and regularly in the temporary storage place. The container 1 can be covered with the embankment 20, and the sandbag 21 can be loaded thereon via the cover 22. It has been proved that there is no problem in strength even when the containers 1 are stacked in multiple stages, as will be described later.

  In the above, the radioactive pollutant storage method of the present invention is used for storing contaminated soil and contaminated sludge containing radioactive substances. However, the present invention is not limited to this, and clothes (work clothes) containing radioactive substances are used. It can also be used to store.

3. Other Embodiments In FIG. 4, the radioactive contaminant storage container 1a is not provided with the recess 2a (FIG. 1). By not providing the recessed part 2a, the thickness of the bottomed cylindrical member 2 can be made uniform, stronger strength can be obtained, and shielding properties can be further ensured.

  Next, FIG. 5 is a perspective view showing a radioactive contaminant storage container 1b according to another embodiment. The configuration of the radioactive contaminant storage container 1b is basically the same as that of the radioactive contaminant storage container 1a of FIG. 4, except that the transport aid 4 on the side of the bottomed cylindrical member 2 is not provided, and The difference is that conveyance auxiliary members 10 are provided at the four corners of the lid member 3a. This will be described in detail below.

  In FIG. 5, the conveyance auxiliary member 10 can be detachably provided at the four corners of the lid member 3a. Moreover, a to-be-fastened part (female screw part) (not shown) to which the conveyance auxiliary member 10 is screwed and fastened can be provided in the bottomed cylindrical member 2. When the lid member 3a is transported, a hook provided on a heavy machine such as a crane can be hooked on the transport aid 4, and the radioactive contaminant storage container 1b in a state where the lid member 3a is combined with the bottomed cylindrical member 2 is transported. Sometimes the hook can be hooked on the conveyance assisting member 10. In addition to the urethane-based, polymer cement-based, and FRP resin-based coating film waterproofing agents, a silane-based or solvent-based permeable water absorption inhibitor can be applied to the inner surface of the bottomed cylindrical member 2. In this way, by applying the permeable water absorption inhibitor, in addition to the improvement of waterproofness, the effect of further improving weather resistance and preventing deterioration is exhibited.

  6 is a perspective view partially showing the lid member 3a. As shown in FIG. 6, the lid member 3a can be provided with a convex portion 30 at the peripheral edge of the lid member 3a. The convex portion 30 forms a concave portion 31 in the lid member 3a. A plurality of groove portions 33 can be formed in the convex portion 30. Moreover, the bottom part of the bottomed cylindrical member 2 (refer FIG. 5) can be provided with the convex part which is not shown in figure fitting to said recessed part 31. FIG. Thereby, in the temporary storage site, the radioactive contaminant storage container 1b can be stably stacked in multiple stages by fitting the convex part into the concave part 31, and the water accumulated in the concave part 31 can be passed from the concave part 31 through the groove part 33. Can be discharged outside. In addition, when loading a radioactive contaminant storage container in multiple stages, the conveyance auxiliary tool 4 and the conveyance auxiliary member 10 are removed.

  Moreover, the hole part (burr hole) 32 for inserting said conveyance auxiliary member 10 is provided in the four corners (part of the convex part 30) of the cover member 3a.

  Next, FIG. 7 is a diagram illustrating a detailed configuration of the conveyance assisting member 10. In FIG. 7, the conveyance auxiliary member 10 includes a main body portion 11, a ring-shaped link portion 12 that is rotatably attached to the main body portion 11, and a bolt portion 13 that is provided at the bottom of the main body portion 11. As the conveyance auxiliary member 10, for example, a frenolink bolt called an omnidirectional eyebolt manufactured by Martec Corporation can be employed. The use load (withstand load) of the frenolink bolt is about 2 tons.

  FIGS. 8A and 8B are views showing the rotation direction of the conveyance assisting member 10 of FIG. In FIG. 8A, the conveyance assisting member 10 can be rotated 180 ° with respect to a plane F perpendicular to the axis of the bolt portion 13 (based on the plane F). Further, in FIG. 8B, the main body part 11 is configured to be able to rotate 360 ° around the axis of the bolt part 13, so that the link part 12 is also connected to the bolt part 13 as the main body part 11 rotates. It is designed to rotate 360 ° around the axis.

  Next, the attachment method of the conveyance auxiliary member 10 will be described. First, the upper opening of the bottomed cylindrical member 2 is closed by the lid member 3a (see FIG. 5). Then, the bolt portion 13 of the conveyance assisting member 10 is inserted into the hole portion 32 of the lid member 3a and screwed into the female screw portion of the bottomed cylindrical member 2. Thereby, the conveyance auxiliary member 10 is attached to the radioactive contaminant storage container 1 b and the lid member 3 a is fixed to the bottomed cylindrical member 2.

  When the radioactive contaminant storage container 1b is transported, the container 1b can be lifted by hooking a hook of a heavy machine such as a crane on the link portion 12 of the transport assisting member 10.

  According to the conveyance auxiliary member 10 as described above, since the conveyance auxiliary member 10 is screwed to the bottomed cylindrical member 2, the safety of lifting is extremely high and there is no possibility of dropping off. Further, in the conveyance assisting member 10, the link portion 12 rotates 360 ° around the axis of the bolt portion 13 and can rotate 180 ° with respect to a plane F perpendicular to the axis of the bolt portion 13. The degree of freedom of lifting is very high. That is, an excessive force is not applied to the conveyance auxiliary member 10 when the radioactive contaminant storage container is lifted. Therefore, the reliability of transporting the radioactive contaminant storage container becomes very high.

  The above is a mode for carrying out the present invention. However, the present invention is not limited by the above embodiment as a matter of course, and it is needless to say that the present invention can be carried out with appropriate modifications within a range that can meet the gist of the present invention. All of these are possible within the scope of the present invention.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited by the following examples, and can of course be implemented with appropriate modifications within a range that can be adapted to the above-described gist. Included in the range.

1. Shielding test The shielding test was performed according to the following procedure. The contaminated soil was put into the radioactive contaminant storage container 1, and the air dose of the contaminated soil was measured without a lid. Next, the radioactive contaminant storage container 1 was covered with the lid member 3, and the air dose at positions 10 cm, 30 cm, 50 cm, and 100 cm away from the side surface of the container 1 and the side surface of the container 1 was measured. The results are shown in FIGS.

  In FIG. 9, L1 is a curve showing the relationship between the dose and distance when the contaminated soil is stored in the container 1 having a thickness of 70 mm. The distance means a distance from the side surface of the bottomed cylindrical member 2, and the dose when the distance is 0 means the dose on the side surface of the bottomed cylindrical member 2. L2 is a curve showing the relationship between the dose and the distance of the contaminated soil before storing in the container 1, and the dose when the distance is 0 means the dose on the contaminated soil. .

  FIG. 10 shows the transmittance obtained from the graph of FIG. 9, the shielding rate is calculated from 100−transmittance, and the relationship between the calculated shielding rate and the distance is summarized. From this result, it was confirmed that the shielding rate of the storage container 1 of the radioactive contaminant storage method according to the present invention was about 60%.

2. Compression test A pressure plate was placed on the radioactive contaminant storage container 1, and a pressure of 100 ton was applied by a compression tester. The number of tests was n = 3.

  As a result, it was confirmed visually that no destruction occurred. Thereby, for example, the weight of the container 1 (weight 800 kg) storing the contaminated soil having a weight of 2 tons is 2.8 tons in total, but when such containers 1 are stacked and stored in three stages, the lowest container 1 Since the weight loaded on the container 1 is about 5.6 tons, it was confirmed that there is no problem in multistage storage of the container 1. In addition, it was also confirmed visually that there was no occurrence of cracks or the like in the container 1.

3. Watertight test Water was put into the radioactive pollutant containment vessel 1, and the presence or absence of water leakage after 48 hours was investigated. The number of tests was n = 3.

  As a result of the watertight test, it was confirmed that none of the test specimens had any water leakage even after 48 hours had passed since the injection.

4). Breathability test When contaminated soil is stored in the radioactive contaminant storage container 1, methane gas may be generated from the soil. Therefore, the breathability of the container 1 was confirmed. In addition, the test was performed in a state in which the container 1 was degassed.

  In this test, after the bottomed cylindrical member 2 was covered with the lid member 3, the pressure in the container 1 was reached when the air injection was stopped 2 minutes after the air was injected into the container 1 (0.25 MPa). Since it became 0 MPa, it has confirmed that the container 1 had air permeability.

5. Workability test A workability test was carried out to confirm whether or not the radioactive pollutant storage container 1 in a state in which the contaminated soil was stored can be suspended with a UNIC. In addition, in order to perform the test more strictly, after the soil was added, it was pressed and hardened so that the amount of stored soil was increased.

  When this test was performed, the container 1 could be lifted without problems and no breakage occurred. Moreover, no abnormality such as breakage occurred even when the container 1 was swung while being lifted. Thereby, it was confirmed that it was excellent also about workability. In addition, it was confirmed that it can be hung without problems even in a rebar-free container containing contaminated soil.

DESCRIPTION OF SYMBOLS 1,1a, 1b Radioactive contaminant storage container 2 Bottomed cylindrical member 3,3a Lid member 4 Conveyance aid 10 Conveyance auxiliary member 11 Main part 12 Link part 13 Bolt part

Claims (2)

A radioactive contaminant storage method for storing radioactive contaminants contaminated with radioactive materials released into the atmosphere following a nuclear power plant accident,
Without including a drum can on the bottomed cylindrical member made of a concrete porous molded body containing the radioactive contaminants, including reinforcing fibers and bubbles in a dispersed state and having a specific gravity in the range of 0.8 to 1.5, Store directly or in a flexible container bag,
The radioactive pollutant is obtained by allowing the bottomed cylindrical member to stand in a temporary storage site or an intermediate storage facility in a state in which an opening at an upper end of the bottomed cylindrical member is closed by a lid member made of the concrete porous molded body. A method for storing radioactive contaminants, characterized by storing The radioactive contaminant storage method according to claim 1, wherein the bottomed cylindrical member has a thickness of 30 to 70 mm.

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