JP2001264488A - Solidifying material for concentrated boric acid aqueous solution and neutron absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cement material solidifying a concentrated boric acid aqueous solution and a neutron absorber using this. SOLUTION: This solidifying material for the concentrated boric acid aqueous solution contains calcium aluminates and a calcium hydroxide, and furthermore contains at least one of an alkali metal salt and/or a clay mineral such as bentonite and zeolite, blast furnace slag, and a silica material such as silica fume and fly ash. A neutron absorber is formed by kneading a mixture of the solidifying material for the concentrated boric acid aqueous solution and a boric acid aqueous solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutron absorber using a solidified boric acid aqueous solution and a neutron absorber mainly generated as radioactive waste from a nuclear reactor or the like.

[0002]

2. Description of the Related Art Boron compounds have neutron absorption properties and are therefore used as neutron absorbers in nuclear reactors and nuclear facilities to prevent the occurrence of criticality and leakage of radioactivity. However, the high-concentration boric acid aqueous solution used as the neutron absorber becomes radioactive waste and cannot be discarded as it is, but is solidified and discarded by some method.

[0003]

The solidified high-concentration boric acid water can be used as a neutron absorber. As means for solidifying high-concentration boric acid water, for example,
It is conceivable that the material is solidified by a cement material or the like.
Since the hardened cement has stability and durability, it can be said to be a preferable method from the viewpoint of reliability. However,
Boric acid and salts thereof are well known as retarders for cement-based materials. In particular, it has not been possible to solidify a high-concentration aqueous boric acid solution with cement-based materials. The present inventors have conducted various studies to solve these problems, and as a result, surprisingly, the use of a solidifying material containing calcium aluminates and calcium hydroxide has solved the problems. The inventor has found that the present invention is feasible and has completed the present invention.

[0004]

That is, the present invention provides (1)
A solidified material of a high-concentration boric acid aqueous solution containing calcium aluminates and calcium hydroxide, (2) a solidified material of a high-concentration boric acid aqueous solution of (1) containing an alkali metal salt, (3) bentonite (1) or (2) a solidified material of a high-concentration boric acid aqueous solution containing at least one or more of siliceous substances such as clay minerals such as iron and zeolite, blast furnace slag, silica fume, and fly ash;
(4) A neutron absorber obtained by kneading and molding the solidified material of the high-concentration boric acid aqueous solution of (1) to (3) and the boric acid aqueous solution.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The calcium aluminates of the present invention are:
Although not particularly limited, specific examples thereof include:
If CaO is C, Al ₂ O ₃ is A, and SiO ₂ is S, CA, C ₁₂ A ₇ , C
₃ A, CA ₂ etc., and C ₁₁ A ₇・ CaF ₂ , C ₁₁ A ₇・ CaCl ₂ , C ₂ AS, C ₄ A ₃
Crystalline compounds such as SO _3, and CaO-Al ₂ O ₃ based amorphous material,
CaO-Al ₂ O ₃ -F ₂ based amorphous material, and CaO-Al ₂ O ₃ -SiO ₂ based amorphous calcium aluminate such as amorphous material, and the like, one or of these Two or more can be used. The particle size of the calcium aluminates is not particularly limited, but usually, the Blaine specific surface area is 3000 to 90.
00 cm ² / g is preferable, and 4000 to 8000 cm ² / g is more preferable.
If it is less than 3000 cm ² / g, the solidification properties and strength development may be deteriorated, and even if the powder is crushed to 9000 cm ² / g or more, further enhancement of the effect cannot be expected.

[0007] Any calcium hydroxide can be used for the present invention, and usually, commercially available slaked lime is used. The particle size of the calcium hydroxide is not particularly limited, usually, preferably 5000 cm ² / g or more in Blaine specific surface area, 6000 cm ² / g or more is more preferable. If the specific surface area of the calcium hydroxide is less than 5000 cm ² / g, material separation may occur or solidification properties may deteriorate.

The solidified material of the high-concentration boric acid aqueous solution (hereinafter, referred to as solidified material) according to the present invention contains calcium aluminates and calcium hydroxide. Calcium hydroxide is preferably 10 to 200 parts, more preferably 30 to 150 parts, and even more preferably 50 to 120 parts based on 100 parts of calcium aluminates. If it is less than 10 parts, material separation may occur or solidification properties may be poor,
If it exceeds 200 parts, the solidification properties may deteriorate or the strength development may deteriorate. In the present invention, parts,%
Represents a mass unit.

In the present invention, an alkali metal salt can be used in combination for the purpose of shortening the solidification time. The type of the alkali metal salt is not particularly limited, for example, sodium hydroxide, potassium hydroxide, and alkali hydroxides such as lithium hydroxide, sodium carbonate, potassium carbonate,
And alkali carbonates such as lithium carbonate, sodium chloride, potassium chloride, and alkali chlorides such as lithium chloride, sodium nitrate, potassium nitrate, and alkali nitrates such as lithium nitrate, sodium sulfate, potassium sulfate,
And alkali sulfates such as lithium sulfate, sodium aluminate, and potassium aluminate, and alkali aluminates such as lithium aluminate, and at least one or more of these can be used. For the purpose of shortening the solidification time of the present invention, it is particularly preferable to use an alkali metal hydroxide or an alkali metal aluminate.

The amount of the alkali metal salt used is not particularly limited, but is preferably 1 to 20 parts, more preferably 3 to 15 parts, based on 100 parts of the total of calcium aluminates and calcium hydroxide. . If it is less than 1 part, the effect of shortening the solidification time is not sufficient.

In the present invention, calcium aluminates,
In addition to calcium hydroxide and alkali metal salts, at least one or more of clay minerals such as bentonite and zeolite, and siliceous substances such as blast furnace slag, silica fume and fly ash (hereinafter referred to as inorganic powder) are used in combination. be able to. These inorganic powders are preferable in that they not only provide material separation resistance, but also reduce hydration heat generation and promote long-term strength enhancement. The particle size of the inorganic powder is not particularly limited, usually, preferably 4000 cm ² / g or more in Blaine specific surface area, 6000 cm ² / g or more is more preferable. If it is less than 4000 cm ² / g, sufficient material separation resistance may not be provided.

The amount of the inorganic powder to be used is not particularly limited. However, it is usually preferable to use the inorganic powder in a range of 50 parts or less based on 100 parts in total of calcium aluminates and calcium hydroxide. -30 parts is more preferable. If it exceeds 50 parts, the solidification properties and the initial strength expression may be deteriorated.

The particle size of the solidified material of the present invention is not particularly limited.
cm ² / g are preferred, 4000~8000cm ² / g is more preferable. If the particle size of the solidified material is less than 3000 cm ² / g, material separation may occur or strength development may be impaired. Even if it exceeds 9000 cm ² / g, further enhancement of the effect cannot be expected.

The ratio of the solidified material of the present invention to the aqueous solution of boric acid and the concentration of the aqueous solution of boric acid are not particularly limited.
From the viewpoint of increasing the throughput of the boric acid aqueous solution, or
From the viewpoint of enhancing the neutron absorption ability, it is preferable to increase the ratio of the boric acid aqueous solution as much as possible to increase the concentration of the boric acid aqueous solution. Usually, 50 to 200 parts of a boric acid aqueous solution is preferable for 100 parts of a solidified material of a boric acid aqueous solution,
~ 150 parts is more preferred. If the amount is less than 50 parts, the treatment amount of the boric acid aqueous solution cannot be increased, and the capacity of the formed neutron absorber may not be sufficient. If the amount exceeds 200 parts, the neutron absorber may not be solidified.

In the present invention, the concentration of the boric acid aqueous solution is 1
0% or more is preferable, and 30% or more is more preferable. If the concentration of the boric acid aqueous solution is less than 10%, the treatment capacity of the boric acid aqueous solution may not be sufficient, or the neutron absorption capacity of the formed cured product may not be sufficient. As a method for increasing the concentration of the boric acid aqueous solution, it is effective to increase the temperature or to dissolve it together with the alkali hydroxide. Further, it may be prepared by dissolving various borates such as sodium borate and potassium borate. The combined use of the alkali hydroxide has an effect of increasing the boric acid concentration, and also has an effect of shortening the time from kneading the boric acid water and the solidifying material to solidifying as described above.

In the present invention, calcium aluminates,
Other than calcium hydroxide, alkali metal salts and inorganic powders, among water reducing agents, high-performance water reducing agents, AE water reducing agents, high-performance AE water reducing agents, superplasticizers, defoamers, thickeners, and setting regulators It is possible to use at least one of them in a range that does not substantially inhibit the object of the present invention.

In the present invention, the method of mixing the respective materials is not particularly limited, and the respective materials may be mixed at the time of construction, or a part or all of them may be mixed in advance. Absent. As the mixing device, any existing device can be used, and examples thereof include a tilting mixer, an omni mixer, a Henschel mixer, a V-type mixer, and a Nauta mixer.

[0018]

The present invention will be described below in detail with reference to examples.

Example 1 Various calcium aluminates shown in Table 1 (hereinafter referred to as CA
) And calcium hydroxide in the proportions shown in Table 1 to prepare a solidified material. On the other hand, tap water heated to 60 ° C. was used to prepare a 50% boric acid aqueous solution. However, sodium hydroxide was added so that the Na / B molar ratio was 0.25. Boric acid aqueous solution / solidified material ratio 10
The mixture was kneaded at 0% and the solidification properties and the compressive strength were measured. The results are shown in Table 1. In addition, as a comparative example,
The measurement was made when ordinary Portland cement and alumina cement were used as solidifying materials. Experiment N in Table 1
For the solidified material having the mixing ratio of calcium aluminate and calcium hydroxide used in o.1-7, the particle size was changed as shown in Table 2 and the same measurement was performed. The results are also shown in Table 2.

<Materials> Calcium hydroxide: commercially available slaked lime, Blaine specific surface area 12
000cm ² / g. CA Ruii: C ₃ A, first grade reagent calcium carbonate and aluminum oxide were mixed and ground by the 3-to-1 mole, fired at 1350 ° C., synthetic repeated twice a step of pulverizing, Blaine specific surface area of 4500cm ² / g . CAs b: C ₁₂ A ₇ , reagent grade 1 calcium carbonate and aluminum oxide were mixed and pulverized at a ratio of 12 to 7 mol, and 1350
The process of baking and crushing at ℃ is repeated twice to synthesize, and the Blaine specific surface area is 4500 cm ² / g. CAs: Synthesized by mixing and pulverizing CA, reagent grade calcium carbonate and aluminum oxide at a ratio of 1: 1 and firing at 1350 ° C. twice and pulverizing twice to obtain a Blaine specific surface area of 4500 cm ² / g. CAs d: C ₁₁ A ₇ .CaF ₂ , reagent grade 1 calcium carbonate, aluminum oxide, calcium fluoride are mixed and pulverized at a ratio of 11 to 7 to 1 mol, and a process of firing and pulverizing at 1350 ° C. is repeated twice. Synthesized, Brain specific surface area 4500cm ² /
g. CAs e: C ₃ A ₃ .CaSO ₄ , reagent grade 1 calcium carbonate, aluminum oxide, calcium sulfate 3 to 3 to 1
The process of mixing and pulverizing in moles, and calcining and pulverizing at 1350 ° C. is repeated twice to synthesize, and the Blaine specific surface area is 4500 cm ² / g. CAs: Amorphous CA, reagent grade calcium carbonate, aluminum oxide, and silicon dioxide are mixed and pulverized at 12: 7: 1 mol, melted at 1650 ° C, quenched, and synthesized.
Blaine specific surface area 4500cm ² / g. Boric acid: Reagent grade 1 boric acid Ordinary Portland cement: Commercial product Alumina cement: Commercial product

<Measurement method> Compressive strength: Measured according to JIS R 5201. Solidification time: Measure the setting time according to JIS R 5201.

[0022]

[Table 1]

[0023]

[Table 2]

From Table 1, it can be seen that the conventional cement-based material does not solidify a high-concentration boric acid aqueous solution at all, whereas the solidified material containing calcium aluminate and calcium hydroxide of the present invention has excellent solidification properties. It turns out that it shows strength development. Table 2 shows that as the particle size of the solidified material of the present invention increases, the strength developing properties improve.

Example 2 A total of 100 parts of 50 parts of CA and 50 parts of calcium hydroxide
The same procedure as in Example 1 was carried out except that various alkali metal salts were blended as shown in Table 3 to prepare a solidified material. The results are also shown in Table 3.

<Materials Used> Alkali metal salt a: Reagent primary sodium aluminate Alkali metal salt b: Reagent primary potassium aluminate Alkali metal salt C: Reagent primary lithium hydroxide Alkali metal salt d: Reagent primary sodium carbonate Alkali metal salt E: reagent primary potassium carbonate Alkali metal salt F: reagent primary lithium carbonate

[0027]

[Table 3]

Table 2 shows that when an alkali metal salt is used in combination with the solidifying material of the present invention, excellent solidifying properties can be obtained.

Example 3 A total of 100 parts of 50 parts of CAs and 50 parts of calcium hydroxide
In Table 4, the alkali metal salt a and various inorganic powders are shown in Table 4.
Example 2 was carried out in the same manner as in Example 2 except that a solidified material was prepared by blending as shown in Table 1. The results are shown in Table 4.

<Materials used> Inorganic powder A: commercially available silica fume, Blaine specific surface area 20
0000cm ² / g. Inorganic powder B: Commercial bentonite, Blaine specific surface area 2500
0 cm ² / g. Inorganic powder C: Commercial blast furnace slag, Blaine specific surface area 6000cm
² / g. Inorganic powder D: Commercial fly ash, Blaine specific surface area 40
00cm ² / g.

<Measurement method> Material separation resistance: visual judgment

[0032]

[Table 4]

From Table 4, it can be seen that when inorganic powder is used in combination with the solidified material of the present invention, excellent solidification properties and long-term strength development properties are obtained without material separation.

[0034]

The solidified material of the high-concentration boric acid aqueous solution according to the present invention solidifies a high-concentration boric acid aqueous solution in a short time and has good strength developing properties. In addition, since a large amount of boron can be uniformly fixed to the solidified body, an excellent neutron absorber can be obtained.

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Claims (4)

[Claims] 1. A solidified material of a high-concentration boric acid aqueous solution containing calcium aluminates and calcium hydroxide. 2. The composition according to claim 1, which comprises an alkali metal salt.
Of high concentration boric acid aqueous solution. 3. The high-concentration boric acid aqueous solution according to claim 1, which contains at least one or more of clay minerals such as bentonite and zeolite, and siliceous substances such as blast furnace slag, silica fume and fly ash. Solidifying material. 4. A neutron absorber obtained by kneading and molding the solidified material of a high-concentration boric acid aqueous solution according to claim 1 and a high-concentration boric acid aqueous solution.