JPS62126400A - Method of solidifying radioactive waste - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method of solidifying radioactive waste θ; in particular, the solidification of concentrated radioactive waste liquid (component of 1:1 sodium sulfate) generated from nuclear power plants, etc. Regarding the method.

[Background of the invention]

Reducing the volume and solidifying radioactive waste generated from nuclear power plants is not only important for securing storage space within the facility, but also an essential factor for land storage, which is one of the final disposal methods. It is.

One of the ways to reduce the volume of radioactive waste is to use concentrated waste liquid (main component N), which is the main waste generated from BWR plants.
A method is known in which a slurry of azSO4) and a powdered ion exchange resin is dried and powdered to remove water, which accounts for most of the volume of radioactive waste, and then pelletized. It has been confirmed that this method can reduce the volume of waste liquid or chiller to about 178 ml compared to the conventional method of directly cementing the waste liquid or chiller.

However, even with this method, there is a problem that it is difficult to pelletize the dry powder, and a method of solidifying the dry powder by homogeneously mixing it with a solidifying material is being considered. Typical homogeneous solidification methods include solidification using plastics, asphalt, and inorganic materials. Plastics and asphalt 1 - The solidification method was developed mainly in response to ocean dumping, but the former has
The latter has a problem in terms of heat resistance. When disposing of waste on land, it is desirable to use an inorganic solidifying agent that is compatible with two rings and rocks, and assimilation methods using cement and sodium silicate (water glass) as solidifying agents are being considered. These solidifying materials are mixed with appropriate water and waste powder to solidify, but unlike when compression molded into a pellet shape, the contact area between the waste powder, assimilated material, and water increases significantly.

Therefore, if the waste powder undergoes a chemical reaction with the solidifying material, it will have a 1R effect on the produced solidified material. In addition, if the waste powder is soluble in water, water will penetrate into the solidified body through minute pores, causing the waste to dissolve and leak outside, and radionuclides will also leak at the same time. do. r+ W R Dry powder of concentrated waste liquid (N, 1zsO
When solidifying 4), the problem in -[] becomes one issue.

For example, when solidified with cement, N+125O4 reacts with calcium aluminate As (3C,'IO・^QzOa) and calcilla hydroxide 1% (C,a(all)Z) in the cement, producing ettringite shown in the lower part. To generate, the volume expands and destroys the solidified body.

3CaOA Q, zos + 3C;l (011)
z + 3NazSO* + 32HzO If sodium silicate (water glass) is used as a solidifying agent, the reaction (1) will not occur and the problem can be avoided, but it is extremely difficult to prevent the elution of soluble sodium sulfate from the assimilate. Like a heron,
Therefore, it is difficult to prevent leakage of radionuclides.

In order to solve the above-mentioned problems, it is necessary to make the soluble sodium sulfate insoluble in water, and as a countermeasure for this, a method of making sodium sulfate insoluble and solidifying it has been studied. There is. In this method, an extremely durable assimilate can be produced, but new equipment such as an insolubilization reaction tank and a moisture evaporator are required.

As mentioned above, there is a simple assimilation method that converts dry powder of 'a'a degenerate liquid, especially dry powder from I'4WRa degenerate liquid whose main component is sodium sulfate, into an inexpensive and highly durable assimilate. Technology is highly desired.

[Objective of the invention] The object of the present invention is to solve the above-mentioned problem when solidifying a dry powder from a radioactive waste liquid containing sodium sulfate as a main component with an inorganic solidifying material, that is, to solve the [Summary of the Invention] The present invention provides a method for producing a highly durable solidified material that prevents the elution of sodium sulfate, has a low cost, and is highly durable. This method is characterized by modifying a dry powder into an insoluble substance in a solidification container, and then synthesizing and solidifying an assimilated material.

Sodium sulfate, the main component of radioactive concentrated waste liquid, has a concentration of 25
It has a solubility in water of about 20% by weight at ℃, and since it has deliquescent properties, it has the property of quickly dissolving in water. Therefore, when mixed with hydraulic solidifying materials such as cement or water glass, sodium sulfate dissolves in water during kneading or causes a tide f'ff, r31 phenomenon, and even after solidifying, it is extremely soluble in water. It is located in Le. When the assimilate is immersed in external water, water enters through the microscopic pores inside the assimilate, and sodium sulfate quickly dissolves and elutes, degrading the solidified product.

On the other hand, if sodium sulfate is insolubilized with an alkaline earth metal hydroxide, the above-mentioned problems will not occur, and sodium silicate, which is an assimilation agent, can be synthesized from the by-produced sodium hydroxide. The present invention focuses on these two points and simplifies the assimilation system 11 by completing these reactions within the assimilation container.

The above-mentioned insolubilization reaction and solidification material synthesis reaction proceed using water as a solvent, and are usually carried out under conditions where water is in excess. Therefore, during assimilation, it was necessary to evaporate and concentrate excess water before assimilating it.

The present invention is capable of completing the reaction without using any excess water from the outside by using barium hydroxide octahydrate for the insolubilization reaction and silicic acid tetrahydrate for the water glass synthesis reaction. Based on. That is, barium hydroxide 11 is normally stable as an octahydrate salt, but at a temperature of 80° C. or higher, the water of crystallization dissolves to form water and dissolves in the form of a slurry.

When a waste powder containing sodium sulfate as a main component is added to this slurry, the sodium sulfate changes into insoluble barium sulfate and sodium hydroxide, as shown in equation (2).

na2+ +2011- +811,0+Na25ot
→nasO4+ 2Na011 + 811zO(2)
(+), (2) reaction takes place at 80°C or higher. The efficiency is 0%, and there is no need to add water from the outside.

Furthermore, by adding silicon oxide tetrahydrate to the reaction product slurry produced in formula (2), silicic acid changes color to sodium silicate. The crystal water of silicon oxide to be added is 2
-6 is desirable; below 2, the viscosity increases and stirring becomes difficult. In addition, if it is less than 6, water becomes excessive and the volume reduction property decreases.If it is more than 6, barium hydroxide, oxidation, and crystal water of silicon are used, so there is no need to add excessive water. Water evaporation operation can be omitted.

As a result, it became possible to complete the insolubilization and solidification material synthesis reactions within the solidification container. In case of solidification, a curing agent may be further added.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. Concentrated waste liquid from concentrated waste liquid tank 2 1. is supplied to the centrifugal thin film dryer 3 and dried and powdered. On the other hand, barium hydroxide octahydrate powder 5 is supplied from the tank 6 to the solidification container 12, and the heater 13
The temperature is maintained at 80°C in advance to convert it into slurry. ” - Supply the dry powder from step 3 to the slurry,
The mixture is reacted for about 1 hour while being stirred by the stirring blade 14.

After that, silicon oxide tetrahydrate 7 is supplied from the tank 8,
React at 80°C for about 1 hour. After the reaction, the mixture is cooled to 20 to 30°C, and then the hardening agent 9 is supplied from the tank 10 and mixed to form a solidified product.

Although it is not necessary to use a centrifugal thin film dryer to dry and powder concentrated waste liquid, the lower the moisture content of the powder, the better. The mixing ratio of the dry powder and barium hydroxide 11 is preferably such that sodium sulfate and barium hydroxide in the dry powder are equimolar. When sodium sulfate is excessive, sodium sulfate that is not insolubilized remains in the solidified material, degrading the solidified material. On the other hand, if barium hydroxide is excessive, the volume reduction property decreases. The addition of silicon oxide is optional, but a molar ratio of 1 to 3 with respect to sodium sulfate is desirable. In addition, the amount of crystal water in silicon oxide is
The smaller the amount, the better the volume reduction properties will be, but the production rate of sodium silicate will be slower.

It is desirable that the amount of water of crystallization is 2 moles or more and 6 moles or less per mole of silicon oxide M.

〔Effect of the invention〕

According to the present invention, the insolubilization of sodium to lithium sulfate, which is the main component of the concentrated waste liquid, and the synthesis and assimilation of the solidifying agent can be carried out all at once in the solidifying container, and an evaporation operation can be made unnecessary. the result,
The durability of the solidified material can be greatly improved, and the assimilation system 11 can be simplified.

[Brief explanation of drawings]

The figure is a system schematic diagram of an embodiment of the present invention.

Claims (1)

[Claims] 1. In a method of solidifying a radioactive waste solution containing sodium sulfate, the radioactive waste solution is dried and powdered, and at least one compound of alkaline earth metal hydroxide containing water of crystallization is added to the dry powder to form an insoluble sulfuric acid solution. A method for solidifying radioactive waste, which comprises generating salt and sodium hydroxide, adding a silicon oxide compound to generate sodium silicate, and then adding a substance that hardens the sodium silicate to solidify it. .