JPS6227697A - Method and device for processing waste liquor containing radioactive substance - 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] <Industrial Application Field> The present invention is applicable to the treatment of radioactive substances such as waste liquid generated in the reprocessing and conversion process of spent nuclear fuel, and waste liquid generated in the refining and processing process of nuclear fuel materials. This is related to the decontamination treatment of various waste liquids contained.

<Conventional technology> Considering the case of removing plutonium, that is, decontaminating the nitric acid waste liquid containing plutonium generated in the plutonium nitrate conversion process, in the conventional method, this waste liquid is evaporated and concentrated in an evaporative concentration tank to remove solutes (plutonium content). ) is concentrated, a neutralizing agent such as caustic soda is added to precipitate plutonium in the form of hydroxide, a solid-liquid separation operation is performed, and then a coagulating precipitant such as ferric nitrate or a polymer flocculant is added. The so-called evaporation-neutralization-precipitation method is adopted, in which the solid-liquid separation operation is performed again after adding .

<Problems to be Solved by the Invention> However, in the conventional method as described above, the structural material of the evaporative concentrator used for heating and concentrating nitric acid waste liquid is exposed to a highly corrosive environment, which reduces the lifespan of the fruiting device. has no choice but to become shorter.

Furthermore, since a neutralizing agent and a flocculating precipitating agent are added, the amount of material to be processed increases as the process progresses. Roughly speaking, when waste liquid is heated and evaporated using evaporative concentration, the waste liquid becomes droplets when it boils and is entrained in the steam, so the solute (plutonium) migrates into the condensate of this steam, and as a result, Obtained decontamination coefficient (solute concentration or amount in pre-treatment solution/
The solute concentration or amount in the treated liquid is only about 10 to 105. Therefore, in order to bring the plutonium concentration to a level where the waste liquid can be released into the environment, it is necessary to repeat the above-mentioned treatment operation multiple times, which also has the disadvantage of increasing the number of process equipment and complicating the operation.

In addition, since the objects to be processed contain radioactive materials,
Process equipment must be installed in a glove box equipped with exhaust ventilation equipment, and operation and maintenance of these equipment must be performed indirectly. In particular, when replacing equipment, the entire glove box must be covered with a special enclosure, roughly called a greenhouse, and the workers must be equipped with special protective equipment, which generates a large amount of radioactive waste and requires a great deal of labor and cost. Is required.

Therefore, it is desired that the process equipment installed in the glove box is durable, has a simple structure, and is easy to operate and maintain.

Therefore, the present invention was made in view of the above-mentioned state of the prior art, and by eliminating the need for high-temperature processing operations such as evaporative concentration, it prevents corrosion of the equipment and improves its durability. To provide a method for treating radioactive substance-containing waste liquid that can increase the decontamination coefficient by eliminating the entrainment phenomenon caused by boiling of radioactive substances, does not require the addition of neutralizing agents, coagulating precipitants, etc., and is easy to operate. It is the purpose.

A further object of the present invention is to provide a radioactive substance-containing waste liquid treatment apparatus that is suitable for carrying out the above method, has a simple structure, and is easy to maintain.

<Means for Solving the Problems> In the present invention, instead of the evaporative concentration operation of the waste liquid in the prior art described above, the waste liquid is freeze-dried, and then only the solvent is sublimed to separate the solvent and the solute. This achieves the above objectives.

In other words, the method for treating radioactive material-containing waste fluid according to the present invention involves freezing the radioactive material-containing waste fluid and then heating it under vacuum to sublimate only the solvent, so that the solute consisting of the radioactive material remains as a dried product or a concentrated product. The sublimated solvent is cooled and recovered as a condensate.

Furthermore, the apparatus for treating radioactive substance-containing waste liquid according to the present invention includes a freezing/sublimation chamber that freezes the radioactive substance-containing waste liquid, heats the frozen material, and sublimates it, and a freezing/sublimation chamber that cools the sublimation component generated in the freezing/sublimation chamber. It is characterized by comprising a condensation chamber for condensation, a conduit for guiding the sublimated components generated in the freezing/sublimation chamber to the condensation chamber, and a device for evacuating the freezing/sublimation chamber and the condensation chamber. be.

<Embodiments> The present invention will be briefly described in detail below with reference to embodiments shown in the drawings.

The accompanying drawing shows an embodiment of the device according to the invention, which comprises a freezing and sublimation chamber 1, a condensation chamber 2 and a conduit 3 connecting these two constrictions in communication. frozen·
Inside the sublimation chamber 1 is a waste liquid containing radioactive substances (hereinafter referred to as “liquid to be treated”).
A tray 5 for receiving a tray 4 (named 4) is placed on a stage 6 for cooling and heating the liquid to be treated, and the liquid to be treated is supplied into the trays 1 to 5 from a liquid supply lower.

On the other hand, a trap 8 is installed in the condensation chamber 2 to cool and collect the sublimed components from the freezing/sublimation chamber 1, and a vacuum exhaust device 9 and a liquid recovery chamber 10 are also installed to condense the sublimated components. It communicates with room 2.

In the figure, reference number @11 is a heating device for heating the stage 6 in the freezing/sublimation chamber 1, and 12 is a freezing device for cooling the stage 6 and the trap 8 in the condensation chamber 2.

Next, the method of the present invention will be explained in detail while explaining the operation of this device. After the liquid to be treated containing radioactive substances such as nuclear fuel materials is supplied from the liquid supply lower into the freezing/sublimation chamber 1 1 to 5, the freezing device 12 is operated to cool the liquid to be treated and the liquid to be treated 4 is transferred to the tray 5. Freeze inside. In the case of process effluents from plutonium nitrate conversion facilities, the freezing temperature is close to 230'. On the other hand, the trap 8 in the condensation chamber 2 is also
Cool down. The lower the temperature of the trap, the higher the condensation recovery rate of the sublimed component, but in this example, the trap temperature is set to about 200°, which is lower than the above-mentioned freezing temperature.

Next, in this state, the evacuation of the inside of the condensation chamber 2 and the inside of the freezing/sublimation chamber 1, which is communicated with this through the conduit 3, is started by the evacuation device 9.

As the degree of vacuum in the system increases, only the solvent in the frozen object sublimates due to the difference in vapor pressure (sublimation pressure) unique to each of the solvent and solute in the liquid to be treated. This sublimated component is introduced into the condensation chamber 2 via the conduit 3 and is condensed and captured on the surface of the trap 8. As the frozen material in the tray 5 is deprived of sublimation heat due to sublimation, a corresponding amount of heat is supplied by the heating device 11 to maintain the temperature of the frozen material slightly lower than the freezing temperature.

When the sublimation component, that is, the solvent in the frozen material sublimates and disappears, only the solute in the frozen material remains in the tray 5 as a dry substance, the degree of vacuum in the system increases, and the heat removed by sublimation increases. As the heat of sublimation disappears, the temperature of the frozen material increases. Therefore, at the end of sublimation, two phenomena are observed: an increase in the degree of vacuum and an increase in the temperature of the frozen object. Naturally, if the operation is stopped while sublimation continues, a concentrate is obtained in which the solute is concentrated in the solvent.

In this way, solvents such as water and nitric acid in the liquid to be treated become sublimated components and condense in the trap 8, and can be collected and recovered in the liquid recovery tube 10, while solutes such as plutonium can be recovered as dry or concentrated substances. It can be collected while remaining in the tray 5.

Thus, according to the present invention, since the liquid to be treated is not boiled and evaporated, there is no entrainment phenomenon of solvent containing solutes into the vapor, and as a result, the liquid is collected in laps 1 to 8 in the condensation chamber 2. The amount of solute that migrates to the solvent is extremely small,
A high decontamination coefficient of 107 or higher has been obtained.

In order to further improve the decontamination performance, there is a method of inserting a filter 13 in the middle of the conduit 3 that connects the freezing/sublimation chamber 1 and the condensation chamber 2, or adding a binder to the liquid to be treated in advance. can also be considered.

Note that an electric heater, a heat medium, etc. can be used as the heating device 11, but the tray 5 may be made of a material such as silicon carbide that is easily heated by high frequency waves, or such a material may be used inside the tray to heat the high frequency waves. If applied, the liquid to be treated can be indirectly heated.

<Effects of the Invention> According to the invention as described above, the following effects can be obtained.

(1) Since the processing temperature of the liquid to be treated is low, below the freezing temperature, there is almost no corrosion or thinning of the structural materials of the equipment as in evaporative concentration equipment, which extends the life of the equipment and makes it possible to use high-quality corrosion-resistant materials. It also eliminates the need to use , which greatly contributes to cost reduction.

(2) Since sublimation is used to separate the solvent (water, nitric acid, etc.) and solute, there is no droplet entrainment phenomenon during boiling that occurs in evaporative concentration operations, and the decontamination coefficient is greatly improved. For example, while the decontamination coefficient obtained by the conventional evaporation concentration method is about 103 to 105, according to the present invention, a high value of 107 or more can be obtained.

(3) Since the sublimation of the solvent and the drying or concentration of the solute can be performed in the same device and high decontamination performance can be obtained, the waste liquid treatment process can be simplified.

(4) Even if flammable or explosive substances are mixed in the liquid to be treated, the low treatment temperature reduces the risk of fire or explosion and is highly safe.

(5) In the heating boiling type evaporation concentration method, it is impossible to increase the decontamination coefficient of thermally volatile elements (for example, ruthenium, etc.), but it is possible according to the present invention.

In the above explanation, this invention has been described as a method and apparatus for treating waste liquid containing radioactive substances. However, when the liquid to be treated, whether radioactive or non-radioactive, is frozen, there is The separation principle of the present invention can also be applied to the treatment of solutions where there is a difference in pressure (pressure), and could be used, for example, to remove and recover heavy metal components in plating waste liquid.

[Brief explanation of the drawing]

The accompanying drawings are explanatory views showing embodiments of the apparatus of the present invention. DESCRIPTION OF SYMBOLS 1... Freezing/sublimation, 2... Condensation palm, 3... Conduit, 4... Liquid to be treated, 5... Tray, 7... Liquid supply port, 8... Trap, 9...Vacuum odor evacuation device.

Claims (1)

[Scope of Claims] 1. Recovery of solutes consisting of radioactive substances as a dry substance or concentrate by freezing radioactive substance-containing waste liquid and then heating it under vacuum to sublimate only the solvent. At the same time, the sublimated solvent is cooled and recovered as a condensate. 2. A freezing/sublimation chamber that freezes radioactive material-containing waste liquid and heats and sublimates the frozen material; a condensation chamber that cools and condenses the sublimed components generated in the freezing/sublimation chamber; 1. An apparatus for treating radioactive substance-containing waste liquid, comprising a conduit that guides the generated sublimated component to the condensation chamber, and a device that evacuates the freezing/sublimation chamber and the condensation chamber.