JPH0150878B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for cementing radioactive waste generated from facilities such as nuclear power plants. Conventional methods for cementing and solidifying radioactive waste include 1) a method of directly mixing and solidifying liquid radioactive waste with cement, and 2) a method of granulating dry radioactive waste and then mixing and solidifying it with cement. However, in method 1, the target waste is essentially limited to concentrated waste liquid; when solidified cement is dumped into the ocean, radioactive materials leached from the solidified solidified material and the swelling of the solidified material due to water absorption is significant; There are disadvantages such as the volume reduction rate is large and the volume of the solidified material is larger than that of the waste. The volume reduction rate here refers to the value shown in the following formula, and a good volume reduction rate means that this value is small. Volume reduction rate = Volume of solidified material / Volume of waste before drying Volume of waste before drying; For waste liquid, the volume is equivalent to 80% moisture, and for used ion exchange resin and filter sludge, the volume is equivalent to 50% moisture. It is. In addition, in method 2, the particles that can be granulated are, for example,
Concentrated waste liquid is the only radioactive waste from BWR nuclear power plants; the main component of concentrated waste liquid, sodium sulfate, is expressed as follows: Na ₂ SO ₄ +10H ₂ O→Na ₂ SO ₄・10H ₂ O (specific gravity: 2.70 ) (Specific gravity: 1.46) Because of the reaction, sodium sulfate leaches out and swells with water even after cement solidification, resulting in embrittlement of the solidified material, making it impractical. Therefore, an object of the present invention is to provide a method for solidifying radioactive waste that eliminates the various drawbacks of the conventional methods. The present inventors have discovered that by solidifying dry waste in the form of particles using a specific binder and solidifying the thus obtained granules with cement, an excellent solidified product free of the drawbacks of conventional methods can be obtained. They discovered this and completed the present invention. That is, in the present invention, radioactive waste in the form of a solution or slurry is dried, mixed with a binder made of a rubber-like elastic polymer at a temperature of 30 to 120°C, kneaded or sintered, and made into particles. This is a method for solidifying radioactive waste, which is characterized by mixing granular materials with cement and solidifying them. The rubber-like elastic polymer used as a binder in the method of the present invention is a polymer substance usually called an elastomer, and it exhibits rubber-like elastic behavior in a physical sense and chemical properties (crosslinking) within the operating temperature range. refers to a group of substances that have the ability to react
In the method of the present invention, it is particularly preferable to use among the above-mentioned materials those having a Young's modulus of 5 to 500 kg/cm ² . Some types of plastics exhibit Young's modulus values within the above range due to their amorphous nature or chlorination ratio; for example, chlorinated polyethylene (chlorinated polyethylene), which is usually treated as a thermoplastic resin. has a chlorine content of 30-40%
The crystalline one is plastic-like, but the amorphous one has rubber-like elasticity and can be used as a binder in the method of the present invention. 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, isobutylene, butyl rubber, chlorinated polyethylene, ethylene-propylene copolymer elastomer, etc.;
Butadiene-based synthetic rubbers, such as butadiene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, methylbutadiene, chloroprene, styrene-butadiene-acrylonitrile copolymer, and the like. In addition to this, urethane 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, the rubber-like elastic polymer alone has a higher contamination rate of waste than thermoplastic resins and thermosetting resins, and can be used as a binder as it is, but dioctyl phthalate can convert waste into a rubbery form. When used together when filling an elastic polymer,
It is particularly preferable to add it because it allows the rubber-like elastic polymer to be highly filled with dry waste without reducing the compressive strength of the resulting pellets. In addition, a plasticizer such as liquid rubber, such as nitrile rubber, and a lubricant such as lead stearate can be added. Particularly in the case of chlorinated synthetic rubber, it is preferable to add a stabilizer such as tribasic lead sulfate. These additives are common plasticizers, lubricants, and stabilizers in synthetic rubber, and their preferred blending ratio is 10 to 50% by weight of plasticizer and 0.5 to 2% by weight of lubricant to the rubbery elastic polymer. and 5~
20% by weight stabilizer. According to the method of the present invention, it is possible to completely solidify waste liquids and slurries generated from facilities such as nuclear power plants, and the following wastes are subject to the method of the present invention. (a) Spent ion exchange resin There are two types: one with a particle size of approximately 0.5 mm/φ and the other with a powder called Powdex (product name), which is used to purify reactor water in a boiling water reactor (BWR). systems, condensate desalination systems, fuel pool water desalination systems, radioactive waste liquid treatment systems, etc., and in pressurized water reactors (PWRs), bypass purification systems (purification desalination, deboronization), fuel pit desalination, extraction coolant treatment, etc. Each occurs in various systems. (b) Concentrated waste liquid Refers to chemical waste liquid (resin recycling waste liquid, etc.) that has been evaporated and concentrated.The water content is around 80%, and it contains Na ₂ SO ₄
(sodium sulfate or sulfate) is the main component. (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. _{Fe2O3 _}
is the main component. (d) Filter sludge Occurs from equipment drains, floor drains, etc. The main ingredient is a pulp-like fine powder filter aid. (e) Incineration ash Emitted from the incinerator. (f) Laundry waste liquid is generated when workers wash contaminated clothing. The process of drying radioactive waste in the form of a solution or slurry and granulating it using a binder in the method of the present invention will be explained with reference to FIG.
FIG. 1 is a process diagram for explaining the work of drying and granulating liquid radioactive waste. A solution or slurry containing radioactive waste generated at a nuclear power plant or the like is 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 crush the resin particles in a slurry state. You can also do that. Dryer 4 converts the waste solution or slurry with a concentration of 5 to 20% by weight into a moisture content of 5% by weight.
It is preferable to use the following methods, such as a thin film dryer or a drum type dryer. A moisture meter 5 checks whether the waste dried in the dryer has reached a predetermined moisture content. High moisture content dry waste that has not been dried to a predetermined moisture content is returned to the return tank 6 and diluted with water, then discharged from the system by the return pump 7 and returned to the stock solution supply tank 1. The waste dried to a predetermined moisture content is once stored in a storage tank 15 and then periodically transferred to a scale 8. On the other hand, a binder containing a rubber-like elastic polymer and an additive is also supplied from the binder hopper 9 to the meter. The dry waste and binder are weighed in predetermined weight proportions and allowed to fall naturally into the mixer 10.
The mixing ratio (weight ratio) of dry waste/binder varies depending on the type of waste, but it is 3/1 to 8/1 for concentrated waste liquid and incineration ash, and for used ion exchange resin and filters. 1.5/1 to 4/1 in Suratji
It is. The mixture of dry waste and binder thoroughly mixed in the mixer is then granulated in a kneading and granulating machine 11. At this time, the rubber-like elastic polymer is kneaded at a temperature of 30 to 120°C, preferably 40 to 120°C, without being melted.
heated to 100°C, more preferably 50 to 60°C,
Usually, in the mixing machine or kneading/granulating machine 11, the temperature of the kneaded material is raised to 50 to 60 DEG C. by frictional heat, so that heating of the kneaded material can be achieved without particular external heating. In the illustrated granulation process, the cutter 12 performs granulation. The shape of the granulated particles is preferably cylindrical, with 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. The particles thus granulated are stored in a storage pit 14 through a vibrating feeder 13. Drums can also be used as storage pits. When cooling the granules on a vibrating feeder, a vibratory cooler equipped with a vibratory feeder having a trough-type tunnel structure can be used. The dried waste granules thus obtained are then solidified using a cement solidifying agent (see Figure 2). Granules 2
4, solidifying material 23, water, and if necessary, gravel etc. are mixed by an out-drum mixing method.After these are thoroughly mixed in an out-drum mixer 21, they are filled into a drum can 22. As the solidifying material, for example, cement such as Boltland cement is used. In the obtained cement solidified body, cylindrical granules 24 are randomly packed in an arbitrary direction. The preferred mixing proportions of the granules, cement solidifying agent, water and, if necessary, gravel are shown in the table below.

[Table] Granular material

Claims (1)

[Claims] 1. Dry radioactive waste, mix, knead, or sludge with a binder made of rubber-like elastic polymer at a temperature of 30 to 120°C to form particles, and mix the resulting granules with cement to solidify. A method for solidifying radioactive waste into cement, characterized by: