JP7210498B2 - Radioactive waste solidification system and radioactive waste solidification method - Google Patents

Description

The present invention relates to a radioactive waste solidification system and a radioactive waste solidification method.

A geopolymer is an amorphous polymer composed of elements such as silicon (Si) and aluminum (Al), and is an inorganic material like cement. Geopolymers are made from a base material (solidifying material) containing elements such as silicon and aluminum and an alkaline material (alkali stimulant) as raw materials. A solidified geopolymer is formed by a polycondensation reaction occurring between the base material and the alkaline material.

Unlike cement, geopolymers do not have hydrates in the solidified structure. Therefore, when the geopolymer is used, even if excess water is removed by drying by heating, the effect on the structure of the solidified body is small. Therefore, geopolymers are attracting attention as materials for use in, for example, solidifying high-dose radioactive waste.

JP 2017-67679 A

A solidified body produced by solidifying radioactive waste may have radionuclides eluted from the solidified body, for example, due to contact with groundwater. In particular, elements that are long half-life radionuclides such as I-129 and exist as anions in the environment of the disposal site are less likely to be affected by the adsorption retardation effect of minerals, etc., and therefore have a large effect on the exposure dose. In addition, since cations such as Cs are present in large amounts, they affect the exposure dose in the later stages such as after the disposal site is closed. Therefore, when solidifying radioactive waste with a geopolymer, it is required to improve the adsorption performance of adsorbing the above-described radionuclides and suppress the elution of radionuclides.

When preparing a solidified body of geopolymer, a slurry is prepared by mixing a base material and an alkaline material. When preparing the slurry, the reaction between the base material and the alkaline material occurs in a short period of time. As a result, the viscosity of the slurry containing the base material and the alkaline material may increase. Therefore, it is necessary to use the slurry containing the base material and the alkaline material before the viscosity of the slurry becomes extremely high and the fluidity is lowered. Due to the above circumstances, when preparing a solidified body of geopolymer, it is not easy to handle the slurry containing the base material and the alkaline material, and the workability may be lowered. In addition, as the fluidity of the slurry decreases, it may become difficult to fill the container with the slurry uniformly, making it difficult to form a dense solidified body.

Therefore, the problem to be solved by the present invention is to provide a radioactive waste solidification system and a radioactive waste solidification method that can suppress the elution of radionuclides and can easily improve workability. It is to be.

An embodiment of a radioactive waste solidification system comprises: a first substrate comprising silicon; a second substrate comprising silicon and aluminum and having more aluminum than the first substrate; a third substrate comprising magnesium; Solidification treatment is performed on radioactive waste by using a geopolymer created using as a raw material. The radioactive waste solidification system includes a first substrate storage for storing a first substrate, a second substrate storage for storing a second substrate, and a third substrate storage for storing a third substrate. an alkali material storage unit for storing the alkali material; and a solution preparation unit for mixing the first base material supplied from the first base material storage unit and the alkali material supplied from the alkali material storage unit to prepare a solution. , creating slurry by mixing the second base material supplied from the second base material storage unit, the third base material supplied from the third base material storage unit, and the solution supplied from the solution creation unit; A slurry preparation unit is provided in which the slurry is put into a waste container in which radioactive waste is stored. The third base material is magnesium hydroxide. Here, solidification is performed using a geopolymer in which the ratio of the amount of magnesium element to the total amount of the amount of silicon element and the amount of magnesium element is more than 0% and 44% or less.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to provide a radioactive waste solidification system and a radioactive waste solidification method that can suppress the elution of radionuclides and can easily improve workability.

FIG. 1 is a diagram schematically showing a radioactive waste solidification system 1 according to an embodiment. FIG. 2 is a flow chart showing the radioactive waste solidification method according to the embodiment. FIG. 3 shows the distribution coefficient Kd results for cesium ions. FIG. 4 shows the partition coefficient Kd results for iodide ions. FIG. 5 is a diagram showing measurement results of unconfined compressive strength.

[A] Radioactive waste solidification system 1
FIG. 1 is a diagram schematically showing a radioactive waste solidification system 1 according to an embodiment.

As shown in FIG. 1, in this embodiment, the radioactive waste solidification system 1 includes a first base material storage unit 10, a second base material storage unit 20, a third base material storage unit 30, and an alkaline material storage unit 40. It has a solution preparation section 50 and a slurry preparation section 60, and is configured to produce a geopolymer using base materials (first base material, second base material) and an alkaline material as raw materials.

Each part constituting the radioactive waste solidification system 1 will be sequentially described below.

[A-1] First base material storage unit 10
The first substrate storage unit 10 is installed to store the first substrate. The first substrate is a geopolymer substrate and is a substance containing silicon as an element. The first substrate is preferably free of aluminum and calcium. The first base material is, for example, silica (silicon dioxide) or silica fume.

In this embodiment, the first base material storage section 10 has a first base material solution tank 11 and a first base material powder tank 12 . In the first base material storage unit 10, the first base material solution tank 11 stores, for example, a silica aqueous solution (water glass) in which silica is dissolved in water as the first base material. On the other hand, the first base material powder tank 12 stores, for example, silica powder as the first base material.

[A-2] Second base material storage unit 20
The second base material storage part 20 includes a tank that stores the second base material. The second substrate is a geopolymer substrate that contains silicon and aluminum as elements and contains more aluminum than the first substrate. The second substrate is, for example, alumina silica. Alumina silica includes metakaolin, blast furnace slag, incineration ash, fly ash, zeolite, mordenite, and the like. A mixture of a substance containing silicon element but not containing aluminum element (silicon dioxide, etc.) and a substance containing aluminum element without containing silicon element (aluminum oxide, aluminum hydroxide, etc.) is used as the second base material. good too. Fly ash includes fly ash. Fly ash is fly ash collected after burning pulverized coal, and is managed as a product.

[A-3] Third base material storage unit 30
The third base material storage part 30 includes a tank that stores the third base material. The third base material is a geopolymer base material containing magnesium as an element. In this embodiment, the third base material is magnesium hydroxide.

[A-4] Alkali material storage unit 40
The alkaline material storage unit 40 includes a tank that stores the alkaline material. Alkaline materials are, for example, alkaline hydroxides and alkaline silicates. Alkaline hydroxides are, for example, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide. Alkaline silicates are, for example, lithium silicate, sodium silicate, potassium silicate, rubidium silicate, cesium silicate. As silicates, various forms such as orthosilicates and metasilicates can be used. In addition to the above, an aluminate may be added as an alkali material.

[A-5] Solution preparation unit 50
The solution preparation unit 50 includes a tank to which the first base material is supplied from the first base material storage unit 10 and the alkaline material is supplied from the alkaline material storage unit 40, and the first base material and the alkaline material are mixed with water. is provided to create a solution dissolved in

Specifically, the solution preparation unit 50 is supplied with an aqueous solution in which the first base material is dissolved in water from the first base material solution tank 11 via the pump P11. Further, the solution preparation unit 50 is supplied with the powder of the first base material from the first base material powder tank 12 and also with the solid of the alkaline material. In the solution preparation unit 50, stirring is performed using, for example, a stirrer (not shown) so that the powdery first base material and the solid of the alkaline material are dissolved in the aqueous solution in which the first base material is dissolved in water. executed. As a result, the solution preparation unit 50 prepares a solution in which the first base material and the alkaline material are dissolved in water.

[A-6] Slurry preparation unit 60
The slurry preparation section 60 is supplied with the second base material from the second base material storage section 20, the third base material from the third base material storage section 30, and the solution from the solution preparation section 50. A tank is provided for forming a slurry in which the second substrate and the third substrate are mixed in the solution.

Specifically, the slurry preparation section 60 is supplied with the solution prepared by the solution preparation section 50 via the pump P50. The slurry preparation unit 60 is supplied with the powder of the second base material from the second base material storage part 20 and the powder of the third base material from the third base material storage part 30 . In the slurry preparation unit 60, stirring is performed using, for example, a stirrer (not shown) so that the powder of the second base material and the powder of the third base material are mixed into the solution. As a result, slurry, which is a suspended dispersion, is formed in the slurry forming section 60 .

The slurry prepared by the slurry preparation section 60 is filled into a waste container 81 containing radioactive waste via a pump P60. In the slurry filled inside the waste container 81, the reaction between the base material (first base material, second base material, and third base material) and the alkali material progresses to create a solidified geopolymer. be.

[B] Radioactive Waste Solidification Method FIG. 2 is a flowchart showing the radioactive waste solidification method according to the embodiment.

As shown in FIG. 2, a geopolymer is produced by sequentially performing a solution preparation step ST10, a slurry preparation step ST20, and a slurry filling step ST30. Although the details will be described later, here, the amount of magnesium element out of the total amount (100%) of the total amount (100%) of the amount of silicon element [Si] (mol) and the amount of magnesium element [Mg] (mol) The solidification process is performed by producing a geopolymer in which the proportion of [Mg] (mol) is more than 0% and 44% or less (that is, 0 (%) < 100 * [Mg] / ([Si] + [ Mg])≦44(%)). Details of each step will be described in order.

[B-1] Solution preparation step ST10
First, in the solution preparation step ST10, as described above, the solution preparation unit 50 prepares a solution by dissolving the first base material and the alkaline material in water.

In the solution prepared in the solution preparation step ST10, each substance is mixed within the following ranges, for example.
- First base material: 2.2 to 23.7 wt. %
・Alkaline material: 31.5 to 40.4 wt. %
- Water: 44.8 to 57.4 wt. %

[B-2] Slurry preparation step ST20
Next, in the slurry preparation step ST20, as described above, the second base material is added to the solution prepared in the solution preparation step ST10 and mixed in the slurry preparation section 60 to prepare slurry. Here, in the base material (first base material, second base material, third base material), the value obtained by dividing the amount of material of silicon element [Si] (mol) by the amount of material of aluminum element [Al] (mol) The second and third base materials are mixed so that ([Si]/[Al]) is 2 ([Si]/[Al]=2).

The slurry prepared in the slurry preparation step ST20 contains, for example, a mixture of substances within the following ranges.
- First base material: 2.2 to 23.7 wt. %
- Second base material: 30.7 to 30.8 wt. %
- Third base material: 0.0 wt. % and 14.9 wt. % or less Alkaline material: 21.9 to 22.0 wt. %
- Water: 31.1 to 31.3 wt. %

[B-3] Slurry filling step ST30
Next, in the slurry filling step ST30, the waste container 81 is filled with the slurry prepared in the slurry preparing step ST20 as described above. The waste container 81 is, for example, a drum containing high-dose radioactive waste as waste. The filled slurry is mixed with waste inside the waste container 81 . After that, in the slurry, the reaction between the base materials (the first base material, the second base material, and the third base material) and the alkali material progresses, thereby creating a solidified body of the geopolymer.

[C] Summary As described above, in the present embodiment, first, a solution is prepared by dissolving the first base material and the alkaline material in water. Then, a slurry is prepared by mixing the second base material and the third base material with a solution in which the first base material and the alkaline material are dissolved in water. After that, the slurry is filled into a waste container 81 to create a solidified body of geopolymer.

Since the first base material contains less aluminum than the second base material, it is less likely to react with the alkaline material than the second base material. Therefore, in the present embodiment, the solution in which the first base material and the alkaline material are dissolved maintains a state of low viscosity. Moreover, magnesium hydroxide, which is the third base material, has low solubility and is less soluble in water than the first base material. When preparing the slurry in this embodiment, the first base material and the alkaline material are already dissolved in water. As a result, the slurry prepared in the present embodiment maintains a lower viscosity state for a longer time than the slurry prepared by simultaneously mixing the first base material, the second base material, the third base material, and the alkaline material. can be done.

Therefore, in the present embodiment, it is possible to easily fill the waste container 81 with the slurry before the fluidity of the slurry decreases, so that workability can be improved. In addition, in accordance with this, in the present embodiment, it becomes easy to uniformly fill the waste container 81 with the slurry, so that a dense solidified body can be formed. This effect can be exhibited more effectively when the first base material does not contain aluminum and calcium.

In addition, as will be described in detail in the following examples, in this embodiment, since magnesium hydroxide is used as the third base material, it is possible to improve the adsorption performance for adsorbing radionuclides. In addition, since the solidified body of the geopolymer is produced so that the ratio of the magnesium element substance amount to the total amount of the silicon element substance amount and the magnesium element substance amount is 44% or less, the uniaxial compressive strength is increased. can be sufficiently ensured.

Examples will be described with reference to Table 1. Table 1 shows the formulation of each component in Examples and Comparative Examples.

[Formation of solidified body]
(Example 1)
In Example 1, as shown in Table 1, silica fume (SiO ₂ ) was used as the first base material, metakaolin was used as the second base material, and magnesium hydroxide (MgOH ₂ ) was used as the third base material. In addition, in Example 1, a potassium silicate solution (K ₂ SiO ₃ ) and potassium hydroxide (KOH) were used as alkaline materials. Here, among all the components in Example 1, the molar ratio of silicon element and magnesium element ([Si]:[Mg]) is the relationship shown in Table 1 (90:10), and the amount of aluminum element FIG. 2 shows that the total amount of the silicon element substance amount [Si] (mol) and the magnesium element substance amount [Mg] (mol) with respect to [Al] has the following relationship. Each component was mixed in the above procedure to form a solidified body.

([Si]+[Mg])/[Al]=2

(Example 2)
In Example 2, as shown in Table 1, among all the components in Example 2, the molar ratio ([Si]:[Mg]) of silicon element and magnesium element has the relationship shown in Table 1 (70:30 ), a solidified body was formed in the same manner as in Example 1, except that

(Example 3)
In Example 3, as shown in Table 1, among all the components in Example 3, the molar ratio ([Si]:[Mg]) of the silicon element and the magnesium element has the relationship shown in Table 1 (60:40 ), a solidified body was formed in the same manner as in Example 1, except that

(Comparative example 1)
In Comparative Example 1, as shown in Table 1, magnesium hydroxide (MgOH ₂ ) as the third base material was not used. That is, of all the components in Comparative Example 2, Example 1 except that the molar ratio ([Si]:[Mg]) of the silicon element and the magnesium element has the relationship (100:0) shown in Table 1. Solidified bodies were formed in the same manner as in .

(Comparative example 2)
In Comparative Example 2, as shown in Table 1, among all the components in Comparative Example 2, the molar ratio ([Si]:[Mg]) of the silicon element and the magnesium element has the relationship shown in Table 1 (50:50 ), a solidified body was formed in the same manner as in Example 1, except that

[Measurement of partition coefficient]
When measuring the distribution coefficient, the solidified bodies prepared in Examples 1, 2, and Comparative Example 1 were pulverized into powder having a particle size of less than 100 μm. Then, the powder obtained by the pulverization was immersed in an aqueous cesium iodide solution for one week under the condition that the liquid-solid ratio (L/S) was 10. Thereafter, the cesium ion concentration and the iodide ion concentration of the supernatant liquid of the cesium iodide aqueous solution were measured by an inductively coupled plasma mass spectrometer (ICP-MS). Partition coefficients were obtained from the changes in the concentration of cesium ions and the changes in the concentrations of iodide ions, respectively, as shown in FIGS. FIG. 3 shows the distribution coefficient Kd results for cesium ions. FIG. 4 shows the partition coefficient Kd results for iodide ions.

As shown in FIG. 3 , Examples 1 and 2 have a higher partition coefficient Kd for cesium ions than Comparative Example 1. Thus, the solidified body in which part of the silicon element is substituted with the magnesium element has improved adsorption performance for cesium ions. Between the case where the molar ratio ([Si]:[Mg]) of silicon element and magnesium element is 90:10 (Example 1) and 70:30 (Example 2), cesium The partition coefficients Kd for the ions were comparable.

As shown in FIG. 4, Examples 1 and 2 have higher partition coefficients Kd for iodide ions than Comparative Example 1. Thus, the solidified body in which part of the silicon element is substituted with the magnesium element has improved adsorption performance for iodide ions. Here, the case where the molar ratio ([Si]:[Mg]) of silicon element and magnesium element is 70:30 (Example 2) is better than the case where it is 90:10 (Example 1). , a high partition coefficient Kd for iodide ions. Therefore, the higher the proportion of elemental magnesium, the more the adsorption performance for iodide ions can be improved.

[Measurement of uniaxial compressive strength]
When measuring the unconfined compressive strength, the slurry prepared in each example was poured into a cylindrical plastic mold (5 cm in diameter, 10 cm in height) and then air-dried for 43 days. Then, the solidified body obtained by removing the plastic mold was measured for uniaxial compressive strength (JIS A1108:2006 Concrete Compressive Strength Test Method).

FIG. 5 is a diagram showing measurement results of unconfined compressive strength. In FIG. 5 , the vertical axis indicates the uniaxial compressive strength, and the “Mg substitution rate” on the horizontal axis is the “substance amount of silicon element [Si] (mol) and the substance amount of magnesium element [Mg] (mol). The ratio of the amount of magnesium element [Mg] (mol) to the total amount (100%).

As shown in FIG. 5, regarding the uniaxial compressive strength, when the molar ratio ([Si]:[Mg]) of the silicon element and the magnesium element is 90:10 (Example 1), the silicon element and the magnesium element When the molar ratio ([Si]:[Mg]) of is 100:0 (Comparative Example 1). On the other hand, when the molar ratio of silicon element and magnesium element ([Si]:[Mg]) is 70:30 (Example 2), when it is 60:40 (Example 3), and , 50:50 (Comparative Example 2) was lower than 100:0 (Comparative Example 1).

In general, when used as a filled solidified body, the uniaxial compressive strength of the solidified body is required to be 30 MPa or more. Therefore, when used as a filled solidified body, as can be seen from the approximate expression in FIG. 5, the amount of silicon element [Si] (mol) and the amount of magnesium element [Mg] (mol) It is preferable that the proportion of the magnesium element substance amount [Mg] (mol) in the total amount (100%) is 26% or less (that is, 100 * [Mg] / ([Si] + [Mg]) ≤ 26 (%)).

In general, when used as a homogeneously solidified body, the uniaxial compressive strength of the solidified body is required to be 10 MPa or more. Therefore, when used as a homogeneously solidified body, as can be seen from the approximate expression in FIG. It is preferable that the ratio of the magnesium element substance amount [Mg] (mol) to the total amount (100%) is 44% or less (that is, 100 * [Mg] / ([Si] + [Mg]) ≤ 44 (%)).

Therefore, when the molar ratio ([Si]:[Mg]) of silicon element and magnesium element is 70:30 (Example 2) and 60:40 (Example 3), the strength is A sufficient solidified body can be obtained.

<Others>
It should be noted that the present invention is not limited to the above-described embodiment as it is, and in the implementation stage, it can be implemented in various forms other than the above-described embodiment. Various omissions, additions, replacements, and modifications can be made to the present invention without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

For example, in the present embodiment described above, regarding the first base material storage unit 10, the first base material solution tank 11 storing an aqueous silica solution (water glass) in which silica is dissolved in water as the first base material; Although the case of including the first base material powder tank 12 storing silica powder as one base material has been exemplified, the present invention is not limited to this. The first base material storage section 10 may be composed of only the first base material powder tank 12 without the first base material solution tank 11 . In this case, in the solution preparation unit 50, the powder of the first base material and the solid of the alkaline material are put into water and mixed to prepare a solution in which the first base material and the alkaline material are dissolved in water. be done.

DESCRIPTION OF SYMBOLS 1... Radioactive waste solidification system, 10... 1st base material storage part, 11... 1st base material solution tank, 12... 1st base material powder tank, 20... 2nd base material storage part, 30... 3rd unit Material storage unit 40 Alkali material storage unit 50 Solution preparation unit 60 Slurry preparation unit P11 Pump P50 Pump P60 Pump.

Claims (2)

A geometries produced by using, as raw materials, a first base material containing silicon, a second base material containing silicon and aluminum and having more aluminum than the first base material, a third base material containing magnesium, and an alkaline material. A radioactive waste solidification system for solidifying radioactive waste by using a polymer,
a first base material storing part for storing the first base material;
a second base material storage part for storing the second base material;
a third base material storage part for storing the third base material;
an alkaline material storage unit that stores the alkaline material;
a solution preparation unit that mixes the first base material supplied from the first base material storage part and the alkaline material supplied from the alkaline material storage part to create a solution;
By mixing the second base material supplied from the second base material storage unit, the third base material supplied from the third base material storage unit, and the solution supplied from the solution preparation unit a slurry preparation unit that prepares a slurry and puts the slurry into a waste container that contains radioactive waste;
The third base material is magnesium hydroxide,
A solidification treatment is performed using the geopolymer in which the ratio of the amount of magnesium element to the total amount of the amount of silicon element and the amount of magnesium element is more than 0% and 44% or less.
Radioactive waste solidification system. A radioactive method for producing a geopolymer using as raw materials a first substrate containing silicon without containing aluminum and calcium, a second substrate containing aluminum and silicon, a third substrate containing magnesium, and an alkaline material as raw materials A waste solidification method comprising:
a solution preparation step of preparing a solution by dissolving the first base material and the alkaline material in water;
a slurry creation step of creating a slurry by mixing the solution created in the solution creation step, the second base material, and the third base material;
a slurry filling step of filling a waste container containing waste with the slurry prepared in the slurry preparing step;
The third base material is magnesium hydroxide,
A solidification treatment is performed using the geopolymer in which the ratio of the amount of magnesium element to the total amount of the amount of silicon element and the amount of magnesium element is more than 0% and 44% or less.
Radioactive waste solidification method.

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