JPH0677075B2 - Method for solidifying radioactive waste - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for treating intermediate-level or low-level radioactive waste generated from radioactive material handling facilities such as nuclear power plants, and particularly pelletized radioactive waste. The present invention relates to a method for solidifying a material.

[Technical Background of the Invention and its Problems] Conventionally, as a method of treating radioactive waste such as radioactive waste liquid or used ion exchange resin, which is generated in a facility for handling radioactive materials such as nuclear power plants, environmental safety is considered. A method of forming a solidified body that is more stable than the viewpoint is widely used.

As a conventionally known solidification treatment method, a cement solidification method, an asphalt solidification method, and a plastic solidification method are known.

In these solidification methods, for example, in the case of radioactive waste liquid, the object to be treated is concentrated and dried into powder consisting mainly of sodium sulfate, and in the case of used ion-exchange resin, it is dried and then cemented It is solidified with a solidifying agent consisting of asphalt or plastic.

Among these solidification methods, the cement solidification method was the most general because it yielded solidified bodies with excellent fire resistance and high mechanical strength, but the water used with the cement solidifies together, so the waste solidifies. It has the drawback of increasing the amount of body generated.

Further, the asphalt solidification method can form a solidified body at a low cost, but has the drawback that the formed waste solidified body has poor fire resistance and is weak against mechanical shock.

Furthermore, the plastic solidification method is a solidification method that has recently been expected to be promising, and it is possible to form a solidified body that is lightweight and has excellent mechanical properties and the like.

In this plastic solidification method, radioactive waste is pulverized after drying treatment and in many cases it is solidified with a thermosetting resin, so that water is not solidified together with the cement solidification method as in the cement solidification method. Significantly improved in volume reduction. In this plastic solidification method, it is possible to reduce the amount of radioactive waste generated to about 1/5 that in the cement solidification method. However, since many of the plastic monomers used are volatile at room temperature, there is a risk of fire during the solidification process, and the solidification agent used is an organic material, which results in solidification. It has the disadvantage of poor fire resistance.

By the way, even if a solidified body of radioactive waste is obtained by the solidification treatment by the above method, most of them are still in the state where the final disposal method has not been established at present. Further, when directly solidifying radioactive waste having a relatively high radioactivity, the surface dose rate of the solidified product obtained will be high by any solidification treatment method, so that there is a problem that it is not easy to handle. is there. In recent years, methods for intermediate storage of radioactive waste have been proposed to address these problems.

This method is a method in which radioactive waste is dried and greatly reduced in volume, and then pelletized to produce a stable intermediate storage, which is temporarily stored in a storage tank in a nuclear facility. According to this method, since the powdery radioactive waste after the drying process is compressed and pelletized, a high volume reduction rate superior to the plastic solidification method can be obtained.

However, the pelletized radioactive waste is
Since the pelletized radioactive waste does not have sufficient physical properties as a final disposal body, it is necessary to solidify the pelletized radioactive waste as a stable solidified body package only after it has been stored for a certain period of time and the radioactivity has decayed.

As a method for packaging the pellet-like radioactive waste into a solidified body package, treatment with the aforementioned solidifying agent which has been conventionally used can be considered. However, when these solidifying agents represented by cement, asphalt, etc. are used for packaging solidified bodies of pelletized radioactive waste, the above-mentioned respective solidification methods still have the drawbacks and the problems are not solved at all. .
Furthermore, when cement is used as a solidifying agent, a large amount of water is required to harden the cement, and the water may even deteriorate the pellets. That is, the cement hardens due to the hydration reaction with water, but since it takes a long time to complete the hardening, free water exists in the cement during that time. The pellets are soaked in this free water, and because the pellets have relatively poor water resistance, they dissolve or swell, and some are destroyed. Therefore, it is particularly difficult to manufacture a stable solidified body package by pelletizing radioactive waste.

[Object of the Invention] The present invention is intended to eliminate the drawbacks of the conventional solidification treatment method of radioactive waste, and solid radioactive waste, particularly pellet-like radioactive waste intermediate storage material excellent in volume reduction property. Another object of the present invention is to provide a method for integrally solidifying the above as a solidified package which has excellent heat resistance and is chemically and mechanically stable upon storage for a long period of time.

[Summary of the Invention] That is, the method for solidifying radioactive waste according to the present invention includes solid radioactive waste that is generated in a nuclear facility and is pelletized in advance. ,
100 parts by weight of at least one selected from alkali metal inorganic salts (excluding silicates) and alkaline earth metal inorganic salts (excluding silicates) and (b) water-soluble phosphates: 30 Inorganic filling and solidifying agent blended in a proportion of ~ 200 parts by weight, and
It is characterized in that the radioactive waste is solidified together at room temperature by adding 1 part by weight of water.

According to the method of the present invention, liquid or slurry radioactive waste generated from facilities such as a nuclear power plant can be completely solidified. Examples of the waste that can be applied to the method of the present invention are as follows. Can be given.

Spent ion-exchange resin with a particle size of about 0.5 mmφ and POWDEX (POWDE
There are some powdery products called X ... (trade name). For boiling water reactors (BWR), reactor water purification system, condensate demineralization system, natural pool demineralization system, radioactive waste liquid treatment system, etc. Occurs in
In a pressurized water reactor (PWR), it occurs in the bypass purification system (purification desalination, deboronization), fuel pit desalination system, extraction coolant treatment system, etc.

Concentrated waste liquid Chemical waste liquid (resin recycling waste liquid, etc.) is evaporated and concentrated, and its water content is around 80% with sodium sulfate as the main component, and sodium sulfate is the main component.

It is a waste liquid containing corrosion products generated from clad equipment and piping, and mainly contains iron oxides and hydroxides.

Filters and sludges Filters such as equipment drains and floor drains, the main component of which is a filter aid (filter aid) which is a fine pulp powder.

Incinerated ash Exit from the incinerator.

Waste laundry liquid Occurs when laundering contaminated clothes by workers.

In the present invention, the radioactive waste liquid in the form of liquid or slurry as described above is first dried and powdered according to a conventional method. Since the powdered radioactive waste is extremely difficult to handle as it is, a pelletizing process is performed in order to suppress the scattering of the powder fine particles as much as possible.

The pelletizing method is a method of pelletizing powder by compressive force like a processing method using a briquetting machine, or a small amount of a rubber-like elastic body as a binder, and pelletizing by this particle sticking force and compressive force. Any method such as a method of doing can be adopted.

The pellets thus produced are filled in a radioactive waste storage container.

In the present invention, in this pellet, (a) an alkali metal oxide, an alkaline earth metal oxide,
At least one selected from an alkali metal inorganic salt and an alkaline earth metal inorganic salt, and (b) a water-soluble phosphate are kneaded with an appropriate amount of water in advance, and an inorganic filler solidifying agent is added and uniformly mixed. To do.

The inorganic filling and solidifying agent mixed with the waste pellets is rapidly cured at room temperature, and after about 1 day, a solidified package of radioactive waste is obtained.

(A) an alkali metal oxide of the above-mentioned inorganic filling and solidifying agent,
As at least one component selected from alkaline earth metal oxides, alkali metal inorganic salts, and alkaline earth metal inorganic salts, either natural or synthetic hard-baked magnesite (a mineral containing magnesium carbonate as a main component) ), Hard-burned dolomite (a mineral whose main component is magnesium carbonate and calcium carbonate), a hard-burned alkali metal or alkaline earth metal aluminate, and hard-burned magnesia (magnesium oxide) alone or in combination of two or more. To be

As the water-soluble phosphate component (b), basic phosphates such as ammonium phosphate, sodium acid phosphates such as magnesium biphosphate, and aluminum biphosphate may be used alone or in combination of two or more. Is used.

Furthermore, by using a polyphosphate together with the water-soluble phosphate, it is possible to impart higher mechanical strength as a solid waste to the solidified package obtained.

Polyphosphate is represented by the general formula M _{n + 2} P _n O _{3 n + 1} (wherein M is
Is a cation) and contains a water-soluble polymerized phosphate compound having a chain length containing two or more phosphoric acid units. Examples of such polyphosphates include sodium tripolyphosphate (Na ₅ P
₃ O ₁₀ ), tetrasodium pyrophosphate (Na ₄ P ₂ O ₇ ), and mixtures thereof.

Further, the inorganic filler-solidifying agent of the present invention is added to the waste pellets, in order to improve the fluidity when mixing, an amount of naphthalene sulfonic acid within the range that does not inhibit the function of the solidifying agent,
Formalin condensate, melamine formalin polymer sulfonate, gluconate and the like can be used.

In the present invention, if necessary, a substance which is inactive to the above-mentioned inorganic filler / solidifying agent can be added as an aggregate or a filler. Examples of such aggregates or fillers include silica, limestone, granite, feldspar, and the like.

The suitable amount of the inorganic filler / solidifying agent of the present invention is usually in the following range.

(A) Oxide or carbonate or aluminate 100 parts by weight (b) Water-soluble phosphate 30 to 200 parts by weight Polyphosphate 1 to 100 parts by weight In the present invention, the reaction of the inorganic filling and solidifying agent is promoted. For which water is added. The appropriate amount of water used is usually 5 to 100 parts by weight per 100 parts by weight of the inorganic filling and solidifying agent.

The inorganic filler-solidifying agent of the present invention hardens at room temperature by a reaction with water like cement, but the amount of water required is much smaller than that of cement, and cement was used as the solidifying agent. The water in the fill does not break the pellets as in the case.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a pellet manufacturing process according to an embodiment of the present invention.

Liquid or slurry radioactive waste 1 generated at a nuclear power plant or the like is temporarily stored in a stock solution supply tank 2 and then
It is guided to the dryer 4 by the stock solution supply pump 3.

Since the granular used ion-exchange resin 1a is difficult to dry as it is, in order to improve the performance of the dryer 4, an in-line pulverizer 5 is installed between the stock solution supply pump 3 and the dryer 4 to form a slurry state. The used ion exchange resin particles may be crushed. The dryer 4 is preferably one capable of reducing the amount of liquid or slurry radioactive waste having a concentration of 5 to 20% by weight to 5% by weight or less. For example, a thin film dryer or a drum type dryer can be used.

The dry radioactive waste 1b dried by the dryer 4 has a moisture meter 6
This confirms that the prescribed water content has been reached. The high-moisture content dry radioactive waste 1c that has not been dried to a predetermined water content is returned to the return tank 7 and diluted with water, and then returned to the stock solution supply tank 2 by the return pump 8.

The dried radioactive waste, which has been dried to reach a predetermined water content, is once stored in the storage tank 9 and then periodically weighed.
Moved to 10.

On the other hand, the binder composition 11 made of a thermosetting resin or a rubber-like elastic polymer is also supplied from the binder hopper 12 to the measuring device 10.

The dry radioactive waste 1b and the binder composition 11 are weighed in predetermined weight ratios and then naturally dropped into the mixer 13.

The mixing ratio (weight ratio) of dry radioactive waste 1b / binder composition 11 differs depending on the type of waste. When a rubber-like elastic polymer is used as the binder composition 11, the above mixing ratio is 3/1 to 8/1 in the concentrated waste liquid and the incinerator.
And the used ion exchange resin and filter sludge are 1.5 / 1 to 4/1. When a thermosetting resin is used as the binder composition, the above mixing ratio is 0.5 / 1 to 2/1 regardless of the type of dry waste.

A mixture 14 composed of the dry radioactive waste 13 and the binder composition 11 that have been thoroughly mixed in the mixer 13 is then granulated by the kneading granulator 15. At this time, when a rubber-like elastic polymer is used as the binder, the mixture 14 has a temperature of 30 to 120 ° C., preferably 4 to 40 ° C.
It is heated at 0 to 100 ° C, more preferably at 50 to 60 ° C without being melted. However, in the usual case, in the mixer 13 or the kneading granulator 15, the mixture 14 is heated to 50 to 60 ° C. due to frictional heat.
Since the temperature is raised to 1, the heating of the mixture can be achieved without external heating. On the other hand, when a thermosetting resin is used, the mixture 14 is usually heated to 180 to 200 ° C.
In the granulation process shown in the figure, the extruder 15 extrudes in a string shape and is a cutter.
Granulation is performed by 16. The shape of the granulated particles is
A columnar one having a diameter of 0.5 to 3.0 cm and a length of 0.5 to 3.0 cm, which is convenient for storage and transportation, is preferable.

The pelletized radioactive waste 17 thus granulated is stored in a storage container 19 through a vibrating feeder 18. A drum can can also be used as the storage container. When cooling the pellet-like radioactive waste 17 on the vibrating feeder 18, a vibrating cooler having a trough type tunnel structure equipped with a vibrating feeder can be used.

The pelletized radioactive waste 17 thus granulated and filled in the storage container 19 is integrally solidified as a solidified body package 20 in the process of the present invention shown in FIG.

The inorganic filling and solidifying agent 21 used in the present invention is sent from the inorganic filling and solidifying agent supply hopper 22 through the inorganic filling and solidifying agent feeder 23 to the in-line mixer 24, and the water feed pump 26 from the water tank 25.
It is kneaded here together with an appropriate amount of water that is sent to the in-line mixer 24 via the.

The inorganic filler-solidifying agent kneaded with water is poured into the voids between the pellets in the storage container 19 containing the pellet-shaped radioactive waste 17, and is integrated with the pellet-shaped radioactive waste 17 to form the solidified body package 20. Form.

Note that air bubbles remain in the inorganic filling and solidifying agent simply by injecting the inorganic filling and solidifying agent. Therefore, it is desirable to vibrate the solidified body package 20 by using the vibrator 28 to remove the bubbles.

Below, the physical-property test result of the solidified body manufactured by the above-mentioned process is shown.

The physical property test was performed according to the physical test method for JIS R52 radioactive waste cement.

That is, each composition was mixed with a kneading machine for strength test, and then the composition was divided into three layers in a mold having a diameter of 50 mm and a height of 100 mm, and each layer was squeezed 25 times with a stick to consolidate. After 24 hours, it was demolded and cured in air at a temperature of 20 ° C. and a humidity of 70% for 7 days, and then the compressive strength was measured.

Regarding the stability in water, after immersing the above compressive strength test piece in water for 28 hours, the presence or absence of swelling or breakage of the test piece was determined.

Regarding the thermal stability, the specimen used for the above-mentioned compressive strength test was left for 6 hours in an electric furnace at 800 ° C., and the presence or absence of disintegration was determined. The properties of the solidified product are shown in Table 2. The numbers in Table 1 are parts by weight per 100 parts by weight of solid radioactive waste pellets. As a result of the above physical test, it has sufficient strength even when it is dumped in the ocean or stored on land, and has sufficient stability without deterioration in water or collapse due to high temperature.

[Effects of the Invention] As described above, according to the present invention, the solidified radioactive waste is an alkali metal and / or alkaline earth metal oxide and / or salt and a water-soluble phosphate having a low water content. Since it is solidified by the inorganic filling and solidifying agent consisting of, it is possible to manufacture a solidified package which is excellent in heat resistance and water resistance and which is chemically and mechanically stable against storage for a long period of time.

[Brief description of drawings]

FIG. 1 is a process drawing showing a pellet manufacturing method according to an embodiment of the present invention, and FIG. 2 is a process drawing showing a solidified package manufacturing method according to an embodiment of the present invention. 1 …… Liquid or slurry radioactive waste 1a …… Granular spent ion exchange resin 1b …… Dry radioactive waste 1c …… Dry radioactive waste containing high water content 2 …… Undiluted solution supply tank 3 …… Undiluted solution supply pump 4 ... … Dryer 5 …… In-line grinder 6 …… Moisture meter 7 …… Return tank 8 …… Return pump 9 …… Storage tank 10 …… Measuring instrument 11 …… Binder composition 12 …… Binder hopper 13 …… Mixer 14 …… Mixture 15 …… Kneading Granulator 16 …… Cutter 17 …… Pelletized radioactive waste 18 …… Vibration feeder 19 …… Storage container 20 …… Solid package 21 …… Inorganic filling solidifier 22… … Inorganic filling and solidifying agent supply hopper 23 ………… Inorganic filling and solidifying agent feeder 24 …… Inline mixer 25 …… Water tank 26 …… Water feeding pump 27 …… Water 28 …… Vibrator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naomi Toyohara 4-1 Ukishimacho, Kawasaki-ku, Kawasaki-shi, Kanagawa Research Institute of Japan Nuclear Power Company (72) Hiroshi Iimori 1071 Nakano-cho, Totsuka-ku, Yokohama-shi, Kanagawa ―2 (56) Reference JP-A-60-122398 (JP, A)

Claims (2)

[Claims] 1. A solid radioactive waste produced in a nuclear facility and pre-pelletized, (a) an alkali metal oxide, an alkaline earth metal oxide,
100 parts by weight of at least one selected from alkali metal inorganic salts (excluding silicates) and alkaline earth metal inorganic salts (excluding silicates) and (b) water-soluble phosphates: 30 Inorganic filling and solidifying agent blended in a proportion of ~ 200 parts by weight, and
A method for solidifying radioactive waste, characterized by comprising adding 1 part by weight of water and solidifying the radioactive waste together at room temperature. 2. The inorganic filling and solidifying agent is an alkali metal oxide,
1 to 100 relative to 100 parts by weight of at least one selected from an alkaline earth metal oxide, an alkali metal inorganic salt (excluding silicate), and an alkaline earth metal inorganic salt (excluding silicate). The method for solidifying radioactive waste according to claim 1, further comprising polyphosphate in a proportion of parts by weight.