JP4482592B2 - How to store radioactive waste in disposal containers - Google Patents

Description

  The present invention relates to a method for containing radioactive waste in a disposal container.

  As is well known, radioactive waste is stored in a disposal container and then carried to an appropriate disposal site for disposal. Conventionally, such a disposal container has a cylindrical shape. However, when it is stored in a disposal site, a dead space is large and storage efficiency is low, and recently, a rectangular container has been used. Such a disposal container has a shielding layer made of a concrete and other shielding material inside a steel plate made of a container body and a container lid, and the container lid is bolted to the upper opening of the container body. In general, the structure is hermetically sealed.

In order to stably confine the nuclides over a long period of time, various ideas have been made regarding the method for containing radioactive waste in the disposal container. For example, a disposal container is filled with mortar and solidified. In addition, there is one in which the radioactive waste put into the metal container is filled with a granular adsorbent and then the metal container is compression molded to give the waste compact a confinement property. (For example, refer to Patent Document 1).
JP-A-4-110799

  Among the methods for containing radioactive waste in the disposal container, in the method for containing radioactive waste in the disposal container according to Conventional Example 1 in which the disposal container is filled with mortar and solidified, moisture remains in the disposal container. It will be buried. For this reason, the water is radiolyzed by the radiation emitted from the radioactive waste, and the disposal container may be corroded by the oxidizing chemical species generated by the radiolysis of the water. In the method for containing radioactive waste in the disposal container according to Conventional Example 2 in which the metal container is compressed and molded around the radioactive waste contained in the metal container, the metal container is compressed and molded. Considering the radioactive waste generated along with this, it is not always possible to perform compression molding, and a compression step is required, which is not efficient. In addition, the volume reduction rate due to compression is unavoidably deteriorated as compared to the case of radioactive waste alone. Furthermore, it is difficult to confirm whether the amount of adsorbent necessary to confine the nuclide during compression molding is secured.

  Accordingly, an object of the present invention is to provide a method for containing radioactive waste in a disposal container that can stably exhibit a nuclide confinement function for a long period of time from the viewpoint of ensuring the confinement property of a nuclide. .

  The present invention has been made in view of the above circumstances, and therefore, in order to solve the above-described problems, the features of the means adopted by the method for containing radioactive waste in the disposal container according to claim 1 of the present invention. In a method for containing radioactive waste in a disposal container that contains radioactive waste in a shielding body in the container body of a disposal container consisting of a container lid and a container body sealed by the container lid, A compression molding material in which bentonite is compression-molded at a high pressure in a space formed between the inner surface of the shield and the radioactive waste and between the radioactive wastes after containing the radioactive waste in the shield. There is a place to fill.

  According to claim 2 of the present invention, the means adopted by the method for containing radioactive waste in a disposal container is characterized in that in the method for containing radioactive waste in a disposal container according to claim 1, the compression molding is performed. The material is in the form of a ball or board.

A feature of the means adopted by the method for containing radioactive waste in a disposal container according to claim 3 of the present invention is that the radioactive material into the disposal container according to any one of claims 1 and 2 is used. In the waste storage method, the space portion is further filled with silica sand.

According to claim 4 of the present invention, the means adopted by the method for containing radioactive waste in a disposal container is characterized in that the radioactive material in the disposal container according to any one of claims 1 to 3 is used. In the waste accommodation method, the space portion is further filled with iron powder.

A feature of the means adopted by the method for containing radioactive waste in the disposal container according to claim 5 of the present invention is that the radioactive material into the disposal container according to any one of claims 1 to 4 is used. In the waste storage method, the space portion is further filled with a cement-based material.

  A feature of the means adopted by the method for containing radioactive waste in a disposal container according to claim 6 of the present invention is that the radioactive material into the disposal container according to any one of claims 1 and 2 is used. In the waste storage method, the compression molded material is mixed with silica sand.

  A feature of the means adopted by the method for containing radioactive waste in a disposal container according to claim 7 of the present invention is that the radioactive material into the disposal container according to any one of claims 1 to 4 is used. In the waste storage method, the compression molding material is mixed with iron powder.

  A feature of the means adopted by the method for containing radioactive waste in a disposal container according to claim 8 of the present invention is that the radioactive material into the disposal container according to any one of claims 1 to 4 is used. In the waste storage method, the compression molding material is mixed with a cement-based material.

Bentonite, silica sand, iron powder, and cement-based materials have the following functions, respectively. That is,
(1) Bentonite Low water permeability, adsorptivity of nuclides, eye opening function (swells and closes openings): Suppression of nuclide migration (2) Silica sand Thermal conductivity: Good heat dissipation (3) Iron powder Good thermal conductivity: Improved heat dissipation Lower Eh (redox potential) value: Corrosion environment control in containers (corrosion suppression)
(4) Cement-based materials Higher pH: Corrosion environment control in containers (corrosion suppression)

  Therefore, according to the method for containing radioactive waste in the disposal container according to claims 1 to 8 of the present invention, moisture can be reduced, so that moisture is radioly decomposed by radiation radiated from the radioactive waste. There is little possibility that the disposal container will corrode from the inside. And, since the disposal container is not compression molded, even radioactive waste that cannot be compressed and molded due to the dismantling of the power plant can be stored in the disposal container and easily disposed of, and the nuclide is confined. It is possible to easily confirm whether or not the amount of adsorbent necessary for the above is ensured. In addition, by filling the disposal container with bentonite, etc., external pressure such as ground pressure and water pressure acting on the disposal container buried in the disposal site can be supported from the inside, so that the deformation of the disposal container is prevented, resulting from the external pressure Breakage of the disposal container can be suppressed.

  Hereinafter, a disposal container for radioactive waste according to an embodiment of the present invention that implements a method for containing radioactive waste in a disposal container according to the present invention will be described with reference to the attached drawings. 1A is a plan view of a radioactive waste disposal container, FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A, and FIG. 2 is a portion B in FIG. 1B. It is an enlarged view.

  Reference numeral 1 shown in FIGS. 1A, 1B, and 2 is a radioactive waste disposal container according to Embodiment 1 of the present invention. The disposal container 1 includes a container body 2 made of a carbon steel plate whose quality is guaranteed by JIS standards for easy quality control. The container main body 2 is formed in a square shape, and its upper opening is configured to be sealed by welding a container lid 3 made of the same material as that of the container main body 2 and having a structure to be described later. Yes. Also, a pair of guide cylinders 3a each having a taper portion on the inner side of the upper end portion of the opening is provided on the upper surface of the container lid 3 and on two diagonal lines Ld connecting the opposite corner portions. ing. At the center position in the radial direction of each of these guide cylinders 3a, a hanging metal fitting 4 having a large-diameter head 4a formed at the top is projected. The hanging bracket 4 is used when the disposal container 1 is stored in the disposal site. By providing the hanging bracket 4 inside the guide tube 3a, the suspension bracket 4 is prevented from being damaged due to interference with other objects. The effect that it can do is acquired.

Legs 2a are provided at four locations on the bottom surface of the bottom plate of the container body 2 (only two locations are shown in FIG. 1 (b)) so that the radial center coincides with the radial center of the guide tube 3a. It has been.
A space into which the hanging bracket 4 can enter is formed inside the leg 2a, and the leg 2a is removably inserted into a guide cylinder 3a provided on the container lid 3 of another container body 2. Considered to get. By adopting such a configuration, when storing in the disposal site, the disposal containers 1 can be stacked in an orderly manner without being displaced from front to back and from side to side, and collapse of the stacked disposal containers can be prevented. And in the disposal container 1 which becomes such a structure, the square-shaped shielding body 5 which becomes the structure mentioned later for accommodating a radioactive waste is assembled.

  The square shield 5 has the same shape as four side shield plates 5a (both having the same shape and dimensions), a bottom shield plate 5b, and the bottom shield plate 5b, and It is comprised from the upper shielding board 5c of the same dimension. More specifically, each of the side shielding plate 5a, the bottom shielding plate 5b, and the upper shielding plate 5c has a stepped combination portion formed at each of the four end portions, and in the container body 2, The adjacent shielding plates are assembled so as to be at right angles, and are configured to have a rectangular parallelepiped shape (square shape). The side shielding plate 5a, the bottom shielding plate 5b, and the upper shielding plate 5c are all set to have the same constant thickness, and are manufactured from radioactive metal waste or concrete.

  The dimensions of the side shielding plate 5a, the bottom shielding plate 5b, and the upper shielding plate 5c are manufactured according to the dimensions of the container body 2 in advance. For this reason, the bottom shielding plate 5b, the side shielding plate 5a, and the top shielding are simply placed in the container body 2 in the order of the bottom shielding plate 5b, the side shielding plate 5a, and the top shielding plate 5c. The position of the plate 5c is automatically determined, and the square shield 5 having a predetermined size is formed.

  In the disposal container 1 according to the present embodiment, the number of steps of the combination part formed at the four end portions of the side shielding plate 5a, the bottom shielding plate 5b, and the upper shielding plate 5c is as shown in FIG. As is well understood from 1 (a) and (b), it has a two-stage configuration. However, since the number of steps of the combination part may be three or more, it is not particularly limited to the number of steps of the combination part. In this case, the type related to the shape and dimensions of the shielding plate differs depending on the shape of the container body 2, but when the shielding layer is one layer, at most three types may be used. There is an economic effect that can be reduced.

By the way, the case of the single-layered rectangular shield 5 including the four side shielding plates 5a and the bottom shielding plate 5b and the upper shielding plate 5c, respectively, has been described above. However, as shown in FIG. 3A of the plan view of the radioactive waste disposal container according to another embodiment and FIG. 3B of the CC cross-sectional view of FIG. 3A, The square shield 5 can have a multilayer structure.
That is, the surface dose value of the disposal container 1 can be easily held within a certain value by forming the square shield 5 in a multilayer structure according to the radiation level of the radioactive waste.

Hereinafter, the configuration of the rectangular shield 5 of the disposal container 1 will be described with the same reference numerals and the same names as those shown in FIGS. 1A and 1B. That is, the rectangular shield 5 of the disposal container 1 is assembled in the container body 2, and is composed of four side shielding plates 5a and one bottom shielding plate 5b and one upper shielding plate 5c. and a first angular shields 5 ₁ made.
Further, a second corner which is assembled in the _first square shield 51 and includes four side shielding plates 5a ′ and one bottom shielding plate 5b ′ and one upper shielding plate 5c ′. and a mold shield 5 _2. Furthermore, the assembled second corner shields 5 _2, "and the bottom shielding plate 5b one by one each" four sides shielding plate 5a third angle type consisting a and upper shield 5c " and a shield 5 _3. in this case, the shielding plate constituting the second angular shields 5 ₂ and the third corner shields 5 _3, each constituting the first corner shields 5 ₁ It is formed to be similar to the shielding plate.

  Hereinafter, a method for storing radioactive waste in the disposal container 1 in which radioactive waste is accommodated in the rectangular shield 5 assembled in the container body 2 of the disposal container 1 will be described. First, radioactive waste (nuclide) is accommodated in the square shield 5. When radioactive waste is accommodated in the rectangular shield 5, a shape corresponding to the shape of the radioactive waste is formed between the inner surface of the rectangular shield 5 and the radioactive waste and between the radioactive wastes. A space is formed. Therefore, the space is filled with a ball-shaped or board-shaped compression molding material in which bentonite is compression-molded at a high pressure by a cold isostatic pressing apparatus according to the shape of the space. Further, in addition to the compression molding material, silica sand, iron powder, and cement-based material are filled.

The compression-molded material made of bentonite, silica sand, iron powder, and cement-based material have the following functions, respectively, and the following effects can be obtained by such functions.
(1) Bentonite Low water permeability, adsorptivity of nuclides, eye opening function (swells and closes openings): Suppression of nuclide migration (2) Silica sand Thermal conductivity: Good heat dissipation (3) Iron powder Good thermal conductivity: Improved heat dissipation Lower Eh (redox potential) value: Corrosion environment control in containers (corrosion suppression)
(4) Cement-based materials Higher pH: Corrosion environment control in containers (corrosion suppression)

  More specifically, since the moisture can be reduced, the moisture is hardly decomposed by radiation emitted from the radioactive waste, and the possibility that the disposal container 1 corrodes from the inside is small. Since the disposal container 1 is not compression molded, even radioactive waste that cannot be compression molded due to the dismantling of the power plant can be stored in the disposal container 1 and easily disposed of, and the nuclide. It is possible to easily confirm whether or not the amount of adsorbent necessary for confining is secured. Further, by filling the disposal container 1 with bentonite or the like, external pressure such as ground pressure and water pressure acting on the disposal container 1 embedded in the disposal site can be supported from the inside, so that the deformation of the disposal container 1 is prevented, and the external pressure Damage to the disposal container 1 due to the above can be suppressed. In addition, the conventional technique of filling the granular adsorbent is not efficient because it requires a compression step, but if a high-density bentonite is filled, it is efficient because the compression step is unnecessary. In consideration of the above-mentioned effects obtained with each filler, it is only necessary to appropriately select and fill materials other than the compression molded material made of bentonite.

  In the method for housing the radioactive waste in the disposal container, the example in which the compression molding material made of bentonite, silica sand, iron powder, and cement-based material are individually filled has been described. However, the present invention is not limited to this, and silica sand, iron powder, and cement-based material are mixed in bentonite in advance, or silica sand, iron powder, and cement-based material are selectively mixed and mixed. And even if it fills a space with what compression-molded the mixture into the shape of a ball or board at high pressure, the effect equivalent to the case by the said filling method filled individually can be acquired.

  In the disposal container 1 which concerns on the above embodiment, the case of the square shielding body 5 which has one shielding layer, and the square shielding body 5 which has three shielding layers was demonstrated as an example. However, the number of shielding layers of the square shielding body 5 assembled in the container body 2 can be two, and can be four or more. It is not limited to the number of shielding layers of the square shield 5. Furthermore, in the above method for accommodating radioactive waste in the disposal container, the case where radioactive waste is accommodated in the rectangular shield 5 assembled in the container body 2 has been described as an example. Since the technical idea of the present invention can also be applied to the disposal container, the present invention is not limited to the method for containing radioactive waste in the rectangular disposal container of the present invention.

FIG. 1A is a plan view of a radioactive waste disposal container, and FIG. 1B is a cross-sectional view taken along line AA of FIG. It is the B section enlarged view of Drawing 1 (a). FIG. 3A is a plan view of a radioactive waste disposal container according to another embodiment of the present invention, and FIG. 3B is a cross-sectional view taken along line CC in FIG. 3A.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Disposal container 2 ... Container main body, 2a ... Leg 3 ... Container lid, 3a ... Guide pipe | tube 4 ... Suspension metal fitting, 4a ... Head 5 ... Square-shaped shielding body, 5a ... Side part shielding plate, 5b ... Bottom part shielding plate, 5c ... Upper shielding plate 5 ₁ ... First square shield, 5a ... Side shield plate, 5b ... Bottom shield plate, 5c ... Upper shield plate 5 ₂ ... Second square shield member, 5a '... Side shield plate 5b '... bottom shielding plate, 5c' ... top shielding plate 5 ₃ ... third square shield, 5a "... side shielding plate, 5b" ... bottom shielding plate, 5c "... top shielding plate Ld ... diagonal line

Claims (8)

  In a method for containing radioactive waste in a disposal container that contains radioactive waste in a shielding body in the container body of a disposal container comprising a container lid and a container body sealed by the container lid, the shielding body is radioactive. After containing the waste, filling the space formed between the inner surface of the shield and the radioactive waste and between the radioactive wastes with a compression molding material obtained by compression molding bentonite at a high pressure. A method for containing radioactive waste in a special disposal container.   The method for containing radioactive waste in a disposal container according to claim 1, wherein the compression molding material has a ball shape or a board shape. The method for containing radioactive waste in a disposal container according to any one of claims 1 and 2, wherein the space portion is further filled with silica sand. The method for containing radioactive waste in a disposal container according to any one of claims 1 to 3, wherein the space portion is further filled with iron powder. The method for containing radioactive waste in a disposal container according to any one of claims 1 to 4, wherein the space portion is further filled with a cement-based material.   The method for containing radioactive waste in a disposal container according to any one of claims 1 and 2, wherein the compression molding material is mixed with silica sand.   The method for containing radioactive waste in a disposal container according to any one of claims 1 to 3, wherein iron powder is mixed into the compression molding material.   The method for containing radioactive waste in a disposal container according to any one of claims 1 to 4, wherein a cementitious material is mixed in the compression molding material.

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