JPH0778553B2 - Method for highly concentrating and drying and solidifying radioactive liquid waste - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for pre-treating radioactive liquid waste, particularly radioactive waste containing boric acid generated in a pressurized light water reactor, and then drying it in a concentrator or a thin film evaporator. Highly concentrated in a container,
Alternatively, the present invention relates to a method of completely drying and granulating, or a highly concentrated liquid or a dried product alone or mixed with solid waste and solidified with cement, asphalt or plastic.

2. Description of the Related Art The technique disclosed in Japanese Laid-Open Patent Publication No. 48-44700, which is known as a treatment method for such a waste liquid, is insolubilized by adding ferrocyanide and cobalt nitrate or nickel sulfate to a concentrated waste liquid, or containing boric acid In the case of liquid waste from a pressurized light water reactor, it is pretreated with aluminum sulfate or caustic soda and then dried in a horizontal thin film evaporator, and in the case of a boiling light water reactor, a vertical centrifugal membrane evaporator using a shaft with movable blades. It is designed to be dried using.

However, in this method, when the inorganic substance in the waste liquid and the borate generated by the pretreatment have a binding force and an adhesive force to each other when they are dried, the heat transfer wall surface and shaft of the dryer are It has the drawback that it adheres and is difficult to completely dry.

The object of the present invention is to increase the volume reduction ratio of liquid and solid radioactive waste and to improve the physicochemical properties of the solidified body.

Means for Solving the Problems Part 1 The features of the present invention are to the binding force and the heat transfer wall surface of the dried matter generated when various salts existing in the liquid waste or produced in the pretreatment step are dried. It is to remove the adhesive force.

Effects of the Invention Therefore, when dried using a drier such as a thin film evaporator, the dried material adheres to the heat transfer wall surface or the rotating shaft of the drier, which increases the rotation load or reduces the heat transfer effect. The liquid waste containing boric acid can be easily highly concentrated with a thin film evaporator or the like or completely dried to obtain a powdery dried product without any drawbacks. Then, this is granulated, or the dried product alone or the dried product is mixed with solid waste such as waste ion exchange resin or incinerated ash, and cement,
It can be solidified with molten asphalt, liquid phase thermosetting resin (unsaturated polyester, epoxy resin, etc.) or molten plastic resin (polyethylene, etc.).

In the present invention, in order to eliminate such conventional defects, insoluble precipitates of particles are obtained by using salts having a binding force with each other, particularly borate, in a pretreatment step, and surrounding the particles of the precipitates. The binding force between particles is eliminated by not surrounding it with another compound having a large binding force, and the pre-treated suspension is generally used in the fixed axis vertical thin film evaporator etc. A method of highly concentrating or drying to a powder using a dryer of the present invention is provided.

Means for Solving Problems Part 2 The gist of the present invention will be described in detail in conjunction with the process embodiments.

The present invention temporarily pre-treats radioactive concentrated waste liquid and obtains a highly concentrated liquid by using a dryer such as a concentrator or a thin film evaporator, or it is dried into a fine powder without water. Is. That is, liquid waste in the primary cooling system of a pressurized light water reactor contains radioactive nuclides and boric acid, but the concentration of nuclides is extremely low compared to the concentration of boric acid, so the evaporative concentration limit and drying conditions are boric acid. And, it will depend largely on the concentration of borate. Therefore, due to the solubility of boric acid or the physicochemical characteristics of nuclide scattering, the liquid waste of the primary cooling water system is currently concentrated so that the concentration of boric acid becomes 12% by weight, and then this concentrated waste liquid is used as cement or asphalt. Most of them are solidified.

Therefore, in the present invention as well, boric acid is added to the concentrated waste liquid concentrated between 12 weight ratio and 26 weight ratio with quick lime having a particle size of 50 mesh to 400 mesh being 0.7% with respect to the molar ratio of boric acid.
Since more than the molar ratio is added and the mixture is stirred, boric acid continuously reacts from the surface of the quick lime to the inside to form an insoluble calcium borate compound and all precipitates.The excess quick lime remaining after the reaction reacts with water. At the same time as it becomes slaked lime, it surrounds a part of the periphery of the calcium borate compound, so that the binding force between the precipitated calcium borate is lost and the calcium borate becomes a particulate insoluble precipitate. At the same time, the alkalinity of slaked lime makes the liquid in the pretreatment tank alkaline, so that polyvalent nuclides such as cobalt are simultaneously precipitated as insoluble hydroxides. Therefore, the rate of precipitation from the solidified body after solidification is very low. The suspension thus obtained in the pretreatment tank is highly concentrated by a condenser such as a condenser or a vertical thin film evaporator maintained at 100 ° C. or higher, or is dried into a fine powder. The highly concentrated or dried product is solidified by the granulating or solidifying medium. An example for this is as follows.

Example 1 371 g of boric acid was dissolved in water to form a solution of 12 to 26% by weight, and 250 g of quick lime was added thereto to obtain a precipitation product.

Example 2 The product obtained in Example 1 was dried in a dryer such as a thin film evaporator to obtain 506 g of a dried product.

Example 3 The product obtained from Example 1 is highly concentrated to contain 30% by weight of water, or 30% by weight of water is added to the dried product obtained from Example 2 and then When compressed at a pressure of 2000 kg / cm ² and granulated, the specific gravity is 1.6
A granulated product was obtained.

Example 4 75.8 g of the dried product obtained in Example 2 was mixed with 70 g of unsaturated polyester, 0.2 g of benzoyl peroxide and 0.1 of dimethylaniline.
After adding ml, they were mixed well and then cured. The solidified product obtained at this time has a specific gravity of 1.59 g and a compression strength of 1670 kg / cm.
^{Was 2} .

Example 5 To 79 g of wet resin from which water was removed was added 10 g of the dried product obtained in Example 2, 50 g of an unsaturated polyester, 0.3 g of benzoyl peroxide and 0.15 ml of dimethylaniline were added, followed by thorough mixing and curing. It was The solidified product cured at this time had a specific gravity of 1.27 and a compressive strength of 232 kg / cm ² .

Then, 81 g of the dried product obtained in Example 2 was added to 8 g of the wet resin, 80 g of the unsaturated polyester, 0.3 g of benzoyl peroxide and 0.15 ml of dimethylaniline were added, mixed well, and then cured. At this time, the solidified body cured has a specific gravity of 1.
The compression strength was 52 and the compression strength was 1620 kg / cm ² .

Example 6 The precipitation reaction product obtained in Example 1 is concentrated so that the amount of water becomes 0.62 by weight with respect to the dried precipitation product such as borate. Then, cement was added thereto so that the weight ratio of the dried precipitate was 0.875, mixed well, and then cured for 4 weeks. The compression strength of the solidified product obtained at this time was 115 kg / cm ² . On the other hand, 120 g of the dried product obtained in Example 2 and 150 g of cement were mixed with 75 g of water, mixed well, and then cured for 4 weeks. The solidified product obtained at this time is 115 kg / cm
There was a compressive strength of ² .

According to the present invention, by efficiently drying and solidifying a liquid waste having harmful radioactivity, the amount of waste generated can be drastically reduced, and the safety of the solidified body can be greatly improved.

To summarize the above, the present invention relates to a method for highly concentrating and drying and solidifying a radioactive waste liquid for treating the radioactive waste liquid, in which powdered quick lime is added to the radioactive concentrated waste liquid to form a particulate precipitate having no mutual binding force. This suspension is obtained as a highly concentrated liquid by using a dryer such as a concentrator or a thin film evaporator, or a method of drying it into a powder form, or a method of highly concentrating or after drying, add water and then compress. It is characterized by granulating or solidifying the highly concentrated liquid and the dried product in various media.

Claims (3)

[Claims] 1. A powdery quicklime is added to a radioactive concentrated waste liquid in an amount of 0.7 molar ratio or more relative to the molar ratio of boric acid to form a fine particle precipitate having no mutual binding force, and this suspension is used as a concentrator or a thin film. Including a method of obtaining a highly concentrated liquid using a dryer such as an evaporator or completely drying into a powder,
Powdered quicklime is added to radioactive concentrated waste liquid in an amount of 0.7 mole ratio or more with respect to the molar ratio of boric acid, and this is highly concentrated in a concentrator or dryer, or after drying, add water and then compress and granulate. A method of highly concentrating and drying and solidifying a radioactive waste liquid, which comprises solidifying a highly concentrated liquid or a dried product in various media. 2. A highly concentrated liquid or a dried product alone or a means for mixing and solidifying with a liquid phase thermosetting resin together with a solid substance such as a waste ion exchange resin or incineration ash, and a highly concentrated liquid or a dried product alone. 2. The method for highly concentrating and drying and solidifying radioactive waste liquid according to claim 1, further comprising means for mixing and solidifying with a molten thermoplastic resin together with a solid substance such as waste ion exchange resin and incineration ash. 3. A highly concentrated and dry solidification of a radioactive waste liquid according to claim 2, comprising the step of putting a solid material mixed with a solidifying medium with a waste filter and metals to solidify the solid material together. Method.