JP2513690B2 - Solidifying agent for radioactive waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is based on a solidifying agent for radioactive waste, more specifically, a hydraulic substance, calcium aluminate, gypsum, ultrafine powder and a superplasticizer, It has high activity and early strength, has a large processing capacity, can be stored permanently, and has little elution of radioactive substances.
It relates to a safe, especially boron-bound radioactive waste solidifying agent.

[Conventional technology and its problems] Radioactive wastes are generated from factories, hospitals, and laboratories that use radioactive isotopes, mining or refining factories of radioactive minerals, etc., but most of them are nuclear facilities of nuclear power plants. Arises from. Also, as boron-containing radioactive waste (hereinafter referred to as “B waste”), so-called low / medium levels such as concentrated waste liquid, used ion-exchange resin, various sludges, and concrete waste discharged during the dismantling of a nuclear power plant. High-level wastes such as B wastes are included.

As a method for solidifying these radioactive wastes, particularly low- and middle-level radioactive wastes, the cement solidification method, the vitamin solidification method, the plastic solidification method, and the like have been put into practical use.

However, the cement solidification method has a relatively large elution property, has a long curing time, and has durability such as the disintegration of the cured product, particularly when boron is contained, the hydration reaction is inhibited and the treatment capacity is small. There was a flaw. In addition, although the bio-solidification method and the plastic solidification method have a large processing capacity, they have drawbacks such as a complicated processing method and a safety problem in terms of durability and the like.

The present applicant has also provided a solidifying agent for radioactive waste containing cementitious substances, ultrafine powder, and a high-performance water reducing agent as main components (JP-A-61-215999). However, even if the above-mentioned solidifying agent is used, the B waste is not sufficient because it delays the hydration reaction of cement and disintegrates the hardened body of the B waste.

From the above, even if the boron content is high, there is durability and early strength, the processing capacity is large, and the elution property is low,
A method for treating B waste, which has excellent durability, has been earnestly desired.

As a result of various studies to eliminate the above-mentioned drawbacks, the present inventors have found that the above-mentioned drawbacks can be improved by using a solidifying agent containing a specific component as a main component, Has been completed.

[Means for solving problems]

That is, the present invention is a hydraulic substance, calcium aluminate, gypsum, ultrafine powder and a high-performance water reducing agent as the main component, the amount of calcium aluminate and gypsum used, the hydraulic substance 22 ~
It is a solidifying agent for radioactive waste, which is 2 to 19 parts by weight per 91 parts by weight.

 The present invention will be described in detail below.

As the hydraulic material referred to in the present invention, normal, early strength, super early strength, white or various Portland cement such as sulfur resistant salt,
Further, mixed cement mixed with blast furnace slag, fly ash, silica or the like can be used. Further, it is also possible to use a mixture of the rapidly cooled blast furnace slag powder and an alkali stimulant such as calcium hydroxide, gypsum and an alkali metal salt.

The calcium aluminate used in the present invention (hereinafter simply referred to as
CA) means the molar ratio of CaO / Al ₂ O ₃ (hereinafter referred to as C / A).
Is preferably 1.5 to 4, and when CaO is C, Al ₂ O ₃ is A, and Fe ₂ O ₃ is F, it is indicated as a composition mineral such as C ₁₂ A ₇ , C ₆ A ₂ F, and C ₄ AF. And CA containing at least one of these as the main component.

The CA may contain a small amount of a component such as SiO ₂ or TiO ₂ as a minute component, or may contain an inorganic material such as Al ₂ O _{3 having} no hydration activity.

The particle size of CA is not particularly specified, but 10 to 30 μ is preferable from the viewpoint of strength.

Setsukou used in the present invention means effluent desorbed from a flue gas desulfurization unit, dihydrated citrus which is a byproduct such as phosphoric acid citrus produced in a phosphoric acid production process, and fluorinated acid produced in a hydrofluoric acid production process. And the like, and also the type III anhydrous sesskou.

Although the particle size of Setsukou is not particularly specified, it is preferably about the same as that of hydraulic substances and CA.

The amount of CA and Setsukou used is 2 to 19 parts by weight with respect to 22 to 91 parts by weight of the hydraulic material, preferably 36
It is 3 to 12 parts by weight for each .about.89 parts by weight. If it is less than 2 parts by weight, it is difficult to obtain early strength, and if it exceeds 19 parts by weight, it becomes difficult to obtain durability. The weight ratio of CA to Setsukou is preferably 0.5 to 4 with respect to CA1.

The ultrafine powder used in the present invention is one having an average particle size lower than that of the above-mentioned hydraulic substances, CA and Setsukou by at least one order, and particularly one having an average particle size of two orders lower is water mixed with the material of the present invention. It is preferable from the standpoint of the flow characteristics of the kneaded product prepared in this way. Specifically, silica dust (silica fume) and siliceous dust produced as a by-product during the production of silicon / silicon-containing alloys and zirconia are particularly suitable. Slag, titanium oxide,
Aluminum oxide, hydraulic material especially alumina cement,
Ultrafine powder such as CA having a C / A ratio of the above composition can also be used.

For the production of ultrafine powder, there is also a method of crushing by combining a classifier and a crusher. In addition, a fine particle having a smaller particle diameter can be obtained from the powder collected by the bag filter in the pulverizing step.

The amount of the ultrafine powder used is preferably 5 to 40 parts by weight, more preferably 65 to 95 parts by weight, based on 60 to 95 parts by weight of a hydraulic substance, a mixture of CA and gypsum (hereinafter referred to as cement).
10 to 35 parts by weight with respect to 90 parts by weight. If it is less than 5 parts by weight, it is difficult to obtain high strength (fastness).
When it exceeds the weight part, the fluidity of the kneaded product is remarkably lowered, molding becomes difficult, and the strength development becomes insufficient.

High performance water reducing agent used in the present invention (hereinafter referred to as water reducing agent)
Is a surfactant with a large dispersibility that does not cause excessive retardation of setting and excessive air entrainment even when added to cement in large amounts, and is a salt of a condensation product of naphthalene sulfonic acid formaldehyde, a high molecular weight lignin sulfonate. And those containing polycarboxylic acid salt as a main component.

The water reducing agent is necessary to obtain a kneaded product at a low water / cement ratio, and the conventional amount used is 0.3 to 1% by weight as solid content with respect to cement. It is preferable to use a larger amount. Specifically, it is used up to about 10 parts by weight as a solid content with respect to 100 parts by weight of a mixture of cement, etc. (hereinafter referred to as powder), and if it is used in a larger amount, it may adversely affect the curing reaction. give. A particularly preferred amount of use is 1 to 5 parts by weight. By combining cement, etc. and ultrafine powder in such an amount of water reducing agent, the water powder ratio is 25%.
Also in the following, it is possible to obtain a flowable kneaded product that can be molded by an ordinary method.

The water used in preparing the mixture in the present invention is necessary for molding, but it is better to make it as small as possible in order to obtain a high-strength cured product, and 12.5 to 3 per 100 parts by weight of the powder.
It is preferably 0 part by weight, more preferably 15 to 28 parts by weight.

If the amount of water is more than 30 parts by weight, it is difficult to obtain a high-strength cured product, and if the amount is less than 12.5 parts by weight, it becomes difficult to form such as ordinary casting. The compaction molding is not limited to this, and molding is possible even when the amount is less than 12.5 parts by weight.

When early fastness is difficult to obtain, inorganic carbonates such as sodium carbonate, potassium carbonate, lithium carbonate and calcium nitrite can be used in combination. Further, when workability is difficult to obtain, it is possible to use a retarder such as oxycarboxylic acid or boric acid together.

To treat boron-containing radioactive waste (hereinafter referred to as the present waste) with the solidifying agent according to the present invention, a conventional cement solidification method can be applied. That is, this waste is mixed with the solidifying agent in a disposal container such as a drum or a concrete container, the waste is mixed with the solidifying agent in advance, and the waste container is filled with the waste. And then filling the voids with a solidifying agent, and conversely filling the solidifying agent into a disposal container in advance, and then depressurizing it or pressurizing this waste to inject it into the disposal container. Etc. are applied. At this time, the amount of the solidifying agent to be added largely varies depending on whether the waste is a solid or a water-containing state, but it is generally about 10 to 500 parts by weight with respect to 100 parts by weight of the waste. From the viewpoint of increasing the processing capacity, the less the solidifying agent is, the more preferable. However, if it is less than 10 parts by weight, it is difficult to solidify, and the effect of suppressing the elution of radioactive substances is poor.

〔Example〕

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

Example 1 0.2 μci ³⁶ Cl / cm ³ was added to the formulations shown in Table 1, Formulation Nos. ^2-3.
A radioisotope is mixed to obtain a test piece of φ5 × 5 cm, and cured at 20 ° C in a closed container. After 3 days of age, a leaching test in 0.1M NaCl solution (radioactive waste related Dissolution test) was performed and the effective diffusion coefficient De was determined from the relationship between the number of days of immersion and the elution amount of radioactive material. In addition, the composition shown in Table-1 Formulation Nos. 5, 6, 9 and 10 has a thickness of 1 cm.
A thin film was prepared, and it was separated by 10 ⁻⁴ containing ¹³⁴ Cs ⁺ on one side.
Mol of CsCl was added to obtain a diffusion coefficient D of ¹³⁴ Cs ⁺ . Table 2 shows the results.

<Materials used> Cement: Ordinary Portland cement, Sumitomo Cement Co., Ltd. CA-a: C ₁₂ A ₇ , C / A was mixed at a ratio of 45/55, electromelted at 1,600 ° C, and rapidly cooled. Grinded to an average particle size of 10μ.

CA-b: C ₄ AF, CaCO ₃ / Al ₂ O ₃ / Fe ₂ O ₃ were blended in a ratio of 400/102/160, baked at 1,350 to 1,360 ° C for 1 hour, and average particle size was 8
Grinded to μ.

Setsukou: Type II anhydrous Setsukou and Setsukou fluoric acid crushed to an average particle size of 12μ.

Ultra fine powder: Silica Hyme, manufactured by Nippon Heavy Chemical Industry Co., Ltd.

Water-reducing agent: Dai-ichi Kogyo Seiyaku Co., Ltd., trade name "Cellflow 11"
0P ”, β-naphthalenesulfonic acid formaldehyde condensate.

Boron: Special grade water: Tap water Comparative Example 1 The procedure of Example 1 was repeated except that the compound No. 1, the compound No. 4, the compound No. 7 and the compound No. 8 were used. Table 2 shows the results.

Example 2 A radioactive waste discharged from a boiling water reactor (BWR), which is a boron-containing ion exchange resin regenerated concentrated waste liquid, was used. This waste liquid was treated with a solidifying agent having the composition shown in Table-3. The waste liquid had a water content of 95%, and the solidifying agent of the composition in Table 3 was 300 parts by weight with respect to 100 parts by weight of the waste liquid.

At that time, the compressive strength at 3 hours and 3 days of age and the dissolution rate in water at 3 days of age were measured and are shown in Table 3.

<Materials used> Cement: Blast furnace cement type A, Sumitomo Cement Co., Ltd. Na ₂ CO ₃ : Reagent first grade Other materials are the same as in Example 1. In addition to Experiment No. 12, 1.0 part by weight of Na ₂ CO ₃ was added. It was

Comparative Example 2 The procedure of Example 2 was repeated except that the composition of Experiment No. 11 was used. The results are shown in Table-3.

[Effects of the Invention] As described above, when the solidifying agent of the present invention is used, the durability and the early strength are high, the processing capacity is large, and the elution property is higher than that of the conventional cement solidification method. A method for the treatment of radioactive waste, especially low in boron content and excellent in durability, has been established. Chemical resistance and weather resistance are superior to those of the solidification method of plastics and plastics, and the treatment method is simple, heat resistance is excellent, and the compressive strength is large, not only temporary storage of waste but also permanent storage. Is also possible.

Claims (1)

(57) [Claims] 1. A hydraulic substance, calcium aluminate, gypsum, ultrafine powder and a high-performance water reducing agent as main components, and the amounts of calcium aluminate and gypsum used are each 22 to 91 parts by weight of the hydraulic substance. 2 to 19 parts by weight of radioactive waste solidifying agent.