JP2001033586A - Chemical decontamination method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently eliminate radioactive nuclide and at the same time, reduce a secondary waste by dipping a metal member into a reduction decontamination liquid that is being circulated and passed by a specific amount per hour into a cation resin tower. SOLUTION: The chemical decontamination of a metal member being contaminated by a radioactive nuclide or the like is performed, for example, a reduction decontamination bath 1 and a pure water bath 3. A reduction decontamination agent with a dicarboxylic acid such as oxalic acid as a main body is effective as decontamination liquid used for the decontamination bath 1. A target metal member is dipped into the decontamination bath 1 for reduction decontamination, the decontamination liquid is continuously circulated to a cation exchange resin 6, and reproduction treatment for absorbing a radioactive nuclide or the like in liquid is made. The reduction decontamination time is within three hours, preferably approximately 2 hours. When the water passage flow rate to a cation exchange resin tower 6 is set to six times larger or more than the decontamination liquid per hour, the concentration of radiation in the decontamination liquid can be fully reduced. Then, the metal member is dipped into the pure water bath 3 for washing, and water in the pure water bath 3 is circulated and purified in a mixed bed resin tower 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nuclear facilities and, more particularly, to a method for chemically removing radionuclides from the surface of a metal member contaminated with radionuclides.

[0002]

2. Description of the Related Art Conventional techniques relating to chemical decontamination include:
As disclosed in JP-A-3-10919, a method of chemically contaminating metal structural parts of a nuclear reactor using permanganic acid as an oxidizing agent and dicarboxylic acid as a reducing agent is described. According to this method, the members constituting the nuclear reactor can be decontaminated with the system configuration kept as it is.

[0003]

The above technique is suitable for removing radioactive nuclides from the surface of a metal member constituting a system. However, components and periodic inspections to be removed and inspected during a periodic inspection are performed. No method is described for removing small contaminants such as jigs and tools and waste members removed from the system. Accordingly, an object of the present invention is to provide a chemical decontamination method and an apparatus for efficiently removing radionuclides from the surface of a small metal member and reducing secondary waste.

[0004]

The radionuclide adhering to the surface of the metal member is mainly taken into the adhered clad or oxide film. The radionuclide that adheres to the jigs and tools used during the periodic inspection is a clad centered on iron,
For dissolving the adhered cladding, a reducing and decontaminating agent containing a dicarboxylic acid such as oxalic acid or citric acid as a main component is effective. In other words, the jig with the clad attached may be immersed in the reduction decontamination tank.

However, unlike the case where the system configuration is directly decontaminated, since the object to be decontaminated is immersed in the decontamination tank, the decontamination liquid is opened to the atmosphere when the object to be decontaminated is taken in and out. .

Accordingly, under the condition of 90 ± 5 ° C. at the time of system decontamination, a large amount of steam rises when the system is opened, and the workability deteriorates. Therefore, when the temperature of the decontamination liquid is 50 ° C. to 80 ° C., preferably 60 ° C. to 70 ° C., the vapor pressure is suppressed to half or less, so that workability can be improved. Lowering the temperature generally lowers the dissolution rate,
If the dissolving power is insufficient, the concentration of the decontaminant is adjusted from 0.2% to 0.1%.
It can be compensated for by increasing it to 5%. Also,
Some of the radionuclides incorporated in the oxide film are not dissolved by the reducing decontamination agent because they are incorporated into chromium oxide, but chromium oxide can be dissolved by immersing it in an oxidizing decontamination agent containing permanganate ions. it can. However, even if the radionuclide is immersed in the oxidative decontamination agent, the rate at which the radionuclide elutes into the liquid at that point is small, so the object can be achieved by immersing the radionuclide again in the reduced decontamination liquid to remove the radionuclide .

[0007] Since radionuclides and metal ions eluted during reduction decontamination can be removed by circulating the reduction decontamination solution through a cation exchange resin, the reduction decontamination agent can be regenerated by the cation exchange resin. . It is experimentally found that the residual amount of the radioactive substance during the decontamination decreases as shown in FIG. 2, and the elution rate largely decreases in a short time. As a result of calculating the change in the radioactivity concentration in the decontamination solution using the ratio of the amount of water passed through the cation exchange resin to the volume of the solution as a parameter on the premise of such an elution rate of the radioactive substance, the result changes as shown in FIG. . Therefore, in order to reduce the radioactivity concentration to 1/20 or less of the peak value after 3 hours, at least 6 times the amount of water should be circulated through the cation tower.

On the other hand, permanganate ion, which is an oxidative decontamination agent, is consumed because it reacts with chromium oxide to decompose. For this reason, it is necessary to discard the deteriorated oxidative decontamination liquid to make a new decontamination liquid. At this time, the oxidative decontamination agent becomes secondary waste. In order to reduce the amount of secondary waste, permanganate ions may be decomposed and adsorbed on the ion exchange resin as manganese ions. The permanganate ion decomposes by reacting with oxalic acid when an appropriate amount of the reduction decontamination liquid is transferred to the oxidation decontamination tank. After the decomposition is completed, the liquid in the oxidation decontamination tank is circulated through the mixed-bed resin tower to return the liquid in the oxidation decontamination tank to almost the pure water level. Thereafter, an appropriate amount of the oxidative decontamination agent may be dissolved.

[0009] Since the drug adheres to the surface of the metal member after decontamination, it must be immersed in a pure water tank to purify the drug component. The water in the pure water tank may be purified by circulating water through the mixed-bed resin tower. As described above, the amount of secondary waste can be reduced by repeatedly using the decontamination solution in the decontamination tank for decontamination of a plurality of decontamination targets, and the decontamination agent is used for each decontamination step. Since no decomposition treatment is performed, the decontamination time can be reduced.

[0010]

(Embodiment 1) A first embodiment of the present invention will be described with reference to FIG. FIG. 1 shows an example of a system configuration of a decontamination apparatus when performing chemical decontamination of a small metal member. The decontamination apparatus includes a reduction decontamination tank 1 and a pure water tank 3 for performing decontamination by immersing a metal member, and a reduction decontamination tank heater 2 is attached to the former. The heater has a sensor and a control circuit for controlling the temperature of the decontamination liquid. The apparatus further includes a reduction decontamination tank circulation pump 4 for circulating the decontamination solution, a pure water tank circulation pump 5, a cation exchange resin tower 6 for removing cations in the reduction decontamination solution, and a pure water tank. Mixed bed resin tower 7 for purifying water, reduction decontamination tank circulation line 8, pure water tank circulation line 9, reduction decontamination tank exit valve 10, reduction decontamination tank circulation pump inlet valve 11, reduction decontamination tank circulation line Valve 14, pure water tank outlet valve 12, pure water tank circulation pump inlet valve 13, pure water tank circulation line valve 15, cation exchange resin tower inlet valve 16, cation exchange resin tower outlet valve 1
7, mixed bed resin tower inlet valve 18, mixed bed resin tower outlet valve T19,
A reduction decontamination tank drain line valve 20, a drain filter 21, a drain filter inlet valve 22, a drain filter outlet valve 23, a pure water tank circulation line return valve 34, a vent line 24 for venting generated gas, a vent line filter 25, And a decontamination agent external take-out valve 26, a reduction decontamination agent external return valve 27, a pure water external take-out valve 28, and pure water outside for supplying a decontamination solution and pure water to an external decontamination target portion. A return valve 29, a reduced decontamination agent external outlet flange 30, a reduced decontamination agent external return flange 31, a pure water external outlet flange 32, and a pure water external return flange 33 are provided.

[0011] Stainless steel with high corrosion resistance is suitable for components such as decontamination tanks, pipes and valves, but corrosion is prevented for decontamination tanks that have been in contact with the decontamination agent for a long time, and the amount of waste generated It is more preferable to use Teflon lining in order to reduce the amount of Teflon.

As a decontamination liquid used in the reduction decontamination tank 1, a reduction decontamination agent containing a dicarboxylic acid such as oxalic acid or citric acid as a main component is effective. For example, a reducing and decontaminating agent of oxalic acid 0.2% can be used at a temperature of 70 ± 5 ° C.

In the decontamination flow, the metal member to be decontaminated is placed in a basket whose surface is coated with a material having high chemical resistance such as Teflon, and the basket is immersed in the reduction decontamination tank 1 to perform the reduction decontamination. Do. At this time, the reduction decontamination liquid is controlled at 70 ± 5 ° C. by the reduction decontamination tank heater 2, and circulating and regenerating are continuously performed using the reduction decontamination tank circulation pump 4 and the cation exchange resin tower 6. At this time, the open / close state of the valve includes a reduction decontamination tank outlet valve 10, a reduction decontamination tank circulation pump inlet valve 11, a reduction decontamination tank circulation line valve 14, a cation exchange resin tower inlet valve 16, and a cation exchange resin tower outlet. Valve 17
Are open and the other valves are closed. By circulating the reduced decontamination liquid using the cation exchange resin tower 6 in this manner, cobalt 60, which is a radionuclide in the liquid,
Cationic components such as cobalt 58, manganese 54, iron 59, and dissolved iron and nickel are adsorbed and removed by the cationic resin.

The radioactivity attached to the metal member decreases with the decontamination time as shown in FIG. That is, the initial 2
The time is particularly large, and thereafter, the reduction rate becomes small even when the time elapses. Therefore, for efficient decontamination, the reductive decontamination time is within 3 hours, preferably about 2 hours. As a result of analyzing the radioactivity concentration in the decontamination agent using the flow rate of water to the cationic resin tower as a parameter when considering such time dependency, the flow rate of water becomes six times or more the volume of the decontamination liquid. It can be seen that the concentration after 3 hours is less than 1/20 of the peak concentration. The lower the radioactivity concentration at the end of decontamination, the lower the radioactivity residual ratio of the object to be decontaminated.Therefore, in order to obtain a sufficient decontamination effect in a short time, reduce the flow rate of water passing through the cationic resin tower. The volume may be at least 6 times the volume of the dyeing liquor.
Thereby, the radioactivity concentration in the decontamination solution can be sufficiently reduced in about 3 hours when the elution is reduced. Since radionuclides eluted from the metal member accumulate in the cation exchange resin tower 6, the cation exchange resin tower 6 is shielded. In addition, by attaching an ultrasonic oscillator to the reduction decontamination tank 1, the decontamination effect can be further enhanced.

The gas generated during reduction decontamination is exhausted through a vent line 24 via a vent line filter 25 attached to the reduction decontamination tank 1.

The end of reductive decontamination can be determined by monitoring the change in the dose rate of the metal member and reducing the contamination to a level below the target level or by time management with an upper limit of 3 hours.
After the completion of the reduction decontamination, the metal member is pulled up from the reduction decontamination tank 1 together with the basket and immersed in the pure water tank 3 as it is in order to remove the decontamination agent component remaining on the surface of the metal member. In order to maintain the purity of the water in the pure water tank 3, water is circulated through the mixed-bed resin tower 7 in the same manner as in the reduction decontamination tank 1. In this purification step, the temperature of the water may be kept at room temperature.

The open / closed state of the valve in the purification process includes:
The pure water tank outlet valve 12, the pure water tank circulation pump inlet valve 13, the pure water tank circulation line valve 15, the mixed bed resin tower inlet valve 18, the mixed bed resin tower outlet valve 19, and the pure water tank circulation line return valve 34 are open. Other valves are kept closed. However, when the reduction decontamination tank drain line valve 20 is closed, the reduction decontamination tank 1 and the deionized water tank 3 can be circulated independently of each other. You can also do the work.

At the end of the cleaning process of the metal member, the value indicated by the conductivity meter provided on the upstream side of the mixed-bed resin tower 7 in the pure water tank 3 or its circulation line 9 becomes a set value, for example, 2 μS / cm or less. Can be determined. Regarding the circulation flow rate, unlike the water flow to the cationic resin tower, the decontamination agent component on the member surface diffuses immediately in the washing step and is not a continuous elution. It is sufficient to secure a flow rate of water more than twice the amount.

When the decontamination is carried out by such an apparatus and method, the decontamination can be performed in a short time because the heating step and the decomposing agent decomposing step are omitted as in the system decontamination, and the same decontamination agent and water can be used. Since it is used while regenerating, the amount of secondary waste can be reduced. Further, since the temperature condition is set lower than that in the system decontamination, corrosion of the material constituting the apparatus can be reduced, so that the life of the pump and the like can be extended.

(Embodiment 2) In the above embodiment, a tool such as a jig having radioactive nuclides weakly adhering to the surface of a metal member is targeted for decontamination. It is conceivable that the target level is not reached only by reductive decontamination as shown in the first embodiment. In this case, the decontamination effect can be increased to the target level by performing oxidative decontamination after reduction decontamination and pure water cleaning and repeating reduction decontamination and pure water cleaning according to the flowchart shown in FIG.

In FIG. 1, there is only one decontamination tank for decontamination. However, as shown in FIG. After the completion of the reduction decontamination, the metal member is pulled out of the reduction decontamination tank 1 together with the basket, immersed in the pure water tank 3 and washed, and then immersed in the oxidation decontamination tank 35. The temperature of the decontamination solution in the oxidation decontamination tank 35 is controlled to 70 ± 5 ° C. using the oxidation decontamination tank heater 36, similarly to the reduction decontamination tank 1. There is no need to circulate the decontamination agent during oxidative decontamination. Oxidation decontamination is usually 2 hours to 4 hours
Time is enough. Those having a high chromium content in the oxide film may be longer, and those having a higher chromium content may be shorter.

After completion of the oxidative decontamination, washing with pure water is performed again, followed by reductive decontamination and washing with pure water. When the pure water washing after the second reduction step is completed, it is confirmed again whether the target level of decontamination has been reached, and when it has been reached, decontamination is terminated. If the target level is not reached, decontamination of oxidation and reduction is repeated until the target level is reached.

In the oxidative decontamination agent, permanganate ions are decomposed and consumed by the reaction as the decontamination is performed. Therefore, after the decontamination is completed, the permanganate ion concentration in the decontamination agent is sampled and analyzed, and when the permanganate ion concentration becomes 100 ppm or less, the remaining permanganate ion is decomposed and the solution is decomposed. The dissolved ions therein are removed with an ion exchange resin, and potassium permanganate is dissolved again to regenerate the oxidative decontamination agent.

Specifically, the reduction decontamination tank outlet valve 10, the reduction decontamination tank circulation pump inlet valve 11, the reduction decontamination tank circulation line valve 14, and the oxidation decontamination tank circulation line return valve 38 are opened, and other valves are opened. Are closed, the reduction decontamination tank circulation pump 4 is activated, and the required amount of the reduction decontamination solution is transferred from the reduction decontamination tank 1 to the oxidation decontamination tank 35 to decompose the permanganate ions in the oxidation decontamination agent. I do.
At this time, the power of the oxidation decontamination tank heater 36 is turned off and the temperature of the solution is naturally lowered. The initial potassium permanganate concentration is 0.05%, and the oxalic acid concentration of the reducing decontamination agent is 0.2%.
When the pH is 2.5 with hydrazine in%, the reduced decontamination solution of about 22% of the volume of the oxidative decontamination agent is the amount required for decomposition. At this time, the amount necessary for the decomposition is set as the initial concentration, as the permanganate ion reacts and disappears,
Although chromium in the oxide film is oxidized from trivalent to hexavalent, a reaction that returns to trivalent again occurs during decomposition, so that the total amount of redox is determined by the initial potassium permanganate concentration.

When the oxidizing agent is decomposed, a gas such as nitrogen or carbon dioxide is generated, and the generated gas is exhausted through a vent line 24 through a vent line filter 25 attached to the oxidation decontamination tank 3.

After the decomposition of the oxidizing agent is completed, the reduction decontamination tank circulation pump inlet valve 11, the reduction decontamination tank circulation line valve 14, and the oxidation decontamination tank circulation line return valve 38 are closed. , Reduction decontamination tank drain line valve 20, pure water tank circulation line valve 15, mixed bed resin tower inlet valve 18, mixed bed resin tower outlet valve 19, drain filter inlet valve 22, drain filter outlet valve 2
3 is opened, and it is confirmed that the liquid temperature is 60 ° C. or less, and the decomposed liquid is passed through a mixed-bed resin tower 7 using a pure water tank circulation pump 5 to remove dissolved substances in the liquid and to remove the liquid. Drain. When drainage is completed, the oxidation decontamination tank outlet valve 37, the reduction decontamination tank drain line valve 20, the pure water tank circulation line valve 15, the mixed bed resin tower inlet valve 18, the mixed bed resin tower outlet valve 19, and the drain filter inlet valve 2
2. The drain filter outlet valve 23 is closed, and pure water is supplied to the reduction decontamination tank 1 and the oxidative decontamination tank 35 by the amount drained to return the liquid amount to the initial state.

When the original liquid volume is reached, all the valves are closed and oxalic acid is added to the diluted reduced decontamination solution in the reduced decontamination tank 1 to return the solution to a predetermined concentration. Potassium permanganate is also added to the liquid in the oxidation decontamination tank 35 to return to a predetermined concentration. It becomes possible to continue decontamination work by these series of regeneration operations,
There is almost no waste liquid of water quality that cannot be drained.

After a series of decontamination operations are completed, the decontamination agent can be stored as it is, but it may be necessary to discard the decontamination agent for inspection of the apparatus. When the decontamination agent is discarded, the decontamination agent is transferred from the reduction decontamination tank to the oxidization decontamination tank to decompose the decontamination agent mutually, as in the regeneration treatment of the oxidative decontamination agent. However, since the reductive decontamination agent is excessive and the reductive decontamination agent remains, all the decontamination agents are decomposed by decomposing the reductive decontamination agent by adding potassium permanganate corresponding to the residue. be able to.

In this case, although the amount of equipment is increased due to the addition of the oxidizing decontamination tank 35, the removal ability of the hardly attached radionuclides is greatly enhanced by adding the oxidizing decontamination. As shown in FIG. 4, the metal member is immersed in the pure water tank 3 while moving from the reduction decontamination to the oxidative decontamination or from the oxidative decontamination to the reduction decontamination to remove the decontaminant adhered to the member surface. Since it can be washed away, the decomposition reaction caused by the contact between the reducing decontamination agent and the oxidizing decontamination agent can be reduced, and the consumption of the decontamination agent can be reduced. Also, since the pure water in the pure water tank is kept at normal temperature, the metal member after decontamination can be immersed to apply thermal shock to the attached clad or oxide film, and the mechanical Peeling occurs, and the effect of increasing the decontamination effect can also be expected. Furthermore, at the end of decontamination, since the metal member has been washed with pure water, it is not necessary to separately consider removing residual chemicals on the member surface.

[0030]

According to the chemical decontamination apparatus of the present invention, it is not necessary to decompose and decontaminate the decontamination agent for each process, so that the time for decomposition treatment can be saved and the contamination can be removed in a short time. Further, since the number of times of the decomposition treatment can be reduced, the running cost can be reduced by reducing the amount of used chemicals and the amount of generated waste.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a system configuration of a decontamination apparatus.

FIG. 2 is a diagram showing a change in a dose rate during reduction decontamination.

FIG. 3 is a diagram showing a change in radioactivity concentration in a decontamination agent using a purification flow rate as a parameter.

FIG. 4 is a diagram showing a flow of a decontamination step.

FIG. 5 is a diagram showing an example of a system configuration of a decontamination apparatus when a pure water tank is added.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reduction decontamination tank, 2 ... Reduction decontamination tank heater, 3 ... Pure water tank, 4 ... Reduction decontamination tank circulation pump, 5 ... Pure water tank circulation pump, 6 ... Cation exchange resin tower, 7 ... Mixed bed resin tower, 8: Reduction decontamination tank circulation line, 9: Pure water tank circulation line, 10: Reduction decontamination tank outlet valve, 11: Reduction decontamination tank circulation pump inlet valve,
12 ... pure water tank outlet valve, 13 ... pure water tank circulation pump inlet valve,
14: reduction / decontamination tank circulation line valve, 15: pure water tank circulation line valve, 16: cation exchange resin tower inlet valve, 17: cation exchange resin tower outlet valve, 18: mixed bed resin tower inlet valve, 19 ...
Mixed bed resin tower outlet valve, 20: reduction decontamination tank drain line valve,
21: drain filter, 22: drain filter inlet valve, 23
... Drain filter outlet valve, 24 ... Vent line, 25 ... Vent line filter, 26 ... Reduction decontamination agent external take-off valve,
27: reduction decontamination agent external return valve, 28: pure water external extraction valve, 29: pure water external return valve, 30: reduction decontamination agent external outlet flange, 31: reduction decontamination agent external return flange,
32 ... pure water external outlet flange, 33 ... pure water external return flange, 34 ... pure water tank circulation line return valve, 35 ... oxidation decontamination tank heater, 36 ... oxidation decontamination tank heater, 37 ... oxidation decontamination tank outlet valve , 38 ... Oxidation decontamination tank return valve.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazunari Ishida 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Power & Electricity Development Division (72) Inventor Fumito Nakamura Sachiyuki Hitachi, Ibaraki Prefecture Hitachi 1-1, Hitachi, Ltd., Hitachi Works, Ltd. (72) Inventor Kazumi Anazawa 3-1-1, Sakaimachi, Hitachi, Ibaraki Prefecture, Hitachi, Ltd.

Claims (14)

[Claims] 1. A chemical decontamination method for chemically removing a radionuclide from the surface of a metal member contaminated with the radionuclide,
After immersing the metal member in the reduction decontamination liquid in the reduction decontamination tank in which the decontamination liquid in the decontamination apparatus is circulated and passed through the cationic resin tower at least 6 times its volume per hour, the metal member is removed. A chemical decontamination method, wherein the decontamination agent remaining on the surface is removed by circulating water from the reduction decontamination tank to a mixed-bed resin tower and transferring it to a pure water tank for continuous purification. 2. The chemical decontamination method according to claim 1, wherein a dicarboxylic acid is used as a reduction decontamination agent in the reduction decontamination tank. 3. The reduction decontamination agent of the reduction decontamination tank in which the dicarboxylic acid contains oxalic acid as a main component and the oxalic acid concentration is 0.1%.
The chemical decontamination method according to claim 2, wherein the amount is from 0.5 to 0.5% by weight. 4. The temperature of the reduction decontamination agent in the reduction decontamination tank is 50 ° C.
4. The temperature is not less than 80 ° C. or less.
The chemical decontamination method described. 5. The chemical decontamination method according to claim 1, wherein the decontamination is performed while irradiating ultrasonic waves in at least one of the steps of reduction decontamination or cleaning in a pure water tank. 6. The chemical decontamination method according to claim 1, wherein the reduction decontamination time is within 3 hours. 7. The chemical decontamination method according to claim 1, wherein the end of the reductive decontamination is determined based on a value indicated by a radiation monitor. 8. For a metal member that does not provide a sufficient decontamination effect only by reduction decontamination, the metal member washed in a pure water tank is immersed in an oxidative decontamination solution in the oxidative decontamination tank, and after the oxidative decontamination, 2. The method according to claim 1, wherein oxidative decontamination, cleaning, reductive decontamination, and cleaning in which the decontamination is performed in the decontamination tank again after the cleaning in the pure water tank is repeated until the target decontamination effect is obtained.
8. The chemical decontamination method according to items 7 to 7. 9. The chemical decontamination method according to claim 8, wherein the oxidative decontamination agent in the oxidative decontamination tank has a permanganate ion concentration of 0.01 to 0.05% by weight. 10. When the oxidative decontamination agent is worn out, the reduction decontamination agent is partially guided from the reduction decontamination tank to the oxidization decontamination tank, and the remaining oxidative decontamination agent is decomposed. 10. The chemical decontamination method according to claim 8, wherein the water is circulated through the column to return to pure water, and the oxidative decontamination agent is again added to a predetermined concentration and used. 11. A line circulating from a reduction decontamination tank, a pure water tank, a cation exchange resin tower, a mixed bed resin tower, a circulation pump, a drain filter, a reduction decontamination tank through a cation exchange resin tower,
A chemical decontamination apparatus comprising a line circulating from a pure water tank through a mixed bed resin tower, a line passing water from a reduction decontamination tank to the mixed bed resin tower, and a line discharging water from a mixed bed tower outlet through a drain filter. 12. The chemical decontamination apparatus according to claim 11, wherein the apparatus has a three-tank configuration in which an oxidation decontamination tank is added to a reduction decontamination tank and a pure water tank. 13. The chemical decontamination apparatus according to claim 11, wherein at least one of the decontamination tanks has an ultrasonic oscillator. 14. The chemical decontamination apparatus according to claim 11, wherein the decontamination tank is provided with a vent treatment for treating gas generated from inside the tank.