JP2007298319A - Container, facility and method for disposing of radioactive waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease the quantity of radioactive substances which reach the ground surface, by restraining organic radioactive substances in radioactive waste that has been buried in the ground from moving. <P>SOLUTION: In a radioactive waste disposal container 1 for accommodating radioactive waste, a member provided by surrounding it is made to contain at least one kind of either rare earth oxide or zirconium oxide to make the organic radioactive substances adsorbed. In this case, the rare earth oxide is at least either europium oxide or praseodymium oxide. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radioactive waste disposal container, disposal facility, and disposal method when radioactive waste is buried in the ground.

  In general, radioactive waste discharged from a nuclear facility or the like is stored in a disposal container and buried in a disposal facility provided underground.

  When storing radioactive waste in a disposal container, fill the gap around the radioactive waste stored in the disposal container with a filler such as cement, and then close the disposal container with a lid. Is done. Multiple disposal containers containing radioactive waste are stored in containers called pits, and are fixedly embedded in disposal facilities. The clearance around the disposal containers in the pit is filled with, for example, cement. The material is filled, and the outer peripheral side of the pit is filled with a filler such as bentonite clay.

  However, radioactive waste buried in the ground deteriorates when the disposal container is exposed to soil and groundwater over a long period of time, and the groundwater enters the disposal container. There is a risk that radioactive elements contained in it will elute into the groundwater and leak out of the disposal container.

  Therefore, in radioactive waste disposal facilities, for example, even if radioactive material leaks out of the disposal container, the radioactive materials are adsorbed on cement, clay filled in the disposal facility, or the bedrock or soil around the disposal facility. Therefore, it is designed to reduce the moving speed of the radioactive substance and sufficiently reduce the radioactive substance reaching the living sphere on the surface to a safe amount.

  By the way, in general, radioactive substances contained in radioactive waste include inorganic substances and organic substances. In particular, organic radioactive materials containing carbon radioisotopes reach the earth's surface because they are less adsorbable to fillers such as cement and clay, rock mass, and soil compared to inorganic radioactive materials. This is a factor that prevents the amount of radioactive material from decreasing.

  In contrast, by adding a photocatalytic substance made of titanium oxide to the filler in the disposal facility and bringing it into contact with the photocatalytic substance, the organic radioactive substance that has eluted into the groundwater and leaked from the processing vessel is more adsorbed. A technique for improving the adsorption performance by oxidative decomposition to a high performance inorganic system has been reported (see Patent Document 1).

  In addition, a method is known in which radiation from radioactive waste decomposes water in the filler, and oxidizes and decomposes organic radioactive substances into inorganic substances by OH radicals generated at that time (see Non-Patent Document 1). ).

JP 2003-107196 A Harakan Center Technical Report (RWMC-TRJ-0402-2), Nuclear Environment Promotion and Fund Management Center, July 2004, p.88-93

  However, in general, the reaction process of oxidatively decomposing organic radioactive substances into inorganic forms has a complicated route. If organic radioactive substances are not completely decomposed into inorganic forms, the radioactive substances are organic. In the form of a system, it will move with the ground water. In this case, in order to reduce the amount of radioactive material that reaches the earth's surface to a safe level, it is necessary to design the depth of the disposal facility deeper.

  In addition, in the case of oxidative decomposition using a photocatalytic substance or oxidative decomposition using OH radicals, radiation from radioactive waste is necessary to advance the oxidation reaction. For this reason, the decomposition rate considering the decrease in the radiation dose, such as when the radiation dose is not sufficient enough away from the radioactive waste, or when the radiation dose in the radioactive waste has decreased after a long period of time after being buried. Evaluation is necessary for the design.

  This invention makes it a subject to suppress the quantity of the radioactive material which suppresses the movement of the organic type radioactive substance in the radioactive waste embed | buried in the ground, and reaches | attains the ground surface.

  First, the principle of the present invention will be described.

  According to the Harakawa Center Technical Report (RWMC-TRJ-0402-2), if the value of the partition coefficient, which is an index representing the adsorption performance of the material in contact with the radioactive substance, is 1 mL / g or more, the moving speed of the radioactive substance Has been reported to have an effect of sufficiently reducing the amount of land reaching the living sphere.

Therefore, the present inventors conducted a test for measuring the distribution coefficient for various materials. In this test, candidate materials capable of adsorbing pure water and organic radioactive substances with high efficiency are put in a test container so that the liquid / solid ratio is 10 mL / g, and released from the radioactive waste. Acetic acid labeled with carbon radioisotope C-14, which is one of the organic radioactive materials, was added to a concentration of 1 × 10 ⁻⁷ mol / L, and the test vessel was sealed. The contents were stirred and mixed while rotating the test container for 2 days. After completion of the test, the contents are filtered to separate into solid and liquid, the concentration of C-14 in the liquid is measured, and the amount of C-14 adsorbed on the solid and the amount of C-14 in the liquid are obtained. 1 was used to calculate the distribution coefficient.

Partition coefficient (mL / g) = (Amount of C-14 adsorbed on solid (mol / g)) / (Amount of C-14 in liquid (mol / mL)) (Equation 1)

As a result of conducting the above test, as shown in Table 1, the metal oxide, particularly the rare earth oxide europium oxide (Eu ₂ O ₃ ) and praseodymium oxide (Pr ₆ O ₁₁ ) show a partition coefficient of 1 or more. I found out. It was also found that zirconium oxide (ZrO ₂ ) has a distribution coefficient of 1 or more. For comparison, the distribution coefficient of the cement-based filler is also shown in Table 1.

  Among the metal oxides added to the filler, as the rare earth oxide, it was confirmed that the adsorptivity of the europium oxide and the praseodymium oxide shown in Table 1 is good. Since the element adjacent to the four elements in the periodic table shows similar properties, holmium oxide, which is the element adjacent to europium, also has a high adsorption performance for organic radioactive materials. Presumed to be.

  Therefore, these rare earth oxides and zirconium oxides can be added to, for example, radioactive waste disposal containers and fillers filled to fill the gaps in the disposal facility, so that It is possible to improve the adsorption performance and sufficiently reduce the amount of radioactive material that reaches the ground surface.

  Here, the rare earth oxide or zirconium oxide added to the filler may be a part of the filler or the whole filler. When the rare earth oxide or the like is added so that the liquid / solid ratio is 10 mL / g as in the above test conditions, sufficient adsorption performance can be obtained. In addition, for example, in the case where adsorption performance similar to that obtained when the distribution coefficient is 1 is obtained, europium oxide is 70 times larger than praseodymium with respect to the liquid / solid ratio in the filler in an actual disposal facility. Rare earth oxides and the like can be reduced to a condition where the liquid / solid ratio is 38 times for oxide and 2.2 times for zirconium oxide.

  Based on the above results, the present invention provides a rare earth oxide, zirconium, which adsorbs organic radioactive waste to a member provided to surround the radioactive waste in a radioactive waste disposal container containing radioactive waste. It is characterized by containing at least one of oxides.

  According to this configuration, even if the disposal container is deteriorated, for example, even if organic radioactive materials are eluted in the groundwater, the rare earth oxide or zirconium oxide in the member provided surrounding the radioactive waste and the organic When the radioactive substance comes into contact, the radioactive substance is adsorbed and held on the surface of these metal oxides. For this reason, the movement of the organic radioactive material accompanying the groundwater can be suppressed, and the amount of radioactive waste reaching the ground surface can be reduced.

  In this case, the member provided surrounding the radioactive waste is, for example, at least one of the filler filled in the void around the radioactive waste stored in the disposal container and the disposal container itself. . That is, the rare earth oxide that adsorbs the organic radioactive material may be added to, for example, a filler filled in the disposal container, added to the disposal container itself, or a sheet on the inner peripheral surface of the disposal container. It may be formed in a shape.

  The rare earth oxide is at least one of europium oxide and praseodymium oxide. According to this, since the high adsorptive power is exhibited with respect to the organic radioactive substance, the movement of the radioactive substance can be effectively suppressed.

  In addition, the present invention is a member disposed around a radioactive waste in a radioactive waste disposal facility in which a plurality of disposal containers storing radioactive waste are stored in a pit and buried in the ground. It is characterized by containing at least one of rare earth oxides and zirconium oxides that adsorb organic radioactive substances.

  In this case, the member provided to surround the radioactive waste is filled with the filling material filled in the void around the radioactive waste stored in the disposal container, the disposal container itself, and the void around the disposal container in the pit. It is assumed that at least one of the filled filler, the pit itself, and the filler filled in the outer peripheral side space of the pit.

  According to this, since it is only necessary to include rare earth oxides and zirconium oxides that adsorb organic radioactive substances in conventional radioactive waste disposal containers, disposal facility fillers or structural materials, etc. It is not necessary to change the structure of the disposal container or the disposal facility, the construction depth of the disposal facility, and the like, and the process required for carrying out the present invention can be changed with a small load.

  In addition, since the disposal facility can be formed with multiple members that surround the radioactive waste, organic radioactive materials can be adsorbed and retained in the disposal facility in sequence, reaching the surface of the earth. The amount of radioactive waste can be sufficiently reduced.

  The present invention also includes a disposal container that contains radioactive waste, is filled with a first filler in a void around the radioactive waste, and is sealed in the space in the pit. A method for disposing of radioactive waste that is filled with a second filler and buried in the ground, wherein any one of the first filler, the second filler, the disposal container itself, and the pit itself The member is characterized by containing at least one of a rare earth oxide and a zirconium oxide for adsorbing an organic radioactive substance.

  By treating the radioactive waste in this way, basically, by the same treatment method as before, the moving speed of the organic radioactive waste leaked from the disposal container is reduced, and the radioactive material reaching the ground surface is reduced. The amount can be reduced.

  In addition, the oxidative decomposition method of the prior art requires radiation when decomposing organic radioactive materials into inorganic ones. Therefore, it is necessary to evaluate the decomposition rate in consideration of the reduction in radiation dose in order to exert its effect. However, according to the present invention, since radiation is not required, there is a design advantage that the installation location of a member containing a rare earth oxide or zirconium oxide that adsorbs an organic radioactive substance is not limited.

  ADVANTAGE OF THE INVENTION According to this invention, the movement of the organic type radioactive substance in the radioactive waste embed | buried in the ground can be suppressed, and the quantity of the radioactive substance which reaches | attains the ground surface can be reduced.

  Hereinafter, a first embodiment to which the present invention is applied will be described with reference to the drawings.

  The radioactive waste disposal method of this embodiment is performed by storing radioactive waste discharged from a nuclear power plant or the like in a disposal container and burying it in a disposal facility formed by excavating underground. .

  FIG. 1 is a longitudinal sectional view showing a state where a disposal container is buried in a radioactive waste disposal facility to which the present invention is applied.

  The disposal facility of the present embodiment includes a disposal container 1 that stores radioactive waste, a pit 2 that stores a plurality of the disposal containers, and a buried hole 3. That is, a pit 2 is fixedly embedded in a buried hole 3 formed by excavating in a disposal facility, and a plurality of disposal containers are accommodated in the pit 2.

  In the gap between adjacent disposal containers 1 in the pit 2, the gap between the disposal container 1 and the pit 2, and the gap between the pit 2 and the buried hole 3, for example, a filler 11 made of cement, bentonite clay, or the like. , 12 are filled.

In the present embodiment, a predetermined metal oxide is added to these fillers 11 and 12. The metal oxide to be added is preferably a rare earth metal oxide, particularly europium oxide (Eu ₂ O ₃ ), praseodymium oxide (Pr ₆ O ₁₁ ), or zirconium oxide (ZrO ₂ ). These metal oxides may be one kind or a mixture of plural kinds.

  When adding a metal oxide to a conventional filler such as cement or clay, in order to increase the contact efficiency with organic radioactive waste, for example, in the form of granules, added to the fillers 11 and 12 in advance, Mix until evenly dispersed.

  The fillers 11 and 12 thus produced are used as gaps between adjacent disposal containers 1 in the pit 2 in the disposal facility, between the disposal container 1 and the pit 2, and between the pit 2 and the buried hole 3. Fill gaps and cover radioactive waste.

  As a result, the radioactive substance eluted from the radioactive waste disposed of in the land moves between the fillers 11 and 12 together with the flow of the groundwater, and is added to the organic radioactive substance and the fillers 11 and 12 at that time. In contact with the metal oxide, radioactive materials are adsorbed with high efficiency. For this reason, the moving speed of an organic type radioactive substance falls, and it becomes possible to reduce the quantity of the radioactive substance which reaches the ground surface.

  Further, in the present embodiment, the example in which the metal oxide is added to the fillers 11 and 12 has been described. However, the present invention is not limited to this example. For example, the structure itself such as the pit 2 is configured to include the metal oxide. May be. In this case, for example, the metal oxide may be formed in a sheet shape on the inner peripheral surface of the pit 2.

  Next, a second embodiment to which the present invention is applied will be described with reference to FIG.

  FIG. 2 is a cross-sectional view of a radioactive waste disposal container to which the present invention is applied.

  As shown in the figure, the radioactive waste 21 is stored in the disposal container 1, and after filling the filler 13 into the gaps generated between the radioactive wastes 21 and between the radioactive waste 21 and the disposal container 1, Seal with a lid 22.

  In the present embodiment, a metal oxide is added to a part of the filler 13, or the entire filler is made a metal oxide.

  The metal oxide to be added is preferably a rare earth metal oxide, particularly europium oxide, praseodymium oxide, or zirconium oxide, as in the first embodiment. These metal oxides may be one kind or a mixture of plural kinds.

  According to the present embodiment, the radioactive substance eluted from the radioactive waste disposed of is moved between the fillers 13 along with the flow of the groundwater. At that time, the radioactive substances are added to the organic radioactive substance and the filler 13. The metal oxide comes into contact and the radioactive material is adsorbed with high efficiency. As a result, the moving speed of the organic radioactive material decreases, and the amount of the radioactive material that reaches the ground surface can be reduced.

  Moreover, although this embodiment demonstrated the example which adds a metal oxide to the filler 13 with which the storage container 1 was filled, it is not limited to this, It is comprised so that a metal oxide may be contained in the storage container 1 itself. May be. In this case, for example, the metal oxide may be formed in a sheet shape on the inner peripheral surface of the disposal container.

  Next, a third embodiment to which the present invention is applied will be described with reference to FIGS.

  In the radioactive waste disposal method of this embodiment, first, as shown in FIG. 2, the radioactive waste 21 is stored in the disposal container 1, the gap 13 is filled with the filler 13, and then sealed with the lid 22. . As shown in FIG. 1, a plurality of the disposal containers 1 are stored in the pit 2, and the filler 11 is placed in the gap between the adjacent disposal containers 1 in the pit 2 and in the gap between the disposal container 1 and the pit 2. After filling, the gap between the pit 2 and the embedding hole 3 is filled with the filler 12 and buried in place.

  In this embodiment, one or both of the rare earth oxide europium oxide and praseodymium oxide are added to the filler 13 in the disposal container 1, and the filler 11 in the pit 2 and the filler 12 in the buried hole 3 are added. Add zirconium oxide.

  As shown in Table 1, europium oxide and praseodymium oxide, which are rare earth oxides, have a higher distribution coefficient than zirconium oxide. This is because europium oxide and praseodymium oxide are more efficient than zirconium oxide. It shows that it can adsorb organic radioactive materials. For this reason, it is considered that the concentration of the radioactive substance released from the radioactive waste 21 is higher in the filler 13 located in the vicinity of the radioactive waste 21 than in the fillers 11 and 12.

  Therefore, by adding a rare earth oxide to the filler 13 and adsorbing the organic radioactive substance with high efficiency, the amount of the organic radioactive substance eluted into the ground water from the radioactive waste can be efficiently reduced.

  On the other hand, since the organic radioactive substance released to the outside of the disposal container 1 is adsorbed by the zirconium oxide added to the fillers 11 and 12, the amount of the radioactive substance moving in the ground can be further reduced.

  Further, since zirconium oxide is less expensive than rare earth oxide, the cost required for the metal oxide to be added can be reduced by using zirconium oxide as the oxide added to the fillers 11 and 12 having a large volume. it can.

  As described above, according to the above-described embodiment, when the disposal container 1 is deteriorated, the organic radioactive material is eluted from the radioactive waste into the groundwater, and further leaked from the disposal container 1 along with the groundwater. However, since radioactive materials are adsorbed and held on rare earth oxides and zirconium oxides contained in fillers and structural materials provided surrounding radioactive waste, the movement of radioactive materials in the ground is suppressed, The amount of radioactive waste that reaches can be reduced.

  In addition, according to the present invention, no radiation is required to decompose organic radioactive materials into inorganic materials, so there are no restrictions on the positions of rare earth oxides and zirconium oxides, and the design flexibility of disposal facilities is increased. Can be improved.

  Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the technical idea of the present invention, and various modifications can be made.

It is a longitudinal cross-sectional view which shows the state by which the disposal container was embed | buried in the disposal facility of the radioactive waste formed by applying this invention. It is sectional drawing of the disposal container of the radioactive waste formed by applying this invention.

Explanation of symbols

1 disposal container 2 pit 3 buried hole 11, 12, 13 filler 21 radioactive waste 22 lid

Claims (8)

In a radioactive waste disposal container for storing radioactive waste, a member provided so as to surround the radioactive waste contains at least one kind of rare earth oxide and zirconium oxide for adsorbing an organic radioactive substance. A radioactive waste disposal container. The member provided surrounding the radioactive waste is at least one of a filler filled in a space around the radioactive waste stored in the disposal container and the disposal container itself. The radioactive waste disposal container according to claim 1. 3. The radioactive waste disposal container according to claim 1, wherein the rare earth oxide is at least one of europium oxide and praseodymium oxide. In a radioactive waste disposal facility where a plurality of disposal containers containing radioactive waste are stored in a pit and buried underground,
A radioactive waste disposal facility, wherein a member provided surrounding the radioactive waste contains at least one of a rare earth oxide and a zirconium oxide for adsorbing an organic radioactive substance. . The member provided to surround the radioactive waste includes a filler filled in a space around the radioactive waste stored in the disposal container, the disposal container itself, and the periphery of the disposal container in the pit. The radioactive waste disposal facility according to claim 4, wherein the facility is at least one of a filler filled in a gap, the pit itself, and a filler filled in a space on the outer peripheral side of the pit. 6. The radioactive waste disposal facility according to claim 4 or 5, wherein the rare earth oxide is at least one of europium oxide and praseodymium oxide. The disposal container, which contains radioactive waste, is filled with a first filler in a space around the radioactive waste and is sealed, is stored in a space in the pit, and is disposed around the disposal container in the pit. A method for disposing of radioactive waste that is filled with filler 2 and buried in the ground,
Among the rare earth oxides and zirconium oxides that adsorb organic radioactive materials to any member of the first filler, the second filler, the disposal container itself, and the pit itself, A disposal method of radioactive waste, comprising at least one kind. 8. The radioactive waste disposal method according to claim 7, wherein the rare earth oxide is at least one of europium oxide and praseodymium oxide.

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