JPH02222899A - Decontamination - Google Patents

Abstract

PURPOSE:To intend a simplification of a decontamination by using a sulfuric acid for the whole process, by carrying out an oxidization pretreatment with addition of a tetravalency cerium ion and by quenching an oxidativity by a redox reaction after completion of the oxidization pretreatment. CONSTITUTION:A decontaminant tank 1 and a decontamination object form a circulation route through a circulation pump 3 and reacting agents are added to a tank 1 from each oxidizer tank 5, hydrogen peroxide tank 6 and reductive decontaminant tank 7. With this constitution, a sulfuric acid is poured into the tank 1, for the first place, and the sulfuric acid is fed to the decontamination object 2 by a pump 3. At this moment, a temperature of the sulfuric acid is raised by a heater 4. Then, an oxidization pretreatment is carried out by an injection of an oxidative cerium into a system. After that, the hydrogen peroxide is injected from the tank 6 to treat residual oxidative cerium. A gas generated at the moment is treated through a quench tank 8. Finally, a reductive decontaminant is injected into the tank 1 to circulate through the system and therewith to carry out a post-decontamination.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for decontaminating equipment and piping in a nuclear facility.

(Prior Art) At nuclear facilities, radioactive materials adhere to equipment, piping, etc., and one worker is exposed to radiation during routine inspections or demolition of the nuclear power plant. Therefore, decontamination is being carried out as appropriate to remove these radioactive substances and reduce exposure.

Chemical decontamination methods include a concentrated decontamination method in which the concentration of the decontaminating agent is as high as several percent, and a dilute decontamination method in which the concentration of the decontaminating agent is low. In general, decontamination at nuclear power plants involves a large amount of iron oxide, so it is effective to use reducing decontamination agents on land. However, if the target to be decontaminated has a high chromium content, it is effective to pre-treat with potassium permanganate and then use a reducing decontamination agent. There is a track record. Oxidation pretreatment using potassium permanganate includes the AP method performed in alkaline conditions and the NP method performed in nitric acid acidity. Since this decontamination is applied to nuclear facilities in service, sufficient consideration has been given to corrosion and other issues to ensure that the functions of equipment and other equipment are not damaged after decontamination.

On the other hand, in decontamination related to reactor dismantling, the health of the equipment is not so important, and it is important to sufficiently clean the objects to be decontaminated through decontamination. Therefore, research is being carried out on methods such as electrolytic decontamination, which electrically dissolves materials such as equipment, and redox decontamination, which uses strong oxidizing ions without dissolving materials (Retozox decontamination).

(Problems to be Solved by the Invention) As mentioned above, if the oxide to be decontaminated contains a large amount of com, the decontamination effect is low with normal reducing chemical decontamination, so it is necessary to However, if oxidation pre-treatment is performed, pre-decontamination must be followed by acid pre-treatment and then post-decontamination.
Normally, reducing decontamination agents are used for surface decontamination and post-decontamination, so if oxidation 1rli treatment using an oxidizing agent is performed in between, chemicals must be added at each step. As a result, a large amount of waste liquid is generated. Therefore, the waste liquid treatment becomes large and complicated, and the equipment and operations must respond to changes in liquid properties such as changes in pI-1 and the type of acid in the decontamination liquid, making it time consuming and complicated. Become.

The present invention has been made in response to the above situation.

To reduce the amount of waste generated during decontamination in chemical decontamination requiring %PL before oxidation, to make the waste itself easier to treat, and to simplify decontamination operations and shorten the time required for it. The purpose is to

[Structure of the invention] (Means for solving problems) That is, the present invention includes pre-decontamination treatment and oxidation pre-treatment.

In a method for decontaminating equipment and piping that performs post-decontamination treatment sequentially, sulfuric acid is used throughout the entire treatment process, and pre-oxidation treatment is performed by adding tetravalent cerium ions to it.
The method is characterized in that after the completion of the oxidation 1VF treatment, the acid F arsenicity is eliminated by a redox reaction, and then a post-decontamination treatment is carried out by adding a post-decontamination treatment agent.

(Function) In the decontamination method of the present invention, a pre-decontamination treatment is first performed using sulfuric acid, and the next steps, oxidation 1 pre-treatment and post-decontamination treatment, are carried out sequentially without removing this sulfuric acid from the system. This is done by adding drugs.

Therefore, no waste liquid is generated in each process, and the type of acid does not change, so the decontamination and drying process is simplified throughout and the number of waste liquid generating groups is reduced.

The tetravalent cerium used in the oxidation pretreatment converts the trivalent chromium into 6
After the 9-acid acid treatment is completed, the remaining oxidized cerium is converted into oxidized cerium and disappeared. The method of the present invention eliminates the need to extract the oxidation pretreatment agent from the system as in the conventional method.However, since oxidizing cerium may dissolve not only the object to be decontaminated but also the f2 village, the method of the present invention does not require disassembly. It is desirable to use previous decontamination, N group where the material is not easily affected by cerium, or a small amount of material fR food for areas where there is no problem.

Reducing decontamination (post-decontamination) is performed after the oxidation pretreatment. This step is performed by adding a reducing decontamination agent to the decontamination solution as described above. The chromium in the object to be decontaminated becomes hexavalent through oxidation pretreatment, and while the object to be decontaminated is often eluted, the object to be decontaminated is easily decontaminated.
A high decontamination effect can be obtained for objects that are difficult to decontaminate and have a high com ratio. There are no particular restrictions regarding the selection of a reducing decontamination agent.

<Example> Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a flow sheet for explaining one embodiment of the present invention. The decontamination agent tank 1 and the decontamination target 2 form a circulation path via a circulation pump 3, and the decontamination agent tank 1 has an oxidizing agent tank 5. The configuration is such that chemicals are added from a hydrogen peroxide tank 6 and a reducing decontamination agent tank 7, respectively. 4 is a heater that heats the decontamination agent tank I.

Further, a quench tank 8 is connected to the decontamination agent tank 1.

Decontamination is carried out in the order of sulfuric acid pre-decontamination, cerium oxidation pre-treatment, and reducing post-decontamination. First, sulfuric acid is put into the decontamination agent tank 1, and the sulfuric acid is supplied to the decontamination target 2 by the circulation pump 3. At this time, the temperature of the sulfuric acid is raised by the heater 4. The concentration of sulfuric acid is determined based on the estimated amount to be dissolved in the object to be decontaminated, the volume of the object to be decontaminated, and the dissolving ability of the acid. Furthermore, the temperature conditions are determined based on the properties of the object to be decontaminated and the temperature conditions applicable to the system.

After the pre-decontamination with sulfuric acid is completed, oxidizing cerium (for example, ceric sulfate Ce (SO4
) A) is injected into the system and subjected to oxidation pretreatment.The cerium concentration is set in accordance with the estimated amount of chromium in the object to be decontaminated. Even if an excessive amount is added, the pretreatment effect will not be greatly improved, and the amount of waste 1A will increase.

The completion of the oxidation pretreatment is judged from the elution status of the amount of chromium in the decontamination solution.

After the oxidation pretreatment is completed, hydrogen peroxide is injected from the hydrogen peroxide tank 6 to treat the remaining cerium oxide. At this time, gas is generated due to the reaction with hydrogen peroxide, so the generated gas is processed from the decontamination agent tank 1 through the quench tank 8. Although a reducing agent other than hydrogen peroxide can be used to treat the residual cerium oxide, hydrogen peroxide is preferable because it does not increase the amount of waste even if the amount of water is increased.

Next, the reducing decontamination agent is injected from the reducing decontamination agent tank 7 into the decontamination agent tank 1 and circulated through the system to perform post-decontamination.The end of the post-decontamination is the elution of the radioactivity concentration and iron concentration. Judging from the situation.

A comparison of the above operations with conventional decontamination methods, AP method and NP method, is shown in the table below.

[Margins below] As is clear from the above table, in the AP method, the decontamination solution that is initially acidic changes to alkaline during pretreatment, and then changes back to acidic during post-decontamination. It is necessary to drain the decontamination liquid and inject a decontamination liquid with different properties each time. Therefore, the amount of waste liquid is also 2@ (if the same decontamination agent is used for pre-decontamination and post-decontamination) or 3 times that of the present invention. In addition, in order to exchange the solution, it is necessary to raise the temperature of the decontamination solution at each step, which requires a lot of time and energy.

In addition, in the NP method, oxidation pretreatment is performed with nitric acid acidity, but in nuclear power plants -a f! Since nitric acid cannot be used1, it is inconvenient in processing, and nitric acid is almost never used in pre-treatment or post-treatment9.Therefore, the oxidation pre-treatment liquid in the NP method must be treated with an ion exchange resin or waste liquid This causes the same inconvenience as the AP method.

On the other hand, in the method of the present invention, pre-decontamination, oxidation pre-treatment, and post-decontamination are carried out using sulfuric acid acidity, so there is no need to exchange the treatment solution in each step, and the process is simply oxidation pre-treatment with a cerium compound, residual cerium treatment, And post-decontamination treatment can be performed continuously by adding chemicals. Therefore, the method of the present invention eliminates the need for discharging the treatment liquid in each process and the accompanying cleaning process, resulting in a reduction in treatment time.Also, since a tank or the like is not required for the drained liquid receiver, the equipment can It takes shape. Furthermore, since there is no need to raise the temperature at each step, there is an effect of energy saving and a reduction in the amount of waste.

In addition, since the decontamination agent used throughout the entire process is sulfuric acid, this waste liquid treatment can be advantageously carried out by neutralization to sodium sulfate J4, which is the most common waste at nuclear power plants. .

[Effects of the Invention] As explained above, according to the decontamination method of the present invention, there is no need to replace the treatment solution many times as in conventional decontamination methods, so the decontamination process can be carried out using a bleaching process. It can be carried out quickly and in a short time, and it can also reduce the amount of waste liquid generated and save energy9.

[Brief explanation of the drawing]

The figure is a flow sheet showing one embodiment of the decontamination method of the present invention. 1...Decontamination agent tank 2...Decontamination target 3...Circulation pump 4...Heater 5...Oxidizing cerium tank 6...Hydrogen peroxide tank 7...Reducing decontamination agent tank 8...Quench Tank (8733) Agent Patent Attorney Yoshiaki Inomata (and 1 others)
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Claims (1)

[Claims] (1) In the decontamination method for equipment and piping that sequentially performs pre-decontamination treatment, pre-oxidation treatment, and post-decontamination treatment, sulfuric acid is used throughout the entire treatment process, and tetravalent cerium ions are added to this pre-oxidation treatment. Decontamination of equipment and piping is carried out by adding a post-decontamination agent, and after the oxidation pre-treatment is completed, the oxidizing property is eliminated by a redox reaction, and then a post-decontamination treatment is carried out by adding a post-decontamination treatment agent. Dyeing method.