JPH073475B2 - Method for solidifying radioactive waste - Google Patents

Description

The present invention relates to a method for solidifying radioactive waste.

[Conventional technology and its problems]

As radioactive waste generated from nuclear facilities such as nuclear power plants and nuclear fuel reprocessing plants, concentrated waste liquid, used ion exchange resin, filter sludge, incinerated ash, miscellaneous solids, various sludges, and the dismantling of nuclear power plants Examples include so-called low- and medium-level radioactive waste, such as concrete waste that is discharged, and high-level radioactive waste.

Although many methods have been proposed for solidifying these radioactive wastes, especially low- and medium-level radioactive wastes, no economical and reliable method has been found. For example, a method of using asphalt or plastic, a method of hardening with cement, a method of hardening with a water glass-cement system, etc. are known.

However, the method using asphalt or plastic has a large processing capacity, but the curing agent is expensive, and there are drawbacks such as a complicated processing method and safety problems in terms of weather resistance. Atsuta

In addition, although the method of hardening with cement and the method of hardening with water glass-cement system have excellent durability, they have a low processing capacity and relatively high leachability, and thus lack long-term stability. There was a flaw.

From the above, there is a strong demand for a method of treating radioactive waste that has a large treatment capacity and is excellent in durability and weather resistance.

The present inventors have conducted various studies in order to eliminate the above-mentioned drawbacks.As a result, the above-mentioned drawbacks are improved by mixing the blast furnace slag after treating the radioactive waste with alkali, and the solidified radioactive waste is pulverized. He found that he did not, and completed the present invention.

[Means for solving problems]

That is, the present invention is characterized in that after treating the radioactive waste with an alkali for 40 minutes or more, the waste is mixed with blast furnace slag having a fineness of 2,000 cm ² / g or more and calcium aluminate and solidified. This is a method of solidifying radioactive waste.

The present invention will be described in detail below.

Blast furnace slag (hereinafter referred to as slag) may have at least a fineness of 2,000 cm ² / g or more in terms of Blaine value, and the higher the fineness, the more preferable in terms of rapid hardening.

The amount of slag added can be changed as appropriate depending on the type and amount of radioactive waste.
The amount is preferably 1 to 400 parts by weight, more preferably 10 to 200 parts by weight, based on 0 parts by weight.

As the alkali according to the present invention, alkali metal or alkaline earth metal hydroxides, carbonates, bicarbonates Na, Li, K
Salt, etc. can be mentioned, but from the viewpoint of economic efficiency, NaOH, CaCO ₃
Are preferred.

The amount of alkali added is 0.1 to 50 per 100 parts by weight of slag.
Part by weight is preferable, and 1 to 10 parts by weight is more preferable.

It is also possible to add an organic acid such as gluconic acid or citric acid and a salt thereof as a setting retarder.

Also used in combination with a water reducing agent whose main component is a salt of naphthalene sulfonic acid formaldehyde condensate, a salt of melamine sulfonic acid formaldehyde condensate, a high molecular weight lignin sulfonate, a polycarboxylate, etc. Doing with favorable results.

Particularly, the lignin system is economically advantageous and preferable.

The water reducing agent may be added in an amount generally used for concrete and the like, and is preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of slag.

If necessary, in order to increase the curing speed, 12CaO ・ 7
The addition of a crystalline or amorphous powder of calcium aluminate such as Al ₂ O ₃ , 11CaO, 7Al ₂ O ₃ · CaX ₂ (where X is a halogen) not only has a curing-accelerating effect, It is also an effective means to prevent cracking. Further, it is effective to use a calcium aluminate-based quick-setting material containing gypsum as the calcium aluminate because the same effect can be obtained.

The amount of calcium aluminate added is preferably 5 to 60 parts by weight based on 100 parts by weight of the slag (as solid content).

Mix the above materials with radioactive waste. When mixing used ion-exchange resins (hereinafter referred to as waste resins) generated from nuclear facilities such as nuclear power plants, the mixing method may be acidic, so the pH must be on the alkaline side. There is.

Ordinary waste resin contains sodium sulphate, and when it is oxidized with Portland cement, it swells after a few days, and in severe cases after 24 hours, and a sulfate reaction causes cracking, which eventually leads to powder. It becomes difficult to achieve the purpose. The main feature of this method is to use only blast furnace slag powder without using highly reactive Portland cement, and a reaction in which an alkali such as a loading alkali acts as the stimulant is applied. Generally, the above-mentioned alkali-slag reaction is one of the well-known hydraulic materials, but when waste resin is mixed therein, a phenomenon that cracks occur after curing is observed. Therefore, in the present invention, first, the waste resin is soaked in an alkaline solution such as caustic alkali, and sufficiently stirred to bring the waste resin and the alkali into contact with each other to cause a possible state change such as swelling in advance, and the appropriate time After that, the slag is mixed and a hardening process is performed.

The method of mixing the waste resin and the alkali is not particularly limited as long as the waste resin and the alkali are sufficiently contacted with each other, but the treatment time of the waste resin and the alkali is 40 minutes or more. .

The time for mixing the slag after mixing and stirring is not particularly limited, but is preferably 40 minutes or more.

The curing or the like in the curing treatment is not particularly limited, and a usual method is sufficient.

INDUSTRIAL APPLICABILITY The method of the present invention can be applied not only to the curing of the target waste resin but also to the curing treatment of other industrial wastes similar to this, and the most economical formulation is the physical condition of the cured product. It is possible to set the one that meets the requirement, and it is also preferable to perform steam curing if necessary.

〔Example〕

 The present invention will be further described based on examples below.

Example 1. To 30 parts by weight of waste resin generated at a nuclear power plant, NaOH was added.
(50%) Add 15 parts by weight of water, add water to a state where dipping is possible, and stir. Treatment time is 20,30,40,60 minutes, 1 day, 3 days,
The slag having a Blaine value of 6,000 cm ² / g was changed to 7 days, and the slag having a Blaine value of 6,000 cm ² / g was added to 55 parts by weight per 100 parts by weight of the mixture of the waste resin and the NaOH solution.
Add 20 parts by weight and make a cylindrical specimen of 20 cmφ after mixing.
The compressive strength, crack and expansion rate were measured according to SR5201. All of the specimens start to set in about 1 hour after kneading with slag, 150kg / cm ^{2 in} 3 hours and 500kg in 7 days.
It exhibited a compressive strength of not less than / cm ² . However, if the alkaline treatment time was less than 40 minutes, cracking began to occur from about 3 days. All of the treatments with a treatment time longer than that maintained good strength and shape, and showed a strength of 600 kg / cm ² or more after 1 month, and showed a stable state even after 1 year.

Example 2 Example 1 was repeated except that the Blaine value of the slag was changed. As a result, the Blaine value of 2,000,4,000,6,00
0cm ² / g compressive strength (3 hours) is 100,140,180kg / cm ² respectively
It was.

Example 3. In the experiment of Example 1, 55 parts by weight of slag and 15 parts by weight of amorphous 12CaO · 7Al ₂ O ₃ were added to 100 parts by weight of the waste resin-alkali mixture that had been contacted with alkali for 1 hour. Then, they were mixed to prepare a test piece in the same manner. Setting time is 10
Minutes, and a compressive strength of 250 kg / cm ² was obtained in 3 hours. There was no cracking, the expansion coefficient was about 1/2, and the effect was smaller than that of no addition, and a stronger cured product was obtained. Other calcium aluminate-based crystals were tested in the same manner, but almost the same results were obtained.

〔The invention's effect〕

 According to the present invention, the following effects can be obtained.

1. There is no solid radioactive waste crack.

2. The strength of the solidified radioactive waste is high.

3. It is possible to treat radioactive waste at any pH, for example, to solidify radioactive waste after acid treatment.

4. Good long-term stability of solidified radioactive waste.

5. Excellent in durability and weather resistance.

Claims (1)

[Claims] 1. A method of treating radioactive waste with alkali for 40 minutes or more, mixing the waste with blast furnace slag having a fineness of 2,000 cm ² / g or more and calcium aluminate and solidifying the mixture. Method for solidifying radioactive waste.