JP2000056087A - Chemical decontaminating method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the water in the outlet of a resin tower satisfy a drainable quality condition and simultaneously attain the reduction in concentration of a decontaminating agent and the regulation of water level by decomposing a reductive decontaminating agent guided from a part to be intended and passing water to a mix bed resin tower. SOLUTION: In decontamination process, a reactor recirculating pump 3 is started, and the temperature is raised by use of a circulating pump 5 and a heater 6. When the temperature reaches a prescribed temperature (90±5 deg.C), oxalic acid as reductive decontaminating agent any hydrazine as pH regulating agent are injected from a chemical tank 26 to a reactor 1 by use of a chemical injection pump 27. When the oxalic acid concentration reaches a prescribed concentration (0.2%), the chemical injection pump 27 is stopped to end the injection of oxalic acid, and reductive decontamination is performed. The cracked gas generated in a reducing agent decomposing device 16 is separated in a surge tank 17 and returned to the reactor 1 through a degassing line 24. Since most of oxalic acid of the decontaminating solution flowing from the tank 17 is decomposed, the decontaminating solution is cooled to 80 deg.C or lower by a cooler 18 and then guided to a mix bed ion exchange resin 19 to remove the undecomposed oxalic acid, metal ions and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-cooled nuclear power plant. It relates to the method of removing.

[0002]

2. Description of the Related Art Conventional techniques relating to chemical decontamination include:
As shown in Japanese Patent Application Laid-Open No. 3-10919, a metal structural component of a nuclear reactor is chemically decontaminated using permanganic acid as an oxidizing agent and dicarboxylic acid which is a kind of organic acid as a reducing agent. As a method for decomposing the organic acid used here, Japanese Patent Application Laid-Open No. 9-510784 describes a method of decomposing the organic acid into carbon dioxide and water using an iron complex and ultraviolet rays.

According to this method, an iron complex acts as a catalyst, and hydrogen peroxide as an oxidizing agent reacts with an organic acid to produce carbon dioxide and water. Therefore, an ion exchange resin for removing the organic acid is used. Is prevented from becoming a large amount of secondary waste.

[0004]

When the above-mentioned decontamination technology is applied to the decontamination of a nuclear system, the amount of water increases by injecting a decontamination agent. When the decontamination liquid is circulated using an existing pump typified by a reactor recirculation pump, the amount of water also increases due to the inflow of seal water from outside the system. There is no problem if the decontamination system has a space that can sufficiently store this amount of water, but in many cases it is necessary to drain the water on the way.

On the other hand, when the decomposition method described in Japanese Patent Application Laid-Open No. 9-510784 is used, the concentration of the organic acid in the system gradually decreases. If water is passed through the ion-exchange resin tower, the load on the ion-exchange resin increases and the meaning of decomposition is reduced. On the other hand, if water is passed after sufficient decomposition, the load on the ion exchange resin will be small, but it will take time to decompose the entire amount of decontamination solution to a certain level, and the drain process will be series after the decomposition process Since it is necessary to carry out, there is a problem that the decontamination time is further increased.

An object of the present invention is to provide a chemical decontamination method and an apparatus which can simultaneously perform drain while decomposing a decontamination agent.

[0007]

In order to achieve the above object, the present invention provides a method for reducing and decontaminating a reduced decontamination agent introduced from a site to be decontaminated by at least 90% or more by a transient method. The dye is decomposed and water is passed through the mixed-bed resin tower. This makes it possible for the water at the outlet of the resin tower to satisfy the water quality conditions that allow drainage. In addition, part or all of this water is cooled down through a cooler, then discharged to a drain system, and the rest is returned to the decontamination target site, thereby reducing the concentration of the decontamination agent in the decontamination target part and reducing the water level. Adjustment is also possible at the same time.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 shows an example of a system configuration when performing system chemical decontamination of a nuclear reactor. The object to be decontaminated is the reactor 1 and the reactor recirculation line 2 including the reactor recirculation pump 3. Temporary devices for carrying out decontamination include a circulation line 7, a circulation pump 5, a heater 6, a purification system pump 8, a cation exchange resin tower 11, a hydrogen peroxide tank 14, Hydrogen oxide injection pump 1
5, Reducing agent decomposition device 16, surge tank 17, cooler 1
8. Mixed bed ion exchange resin tower 19, drain water cooler 22 connected to drain line 23, gas vent line 2
4, a chemical tank 26 connected to the chemical injection line 25,
Valves 9, 10, 12, 2 for controlling the flow to the chemical injection pump 27, the vent line 28, and the vent cooler 29
0, 21 are used.

As the decontamination agent, a reduced decontamination agent prepared by adding hydrazine to 0.2% of oxalic acid to adjust the pH and an oxidative decontamination agent of 0.05% potassium permanganate are used. In the decontamination step, as shown in FIG. 2, the reactor recirculation pump 3 is started, and then the temperature is raised by using the circulation pump 5 and the heater 6 to reach a predetermined temperature (90 ± 5 ° C.). Then, oxalic acid as a reducing decontamination agent and hydrazine as a pH adjuster are injected into the nuclear reactor 1 from a chemical tank 26 using a chemical injection pump 27.

When the concentration of oxalic acid reaches a predetermined concentration (0.2%), the chemical solution injection pump 27 is stopped to terminate the injection of oxalic acid, thereby performing reductive decontamination. While the reactor recirculation pump 3 is operating, the sealing water flows into the reactor 1 from the pump 3, so that the water level inside the reactor 1 gradually rises. During the reduction decontamination, the purification system pump 8 is started to remove dissolved metal ions and radioactive ions, and the valve 10 is operated.
, 13 and 20 are closed, the valves 9 and 12 are opened, and a part of the decontamination liquid is passed through the cation exchange resin tower 11.

Reduction decontamination step (about 4 to 15 hours)
At the stage of decomposing the decontamination agent after the completion of
20 and 21 are opened, valves 9 and 12 are closed and the flow is changed to direct the decontaminant to the reductant decomposer 16. At this time, in order to decompose oxalic acid and hydrazine, hydrogen peroxide is injected from the hydrogen peroxide tank 14 to the upstream side of the reducing agent decomposer 16 using the injection pump 15. The injection amount of hydrogen peroxide at this time is set so that the molar concentration of hydrogen peroxide is equal to the sum of twice the molar concentration of oxalic acid and the molar concentration of hydrazine in the decontamination solution after injection.

As the reducing agent decomposing device 16, an ultraviolet irradiation device or a catalytic decomposing device can be applied. Decomposed gas generated in the reducing agent decomposition device 16 is separated in the surge tank 17 and returned to the reactor 1 through the gas release line 24. Since most of the oxalic acid in the decontamination liquid flowing out of the surge tank 17 has been decomposed, the temperature of the oxalic acid is reduced to 80 ° C. or less by the cooler 18 and then guided to the mixed-bed ion exchange resin tower 19, where undecomposed oxalic acid is removed. And other metal ions and the like are removed.

Since the effluent of the mixed-bed ion exchange resin tower 19 is almost close to pure water, part or all of the effluent is drained to a waste liquid treatment system of the plant through a drain water cooler 22 installed in a drain line 23. can do. The use of the cooler 22 is for lowering the temperature of the decontamination liquid and reducing the release of steam. Thus, the load on the ion exchange resin is reduced by temporarily decomposing the decontaminant at a high decomposition rate, and the decontamination solution is decomposed during the decontamination agent decomposition step by using a mixed bed ion exchange resin tower. Part of it can be drained.

Accordingly, the water level increased during the reductive decontamination step can be returned to the original level during the decontamination agent decomposition. The gas generated when the reducing agent is decomposed is finally condensed and removed by a vent cooler 29 through a vent line 28 installed in the upper part of the reactor 1 and discharged to an exhaust system.

After the decomposition of the reduction decontamination agent is completed, potassium permanganate, which is an oxidative decontamination agent, is injected into the system from the chemical solution tank 26 by using a chemical injection pump 27 and adjusted to a predetermined concentration (0.05%). I do. At this time, only the valves 9 and 10 are opened, and the others are closed to prevent the oxidizing agent from contacting the ion exchange resin. This is to prevent the oxidizing agent from deteriorating the catalyst and the ion exchange resin.

After completion of the oxidative decontamination step (about 4 to 8 hours), oxalic acid is injected again to decompose permanganate ions and reduce them to divalent manganese ions. The gas generated when the oxidizing agent is decomposed is, like the gas generated when the reducing agent is decomposed, finally condensed and removed by a vent cooler 29 through a vent line 28 provided above the reactor 1. Release to exhaust system. After the decomposition of the oxidizing agent, the flow of water to the cation exchange resin tower 11 is restarted to remove the eluted radioactivity and manganese ions and potassium ions generated by the decomposition of the oxidizing agent.

After the completion of the second reduction step, decomposition is carried out in the same manner as in the first reduction agent decomposition step, and after completion of the decomposition, final purification is performed using a mixed bed resin. In FIG. 2, the process assumes two cycles, but if a higher decontamination effect is desired, three or more cycles may be used. In the case of three or more cycles, the oxidation step, the oxidizing agent decomposition step, the reducing step, the reducing agent decomposition step, and the purification step are defined as one cycle, and
It may be a step inserted between cycles.

[0018]

According to the decontamination method of the present invention, a part of the system water can be drained during the step of decomposing the reducing decontaminant, so that the water level can be adjusted without extending the decontamination time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a system configuration when performing chemical decontamination of the present invention.

FIG. 2 is a diagram showing an example of a decontamination step.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor, 2 ... Reactor recirculation line, 3 ... Reactor recirculation pump, 4 ... Control rod guide tube, 5 ... Circulation pump, 6 ... Heater, 7 ... Temporary circulation line for decontamination, 8 ... Purification system Pump, 9, 10, 12, 13, 20, 21 ... valve, 11 ... cation exchange resin tower, 14 ... hydrogen peroxide tank, 15 ... hydrogen peroxide injection pump, 16 ... reducing agent decomposition device, 17 ... surge tank, 18 ... cooler, 19 ... mixed bed ion exchange resin tower, 22 ... cooler for drain water, 23 ... drain line,
24 ... gas release line, 25 ... chemical liquid injection line, 26 ...
Chemical solution tank, 27: Chemical solution injection pump, 28: Vent line, 29: Vent cooler.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Makoto Nagase 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Power and Electricity Development Division (72) Inventor Fumito Nakamura Yukicho, Hitachi City, Ibaraki Prefecture 3-1-1, Hitachi, Ltd., Hitachi Plant, Hitachi, Ltd. (72) Inventor Kazumi Anazawa 3-1-1, Sakaimachi, Hitachi, Ibaraki Prefecture, Hitachi, Ltd. Hitachi Plant, Hitachi Plant (72) Inventor ▲ Yoshikawa Hiroo 2-22-22 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Kurita Engineering Co., Ltd. (72) Inventor Seiji Furukawa 7-1 Morinosato Wakamiya, Atsugi City, Kanagawa Prefecture Kurita Kogyo Co., Ltd.

Claims (4)

[Claims] 1. A chemical decontamination method for chemically removing radionuclides from the surface of a metal member contaminated with radionuclides, the method comprising the steps of: The decontamination agent is decomposed in a single pass using a decontamination device for the reducing decontamination agent, and after passing through a mixed-bed resin tower to remove undecomposed components, draining part or all of the decomposed agent to decompose the reducing agent A chemical decontamination method comprising adjusting the water level during the process. 2. The chemical decontamination method according to claim 1, wherein the dicarboxylic acid of the reduction decontamination agent is oxalic acid. 3. The chemical decontamination method according to claim 1, wherein hydrazine is added as a reducing decontamination agent. 4. A decomposer for decomposing a reducing decontaminant, and a mixed-bed ion-exchange resin tower downstream of the decontamination device are provided in an annular conduit led out of the site to be decontaminated and returned to the site to be decontaminated. A chemical decontamination apparatus characterized in that there is a branch pipe connected to the outside of the tubular conduit on the downstream side.