JPS62267699A - Method of solidifying and processing 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] [Object of the Invention] (Industrial Application Field) The present invention is applicable to handling of radioactive materials in nuclear fuel reprocessing facilities, etc.! I
The present invention relates to a method for treating medium- to low-level radioactive waste generated in Japan, and particularly to a method for solidifying radioactive waste that has excellent long-term stability, durability, and fire resistance.

(Conventional technology) Conventionally, as a method for treating radioactive waste such as radioactive concentrated waste liquid and sludge generated in nuclear fuel reprocessing facilities, etc., where radioactive materials are handled, concentrated waste liquid is subjected to asphalt solidification treatment, and sludge Types of waste are stored as is.

In this solidification treatment method, the radioactive waste liquid is concentrated and dried to form a powder mainly consisting of sodium nitrate.
This radioactive waste is solidified using a solidifying material made of asphalt.

However, even if solidified radioactive waste is obtained by processing these methods, the final disposal method for most of it has not yet been established.

On the other hand, methods have recently been proposed for temporarily storing radioactive waste generated from BWR power plants in the form of intermediate storage bodies.

This method involves drying radioactive waste to significantly reduce its volume, then pelletizing it to produce a stable intermediate storage body, which is then temporarily stored in a storage tank within a nuclear facility. According to this method, a compressive force is applied to the powdered radioactive waste after drying and the waste is pelletized, resulting in a high volume reduction rate.

However, it occurs in nuclear fuel reprocessing facilities,” cs, 93.
The half-life of radioactivity in R is approximately 30 years, so it is virtually impossible to attenuate the radioactivity in this way, and even if it were possible, it would be stored for a certain period of time and the radioactivity would decay before it could be used again. It is necessary to solidify them into a stable solidified package.

In addition to these wastes, nuclear fuel reprocessing facilities also generate miscellaneous solid wastes such as metals, concrete, and insulation materials. Since there are a wide variety of these materials and their shapes are indeterminate, at present they are cut appropriately as needed and placed in storage containers. Such miscellaneous solids also need to be solidified into a stable solidified package.

As a method of solidifying and packaging such radioactive waste, treatment using the aforementioned solidifying material, which has been conventionally used, can be considered.

(Problems to be Solved by the Invention) However, in the above-mentioned asphalt solidification method, since the solidification material is a solid material, there is a problem in terms of stability over a long period of several hundred years or more.

Another option is to use cement as a solidifying agent, but in this case, a large amount of water is required, and the moisture will cause the pellets to absorb water and swell, especially when solidifying pellet-shaped radioactive waste. Deterioration of the pellets and hardening agent may occur. If cement is used that suppresses the water necessary for hardening to the minimum level, it is possible to prevent the deterioration of the pellets and hardening agent, but There is a problem in that the viscosity of the material increases, making it difficult to densely fill the pellets.

Furthermore, it is desirable that the formed solidified body of radioactive waste is chemically and mechanically stable for a long period of time, and that release of radioactive substances from the solidified body is prevented as much as possible. However, when a conventional hydraulic binder such as Portland cement is used as a solidifying agent to produce a solidified material, the water present in the solidified material is mixed with water of crystallization chemically bonded by reaction with the binding material and minute particles in the solidified material. However, the presence of this free water facilitates the movement of radionuclides through diffusion within the solidified material, increasing the leaching of radioactive materials and further increasing the amount of radioactive material in the solidified material. If more water exists in the solidified material than is necessary during solidification, this excess water may evaporate by drying or the like, and the solidified material may become microscopically porous. As a result, the stability and durability of the solidified product are significantly reduced. Also Zara,
If the solidified material is exposed to high temperatures for a long period of time due to fire, etc., the moisture in the solidified material will evaporate to the outside. There is also the problem that the target strength decreases. Therefore, in order to prevent the release of radioactive substances from the solidified material, it is desirable that the amount of water M in the solidified material be as small as possible. However, it has been extremely difficult to produce a solidifying material that simultaneously satisfies the contradictory conditions of low water content and low viscosity.

The present invention was made to solve such problems, and is a method for solidifying radioactive waste generated from nuclear fuel reprocessing facilities, etc., in which radioactive waste is chemically treated for a long period of time with excellent fire resistance. The object of the present invention is to provide a method for solidifying the materials into a solidified package that is both mechanically and mechanically stable and prevents the release of radioactive substances.

[Structure of the Invention] (Means for Solving the Problems) The method for solidifying radioactive waste of the present invention is to process radioactive waste generated at a nuclear facility into (a) alumina cement 1- and (b) bones. (c) an inorganic fluidizing agent; and (d) a dispersing agent.

The (oral) component aggregates used in the present invention include, for example, alumina grains, chamotte grains, naturally occurring sand, gravel,
Crushed rocks and mixtures thereof can be used.

In addition, as the inorganic fluidizing material of component (c), the radius is 5 μm.
The following inorganic oxides of alumina fine powder, siliceous fine powder, and mixtures thereof can be used.

As the dispersant for component (d), condensed phosphates, polycarboxylic acid type polymeric surfactants, alkali silicates, and mixtures thereof can be used. Examples of the above condensed phosphates include sodium birophosphate, acidic sodium birophosphate,
Examples include sodium tripolyphosphate, sodium te1-laboriphosphate, sodium metaphosphate, and β-naphthalenesulfonic acid formalin high condensate sodium salt.

The blending amounts of these components are (a) 15 to 50 parts of alumina cement, and 30 to 75 parts of aggregate (b).
0.05 to 0.5 parts by weight of the dispersant per 100 parts by weight of the heavy colored part and 10 to 20 parts by weight of the inorganic fluidizing agent component (c).
8 to 20 parts by weight of the heavy foot and added water is suitable. With this configuration, the amount of added water can be kept as small as possible, and a solidified body with good physical properties such as solidified body strength can be obtained.

If the amount of alumina cement is less than 15 parts by weight, the solidified product will not have sufficient strength and quick hardening properties, and if it exceeds 50 parts by weight, cracks may occur due to shrinkage during hardening of the alumina cement, or moisture in the solidifying material may occur. Problems arise as the amount increases.

If the amount of aggregate is less than 30 parts by weight, cracks are likely to occur, and if it exceeds 75 parts by weight, sufficient solidified strength cannot be obtained and fluidity is also reduced.

In addition, even if the amount of inorganic fluidizing agent is less than 10 parts by weight,
The fluidity of the solidified material decreases even if the temperature exceeds 0.
Cracks begin to occur due to shrinkage beyond the overlapped part.

If the dispersant addition value of formulation a is less than 0.05 parts by weight, the dispersion effect will decrease, and if it exceeds 0.5 parts by weight, the solidifying material will not have adequate viscosity or sufficient fluidity. .

(Function) The alumina cement used as the inorganic binder in the present invention is a cement whose main component is calcium aluminate and has excellent fire resistance and chemical resistance. By producing a solidified body with materials, it is possible to obtain a solidified body of radioactive waste imbued with fire resistance and resistance to chemicals. Furthermore, due to the quick hardening properties of alumina cement, a solidified product can be formed in a short period of time. Therefore, the coagulation time of the solidifying material is short, and phenomena such as swelling of the pellets due to absorption of moisture in the solidifying material and salt elution from the pellets are unlikely to occur.

Moreover, the aggregate prevents shrinkage when the alumina cement hardens, improves the strength of the obtained solidified body, and exists as particles in the solidified body. By adding this aggregate, the amount of alumina cement used can be reduced, and as a result, the amount of water contained in the hardening agent for hardening the alumina cement can also be reduced.

The dispersant and the inorganic fluidizing agent are used to form a solidified body using the solidifying agent of the present invention, in which individual particles of the inorganic fluidizing agent are dispersed by the action of the dispersing agent, and particles of the alumina cement and aggregate are dispersed. and improves the sliding between these particles. At the same time, fine particles among the alumina cement particles are similarly dispersed and enter between other large-sized alumina cement particles and aggregate particles. As a result, the particles in the slurry-like solidified material are uniformly dispersed by the action of the dispersant and become easily movable. Therefore, even in cases where it is difficult to fill the container without gaps, such as by filling radioactive waste in advance into a container and then injecting and solidifying the slurry-like solidifying material, the solidifying material flows easily over the surface of the waste and is easily inserted into the container. The interior can be completely filled without any gaps.

(Example) Examples of the present invention will be described below.

Examples 1 to 4 With the composition shown in Table 1, alumina cement i., aggregate, and an inorganic fluidizing agent were uniformly mixed, an aqueous solution of a dispersant dissolved in added water was added, and these were kneaded. A slurry solidified material was obtained. The values in Table 1 are based on weight.

In the comparative example in the table, a solidified material in the form of slurry was similarly prepared using Portland cement as a binder and having the composition shown in Table 1. At this time, a β-naphthalene sulfonic acid formalin high condensate sodium salt aqueous solution was used as a dispersant. The chemical components of the alumina cement and portland cement used at this time are not shown in Table 2.

(Left below) First, after drying a simulated concentrated waste liquid containing sodium nitrate as its main component, which simulates the concentrated waste liquid generated from a nuclear fuel reprocessing plant, the pellets obtained by granulation are filled into a container in advance, and the above-mentioned Each solidifying material was injected and filled at room temperature. The viscosity of each solidifying agent at this time was as shown in Table 3. All had good fluidity and good filling conditions. Table 3 also shows the opening rate of each solidifying material upon setting.

As shown in Table 3, the solidifying material using alumina cement as a binder started setting in a short time, and therefore finished setting in a short time. In this way, the solidification material of the example using alumina cement has quick hardening properties and can solidify radioactive waste such as pellets in a short time, and during solidification, the pellets absorb moisture in the solidification material and swell. Phenomena such as salt leaching or salt elution from the pellets are less likely to occur. In addition, when transporting or moving solidified radioactive waste packages, we ensure that they are completely solidified so that even if the solidified package falls over, the radioactive material inside the container will not spill out and contaminate the surrounding area. It is necessary to temporarily store the solidified package until the hardening of the solidified material is completed, but if the hardening of the solidified material is completed in a short time,
The storage time is also short, and as a result the space required for storage can be reduced, resulting in economic savings.

The formed solidified body was a strong solidified body with good appearance and no bleeding or cracking.

Furthermore, in order to investigate the unconfined compressive strength of the solidified materials, for the solidified materials of Examples and Comparative Examples, only the solidified materials that do not contain simulated waste pellets were tested at 50M (diameter) x 10.
When solidified at a size of 0 m (height), the results were as shown in Table 4.

Table 4 In order to evaluate the fire resistance of the solidified bodies formed, the solidified bodies were prepared by filling a 200J2 drum with the solidifying materials of Examples and Comparative Examples, and placed in a firing furnace heated to 800°C. The sample was held and changes in the solidified material were observed. The results are shown in Table 5.

(Margins below) Table 5: No cracks or breakage were observed in the solidified bodies formed from the solidified materials of Examples, but cracks occurred on the heated surface of the solidified bodies formed from the solidified materials of Comparative Examples. The surface became lumpy and fell off. As can be seen from these results, by using alumina cement as a binder, a solidified material with excellent fire resistance can be obtained, and radioactive waste can be processed as a solidified package with excellent fire resistance. As a result, even if a fire occurs during transportation, storage, or disposal of solidified radioactive waste, the solidified material will hardly deteriorate, and radioactive waste can be safely handled and managed.

Example 5 Next, a slurry solidified material was obtained using the composition shown in Table 6 in the same manner as in the Examples and Comparative Examples.

and 148K of simulated miscellaneous solid waste with the contents shown in Table 7.
After putting g into a drum, the above-mentioned solidifying material was injected and solidified.

(Left below) Table 7 The chemical components of the alumina cement used at this time are the same as those shown in Table 2. The amount of solidified material required for filling was 335 kg. As a result, coagulation was completed 4 hours after the injection of the solidifying material, and a dense solidified body with no gaps was obtained.

As can be seen from this result, the solidification material containing an inorganic fluidization agent and a dispersion material has low viscosity and high fluidity, so it is possible to treat radioactive waste such as miscellaneous solids as a dense solidified package with no gaps. Can be done.

[Effects of the Invention] As explained above, according to the present invention, radioactive waste can be converted into a solidified package that has excellent fire resistance, is chemically and mechanically stable over a long period of time, and prevents the release of radioactive substances. It can be solidified in a short time.

Claims (6)

[Claims] (1) Radioactive waste generated at nuclear facilities is treated with a hydraulic solidifying agent that is a mixture of (a) alumina cement, (b) aggregate, (c) inorganic fluidizing agent, and (d) dispersant. , a method for solidifying radioactive waste characterized by solidifying it in one piece. (2) The method for solidifying radioactive waste according to claim 1, wherein the radioactive waste is composed of one or more selected from pellets and miscellaneous solids. (3) The aggregate consists of one or more types selected from alumina grains, chamotte grains, naturally occurring sand, gravel, and crushed rock materials; The method for solidifying radioactive waste as described in paragraph 2. (4) Claims characterized in that the inorganic fluidizing agent is made of one or more inorganic oxides selected from inorganic oxides such as alumina fine powder and silica fine powder with a particle size of 5 μm or less. The method for solidifying radioactive waste according to any one of paragraphs 1 to 3. (5) The dispersant consists of one or more selected from condensed phosphates, polycarboxylic acid-type polymer surfactants, alkali silicate, and formalin high condensate sodium salt of β-naphthalenesulfonic acid. A method for solidifying radioactive waste according to any one of claims 1 to 4, characterized in that: (6) The blending amount of the solidifying agent is (a) 15 to 50 parts by weight of alumina cement, and (b) 30 to 75 parts by weight of aggregate.
The inorganic fluidizing agent (c) is 10 to 20 parts by weight, a total of 10
0 parts by weight, the dispersant is 0.05 to 0.5 parts by weight, and the added water is 8 to 20 parts by weight. The solidification treatment method for radioactive waste described.