JPH03115896A - Processing method for solidification of radioactive waste - Google Patents

Abstract

PURPOSE:To enable solidification of a large amount of radioactive waste with a small amount of binder by mixing or kneading the waste being dried and a rubber-form elastic macromolecular substance at a temperature of 30 to 120 deg.C. CONSTITUTION:A rubber-form elastic macromolecular substance which is the main constituent of a rubber-form elastic macromolecular binder used in the present method is macromolecules being usually called elastomer, and it is preferable to use the ones of Young's modulus 5 to 500kg/cm<2>, in particular. In more detail, a natural rubber derivative of natural rubber, rubber hydrochloride or the like, synthetic rubber of olefin, e.g. isoprene rubber, isobutylene rubber, butyl rubber or ethylene-propylene ternary rubber, or synthetic rubber of butadiene, e.g. butadiene rubber or butadiene-styrene rubber, can be used, for instance. According to the present method, waste can be mixed in more amount only with the rubber-form elastic macromolecular substance than with thermoplastic resin or thermosetting resin.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for solidifying radioactive waste generated from nuclear power plants and the like.

Traditionally, the conventional method of solidifying radioactive waste has been to homogeneously solidify radioactive waste with cement, asphalt, or plastic, but currently, no decisions have been made by administrative agencies regarding the final disposal method, It is difficult to say that a sufficient solution has yet been reached as to whether or not radioactive waste will be able to comply with any regulations that may be imposed in the future. Furthermore, these conventional methods have drawbacks and difficulties in volume reduction, mechanical strength, combustibility, etc., which will be described later, in addition to being compatible with the final disposal method.

Recently, a method has been developed in which dry waste is pulverized and stored as an interim storage method until a future final disposal method is determined.

Although this treatment method is excellent from the viewpoint of adaptability to final disposal, it has drawbacks such as limited selectivity of waste.

The present inventors have researched treatment methods taking into consideration the adaptability to the final disposal regulations for radioactive waste that will be decided in the future, and have developed a new and useful treatment method by overcoming the drawbacks of conventional waste treatment methods. Through this development, we have completed the present invention.

The advantages and disadvantages of the prior art are as follows.

1) Cement solidification method: Solidified radioactive waste has high mechanical strength and specific gravity and is nonflammable, but has poor volume reduction (
(Volume reduction rate Z2) There is a drawback that the target waste is limited.

The volume reduction rate here refers to the value shown in the following formula, and a good emptied weight means that this value is small.

Volume of waste before drying: Waste liquid has a volume of 80% water, and used ion exchange resin and filter slange have a volume equivalent to 50% water.

2) Asphalt solidification method: Good volume reduction property (volume reduction rate zO
13-0.5) It has excellent water resistance, but has low mechanical strength and is easily flammable, so the target waste is limited.

3) Plastic solidification method: A recently developed method for solidifying radioactive waste. Depending on the type of solidification material, there are two methods: a melt solidification method that uses thermoplastic resin as the solidification material, and a melt solidification method that uses thermosetting resin as the solidification material. There is a polymerization solidification method.

In all of these methods, plastic as a solidifying material is mixed with waste in a fluid state (molten or liquid), and the solidifying material is hardened by cooling, using a catalyst, or heating to form a solidified body. This plastic solidification method has the following drawbacks: i) Waste mixture rate required to satisfy physical properties such as mechanical strength required for solidified radioactive waste = weight of dry waste / solidification material The weight of is at most 1.
5/1 or less, which is still insufficient for the solidification treatment of radioactive waste, which requires good volume reduction; 11) When using thermoplastic resin, a heating melting temperature of around 200°C is required. Furthermore, when a thermosetting resin is used, heat is generated during curing, and the temperature usually rises to about 120°C.

Therefore, such heating or heat generation may cause decomposition or foaming of the waste, and the method of cooling the obtained high-temperature solidified material is difficult, and cavities or cracks may occur in the solidified material during cooling. ; iii) When it is desired to apply the granulation treatment of radioactive waste that has been carried out in recent years, it is necessary to use plastics in a molten or liquid state in both the melting and solidifying methods using thermoplastic resins and the polymerizing and solidifying methods using thermosetting resins. Since it is mixed with waste, granulation requires a complicated process. Furthermore, if the plastic is pulverized after hardening, the resulting solidified material must be pulverized, which is extremely uneconomical.

4) Direct granulation method of dry waste - Good volume reduction (volume reduction type piece 0.1), but has some drawbacks in terms of safety. For example, (a) mechanical strength is low and particle surface is This results in peeling.

(b) There is scattering of dust.

(c) The scope of target waste is narrow.

As mentioned above, all of the conventional technologies have advantages and disadvantages, and they satisfy all of the requirements of volume reduction, specific gravity, mechanical strength, combustibility (fire resistance), weather resistance/radiation resistance, and waste selectivity. Such radioactive waste solidification methods have not yet been perfected.

The present invention aims to provide a method for solidifying radioactive waste that solves all of the above-mentioned drawbacks of the prior art, such as poor volume reduction properties, low mechanical strength, and limited selectivity of target waste. It has been done.

That is, in the present invention, dry radioactive waste and rubber-like elastic polymers (excluding chlorinated polyethylene) are
This method of solidifying radioactive waste is characterized by mixing, kneading, or kneading at a temperature of 120°C.

The solidified material in the form of particles obtained by the method of the present invention can be further solidified with a conventional solidifying material, thereby doubly containing radioactive waste. According to the method of the present invention, it is possible to completely solidify waste liquid and slurry generated from facilities such as nuclear power plants, and the target wastes of the method of the present invention include the following.

(a) There are two types of used ion exchange resin particles: granular ones with a diameter of approximately 0.5 m/mΦ, and powdered ones called powderex (product name). In water purification systems, condensate desalination systems, fuel boule water desalination, radioactive waste liquid treatment systems, etc., and in pressurized water reactors (PWRs), bypass purification systems (purification desalination, deboronization), fuel bit desalination, extraction cooling. These occur in material processing systems, etc.

(b) Concentrated waste liquid Refers to the evaporation and concentration of chemical waste liquid (resin regeneration waste liquid, etc.), the water content is around 80%, and the main components are Na and S Os (sodium sulfate or sulfur sulfate).

(c) Waste liquid containing corrosion products generated from equipment and piping (referred to as crud) Generated from equipment and piping that come into contact with fluids. The main component is FezOz.

(d) Filter sludge resulting from filtration of equipment drains, floor drains, etc. The main ingredient is a bulb-shaped fine powder filter aid.

(e) Incineration ash Exit the incinerator.

(f) Laundry waste liquid Occurs when workers wash contaminated clothing.

The binder used in the method of the present invention is mainly composed of a rubber-like elastic polymer, and if necessary, conventional plasticizers, stabilizers, and lubricants are further added. Although the polymer alone can be used as a binder, a binder in which a rubber-like elastic polymer is blended with a plasticizer and a lubricant gives particularly excellent results.

The rubber-like elastic polymer, which is the main component of the rubber-like elastic polymer binder used in the method of the present invention, is a polymeric substance usually called an elastomer, and is a polymer substance that is a rubber in the physical sense within the operating temperature range. It refers to a group of substances that have elastic behavior and chemical substances (capable of crosslinking reaction), and in the method of the present invention, among the above substances, materials with a Young's modulus of 5 to 500 k are used.
It is preferable to use one with g/C11l.

Examples of rubbery elastomeric polymers that can be used as binders in the method of the invention are natural rubbers and synthetic rubbers, more specifically the following: natural rubbers, hydrochloric acid rubbers, etc. Derivatives: Olefin-based synthetic rubbers such as isoprene rubber, isobutylene rubber, butyl rubber, ethylene-propylene ternary rubber, etc. (homopolymer resins of ethylene and propylene, copolymers of ethylene and other vinyl compounds, α-olefins, etc.) Polyolefin resins such as copolymer resins of propylene and ethylene or α-olefins do not have rubber-like elasticity and are therefore not included in the rubber-like elastic polymers of this application.): Butadiene-based synthetic rubbers For example, butadiene rubber, butadiene -Styrene rubber, butadiene-acrylonitrile rubber, methylbutadiene rubber, chloroprene rubber, styrene-butadiene-acrylonitrile rubber, etc. In addition to this, polyurethane rubber, silicone rubber, etc. can also be used. These rubber-like elastic polymers can be used alone or in combination.

According to the method of the present invention, more waste can be mixed with the rubber-like elastic polymer alone than with thermoplastic resins or thermosetting resins. Furthermore, in the method of the present invention, dioctyl phthalate can be used as an additive if necessary. When filling a rubber-like elastic polymer with waste, this dioctyl phthalate has the effect of highly filling the rubber-like elastic polymer with dry waste without reducing the compressive strength. This effect was first recognized by the present inventors. Note that if dioctyl phthalate and polyolefin resin are used together as additives, the above-mentioned effects of dioctyl phthalate will not be exhibited effectively, so if dioctyl phthalate is to exhibit the above-mentioned effects, it is best to avoid using dioctyl phthalate and polyolefin resin together. desirable. In the method of the present invention, in addition to dioctyl phthalate, plasticizers such as liquid rubber such as nitrile rubber, lubricants such as lead stearate, stabilizers such as tribasic lead sulfate, etc. Additives such as agents, lubricants, stabilizers, etc. can be added.

The preferred proportions of these components are 10 to 50% by weight of plasticizer, 0.5 to 2% by weight of lubricant, and 5 to 20% by weight of stabilizer based on the rubbery elastic polymer.

Embodiments of the method of the present invention will be described with reference to process diagrams.

A solution or slurry containing radioactive waste generated at a nuclear power plant or the like is first stored in a stock solution supply tank (1) and then guided to a dryer (4) by a stock solution supply pump (2).

Granular used ion exchange resin is difficult to dry as it is, so in order to improve the performance of the dryer, an in-line crusher (3) is installed between the stock solution supply pump and the dryer to grind the resin particles in a slurry state. It can also be crushed. The dryer (4) is preferably one that can reduce the water content of a waste solution or slurry having a concentration of 5 to 20% by weight to less than 5% by weight, such as a thin film dryer or a drum type dryer. The waste dried in the dryer is checked by a moisture meter (5) to see if it has reached a predetermined moisture content. High moisture content dry waste that has not been dried to the specified moisture content is stored in a return tank (
After being diluted with water, it is discharged to the outside of the yarn by a return pump (7) and returned to the stock solution supply tank (1).

The waste that has been dried to a specified moisture content is temporarily stored in a storage tank (15
) and then periodically transferred to a weighing machine (8). On the other hand, a rubber-like elastic polymer binder, which is a mixture of a rubber-like elastic polymer and optionally added additives, is also supplied to the meter from the binder hopper (9). That is, after weighing the dry waste, a rubber-like elastic polymer binder is added to the dry waste and weighed to a predetermined weight ratio, and then allowed to fall naturally into the mixer (10). The mixing ratio (weight ratio) of dry waste/rubber-like elastic polymer binder varies depending on the type of waste, but in the case of concentrated waste liquid, incineration ash, and used ion exchange resin, it is 3/1 to 8/1. and for filter sludge, it is 1.5/1 to 4/1.

The mixture consisting of the dry waste and the rubber-like elastic polymer binder thoroughly mixed in the mixer is granulated in the next kneading and granulating machine (11). At this time, the kneaded material is not melted and is
The kneaded material is heated at 120°C, preferably 40 to 100°C, and more preferably 50 to 60°C, but usually in a kneader or kneading granulator (11), the kneaded material is heated to 50 to 60°C due to frictional heat.
Since the temperature is raised to , heating of the kneaded material can be achieved without particular external heating.

In the illustrated granulation process, granulation is performed by a cutter (12). The granulated particles have a diameter of 0, which is convenient for storage and transportation.
．． 5-3. 0cm, length 0.5~3. A cylindrical one with Qc+i is preferable. The particles thus granulated pass through a vibrating feeder (13) and are stored in a storage pinto (14). Drums can also be used as storage bins. When cooling the granules on a vibrating feeder, a vibratory cooler equipped with a vibrating feeder having a trough-type tunnel structure can be used.

Alternatively, instead of the kneading and granulating machine, the mixture may be kneaded using a kneading extruder or a Banbury type kneading machine, and then placed in a container such as a drum for solidification.

The radioactive waste particles obtained in this way can be stored for an intermediate period of time, and after storage, the particles can be heated to 30 to 120 degrees Celsius to soften them and then reformed into blocks, or the particles can be solidified as they are with other solidifying materials. You can also

During granulation, the particle filling rate in a storage pint or drum can be increased by using two or more hole diameters in the granulation die to produce particles with different particle sizes. That is, the particle filling rate can be increased by mixing two or more types of particles that have the same particle shape but different particle sizes. In reality, it is preferable to form 2.3 types of particle groups and set the size ratio of adjacent particles to 1/2 to 115. In addition, the weight ratio of large particles to small particles that should be adjacent to them is 5/1 to 30/
It is 1.

When the kneaded product of dried waste and rubber-like elastic polymer binder composition produced by the method of the present invention is microscopically examined, the binder forms countless rubber-like fiber lattices, and within this lattice, the waste particles are finely powdered. appears to be strongly contained. Therefore, a large amount of waste can be solidified with a small amount of binder, and the weight ratio of dry waste/binder is 2 to 5 times higher than that in conventional plastic solidification. Furthermore, according to the method of the present invention, the kneading operation of the dry waste and the rubber-like elastic polymer binder composition does not require high temperatures (200°C) for melting, which is required in the case of plastic solidification, but at most 120°C. Usually 50-6
There is an advantage that the required operating temperature can be obtained at 0° C. by spontaneous heat generation due to mixing, and the granulation operation can be easily carried out by simply cutting the mixture obtained by mixing with shear force.

The present invention will be explained in more detail with reference to the following examples.

Example 1 100 parts by weight of urethane rubber was mixed with 800 parts by weight of dried waste (moisture 1% or less) of concentrated waste liquid from nuclear power plants (
tri-blend) and the mixture was kneaded in a twin-screw type kneader heated to 120'C. The kneaded product is extruded into a strand shape (rod shape) using a single screw extruder heated to 60°C, and at the exit of the extruder,
A cylindrical pellet was formed using a cutter.

The dimensions of this pellet are 15 mm in diameter and 15 mm in length. The specific gravity of this pellet is 2.3 and the compressive strength is 1000.
kg/ctA, and the volume reduction rate was 0.12.

Comparative Example l Commercially available thermoplastic polyethylene (density 0.9
2g/cm') was melt-kneaded with 1000g of the concentrated waste liquid dry waste of Example I in a twin-screw kneading extruder heated to 160°C, and the mixture was cooled to obtain a solidified product. The specific gravity of this solidified body is 1.35, and the compressive fracture strength is 260 K.
g/cIfl, the volume reduction rate was 0.36.

Comparative Example 2 The same procedure as in Comparative Example 1 was carried out except that 1000 g of used ion exchange resin dry waste (granular resin: water content of 1% or less) from a nuclear power plant was used as the dry waste. The obtained solidified material had a specific gravity of 1.05, a compressive breaking strength of 280 kg/cm, and a volume reduction rate of 0.95.

From the results of Example 1 and Comparative Examples 1 and 2, it can be seen that the solidified material obtained by the method of the present invention is much superior to the Comparative Examples in terms of compressive fracture strength and volume reduction rate.

[Brief explanation of drawings]

The drawings are process diagrams for explaining embodiments of the method of the present invention. Codes in the figure: 1... Stock solution supply tank, 2... Stock solution supply pump, 3... Pulverizer, 4... Dryer, 5
・・・Moisture meter, 6...Return tank,・
...Return pump, ...Binder hopper...Pelletizer, ...Vibration feeder...Storage tank. 8... Measuring device, 10... Mixer, 12... Cutter 4... Storage bit,

Claims (1)

[Claims] A method for solidifying radioactive waste, which comprises mixing, kneading, or kneading dried radioactive waste and a rubber-like elastic polymer (excluding chlorinated polyethylene) at a temperature of 30 to 120°C.