JPH0668555B2 - Radioactive waste solidification method - Google Patents

Description

Description: FIELD OF APPLICATION OF THE INVENTION The present invention relates to a method for producing a radioactive waste solidified body, and in particular,
The present invention relates to a method for producing a solidified radioactive waste, which is obtained by solidifying radioactive waste solidified with water glass.

[Background of the Invention]

Reducing and solidifying radioactive waste generated from a nuclear power plant is not only a weight in securing storage space for facilities inside the power plant, but also an essential factor for land storage, which is one of the final disposal laws. Is. As one of the methods to reduce the volume of radioactive waste, concentrated waste liquid (main component Na ₂ SO ₄ or Na ₂ B ₄ O ₇ ) which is the main waste generated from BWR power plant and slurry of used ion exchange resin A method of drying and powdering to remove water occupying most of the volume of radioactive waste and solidifying this is being studied. It has been confirmed that this method can reduce the volume to about ⅛ as compared with the conventional method of directly solidifying waste liquid or slurry. Typical solidifying materials for solidifying the dry powder of the radioactive waste are plastics, asphalt and inorganic materials.

For the plastic solidification, the thermosetting resin is used as the solidifying material, but the thermosetting resin cannot exhibit the desired performance as the solidifying material when a small amount of water is mixed therein. That is, if water is brought into the system during solidification, the curing accelerator (cobalt naphthenate, etc.) in the thermosetting resin will be decomposed and the thermosetting resin will not cure, so some of the thermosetting resin will be added. It will exist as it is at the time (liquid). The dry powder of radioactive waste liquid may not be able to completely remove water even if it is carefully dried. Therefore, if a dry powder of radioactive waste liquid containing a very small amount of water and a thermosetting resin are mixed and solidified, it becomes impossible to obtain a solidified product having high strength. For this reason, the dried powder requires thorough moisture management with a moisture content measuring instrument such as a neutron moisture meter.

Regarding the solidification of asphalt, the moisture management is not required because the solidification is performed after the moisture is removed by heating while mixing the radioactive waste powder and the alfalto. However, since Alfalto is thermoplastic, it is 40-50 ° C.
It is not suitable for land storage / disposal due to the problem of fluidization.

The solidification by the inorganic material is a desirable solidification material for land storage and disposal because it has good compatibility with soil and rocks, and various studies have been conducted. The most common are
Although it solidifies with cement, cement is not desirable because it easily interacts with radioactive waste powder. For example,
When sodium sulfate (Na ₂ SO ₄ ) which is a dry powder of concentrated waste liquid from the BWR power plant is solidified with cement, calcium aluminate (3CaO ・ Al ₂ O ₃ ) and calcium hydroxide (Ca (OH ) ₂ ) and dry powder Na ₂ SO ₄ react to form ettringite, which causes volume expansion, and the soundness of the solidified product cannot be maintained.

(Miscellaneous Theory of Cement Chemistry, Goto, Daimon, p57.) When solidifying sodium borate (Na ₂ B ₄ O ₇ ) which is a dry powder of concentrated waste liquid from a PWR power plant, Ca in the cement component is also solidified. There is a problem in that (OH) ₂ and borate ions (▲ BO ³ _-3 ), which are generated by dissolution of sodium borate, react as shown in formula (1) and the solidified product deteriorates.

_{▲ 3Ca (OH) 2 + 2BO} 3- 3 ▲ → Ca 3 (BO 3) 2 + 60H - (1) In this manner, because the cement is difficult to healthy solidified body made of radioactive waste, radioactive waste A method of solidifying water by lath (alkali silicate aqueous solution), which has little interaction with powder, has been proposed.

The water glass itself is a viscous aqueous solution of alkali silicate,
Although it is self-hardening by reducing water content, the solidified product is weak. It cures quickly by adding an appropriate curing agent. As a curing agent, zinc oxide (Japanese Patent Application Laid-Open No. 50-151221), sodium silicate (Fujii, Ishido, Tokyo Tech. Report 56,205 (1961)) and the like have been proposed for use as an inorganic adhesive. These curing agents are effective for the purpose of rapid solidification, but are not suitable for mixing with radioactive waste to produce a solidified product from the viewpoint of workability. Silicon phosphate (P ₂ O ₅ (SiO ₂ )), which has a gradual hardening action, is effective for solidifying radioactive waste. However, in this method, in order to complement the water resistance and strength of the solidified product, it has always been necessary to add various additives such as barium silicate.

[Object of the Invention]

An object of the present invention is to provide a method for producing a radioactive waste solidified body, which is capable of obtaining a stable radioactive waste solidified body having a predetermined strength.

[Outline of Invention]

The feature of the present invention is to add silicon phosphate which is a curing agent so that the molar ratio of the curing agent / the water glass is 0.8 to 1.2 to solidify the dry powder or the pellet. Especially.

This is 150 Kg / cm by the experiment changing the molar ratio.
² (standard for ocean dumping) Based on the experimental results, the above range is sufficient to obtain solidified products above the level, and the above strength can be obtained without adding other additives.

One of the specific examples of the present invention is to use the water glass having a water concentration of 1.9 or less in a weight ratio of water / water glass solid component during kneading before curing. This is also based on the same experimental result as the above molar ratio experiment.

Example of Invention

 The basic principle of the present invention will be described.

The water glass (alkali silicate aqueous solution) used in the experiment was sodium silicate (Si / Na molar ratio of 1), and it was found from the experiment that curing proceeds according to the following equation.

FIG. 1 shows the result of an experiment conducted with the addition molar ratio of the curing agent (silicon phosphate) added to the water glass added. From this result, 150 Kg / c, which is the standard for ocean dumping
The result can be derived that the curing agent may be added in a molar ratio of 0.8 to 1.2 to satisfy m ² . Next, FIG. 2 shows the result of an experiment in which the water content of water glass, which is the main curing agent, was examined. Similarly, it has been found that 1.9 or less is sufficient to satisfy 150 kg / cm ² . In terms of workability, the range of 1.9 to 1.0 is optimal for obtaining a more solidified body.
If it is less than 1.0, the workability will decrease.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
3 and 4 show the process of the embodiment of the present invention. It will be described from FIG.

The radioactive concentrated waste liquid (for example, sodium borate 10 wt%) 2 is supplied from the radioactive concentrated waste liquid tank 1 to the dry powder device 3, and the radioactive concentrated waste liquid is converted into a dry powder. Dry powder
The pellets may be converted into pellets 13 by the pelletizer 10 or may be solidified as powder without pelletization. First, an embodiment in the case of forming a pellet will be described. Pellet produced by the pellet maker 10 (20φ x 1
0 mm) is filled into 200 solidification vessels. The size of the pellet may be arbitrary, but in consideration of the storage rate in the solidification container, a cylindrical shape having an outer diameter of 5 to 30 mm, or a sphere or an almond shape is desirable. The pellet 13 filled in the solidification container 11 is carried to a solidification facility, and the solidifying material 9 is injected into the pellet gap. The solidifying material 9 is composed of water glass 7 in the tank 6 and silicon phosphate as a curing agent in the tank 6
Kneading tank 4 adjusted to have a water glass molar ratio of 1.0
Knead to prepare. The strength of the pelletized solidified by using the solidifying agent kneaded at a molar ratio of 1.0 is 150 kg / cm ²
The above is sufficient to satisfy the standard value of 150 Kg / cm ² for ocean dumping.

Next, a case will be described in which the dry powder is not pelletized but is uniformly kneaded and solidified as the powder. The dry powder powdered by the dry powder unit 3 is mixed and kneaded in the mixing tank 4 together with the solidifying material. In that case, the larger the mixing ratio of the dry powder is, the more preferable from the viewpoint of the volume reduction of the waste, but the mixing ratio of the dry powder is preferably 40 to 70 wt% from the viewpoint of the strength of the solidified body.
Also in this example, an experiment was conducted with the dry powder ratio set to 50 wt%. The curing agent is added at a molar ratio of silicon phosphate / water glass of 1.0, and the water glass water content is mixed at a weight ratio of water / water glass solid components of 1.50 to obtain a kneaded product 5, which is solidified through a valve 16. Then, the solidified body 12 was produced. The strength of the solidified body was 150 Kg / cm ² or more.

FIG. 4 shows a system flow diagram including the water glass synthesis process. Water glass is sodium hydroxide (NaO
It is easily synthesized from H) and silicic acid (H ₂ SiO ₃ ). Sodium hydroxide in tank 6 and silicic acid in tank 6 are
And stirred for about 1 hour in the temperature range of 50 to 90 ° C. to synthesize water glass 7. Sodium hydroxide to be used may be newly introduced as a reagent, or may be a sub-substance when radioactive waste discharged from a nuclear power plant is treated (specifically, sodium sulfate is insolubilized with barium hydroxide). Fresh sodium hydroxide may be used. At that time, the water glass to be synthesized has a Si / Na molar ratio of NaOH and H ₂ SiO ₃
And can be easily adjusted by changing the mixing ratio. In this example, the Si / Na molar ratio was 1. Further, the superheater 21 is used to adjust the water content in the synthetic water glass. Next, water glass 7 and 1 mol equivalent of the hardener powder 8 were charged together with the waste material 19 into the solidification container 20, and mixed and stirred by the stirring blade 15 until the mixture became homogeneous to obtain a solidified body. Regarding the curing agent, phosphate alone was used in this experiment, but cement or the like can be mixed depending on the type of waste and the water glass water content. The waste 19 may be a dry powder, an aqueous solution, or an individual. In this embodiment, BW
R concentrated waste liquid powder, PWR concentrated waste liquid powder, dry powder of ion exchange resin, all 150 kg strength
A solidified body having a strength of not less than / cm ² could be produced.

〔The invention's effect〕

According to the present invention, it is possible to obtain a stable solidified radioactive waste having a predetermined strength and capable of being dumped in the ocean.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the molar ratio of silicon phosphate and water glass on the strength during mixing in the example of the present invention, and FIG. 2 is the water concentration in the water glass on the strength of the solidified body. A diagram showing the influence, FIG. 3 is a system schematic diagram of the present embodiment, and FIG. 4 is a system schematic diagram of the present embodiment including water glass synthesis. 2 ... Radioactive concentrated waste liquid, 3 ... Dry powder device, 4 ... Kneading tank, 5 ... Kneading material, 6 ... Tank, 7 ... Water glass, 9
...... Solidifying material, 10 ...... Pellet maker, 11 ...... Solidifying container, 12 ...... Solidified body, 13 ...... Pellet, 14 ...... Motor, 15 ...... Stirring blade, 16 ...... Valve, 18 ...... Reaction tank .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP58-15060 (JP, A) JP60-56299 (JP, A) JP61-209942 (JP, A)

Claims (2)

[Claims] 1. A method for producing a solidified body of radioactive waste, wherein either dry powder of radioactive waste liquid filled in a solidification container or pellets made of this powder is solidified with water glass. A method for producing a radioactive waste solidified product, which comprises adding silicon phosphate as an agent so that a molar ratio of the curing agent / the water glass is 0.8 to 1.2 to solidify the dry powder or the pellet. . 2. A method for producing a radioactive waste solidified product according to claim 1, wherein said water glass having a water concentration of water / water glass solid component weight ratio of 1.9 or less is used.