JPS63243797A - Solidifying processing method of 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] (Field of Industrial Application) The present invention relates to a method for treating medium-level to low-level radioactive waste generated in facilities handling radioactive materials such as nuclear fuel reprocessing facilities. In particular, the present invention relates to a method for solidifying radioactive waste that has a high filling rate and has excellent long-term stability, durability, and fire resistance.

(Prior art) Conventionally, as a method for treating radioactive waste such as radioactive concentrated waste liquid and sludge generated in facilities handling radioactive materials such as nuclear fuel reprocessing facilities, concentrated waste liquid is subjected to asphalt solidification treatment, and sludge is About sled, t
There is a practice of storing food.

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 through solidification using such a method, the final disposal method for most of it has not yet been established.

On the other hand, a method has 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, and 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, compressive force is applied to the powdered radioactive waste after drying and the radioactive waste is pelletized, resulting in a high volume reduction rate.

However, 1"Cs and 2Cs generated in nuclear fuel reprocessing facilities
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 the material into a stable solidified material.

In addition to such pellet-shaped waste, nuclear fuel reprocessing facilities also generate miscellaneous solid waste such as metal, concrete, and insulation materials. Since these products come in a wide variety of types and their shapes are indeterminate, at present they are cut into appropriate sizes 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 asphalt solidification method, since the assimilation agent is an organic substance, there is a problem in terms of long-term stability of several hundred years or more.

Another possibility is to use cement as the solidifying material, but in this case a large amount of water is required, especially when solidifying pellet-shaped radioactive waste. If cement is used that suppresses the amount of water necessary for hardening to the minimum level, it is possible to prevent deterioration of the pellet and the hardening agent, but the viscosity of the hardening agent becomes large. Therefore, there is a problem in that it becomes difficult to fill the pellet precisely.

As a very effective means to solve such problems, the applicant has previously proposed a method for solidifying radioactive waste using a hydraulic solidifying material that has extremely low water content and high fluidity. (Japanese Patent Application No. 61-111941 and No. 61-111942), it is attempted to fill and solidify pellets placed in a container using such an assimilating material with low water content and high fluidity. If the pellet itself does not contain a binder and is therefore very easily dissolved, or if there is a large amount of dust generated during the production of the pellet and it is easy to dissolve, the dissolved substance may be removed from the pellet. However, especially sodium sulfate dissolved in pellets of concentrated waste fluid mainly composed of sodium sulfate generated at BWR power plants, and sodium nitrate dissolved in pellets of waste fluid mainly composed of nitrates generated from nuclear fuel reprocessing facilities. , sodium nitrite, sodium carbonate, etc., which themselves have very strong cohesive force, the water contained in the hydraulic solidifying material may be absorbed while the solidifying material flows through the gaps between the pellets. Hard inorganic compounds and inorganic fluidizing agents may aggregate and lose fluidity.
As a result, voids remain in the solidified body, which causes problems when not only the homogeneity but also the strength of the solidified body is lost.

In addition, metals, concrete, etc. often have oil attached to them, and since such oil also has a flocculating effect, these wastes are filled and solidified in containers using the solidifying material mentioned above. Even when attempting to do so, there is a similar problem in that voids are likely to occur.

The present invention aims to eliminate the drawbacks of the conventional solidification treatment method for radioactive waste, and it is an object of the present invention to solve the drawbacks of the conventional solidification treatment method for radioactive waste, and to solve the problem of solidification of radioactive waste, especially pellet-shaped radioactive waste intermediate storage with excellent volume reduction properties and miscellaneous solid waste such as metals. The purpose of the present invention is to provide a method for creating a homogeneous solid package with no voids.

[Configuration of the Invention (Means for Solving the Problems) The radioactive waste solidification treatment method of the present invention comprises radioactive waste, a hydraulic inorganic compound, an aggregate, an inorganic fluidizing material,
It is characterized by solidifying the radioactive waste, a hydraulic inorganic compound, and a solidifying agent containing a reaction inhibitor for suppressing the agglomeration reaction of the inorganic fluidizing material.

The radioactive waste to be treated in the present invention consists of powder, pellets, miscellaneous solids, sludge, or a mixture thereof, and these wastes contain alkali metal salt compounds and alkaline earth metals as substances with strong flocculating action. Any compound containing a salt compound may be used.

The hydraulic inorganic compound used in the present invention is a hydraulic cement whose main components are calcium silicate and calcium aluminate, such as Portland cement,
Blast furnace cement, fly ash cement, and alumina cement can be used.

As aggregates it is possible to use, for example, alumina grains, chamotte grains, naturally occurring sands, gravels, rocks and mixtures thereof.

Further, as the inorganic fluidizing agent, it is possible to use an inorganic oxide powder with a particle size of 10 μl or less, such as fine silica powder, fine alumina powder, fine zirconium powder, or a mixture thereof.

Furthermore, aluminum lactate, which is a basic metal salt, is used as the reaction inhibitor in the present invention.

Further, it is very effective to use lithium citrate as an auxiliary agent for the reaction inhibitor, and it plays a good role as an agent for adjusting the curing time and improving the strength properties of aluminum lactate, which is a reaction inhibitor.

Furthermore, it is particularly important that aluminum lactate, which is a reaction inhibitor, acts on the uniform dispersion of the inorganic fluidizing agent and hydraulic inorganic compound, which are the other components of the solidifying agent, and achieves high fluidity with low water content. It has an excellent dispersion effect as well as a reaction suppressing effect.

The proportions of these components are: 15 to 50 parts by weight of cement as a hydraulic inorganic compound, 30 to 75 parts by weight of aggregate,
The amount of the inorganic fluidizing agent is 10 to 20 parts by weight, and the amount of the reaction inhibitor is 0.
Added water 8 to 5 parts by weight to a total of 100 parts by weight of 01 to 5 parts by weight.
20 parts by weight is suitable. With this configuration, the amount of added water can be kept as small as possible, and the voids of radioactive waste containing coagulating sodium nitrate and sodium carbonate can be completely filled without losing fluidity.

If the amount of cement as a hydraulic inorganic compound is less than 15 parts by weight, sufficient strength and quick hardening of the solidifying agent cannot be obtained, and if it exceeds 50 parts by weight, cracks may easily occur due to shrinkage during cement hardening. , a problem arises in that the amount of water in the solidifying material 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 will not be obtained and fluidity will also decrease.

Furthermore, if the blending amount of the inorganic fluidizing agent is less than 10 parts by weight or more than 20 parts by weight, the fluidity of the solidifying agent decreases, and
If it exceeds 0 parts by weight, cracks are likely to occur due to shrinkage.

Furthermore, if the reaction inhibitor is less than 0.01 parts by weight, the cohesive force due to eluates from radioactive waste cannot be sufficiently suppressed, and if it exceeds 5 parts by weight, the solidified product will not have sufficient strength.

(Function) In the radioactive waste solidification treatment method of the present invention, each particle of the inorganic fluidizing agent whose particle size has been adjusted is dispersed by the dispersing effect of aluminum lactate, and at the same time, the particles of the hydraulic inorganic compound are dispersed. Fine particles of 10 μm or less are also dispersed and intercalated between other large-sized hydraulic inorganic compound particles and the aggregate, thereby improving the slipperiness between these particles. As a result, the particles constituting the solidifying material are uniformly dispersed in the added water and become movable. Furthermore, even if strong cohesive substances such as sodium nitrate, sodium carbonate, etc. contained in radioactive waste or oil adhering to metal or concrete are present when filling the solidifying material, the reaction suppression effect of aluminum lactate , no aggregation of hydraulic inorganic compound particles or inorganic fluidizing material occurs. Therefore, when filling the solidifying material, the solidifying material easily flows onto the surface of the waste to be treated, and it is possible to easily fill the container of the solidified material package without any gaps, thereby forming a dense solidified material package. .

With conventional solidifying materials, a large amount of water must be added in addition to the water required for hardening to uniformly mix hydraulic inorganic compounds and aggregates during kneading and to provide appropriate fluidity. However, in the assimilated material of the present invention, due to the dispersion effect of the inorganic fluidizing agent and aluminum lactate, the amount of water added is the minimum amount necessary for curing the hydraulic inorganic compound.

Therefore, in this solidified material, there are no parts that impair the homogeneity of the solidified material, such as voids, and the entire solidified material is filled with the solidified material, and the solidified material contains crystals incorporated in the crystals. Since almost nothing other than water is present, it is possible to obtain a dense and stable solidified material.

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

Example 1.2 With the composition shown in Table 1, a hydraulic inorganic compound, aggregate, inorganic fluidizing agent, and reaction inhibitor were uniformly mixed, and water was added and kneaded to form two types of slurry. Get solidifying material.

The comparative examples in the table are listed for comparison with the present invention, and are solidified materials prepared without adding a reaction inhibitor. Further, the numbers in Table 1 indicate parts by weight.

(The following are blank spaces) Table 1 Next, the slurry solidified material obtained in this manner is used to form sodium sulfate pellets prepared by adding a binder, sodium sulfate pellets prepared by compression molding, and pellets prepared by a similar method. 80% by weight of sodium nitrate-
2 containing 20% by weight sodium carbonate pellets each
Each was filled into a 00° C. drum (pellet filling rate: 60% by volume). Similarly, the slurry solidifying material was also filled into 200J2 drums (pipe filling rate: 20% by volume) containing SOS 304 pipes coated with oil. The solidifying material was injected up to the top of the drum. After the solidifying material had hardened, the drum was cut with a diamond cutter and the filling status of the solidifying material was observed.
The filling situation was as shown in Table 2.

However, in the table, 0 indicates "complete filling," Δ indicates "partial voids," and X indicates "large voids."

(Left below) Table 2 As is clear from Table 2, the solidifying material without a reaction inhibitor cannot completely fill the highly soluble berent, whereas the solidifying material with a reaction inhibitor added Can be completely filled.

[Effects of the Invention] As explained above, according to the radioactive waste solidification treatment method of the present invention, a reaction inhibitor that also has a dispersion effect is added to a hydraulic solidification material with low water content and low viscosity. Since it is added and used, radioactive waste that elutes highly cohesive substances can be immobilized at a high filling rate into a solidified package that is chemically and mechanically stable for a long period of time.

Applicant: Japan Atomic Energy Corporation
Toshiba Corporation

Claims (5)

[Claims] (1) Radioactive waste, hydraulic inorganic compound, aggregate,
Radioactive waste characterized by being solidified integrally with a solidifying agent containing an inorganic fluidizing material and a reaction inhibitor for suppressing the aggregation reaction of the radioactive waste, a hydraulic inorganic compound, and the inorganic fluidizing material. Solidification treatment method. (2) The method for solidifying radioactive waste according to claim 1, wherein the radioactive waste contains at least one of an alkali metal salt compound and an alkaline earth metal salt compound. (3) The method for solidifying radioactive waste according to claim 1 or 2, wherein the reaction inhibitor comprises aluminum lactate or a combination of aluminum lactate and lithium citrate. (4) Solidification of radioactive waste according to any one of claims 1 to 3, wherein the hydraulic inorganic compound is a hydraulic cement consisting of calcium silicate and calcium aluminate. Processing method. (5) Solidification of radioactive waste according to any one of claims 1 to 4, wherein the inorganic fluidizing material is made of inorganic oxide powder with a particle size of 10 μm or less. Processing method.