JP2509654B2 - Chemical decontamination waste liquid treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a method for treating a chemical decontamination waste liquid for radioactive contamination equipment and piping in a nuclear power generation facility.

(Prior Art) Workers may be exposed to radiation in a nuclear power plant due to the deposition of radioactive materials on equipment and piping. Therefore,
Chemical decontamination is performed as a means of removing these radioactive substances and reducing exposure.As a treatment method for waste liquid generated by this chemical decontamination, decontaminating agents are used when the decontaminating agent concentration is as high as several%. When the decontamination agent concentration is low, the decontamination waste solution is treated with an ion exchange resin.

(Problems to be solved by the invention) By the way, the chemical decontamination currently performed in Japan is a small scale, but if it is carried out on a large scale in the future, some problems will occur.

FIG. 2 is a system diagram of waste liquid treatment of the Dresden method, which is a typical treatment method of the concentrated chemical decontamination treatment method. In the figure, the decontamination waste liquid is collected in the collection tank 21 and then the concentrator 22
Is concentrated in. The concentrated waste liquid is transferred to the concentrated waste liquid receiving tank 26 and then solidified by the solidification device 27. The solidified product is placed in a drum can and stored in the drum can storage 28. The solidified material contained in the drum has a high level of radioactivity and a very high dose. Moreover, there is a problem that the number of drums is large. The condensate of the concentrator 22 is cooled by the cooler 23.
It is cooled by and is guided to the condensation tank 24, and further desalination tower 25
It is desalted to form a clean liquid with no radioactivity and released to the waste treatment system.

The Dresden method described above was implemented at Unit 1 of the Dresden Power Plant in the United States, but its waste liquid treatment facility is larger than the main waste building of the power plant, so it is costly, and as a future decontamination treatment method Hard to say.

FIG. 3 is a system diagram of the waste liquid treatment of the CANDECON method, which is an example of the dilute decontamination waste liquid treatment method. In the figure, equipment to be decontaminated
30 The decontaminated waste liquid is cooled by the cooler 34, passes through the anion resin tower 32 and the cation resin tower 33, and again passes through the decontaminating agent tank 31.
Is returned to. In the anion resin tower 32, a large amount of decontaminating agent or the like is collected with a low dose. In the cation resin tower 33, a high dose of radioactive material is recovered. This CANDECON
This method is troublesome because the method produces ion exchange resin as secondary waste.

FIG. 4 is a system diagram of the waste liquid treatment of the LOMI method which is another example of the dilute decontamination waste liquid treatment method. The LOMI method shown in Fig. 4 is also described above.
Processing similar to the CANDECON method is performed. That is, the waste liquid decontaminated by the decontamination target device 30 collects the anion component of the decontamination agent by the anion resin tower 32, and also the radioactivity and the decontamination agent cation component (high concentration and low level) by the cation resin tower 33. However, as with the CANDECON method, ion-exchange resin is generated as secondary waste, so this process is extremely troublesome.

Since the above-mentioned CANDECON method and LOMI method have a drug concentration of 1% or less, they are adsorbed on an ion-exchange resin to simplify the processing equipment. Further, since the radioactivity is confined only in the ion exchange resin, the exposure during the work can be reduced by shielding only around the ion exchange resin.
This treatment method is easy to carry to the disposal site,
It is popular in the United States. However, in Japan, there is no facility for storing radioactive waste in the form of an ion exchange resin, and since the cleaning waste liquid contains a chelating agent, it is desired to stabilize these. Currently, the final form of waste is recognized as solidified cement or solidified plastic, and it is a good idea from the viewpoint of reducing the amount of waste to make the ion exchange resin into such solidified form. I can't say.

Conventional chemical decontamination agents have been formulated to efficiently dissolve and remove radioactive corrosion products without impairing the soundness of structural materials. In particular, the requirements for material soundness are strict and satisfy this performance. The drug is formulated as follows.

Then, the problems in treating the chemical decontaminating agent as described above with the waste liquid are listed below.

(1) A large amount of chemicals is required stoichiometrically to dissolve and remove the iron rust scale radioactive corrosion products adhering to the pipes and equipment.

(2) Since the product of the liquid ratio and the concentration is proportional to the scale amount per unit area, the amount of chemicals used is extremely large. For this reason, when solidification of cement, which is a normal radioactive waste treatment, is performed,
Due to the drug, the filling amount is small and the solidified amount is necessarily very large. The same applies to plastic solidification and asphalt solidification, and the amount of solid waste is large.

(3) The chemicals include scale components, components that dissolve radioactive components, components that decompose dissolved substances, components that suppress corrosion of materials, etc., and there are many chelate-based chemicals, and the amount of waste liquid itself If the waste liquid is treated as it is because of the large amount, a large reactor is required to decompose these chemical cleaning agents.

(4) It is necessary to treat the decontamination waste liquid with a device that is as simple as possible and has a large single unit throughput, and divide it into a large amount of low-efficiency waste liquid and a small amount of high-concentration waste liquid. A small amount of high-concentration waste liquid is concentrated with chemicals, especially organic acid scale components, and also with scale components and radioactive components. If the chelating agent is acidic and concentrated, it will precipitate due to its solubility. When neutralized, the solubility of the chelating agent increases and does not precipitate, but when the chelating agent is decomposed, scale components and radioactive components precipitate in the neutral region as the chelating agent decomposes. Since inorganic substances are used for neutralization, the amount of secondary waste generated increases.

(5) In order to decompose the chelating agent and the organic acid in the neutral region into inorganic scale components and radioactive components, there are only treatment methods such as incineration soot calcination, calcination, and thermal decomposition.
Further, since the chelating agent stabilizes the radioactive component, it cannot be electrolyzed or electrodeposited.

(6) In the process of separating a large amount of low-concentration waste and a small amount of high-concentration waste, either evaporative concentration or reverse osmosis membrane treatment is effective for the waste liquid. From above, it is treated as alkaline or neutral to obtain a relatively high-purity distillate, which is sent to the waste treatment system, where the concentrated liquid is treated as a highly concentrated waste liquid.
The evaporative concentrator has problems such as large mechanical equipment and large heat source with respect to processing capacity, and it is difficult to make temporary equipment. Even if the concentrated solution is treated, it becomes strongly alkaline with organic acid decomposition, so a step of neutralizing with an acid is required, and scale components and radioactive components are precipitated, and the precipitation is bulky and the water content is high. High, very difficult to handle and difficult to handle. Also, it cannot be sent to the waste treatment system due to its high salt concentration. Therefore, when the neutralization or alkaline concentration treatment is performed, there is no precipitation at that point, but the concentration treatment time becomes a problem. The same can be said for the reverse osmosis membrane treatment.

The present invention has been made in view of the above circumstances, and an object thereof is to reduce the final waste amount of waste liquid generated by chemical decontamination to form a small amount of stable solidified body, and to generate a large amount of low-level waste liquid in a nuclear power plant book. An object of the present invention is to provide a chemical decontamination waste liquid treatment method that can be treated by an installed treatment device.

[Means for Solving the Problems] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for treating a chemical decontamination waste liquid generated in a nuclear power generation facility, wherein a concentrated chemical of the chemical decontamination waste liquid is used. The decontamination waste liquid is separated into treated water and concentrated liquid by a reverse osmosis membrane device, sulfuric acid and hydrogen peroxide are added to the concentrated liquid, and the chemical decontaminating agent components are decomposed by heating to several tens of degrees Celsius or more, and then It is characterized in that a radioactive component and a metal component of iron rust are electrodeposited and recovered from the chemical decontaminating agent decomposition solution, and the recovered product is stored in a shielded cask.

(Operation) According to the chemical decontamination waste liquid treatment method of the present invention, the construction period in the decontamination work can be shortened, so that the exposure during the waste liquid treatment can also be reduced. In addition, the amount of waste generated by decontamination can be reduced and stable storage of waste can be achieved, so that the cost of decontamination waste disposal can be reduced.

Generally, if the chemical decontamination waste liquid is divided into a drug and a scale component, and a non-radioactive drug is released to solidify only the scale, the secondary waste becomes extremely small. Even if the liquid obtained by separating radioactive components from the waste liquid containing non-radioactive drug is not released, it can be processed by the existing waste treatment system, and a small amount of waste liquid containing radioactive components can be treated alone or discarded. The treatment with the material treatment system greatly simplifies the waste liquid treatment process in the cleaning work, and reduces the exposure dose associated with this waste liquid treatment.

For that purpose, in consideration of the characteristics of the decontaminating agent component and the waste as described above, concentrate on the acidic side, decompose the organic acid and chelating agent of the concentrated solution before the precipitation of the chelating agent begins, To prevent. As the decomposition progresses, it moves to the neutral side, the chelating agent is also decomposed and the metal hydroxide precipitates, so in order to prevent this, sulfuric acid is dropped while watching the pH, and PH2 to 3 is maintained. To do so. This makes it possible to prevent scale components from precipitating as hydroxides and to dissolve them. Decomposition of the chelating agent and organic acid was confirmed by analysis with a TOC meter, electrolytic reduction was performed, and metal ions of scale components such as iron, chromium, nickel, and copper were electrodeposited, and the radioactive component cobalt 58 , Cobalt 60, manganese 54, iron 59, etc. are removed from the waste liquid. When the radioactive component is removed, it is sulfuric acid waste liquid, so it can be easily treated by neutralizing it and discharging it to the chemical waste liquid system of the waste treatment system of the main facility.

The chemical decontamination waste liquid to be treated here is a chelating agent belonging to the concentrated decontamination method and an organic acid type, and has a considerably high dissolved component and a use concentration of about 1% to 8%. Of course, it can also be used to treat diluted decontaminating agents of 1% or less, but the amount of diluted decontaminating agents is small and the decontaminating agent is regenerated during decontamination by the CANDECON method, etc. There is no particular advantage to using this method as it is removed from the agent and concentrated towards secondary waste.

According to the results of the basic test, the acid concentration and the metal ion concentration in the liquid are high, and the reaction proceeds in 1 to 2 hours in the region of several% or more,
It was found that the reaction becomes extremely slow in the range of less than%, especially in the PPM region. In addition, the actual amount of waste liquid is large, the organic acid concentration is high, but the metal concentration is thin at a few 1000 PPM or less, and it is diluted to cause a sufficient reaction, so if you decompose it with hydrogen peroxide at that concentration, It was found that it took a considerable amount of time and that the reaction ended prematurely and the chelating agent could not be completely decomposed.

Therefore, the chemical decontamination waste liquid treatment method of the present invention was devised in order to accelerate the reaction, combine the functions of the decontamination target system with rinsing and flushing, and proceed smoothly with the decontamination waste liquid.

In addition, using ferrous sulfate as a catalyst,
The method of degrading proteins is known as the Fenton method, and in subsequent research, it also reacts with ferric iron, it reacts slowly with organic acids even if it is not a sulfate group, but it reacts similarly. It has become clear that hydrocarbons such as paraffin and lubricating oil can also be decomposed.

Although the individual unit operations are known as described above, the chemical decontamination waste liquid treatment method of the present invention combines these unit operations to treat the concentrated chemical decontamination waste liquid and treats the treated water with the existing waste treatment system. Most of the radioactivity is electroplated so that it can be treated with, and it is stored as a small amount of metal scraps in a cask, which is a relatively simple and quick waste liquid treatment.

(Example) Hereinafter, the Example of this invention is described with reference to drawings.

 FIG. 1 is a system diagram of an embodiment of the present invention.

The waste liquid obtained by chemically decontaminating the decontamination target device pipe 1 is discharged to the makeup tank 2. Further, the makeup tank 2 is heated by the heater 7 supplied with a decontaminating agent. The heated decontamination waste liquid is circulated from the makeup tank 2 to the circulation pump 10,
The decontamination target device pipe 1 is decontaminated by the decontamination system that returns to the decontamination target device pipe 1 via the heater 17. 18 is a pressure gauge and 19 is a flow meter. Also, makeup tank 2
When the decontamination waste liquid is bypassed from the above and supplied to the reverse osmosis membrane (RO) separator 3 by the high-pressure pump 11, clear water is obtained. This clear water is of a quality that can be stored in the surge tank 8 and then discharged as it is to the existing waste treatment system. Alternatively, it may be recycled to the decontamination system without being discharged and used for flushing of the decontamination system. In this case, the concentration on the inlet side of the reverse osmosis membrane decreases, so that concentration takes time and recycling increases. The reverse osmosis membrane separator 3 is capable of concentrating up to 30%, but at about 20%, crystal precipitation of low-solubility components begins, so concentrating up to about 15%. The used RO module is packed here and incinerated. Also, after concentrating to about 15%, a part of it is discharged and sent to a digester (digestion device) 4, where hydrogen peroxide and sulfuric acid are added to decompose organic acids and chelating agents while keeping PH at about 2. To go. Then, it is analyzed with a meter 20, such as a PH meter, oil meter, TOC meter or COD meter, and when the decomposition proceeds to below a predetermined organic matter concentration, the decomposed waste liquid is sent to the electrodeposition tank 5 and a DC power source 9 is applied to turn it on. It is deposited to recover metals such as iron, chromium, nickel and copper, which are easy to electrodeposit. Any anode may be used as long as it is an inactive electrode. The above-mentioned metal is deposited on the cathode, but it is not necessary to specify the cathode material. The current density should be increased as much as possible, and the electrodeposit should adhere to the extent that it does not peel off. This electrodeposit should be stored in a warehouse in a shielded cask. When most of the radioactivity has been separated by electrodeposition, the waste liquid is transferred to the neutralization tank 6, neutralized and discharged to the waste treatment system.

The regenerated waste liquid of the ion exchange resin becomes a very thin waste liquid of sodium sulfate. It can be treated by evaporative concentration desalination. Manganese 65 is not removed, but this element does not exist to the extent that it is precipitated by neutralization, and since gamma ray energy is low, it does not pose a problem. Therefore, it can be sufficiently treated in the existing waste treatment system.

When the electrodeposition of cobalt is insufficient, cobalt sulfate is added to the electrodeposition tank 5 to scavenge radioactive cobalt.

 In addition, 12 is a circulation pump, and 13, 14 and 16 are pumps.

As described above, since the decontamination waste liquid treatment apparatus used in this embodiment is compact and portable, it does not require a large-scale dedicated waste treatment facility as in the past. Further, the waste liquid treatment speed is considerably fast, and a large amount of waste liquid is treated to form a small amount of concentrated liquid before proceeding to the next treatment, so that the required time can be shortened.

Therefore, the amount of secondary waste is small and most of the radioactivity is in an extremely compact form, which is easy to shield and easy to handle. In addition, highly radioactive materials are compact and are enclosed in a small volume, so they are easy to shield. When the entire primary reactor system is decontaminated, Curie-order radioactivity is handled, so the merit of the size of this device is important. Moreover, the waste liquids are RO treatment liquid and electrodeposition waste liquid, both of which are in a state that can be treated in the chemical waste liquid system of the existing waste treatment system, so by treating this large amount of waste liquid in the existing waste treatment system, The waste treatment device can be simplified. Since the operation is simple and the number of workers is small as described above, the total amount of radiation exposure can be suppressed.

[Effects of the Invention] As described above, according to the present invention, the construction period in the decontamination work can be shortened, so that the exposure during the waste liquid treatment can also be reduced. In addition, the amount of waste generated by decontamination can be reduced, and since stable storage of waste can be achieved, it is possible to reduce the cost of disposal of decontamination waste, which is an excellent effect.

[Brief description of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention, FIG. 2 is a system diagram showing a conventional concentrated decontamination waste liquid treatment method, and FIGS. 3 and 4 are system diagrams showing a dilute decontamination waste liquid treatment method, respectively. Is. 1 ... Decontamination target equipment piping system 2 ... Make-up tank 3 ... RO membrane separator 4 ... Digester 5 ... Electrodeposition tank, 6 ... Neutralization tank 7,10 ... Heater, 8 ... Surge tank 9 ... DC power supply, 10, 12 ... Circulation pump 11, 13-16 ... Pump, 18-20 ... Meter

Claims (1)

(57) [Claims] 1. A method for treating a chemical decontamination waste liquid generated in a nuclear power generation facility, wherein a concentrated chemical decontamination waste liquid of the chemical decontamination waste liquid is separated into treated water and a concentrated liquid by a reverse osmosis membrane device, Sulfuric acid and hydrogen peroxide are added to the concentrated solution, heated to several tens of degrees Celsius or higher to decompose the chemical decontamination reagent components, and then the radioactive components and metal components of iron rust are electrodeposited and recovered from the chemical decontamination reagent decomposition liquid. Then, the chemical decontamination waste liquid treatment method is characterized in that the recovered material is stored in a shielded cask.