JPS623698A - 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] [Technical Field of the Invention] The present invention relates to a method for treating medium-level to low-level radioactive waste generated from facilities handling radioactive materials such as nuclear power plants, and particularly relates to a method for treating radioactive waste that has been pelletized. Concerning methods for solidifying objects.

[Technical background of the invention and its problems] Conventionally, environmentally safe methods have been used to dispose of radioactive waste, such as radioactive waste liquid and used ion exchange resin, generated in facilities that handle radioactive materials such as nuclear power plants. From a viewpoint, methods of forming a stable solidified material are widely used.

Conventionally known solidification treatment methods include a cement solidification method, an asphalt solidification method, and a plastic solidification method.

In these solidification methods, for example, in the case of radioactive waste liquid, the object to be treated is concentrated and dried to form a powder mainly consisting of sodium 1i11E acid, and in the case of used ion exchange resin, it is dried and then processed. cement,
It is solidified with a hardening agent made of asphalt or plastic.

Among these solidification methods, the cement solidification method was the most common because it produced a solidified material with excellent fire resistance and high mechanical strength. The disadvantage is that the body produces a large amount.

Furthermore, although the asphalt solidification method can form solidified bodies at low cost, it has the disadvantage that the formed solidified waste bodies have poor fire resistance and are susceptible to mechanical shock.

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

In this plastic solidification method, radioactive waste is turned into powder by drying and is often solidified with thermosetting resin, so water is not solidified with it as in the cement solidification method. Significantly improved volume reduction properties. In this plastic solidification method, it is possible to reduce the amount of radioactive waste generated to about 115 compared to the cement solidification method. However, since many of the monomers used in plastics are volatile at room temperature, there is a risk of fire during the solidification process, and because the solidification agent used is an organic material, the solidification caused by The disadvantage is that the body has poor fire resistance.

By the way, even if a solidified body of radioactive waste is obtained by the solidification treatment using the above-mentioned method, the final disposal method for most of it has not yet been established at present. In addition, when radioactive waste with relatively high radioactivity is directly solidified, the surface FA content of the resulting solidified material is high regardless of the solidification treatment method, so there is a problem that it is not easy to handle. There is. To address these problems, methods for interim storage of radioactive waste have been proposed in recent years.

This method involves drying radioactive waste to significantly reduce its volume, and then processing it into pellets 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 immediately after drying to pelletize it, so a higher volume reduction rate than the plastic solidification method can be obtained.

However, radioactive waste that has been pelletized is
Because it does not have sufficient physical properties to be used as a final disposal material, it is necessary to store the radioactive waste pellets for a certain period of time so that the radioactivity attenuates and then solidify them again into a stable solid package.

As a method of solidifying radioactive waste pellets into a solid package, treatment using the previously used solidifying agent described above can be considered. However, when these solidifying agents, such as cement and asphalt, are used to package pelleted radioactive waste, the drawbacks of each of the solidifying methods described above still exist, and the problems are not solved. .

Furthermore, when cement is used as a hardening agent, a large amount of water is required to harden the cement, and the water may even cause deterioration of the pellet.

In other words, cement hardens through a hydration reaction with water, but
Since it takes a long time to complete hardening, free water is present in the cement during that time. The pellets are immersed in this free water, and since the pellets are relatively water resistant, they dissolve or swell, and some of them are destroyed. The production of stable solidified cement packages of pelleted radioactive waste is therefore particularly difficult.

[Object of the Invention] The present invention aims to eliminate the drawbacks of the conventional solidification treatment method for radioactive waste, and provides an intermediate storage medium for solid radioactive waste, especially pellet-shaped radioactive waste with excellent volume reduction properties. The object of the present invention is to provide a method for solidifying these into a solid package that has excellent heat resistance and is chemically and mechanically stable for long-term storage.

[Summary of the Invention] That is, the method for solidifying radioactive waste of the present invention includes adding (a) an alkali metal and/or alkaline earth metal oxide and/or to liquid radioactive waste generated at a nuclear facility.
Alternatively, the method is characterized in that an inorganic filling solidifying agent consisting of an inorganic salt and (b) a water-soluble phosphate is added together with water to solidify the radioactive waste in one piece.

According to the method of the present invention, liquid or slurry radioactive waste generated from facilities such as nuclear power plants can be completely solidified. Examples of wastes that can be subjected to the method of the present invention include the following: can be given.

■ Used ion exchange resin particles with a particle size of approximately 0.5 mmφ and Boudex (
There is a powder called POWDEX (trade name), and in boiling water reactors (BWR), it is used in reactor water purification systems, condensate desalination systems, fuel pool desalination systems, radioactive waste liquid treatment systems, etc. In a pressurized water reactor (PWR), bypass purification system (purification desalination, deboronization), fuel bit desalination system,
Occurs in the extraction coolant treatment system, etc.

■Concentrated waste liquid Contains sodium sulfate, which is obtained by evaporating and concentrating chemical waste liquid (resin recycling waste liquid, etc.), and has a water content of around 80%.
51! Sodium chloride is the main component.

■It is a waste liquid containing corrosion products generated from cladding equipment and piping, and its main components are iron oxides and hydroxides.

■Filter sludge The main component of the filtrate from equipment drains, floor drains, etc. is filter aid (illll side), which is a valve-shaped fine powder.

■Incineration ash Exit the incinerator.

■Laundry waste liquid Occurs when workers wash contaminated clothing.

In the present invention, the above-mentioned liquid or slurry radioactive waste liquid is first dried and powdered according to a conventional method. Powderized radioactive waste is extremely difficult to handle as it is, so it is pelletized to minimize the scattering of powder particles.

Pelletization can be made into pellets using compression force, such as a processing method using a briquetting machine, or by using a small amount of rubber-like elastic material as a binder, and using this particle adhesion and compression force to form pellets. Any method such as a method can be adopted.

The thus prepared pellets are filled into a radioactive waste storage container.

In the present invention, (a) an alkali metal and/or alkaline earth metal oxide and/or inorganic salt, and (b) a water-soluble phosphate are added to the pellet in advance in an appropriate amount of water. Add the kneaded inorganic filling solidifying agent and mix uniformly.

The inorganic filling solidifying agent mixed with the waste pellet hardens rapidly at room temperature, and a radioactive waste solidified package 19 with sufficient strength is obtained in about one day.

(a) Alkali metal and/or alkaline earth metal oxide and/or sulfur
Salt components include hard-burned magnesite (a mineral whose main component is magnesium carbonate), either naturally produced or synthetic;
Hard-burned dolomite (a mineral whose main components are magnesium carbonate and calcium carbonate), hard-burned alkali metal or alkaline earth metal aluminate, and hard-burned magnesia (magnesium oxide) are used alone or in combination V of two or more types. .

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

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

The polyphosphate has the general formula Mfi, P, 03°. , (where M is a cation) and contains a water-soluble combined phosphate compound with a continuous length containing two or more phosphoric acid units. Examples of such polyphosphates include tripolyphosphate (Na
5P3010), tetrasodium birophosphate (Na
<Pz○7), and mixtures thereof.

In addition, in order to improve fluidity when adding and mixing the inorganic filling solidifying agent of the present invention to waste pellets, naphthalene sulfonic acid, formalin condensate, and melamine formalin are added in amounts within a range that does not inhibit the function of the solidifying agent. Polymeric sulfonates, gluconates, etc. can be used.

In the present invention, a substance that is inert to the inorganic filling and solidifying agent may be added as aggregate or filler if necessary. Such aggregates or fillers include, for example, silica, limestone, granite, feldspar, and the like.

The amount of the inorganic filling and solidifying agent of the present invention is usually within the following range.

(a) Oxide or carbonate or aluminate 100 parts (b) Water-soluble phosphate 30 to 200 parts polyphosphate 1 to 100 parts by weight In the present invention, the reaction of the inorganic filling solidifying agent is promoted. Water is added to thicken. The machine that uses this water usually has an inorganic filling solidifying agent of 10
The most suitable part is 5 to 100 parts compared to 0 parts.

The inorganic filler solidifying agent of the present invention hardens at room temperature by reacting with water like cement, but requires much less water and mold than cement, making it possible to use cement as a solidifying agent. The pellets will not be destroyed by water in the filling, as would be the case if the pellets were filled with water.

[Embodiments of the invention] Embodiments of the present invention will be described below based on 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 etc. is once stored in a raw solution supply tank 2, and then
The stock solution 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 crusher 5 is installed between the stock solution supply pump 3 and the dryer 4 to turn it into a slurry state. The spent ion exchange resin particles may be pulverized. The dryer 4 is preferably one capable of reducing 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.

It is confirmed by the moisture meter 6 that the dried radioactive waste 1b dried in the dryer 4 has reached a predetermined moisture content. High moisture content dry radioactive waste 1C that has not been dried to a predetermined moisture 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 that has been dried until it reaches a predetermined moisture content is once stored in the storage tank 9 and then periodically transferred to the scale radioactive waste.

On the other hand, the binder composition 11 made of a thermosetting resin or a rubber-like elastic polymer is also transferred from the binder hopper 12 to the scale 1.
0.

The dry radioactive waste 1b and the binder composition 11 are each weighed at a predetermined weight ratio and then allowed to fall naturally into the mixer 13.

Mixing ratio of dry radioactive waste 1b/binder composition 11 (
weight ratio) 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 for concentrated waste liquid and incineration ash.
/1 to 8/1, and for used ion exchange resin and filter sludge, it is 1.5/1 to 4/1. In addition, when a thermosetting resin is used as the binder composition, the above mixing ratio is 0.5/1 to 2, regardless of the type of dry waste.
/1.

The mixture 14 consisting of the dry radioactive waste 13 and the binder composition 11 thoroughly mixed in the mixer 13 is then granulated in the kneading and granulating machine 15. At this time, when a rubber-like elastic polymer is used as a binder, the mixture 14 has a content of 30 to 12
0°C, preferably 40-100°C, more preferably 5
Heated without melting at 0-60°C. But usually mixed! In the kneading/granulating machine 113 or the kneading/granulating machine 15, the temperature of the mixture 14 is raised to 50 to 60° C. due to frictional heat, so that heating of the mixture can be achieved without particularly external heating. -When using universally curable resin,
Typically, mixture 14 is heated to 180-200°C. In the illustrated granulation process, the extruder 15 extrudes the pellets into a string shape and the cutter 1
Granulation is performed by step 6. The shape of the granulated particles is
Diameter 0.5 to 3, convenient for storage and transportation. Ol, length 0.5
A cylindrical shape with a CI of 11 to 3.0 is preferred.

The pellet-shaped radioactive waste 17 thus granulated passes through a vibrating feeder 18 and is stored in a storage container 19. Drums can also be used as storage containers. When the pellet-shaped radioactive waste 17 is cooled on the vibrating feeder 18, a trough-type tunnel structure vibrating cooler equipped with a vibrating feeder can be used.

The pellet-shaped radioactive waste 17 thus granulated and filled into the storage container 19 is solidified into a solid package 20 in the process of the present invention shown in FIG.

The inorganic filling solidifying agent 21 used in the present invention is sent from the inorganic filling solidifying agent supply hopper 22 to the inorganic filling solidifying agent supply Ia 23 to the inline mixing 124, and from the water tank 25 to the inline mixer 24 via the water supply pump 26. It is mixed here with an appropriate amount of water.

The inorganic filling solidifying agent mixed with water is poured into the spaces 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 package 20. Form.

Note that simply injecting the inorganic filling solidifying agent leaves air bubbles in the inorganic filling solidifying agent, so it is desirable to vibrate the solidified package 20 using the vibrator 28 in order to remove these bubbles.

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

The physical property test was conducted according to J JSR52 Physical Test Method for Radioactive Waste Cement.

That is, each composition was mixed using a kneader for strength testing, and then packed in three layers in a mold with a diameter of 50 u% and a height of 100 nm, and each layer was compacted by poking 25 times with a punch rod.

After 24 hours, the mold was removed and cured in air for 7 days at a temperature of 20° C. and a humidity of 70%, and then the compressive strength was measured.

The underwater stability was determined by immersing the compressive strength specimen in water for 28 hours, and determining the presence or absence of swelling and destruction of the specimen.

In addition, thermal stability was determined by leaving the specimen used in the above compressive strength test in an electric furnace at 800°C for 6 hours, and determining the presence or absence of disintegration of the solidified filler. Table 1 shows the composition of the solidified filler. The properties of the solidified body are shown in Table 2. Note that 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 tests, it has sufficient strength even when dumped at sea or stored on land, and does not deteriorate in water or collapse due to high temperatures.
It has sufficient stability.

(The following is a blank space) Table 2 [Effects of the Invention] As explained above, according to the present invention, solid radioactive waste can be treated with alkali metal and/or alkaline earth metal oxides and/or Because it is solidified using an inorganic filling solidifying agent consisting of salt and water-soluble phosphate, we can create a solidified package that has excellent heat resistance and water resistance, and is chemically and mechanically stable for long-term storage. can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing a method for producing pellets according to an embodiment of the present invention, and FIG. 2 is a process diagram showing a method for producing a solid package according to an embodiment of the present invention. 1...Liquid or slurry radioactive waste 1a...Granular used ion exchange resin 1b...
...Dried radioactive waste 1C...Dried radioactive waste containing high moisture 2...
..... Stock solution supply tank 3 ..... Stock solution supply pump 4 ..... Dryer 5 ..... Inline crusher 6 ...・・・・・・
... Moisture meter 7 ... Return tank 8 ... Return pump 9 ... Storage tank 10 ...・Measurer 11...Binder composition 12...Binder hopper~13...
...Mixer 14...Mixture 15...Kneading and granulating machine 16...Cutter 17... ...Bellet-shaped radioactive waste material 18.
......Photo feeder 19...
・Storage container 20...Solid package 21...
...Inorganic filling solidifying agent 22...Inorganic filling solidifying agent supply hopper 23...Inorganic filling solidifying agent supply machine 24... ...Inline mixer 25...Water tank 26...Water supply pump 27...Water 28...・Photographer

Claims (1)

[Claims] (1) Solid radioactive waste generated at nuclear facilities contains (a) oxides and/or inorganic salts of alkali metals and/or alkaline earth metals, and (b) water-soluble phosphates. 1. A method for solidifying radioactive waste, comprising adding an inorganic filling solidifying agent comprising water together with water to solidify the radioactive waste. (2) The method for solidifying radioactive waste according to claim 1, wherein the inorganic salt of an alkali metal and/or alkaline earth metal is a carbonate or an aluminate. (3) The method for solidifying radioactive waste according to claim 1 or 2, wherein the alkali metal oxide and/or inorganic salt is hard-burned magnesite. (4) The method for solidifying radioactive waste according to any one of claims 1 to 3, wherein the water-soluble phosphate is ammonium phosphate. (5) The method for solidifying radioactive waste according to any one of claims 1 to 4, wherein the water-soluble phosphate is magnesium biphosphate. (6) The blending amount of the inorganic filler solidifying agent is as follows: 100 parts by weight of the alkali metal and/or alkaline earth metal oxide and/or inorganic salt in (a), and the water-soluble phosphate in (b) The method for solidifying radioactive waste according to any one of claims 1 to 5, characterized in that the amount of the radioactive waste is 30 to 200 parts by weight. (7) The method for solidifying radioactive waste according to any one of claims 1 to 6, wherein an inorganic filling solidifying agent is added to radioactive waste that has been pelletized in advance. (8) Solid radioactive waste generated at a nuclear facility is mixed with (a) 100 parts by weight of an oxide and/or inorganic salt of an alkali metal and/or alkaline earth metal, and (b) 30 parts by weight of a water-soluble phosphate. (c) an inorganic filling solidifying agent consisting of 1 to 100 parts by weight of a polyphosphate; and (d) 5 to 100 parts by weight of water per 100 parts by weight of this inorganic filling solidifying agent. 1. A method for solidifying radioactive waste, comprising: adding and solidifying the radioactive waste. (9) The method for solidifying radioactive waste according to claim 8, wherein the inorganic salt of an alkali metal and/or alkaline earth metal is a carbonate or an aluminate. (10) The method for solidifying radioactive waste according to claim 8 or 9, wherein the alkali metal oxide and/or inorganic salt is hard-burned magnesite. (11) The method for solidifying radioactive waste according to any one of claims 8 to 10, wherein the water-soluble phosphate is ammonium phosphate. (13) The method for solidifying radioactive waste according to any one of claims 8 to 11, wherein the water-soluble phosphate is magnesium biphosphate. (14) The method for solidifying radioactive waste according to any one of claims 8 to 13, wherein an inorganic filling solidifying agent is added to the radioactive waste that has been pelletized in advance.