JP2012108073A - Decontamination method and decontamination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination method and a decontamination device that can shorten a decontamination work period with high decontamination effect for pipes and instruments such as system pipe, etc. where an oxide film including radioactive substances is formed.SOLUTION: A decontamination device 10 uses chemical decontamination processing to remove a to-be-removed oxide film through a step for attaching a chemical decontamination processing liquid supplied from a chemical decontamination processing system to a to-be-decontaminated metal part 3 on a surface of which the to-be-removed oxide film consisting of the oxide film including radioactive substances is formed. The chemical decontamination processing system 20 comprises: a decontamination processing liquid pipe 21 for supplying the chemical decontamination processing liquid to the to-be-decontaminated part 3; a chemical tank 30 for supplying the chemical decontamination processing liquid to the decontamination processing liquid pipe 21; and a microbubble generator 40 for generating microbubble within the chemical decontamination processing liquid in the chemical tank 30.

Description

  The present invention relates to a decontamination method and a decontamination apparatus for removing a metal oxide film formed on the surface of a metal material such as piping in order to reduce the radiation dose of piping / equipment of nuclear power plants and radioactive material handling facilities.

Some piping / equipment such as nuclear power plants and radioactive material handling facilities contain radioactive materials composed of hematite, chromium oxide, nickel ferrite (NiFe ₂ O ₄ ), etc. on the surface of the metal material constituting the equipment and piping. Oxide film adheres and is radioactively contaminated. About the metal material to which this oxide film adhered, the decontamination process which removes an oxide film from the surface of a metal material is required.

  Effective decontamination methods include, for example, physical methods (physical decontamination) using abrasive injection, water flow, cavitation in water, microbubbles, and chemical methods (chemical decontamination) using chemicals. Many methods have been proposed in which a chemical method and a physical method are used in combination. As chemical decontamination methods, oxidative decontamination using an oxidizing agent, reducing decontamination using a reducing agent, and oxidation-reduction decontamination that performs oxidative decontamination and reductive decontamination are known.

  Among physical decontamination methods, as a method using a water flow or a steam flow, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2000-75095), an abrasive is sprayed onto a decontamination object using steam as a medium. A decontamination method for grinding and removing the oxidized film is described. Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-116295) describes a decontamination method that removes a contaminated oxide film by using both physical decontamination with a water jet and chemical decontamination with a chemical. . Further, Patent Document 3 (Japanese Patent No. 4320977) describes a cavitation jet using water as a medium and a method of peeling a contaminated oxide film by supplying an abrasive to the flow thereof. Note that the inventions described in Patent Documents 2 and 3 utilize the effect of cavitation in addition to the effect of water flow.

  As a method using cavitation among physical decontamination methods, for example, Patent Document 4 (Japanese Patent Application Laid-Open No. 2008-62162) describes a method of cleaning a wetted surface by generating cavitation in water by ultrasonic waves. ing. Patent Document 5 (Japanese Patent Application Laid-Open No. 2005-351717) describes a method for generating cavitation in a fluid using ultrasonic waves, although it is not intended for decontamination.

  As an oxidative decontamination method using ozone among chemical decontamination methods, for example, Patent Document 6 (JP 2007-309864 A) discloses a decontamination method in which a liquid containing ozone microbubbles is brought into contact with an object to be decontaminated. Is described. Patent Document 7 (Japanese Unexamined Patent Application Publication No. 2009-125684) discloses a water treatment technique for decontamination process water of a nuclear power plant using ozone microbubbles. In addition, although the invention described in patent documents 6 and 7 uses microbubble, it is not the physical decontamination method using microbubble but the oxidative decontamination method using ozone from the description in a specification. It is judged that there is.

In recent years, chemical decontamination has been frequently performed in system piping of nuclear power plants. However, depending on the water quality used in the nuclear power plant and the type of material of the decontamination target, the oxide film formed on the surface of the pipe and equipment is chemically dissolved, for example, nickel ferrite (NiFe ₂ O ₄ ). It can be difficult. About such a hardly soluble oxide film, even if it decontaminates only with a chemical decontamination method, decontamination efficiency is bad and the decontamination construction period becomes long. For this reason, it is desired to improve the efficiency of decontamination by using both the chemical decontamination method and the physical decontamination method.

JP 2000-75095 A JP 2002-116295 A Japanese Patent No. 4302097 JP 2008-62162 A JP-A-2005-351717 JP 2007-309864 A JP 2009-125684 A

  However, as the physical decontamination method, when using the methods shown in the above Patent Documents 1 to 6, since it is difficult to insert into the piping, the injection nozzle, the ultrasonic vibrator, etc., the primary cooling system There is a problem that it is difficult to apply to decontamination of piping.

  For example, in the water jet injection nozzle described in Patent Document 2, the operation of inserting the nozzle into the pipe requires skill, and cannot cope with a complicated pipe configuration, and the plant cannot secure a nozzle insertion port. Not applicable.

  Moreover, the cavitation generator described in Patent Documents 4 and 5 generates cavitation in the fluid by ultrasonic waves from the outside of the pipe. In the cavitation generating device described in Patent Documents 4 and 5, in order to efficiently generate cavitation, it is necessary to devise such as installing a plurality of generators or installing a material that resonates with the pipe thickness. Therefore, it is difficult to generate cavitation in the decontamination liquid that fills the entire system piping.

  The present invention solves the above-mentioned problems, and has a high decontamination effect on piping and equipment such as system piping on which an oxide film containing a radioactive substance is formed, and a decontamination method and decontamination that can shorten the decontamination work period. The object is to obtain a dyeing device.

  In the present invention, when microbubbles are supplied to the entire fluid during chemical decontamination of piping and equipment such as system piping on which an oxide film containing a radioactive substance is formed, the decontamination work period can be shortened due to the high decontamination effect. It was made by finding what can be done.

  That is, the decontamination method of the present invention is for solving the above-mentioned problem, and the chemical decontamination treatment liquid is in contact with the oxide film to be removed, which is made of an oxide film containing a radioactive substance and adheres to the surface of the metal material. In the decontamination method for removing the oxide film to be removed by chemical decontamination treatment, the chemical decontamination treatment is a decontamination treatment for deoxidizing the oxide film to be removed with a chemical decontamination treatment liquid containing a decontamination agent. A decontamination process for decomposing the decontamination agent in the chemical decontamination treatment liquid after the decontamination process, and removing impurity ions in the chemical decontamination treatment liquid after the decontamination process. The chemical decontamination treatment liquid used in at least one process selected from the decontamination process, the decontamination agent decomposition process, and the purification process contains microbubbles.

  In addition, the decontamination apparatus of the present invention is for solving the above-described problems, and the chemical decontamination is performed on a metal decontamination target site having an oxide film to be removed made of an oxide film containing a radioactive substance attached to the surface. A decontamination apparatus that contacts a chemical decontamination treatment solution supplied from a decontamination treatment system and removes the removal target oxide film by a chemical decontamination treatment, wherein the chemical decontamination treatment system includes the decontamination target part. A decontamination treatment pipe for supplying chemical decontamination treatment liquid to a chemical liquid tank, a chemical liquid tank for supplying chemical decontamination treatment liquid to the decontamination treatment liquid pipe, and microbubbles in the chemical decontamination treatment liquid in the chemical liquid tank. And a microbubble generator to be generated.

  According to the decontamination method and the decontamination apparatus of the present invention, the decontamination effect of piping / equipment such as system piping on which an oxide film containing a radioactive substance is formed is high, and the decontamination work period can be shortened.

The schematic block diagram which shows 1st Embodiment of the decontamination apparatus which concerns on this invention. The flowchart which shows an example of the process of the decontamination method concerning this invention. The graph which shows the influence by the water temperature of the destructive force by the bubble which generate | occur | produced in water by the cavitation by ultrasonic vibration. The graph which shows the relationship between pH of a chemical decontamination processing liquid, and the zeta potential of a metal oxide and a microbubble. Explanatory drawing which shows typically the effect | action of the decontamination by a microbubble in the state in which a microbubble has the electric charge of the code | symbol opposite to the zeta potential of the oxide film to be removed. The graph which shows the difference in the decontamination effect by the presence or absence of a microbubble. The schematic block diagram which shows 2nd Embodiment of the decontamination apparatus which concerns on this invention. The graph which shows distribution of the bubble diameter of the micro bubble generated in 2nd Embodiment of the decontamination apparatus which concerns on this invention. The schematic block diagram which shows 3rd Embodiment of the decontamination apparatus which concerns on this invention. Sectional drawing which shows typically the microbubble generator used for 3rd Embodiment of the decontamination apparatus which concerns on this invention. The graph which shows distribution of the bubble diameter of the micro bubble produced | generated by 3rd Embodiment of the decontamination apparatus which concerns on this invention.

  Hereinafter, a decontamination apparatus and a decontamination method according to the present invention will be described with reference to the drawings.

[Decontamination equipment]
(First embodiment)
FIG. 1 is a schematic configuration diagram showing a first embodiment of a decontamination apparatus according to the present invention. A decontamination apparatus 10 shown in FIG. 1 is a decontamination apparatus for decontaminating a reactor coolant recirculation system 3 of a nuclear power plant 1 having a boiling water reactor (BWR).

  In the present embodiment, the reactor coolant recirculation system 3 that is a decontamination target is a system in which the coolant circulates during normal operation of the nuclear power plant 1, and the reactor recirculation system piping 4 and the reactor recirculation system. And a recirculation pump 5 provided in the middle of the system piping 4.

  In the present embodiment, an example of a decontamination apparatus for decontaminating the reactor coolant recirculation system 3 of the nuclear power plant 1 having a boiling water reactor (BWR) is shown. As the power plant 1, it is good also as a decontamination apparatus which decontaminates the primary system of the nuclear power plant which has a pressurized water nuclear reactor (PWR) which is not illustrated.

  The reactor recirculation system pipe 4 extends in a substantially vertical direction from the outlet (delivery) side of the recirculation pump 5 and transfers a coolant from the recirculation pump 5 upward. A PLR (Primary Loop Re-circulation System): Primary coolant recirculation system) The vertical pipe 6 is connected to the upper end of the PLR vertical pipe 6 and is positioned above the PLR vertical pipe 6 and is installed in a substantially horizontal ring around a reactor pressure vessel (not shown). It has a PLR horizontal pipe 7 and a PLR riser pipe 8 that communicates with the pipe wall of the PLR horizontal pipe 7 and extends upward. A branch pipe 9 to which a chemical decontamination treatment liquid is supplied from the decontamination apparatus 10 is provided in the middle of the PLR vertical pipe 6.

  The reactor recirculation system piping 4 and the equipment (not shown) constituting the reactor coolant recirculation system 3 that is a decontamination target part are usually made of a metal such as low carbon stainless steel at a portion in contact with the coolant. It consists of a metal material.

When these metal materials come into contact with the coolant of the nuclear power plant 1, a corrosive oxide composed of hematite, chromium oxide, nickel ferrite (NiFe ₂ O ₄ ) or the like is generated on the surface. When the corrosive oxide is peeled off, the corrosive oxide moves with the coolant and reaches the core or the like, and may be activated to become a radioactive oxide. This radioactive oxide circulates in the reactor coolant recirculation system 3 together with the coolant, and again adheres to the surface of the metal material in the reactor coolant recirculation system 3 to form an oxide film containing a radioactive substance.

The oxide film containing the radioactive substance is usually made of hematite, chromium oxide, nickel ferrite (NiFe ₂ O ₄ ) or the like, like the corrosive oxide. Nickel ferrite (NiFe ₂ O ₄ ) is a hardly soluble oxide that is difficult to be decontaminated by conventional chemical decontamination.

  In the present invention, such an oxide film, that is, an oxide film containing a radioactive substance attached to the surface of a metal material, which is a decontamination target site, is referred to as a removal target oxide film. The decontamination apparatus 10 is an apparatus that removes an oxide film to be removed from the reactor coolant recirculation system 3 that is a decontamination target part.

  In the present invention, the chemical decontamination treatment liquid supplied from the decontamination apparatus 10 to the branch pipe 9 means a liquid supplied from the decontamination apparatus 10 to the reactor coolant recirculation system 3 as a decontamination target site. To do. Note that the composition of the liquid supplied from the decontamination apparatus 10 to the decontamination target site 3 varies depending on the status of the decontamination work such as the decontamination process, the decontamination agent decomposition process, and the purification process. The composition of the chemical decontamination solution is not constant.

Specifically, the chemical decontamination treatment liquid is pure water similar to a coolant, an aqueous solution containing a decontamination agent in pure water, a chemically decomposed decontamination agent or a decontamination target site. For example, an aqueous solution containing metal ions separated from the reactor coolant recirculation system 3 in pure water.
Examples of the decontamination agent contained in the chemical decontamination treatment liquid include reductive decontamination agents such as oxalic acid, and oxidative decontamination agents such as ozone gas and permanganate.

  The decontamination apparatus 10 is supplied from the chemical decontamination processing system 20 to the reactor coolant recirculation system 3 as a metal decontamination target site to which a target oxide film made of an oxide film containing a radioactive substance is attached. In this decontamination apparatus, the supplied chemical decontamination treatment liquid is contacted and the oxide film to be removed is removed by chemical decontamination treatment.

  The chemical decontamination processing system 20 of the decontamination apparatus 10 includes a decontamination processing liquid main circulation line 21 as a decontamination processing liquid pipe for supplying a chemical decontamination processing liquid to the decontamination target site 3, and this decontamination processing liquid main. A chemical liquid tank 30 that supplies chemical decontamination processing liquid to the circulation line 21 and a microbubble generator 40 that generates microbubbles in the chemical decontamination processing liquid in the chemical liquid tank 30 are provided.

  The chemical decontamination processing system 20 includes an ozone generator 50 that supplies ozone into the chemical decontamination treatment liquid in the decontamination treatment liquid main circulation line 21 using a mixer 51, and the decontamination treatment liquid main circulation line 21. A decontamination agent decomposing apparatus 62 for decomposing the decontamination agent in the chemical decontamination treatment liquid, and a cation exchange resin tower (ion exchange resin tower) 63 for adsorbing and removing cationic impurity ions in the chemical decontamination treatment liquid. And an anion exchange resin tower (ion exchange resin tower) 64 that adsorbs and removes anionic impurity ions in the chemical decontamination treatment liquid.

  The decontamination treatment liquid main circulation line 21 has one end connected to the branch pipe 9 of the reactor recirculation system pipe 4 and the other end connected to the decontamination liquid discharge port 93 of the reactor recirculation system pipe 4. The The decontamination treatment liquid main circulation line 21 is provided with a chemical decontamination treatment liquid circulation pump 22 for feeding a chemical decontamination treatment liquid flowing through the decontamination treatment liquid main circulation line 21. Thereby, in the nuclear power plant 1, the chemical decontamination treatment liquid can be circulated in a loop between the decontamination treatment liquid main circulation line 21 and a part of the reactor recirculation system piping 4.

<Chemical solution tank>
The chemical tank 30 is a tank for supplying a decontamination agent into the chemical decontamination treatment liquid in the decontamination treatment liquid main circulation line 21.

  The chemical liquid tank 30 is provided in the middle of the chemical liquid line 31 that bypasses a part of the decontamination processing liquid main circulation line 21 and joins the decontamination processing liquid main circulation line 21 again. In the middle of the chemical liquid line 31, a chemical liquid line pump 32 is provided for feeding the chemical decontamination processing liquid discharged from the chemical liquid tank 30 to the decontamination processing liquid main circulation line 21. Thereby, in the decontamination apparatus 10, a chemical decontamination treatment liquid can be prepared in the chemical tank 30 separately from the chemical decontamination treatment liquid flowing in the decontamination treatment liquid main circulation line 21.

  In addition, the chemical tank 30 includes a chemical heating line 35 that temporarily takes out the chemical decontamination treatment liquid (chemical liquid) in the chemical tank 30 and returns it to the chemical tank 30 and a chemical decontamination treatment liquid in the chemical heating line 35. A heater 33 for heating and a chemical heating line pump 34 for feeding the chemical decontamination processing liquid in the chemical heating line 35 to the chemical tank 30 are provided. The heater 33 facilitates temperature adjustment of the chemical decontamination treatment liquid in the chemical liquid heating line 35 in the decontamination apparatus 10.

  In the chemical liquid tank 30, a chemical such as a decontamination agent is usually added to the solution newly charged in the chemical liquid tank 30 or to the chemical decontamination liquid introduced from the decontamination liquid main circulation line 21. The drug solution is prepared. Examples of the chemical solution added in the chemical solution tank 30 include oxalic acid or a reducing agent such as this aqueous solution, permanganate or an oxidizing agent such as this aqueous solution.

  In the chemical solution tank 30, it is not always necessary to prepare the chemical solution. For example, the chemical tank 30 is also used for the purpose of including microbubbles without adding a chemical to the chemical decontamination treatment liquid introduced from the decontamination treatment liquid main circulation line 21.

<Microbubble generator>
The microbubble generator 40 is a device that generates microbubbles in the chemical decontamination processing liquid in the chemical tank 30. The microbubble generator 40 is provided in a chemical solution circulation line 41 that takes out the chemical decontamination processing solution in the chemical solution tank 30 and returns it to the chemical solution tank 30 again.

  The microbubble generator 40 shown in FIG. 1 is an example in which the microbubble generator 40 is provided only in the middle of the chemical liquid circulation line 41, but the microbubble generator 40 used in the present invention is a chemical liquid circulation line. It is not restricted to what is provided only in the middle of 41. For example, the microbubble generator 40 may be provided only in the chemical liquid tank 30, or a plurality of apparatuses provided both in the middle of the chemical liquid circulation line 41 and in the chemical liquid tank 30 cooperate. It may be a thing.

  In the present invention, the microbubbles mean bubbles that cause a collapse phenomenon in the chemical decontamination treatment solution, that is, a phenomenon in which the bubble diameter is reduced with the passage of time and finally becomes zero and the bubbles disappear.

  It is said that the bubble diameter needs to be a predetermined value or less in order for the bubbles to cause a crushing phenomenon in the chemical decontamination treatment liquid. The upper limit value of the bubble diameter that causes this crushing phenomenon is called the critical bubble diameter, and the critical bubble diameter is said to be about 65 μm. For this reason, the microbubble is a bubble having a bubble diameter of 65 μm or less when the bubble diameter is maximum.

  It is believed that the smaller the bubble diameter, the greater the energy when the bubble disappears due to the crushing phenomenon, resulting in higher decontamination efficiency. For this reason, it is preferable that the bubble diameter is smaller than 65 μm when the bubble diameter is maximum. The bubble diameter of the microbubbles is preferably 56 μm or less, more preferably 10 μm to 50 μm, and more preferably 10 μm to 30 μm.

  The crushing phenomenon will be described. In the crushing phenomenon, it is said that the microbubbles rapidly increase in pressure inside the bubbles due to the reduction of the bubbles, and the temperature inside the bubbles rapidly increases due to adiabatic compression. As a result, when the bubbles disappear, a region of several thousand degrees and several thousand atmospheres microscopically appears in the bubble extinguishing part, and this region of several thousand degrees and several thousand atmospheres generates a strong impact force on the surrounding medium. It is said to let you. The decontamination apparatus 10 uses this strong impact force to peel and remove the removal target oxide film on the surface of the reactor coolant recirculation system 3 that is the decontamination target site.

  It should be noted that the phenomenon of generating a strong impact force on the surrounding medium by the crushing phenomenon of microbubbles of the present invention is considered to be the same phenomenon as the generation and collapse of cavitation due to ultrasonic vibration. By the way, the bubble diameter of bubbles generated by cavitation by general-purpose low frequency 45 kHz ultrasonic vibration is about 30 to 50 μm. The bubble diameter of the microbubbles generated by the microbubble generator 40 of the present invention is usually 65 μm or less, preferably 56 μm or less, more preferably 10 μm to 50 μm, and more preferably 10 μm to 30 μm. Therefore, the bubble diameter is less than 30 μm. When a certain microbubble is used, it is presumed that the effect of physical decontamination by the bubble is higher than when a bubble generated by cavitation by ultrasonic vibration is used.

  Moreover, as for the microbubble, generally, the rising speed of the bubble in a liquid becomes small, so that a bubble diameter is small. For example, when the bubble diameter of the microbubbles is 10 μm to several tens of μm, the rising speed of the microbubbles is as small as about 3 mm / min.

  By the way, when the nuclear power plant 1 is a nuclear power plant having a boiling water reactor, the residence time in the system of the chemical decontamination treatment liquid at the time of system decontamination of the reactor coolant recirculation system 3 is usually 10 minutes. Degree. For this reason, when decontamination is performed using a chemical decontamination treatment liquid containing microbubbles having a bubble diameter of 10 μm to several tens of μm, the rising speed of microbubbles for 10 minutes, which is the residence time in the system, is about 3 cm.

  The pipe diameter of the reactor recirculation system piping 4, the PLR vertical pipe 6, the PLR horizontal pipe 7, the PLR riser pipe 8, etc. of the reactor coolant recirculation system 3 is usually about 50 cm. For this reason, when decontaminating the piping of the reactor coolant recirculation system 3 using a chemical decontamination treatment liquid containing microbubbles having a bubble diameter of 10 μm to several tens of μm, most of the microbubbles are chemically decontaminated. The chemical decontamination treatment liquid can be retained in the piping of the reactor coolant recirculation system 3 while being retained in the dyeing treatment liquid, and adheres to the inner surface of the entire reactor coolant recirculation system 3. The oxide film to be removed is efficiently decontaminated.

  In the microbubble generator 40, the gas used to form the microbubbles is not particularly limited, and for example, an inexpensive gas such as air, oxygen, or nitrogen is used. Note that when oxygen is used as a gas used to form microbubbles, oxygen is an oxidant, so that the microbubbles can also act as an oxidizing decontamination agent.

  The microbubble generator 40 is not particularly limited as long as it is a device that can generate microbubbles in the chemical decontamination processing liquid in the chemical tank 30. For example, a pressurized microbubble generator, a swirl flow, and the like A type microbubble generator or the like is used.

  Here, the pressurization type microbubble generator means that chemical decontamination treatment liquid is dissolved by supersaturating the gas in the chemical decontamination treatment liquid by pressurizing the gas, and then the pressure applied to the chemical decontamination treatment liquid is reduced. It is an apparatus that generates microbubbles in the dyeing solution.

  The swirling flow type microbubble generator is a chemical decontamination treatment liquid and a gas that form a two-phase swirl flow between the chemical decontamination treatment liquid and the gas. It is an apparatus that generates microbubbles in the chemical decontamination treatment liquid by applying shearing force to the gas swirled at high speed by being discharged into the liquid.

  A pressurization type microbubble generator and a swirl flow type microbubble generator, which are specific examples of the microbubble generator 40, will be referred to as a pressurization type microbubble generator 40A, a swirl type microbubble generator 40B and the like in a later embodiment. Detailed description.

<Ozone generator>
The ozone generator 50 generates ozone as an oxidative decontamination agent, and uses a mixer 51 provided in the middle of the decontamination treatment liquid main circulation line 21 to perform chemical decontamination treatment liquid in the decontamination treatment liquid main circulation line 21. It is a device that supplies ozone inside.

The ozone generator 50 is connected to a mixer 51 provided in the middle of the decontamination liquid main circulation line 21 via an ozone supply line 52. The ozone introduced into the mixer 51 is mixed with the chemical decontamination treatment liquid in the decontamination treatment liquid main circulation line 21 and included in the chemical decontamination treatment liquid.
Ozone is an oxidizing agent, and ozone contained in the chemical decontamination treatment liquid functions as an oxidizing decontamination agent.

<Decontamination device decomposition device>
The decontamination agent decomposing apparatus 62 is an apparatus for decomposing the decontamination agent contained in the chemical decontamination treatment liquid in the decontamination treatment liquid main circulation line 21.

  The decontamination agent decomposing apparatus 62 is provided in the middle of the decontamination agent decomposition / ion exchange line 61 that bypasses a part of the decontamination treatment liquid main circulation line 21 and rejoins the decontamination treatment liquid main circulation line 21. The decontamination agent decomposition / ion exchange line 61 enables part or all of the chemical decontamination treatment liquid in the decontamination treatment liquid main circulation line 21 to be sent to the decontamination agent decomposition / ion exchange line 61. ing.

Further, in the middle of the decontamination agent decomposition / ion exchange line 61, the decontamination agent decomposition / ion exchange line 61 sends the chemical decontamination treatment liquid in the decontamination agent decomposition / ion exchange line 61 to the decontamination treatment liquid main circulation line 21. An ion exchange line pump 65 is provided.
Examples of the decontaminating agent decomposing apparatus 62 include an ultraviolet irradiation apparatus, a hydrogen peroxide solution injecting apparatus, or an apparatus combining these.
When the decontaminating agent decomposing device 62 is an ultraviolet irradiation device, for example, a decontaminating agent composed of a reducing agent such as oxalic acid can be decomposed.

<Cation exchange resin tower (ion exchange resin tower)>
The cation exchange resin tower (ion exchange resin tower) 63 is an apparatus that adsorbs and removes cationic impurity ions contained in the chemical decontamination treatment liquid of the decontamination treatment liquid main circulation line 21. As the cation exchange resin filled in the cation exchange resin tower 63, a known cation exchange resin can be used.

Examples of the cationic impurity ions contained in the chemical decontamination treatment liquid and adsorbed / removed by the cation exchange resin tower 63 include, for example, iron ions Fe ²⁺ and Fe ²⁺ and Fe ions that are decomposed by chemical decontamination. ^Examples thereof include metal ions such as ³⁺ , cobalt ion Co ²⁺ , and nickel ion Ni ²⁺ .

<Anion exchange resin tower (ion exchange resin tower)>
The anion exchange resin tower (ion exchange resin tower) 64 is an apparatus that adsorbs and removes anionic impurity ions contained in the chemical decontamination treatment liquid in the decontamination treatment liquid main circulation line 21. As the anion exchange resin packed in the anion exchange resin tower 64, a known anion exchange resin can be used.

Anionic impurity ions contained in the chemical decontamination treatment liquid and adsorbed / removed by the anion exchange resin tower 64 include, for example, dichromate ion Cr ₂ O in which chromium oxide produced in the oxidation step is oxidized and dissolved. ₇ ²⁻ , oxalate ion C ₂ O ₄ ²⁻ which is a decontamination agent, and carbonate ion CO ₃ ²⁻ formed by decomposition of oxalic acid.

<Action>
Next, the operation of the decontamination apparatus 10 will be described with reference to FIG.

  FIG. 2 is a flowchart showing an example of the steps of the decontamination method according to the present invention using the decontamination apparatus 10.

  The decontamination method shown in FIG. 2 consists of an oxide film containing a radioactive substance, and a chemical decontamination is performed on the oxide film to be removed attached to the surface of the metal material constituting the reactor coolant recirculation system 3 of the nuclear power plant 1. This is a decontamination method in which a treatment liquid is brought into contact with the target oxide film to be removed by chemical decontamination treatment.

  The chemical decontamination process of the decontamination method shown in FIG. 2 is performed after the first chemical decontamination process part (step group S100) consisting of a plurality of steps and the first chemical decontamination process part (S100). The second chemical decontamination processing part (step group S200) and the final purification process (step S301) performed after the second chemical decontamination processing part (S200).

  The first chemical decontamination processing part (step group S100), the second chemical decontamination processing part (step group S200), and the final purification process (step S301) are performed in this order. In addition, the second chemical decontamination processing portion (step group S200) is repeatedly performed once or twice or more before the final purification step (step S301). For example, the second chemical decontamination process part (step group S200) may be performed only once between the first chemical decontamination process part (step group S100) and the final purification process (step S301). It may be repeated more than once. The number of repetitions of the second chemical decontamination processing part (step group S200) is appropriately performed according to circumstances such as the degree of decontamination.

[First chemical decontamination processing part]
The first chemical decontamination process part (step group S100) includes a first reduction process (step S101) in which the removal target oxide film is subjected to a reduction decontamination process using a chemical decontamination process liquid containing a reducing agent, and the first reduction. A first reducing agent decomposition step (step S102) for decomposing the reducing agent in the chemical decontamination treatment liquid after the step, and a first removal of impurity ions in the chemical decontamination treatment liquid after the first reducing agent decomposition step. And a purification process (step S103).

(First reduction step)
The first reduction process (step S101) is a process for reducing and decontaminating the oxide film to be removed using a chemical decontamination treatment liquid containing a reducing agent.

  Examples of the reducing agent used in this step include oxalic acid. The reducing agent includes the reducing agent in the chemical liquid tank 30 by being added to, for example, chemical decontamination processing liquid stored in the chemical liquid tank 30 or water newly charged in the chemical liquid tank 30. A chemical decontamination solution is prepared. Examples of the chemical decontamination treatment liquid containing the reducing agent include an oxalic acid aqueous solution in which oxalic acid is dissolved in pure water.

The temperature of the chemical decontamination treatment liquid in this step is usually adjusted to a high temperature of 80 ° C to 100 ° C in order to enhance the solubility of the removal target oxide film.
Adjustment of the temperature of the chemical decontamination solution in this step is usually performed by controlling the heating of the heater 33.

  The pH of the chemical decontamination solution in this step is usually 1 to 3, preferably about 1.5 to 2.5.

  The chemical decontamination treatment liquid containing the reducing agent prepared in the chemical tank 30 is supplied to the reactor coolant recirculation system 3 via the decontamination treatment liquid main circulation line 21, and the reactor coolant recirculation system 3. Reductive decontamination treatment is performed on the oxide film to be removed.

  Specifically, after the valve 91 of the reactor recirculation system pipe 4 is closed and the valve 92 is opened, the chemical decontamination liquid containing the reducing agent in the chemical liquid tank 30 is decontaminated by the chemical liquid line pump 32. The liquid is sent to the main circulation line 21 and further supplied to the branch pipe 9 of the reactor recirculation pipe 4 by the chemical decontamination liquid circulating pump 22.

  The chemical decontamination processing liquid containing the reducing agent supplied from the branch pipe 9 to the reactor recirculation system pipe 4 is, for example, the reactor recirculation system pipe 4, the recirculation pump 5, the PLR vertical pipe 6, and the PLR horizontal pipe 7. And the PLR riser tube 8 is filled. Then, the oxide film to be removed attached to the surface of the metal material such as the reactor recirculation pipe 4 is decontaminated by contacting with a chemical decontamination treatment liquid containing a reducing agent.

  At this time, if the valve 92 shown in FIG. 1 is opened and the chemical liquid line pump 32 and the chemical decontamination treatment liquid circulation pump 22 are operated, the decontamination treatment liquid main circulation line 21 and the reactor recirculation piping 4 The chemical decontamination liquid can be circulated in a loop between a part of the two.

The oxide film to be removed is made of, for example, hematite, chromium oxide, nickel ferrite (NiFe ₂ O ₄ ) or the like containing a radioactive substance. For example, hematite or nickel ferrite (NiFe ₂ O ₄ ) in the oxide film to be removed dissolves when it comes into contact with a chemical decontamination treatment liquid containing a reducing agent and is decontaminated, for example, iron ions Fe ^2+. , Fe ³⁺ and nickel ion Ni ²⁺ are eluted. In addition, radioactive cobalt ions Co ²⁺ incorporated in the oxide film to be removed during decontamination are also eluted. The eluted iron ions Fe ²⁺ , Fe ³⁺ , cobalt ions Co ^2+, and nickel ions Ni ²⁺ are contained as impurity ions in the chemical decontamination treatment liquid that has undergone this step.

The chemical decontamination treatment liquid after this step (first reduction step) usually contains radioactive impurity ions such as iron ions Fe ²⁺ , Fe ³⁺ , cobalt ions Co ²⁺ , nickel ions Ni ²⁺ . Further, the chemical decontamination treatment liquid after this step may contain a remaining reducing agent.

  The chemical decontamination treatment liquid that has finished this step is returned to the decontamination treatment liquid main circulation line 21 from the reactor recirculation system piping 4 of the reactor coolant recirculation system 3. In addition, the chemical decontamination processing liquid which finished this process is between a part of the reactor recirculation system piping 4 of the reactor coolant recirculation system 3 and the decontamination processing liquid main circulation line 21 as necessary. It may be circulated in a loop.

  In addition, the process shown below is performed after this process. At this time, the chemical line pump 32 and the chemical decontamination treatment liquid circulation pump 22 may be stopped to discharge the chemical decontamination treatment liquid from the reactor coolant recirculation system 3. It is not necessary to drain the chemical decontamination treatment liquid by continuing to operate the circulation pump 22. Specifically, the chemical decontamination liquid circulating pump 22 is operated to circulate the chemical decontamination liquid in a loop between the decontamination liquid main circulation line 21 and the reactor coolant recirculation system 3. By doing so, it is possible to carry out the steps shown below while the reactor coolant recirculation system 3 is filled with the chemical decontamination treatment liquid.

(First reducing agent decomposition step)
The first reducing agent decomposition step (step S102) is a step of decomposing the reducing agent in the chemical decontamination treatment liquid after the first reduction step.

As a method for decomposing the reducing agent in the chemical decontamination treatment liquid, for example, using a decontaminating agent decomposing apparatus 62 that is an ultraviolet irradiation apparatus, chemical decontamination including the reducing agent in the decontaminating agent decomposing / ion exchange line 61 is performed. A method of irradiating the treatment liquid with ultraviolet rays is exemplified. For example, when the chemical decontamination treatment liquid containing a reducing agent is an oxalic acid aqueous solution, oxalic acid or oxalate ions are decomposed by ultraviolet rays to generate carbon dioxide.
The temperature of the chemical decontamination treatment liquid in this step is usually 70 ° C to 90 ° C, preferably 75 ° C to 85 ° C.

  The decomposition of the reducing agent in the chemical decontamination treatment liquid in this step does not require the high temperature of the chemical decontamination treatment liquid as in the first reduction process (step S101). Further, the lower the temperature of the chemical decontamination treatment liquid, the better the ion exchange efficiency of the chemical decontamination treatment liquid in the first purification process (step S103) which is the next process of this process. From these viewpoints, the temperature of the chemical decontamination treatment liquid in this step is preferably low.

  On the other hand, in the oxidation process (step S201) and the second reduction process (step S202) of the second chemical decontamination process part (step group S200), which is a subsequent process of this process, the solubility of the removal target oxide film is increased. Therefore, the temperature of the chemical decontamination treatment liquid is preferably high. For this reason, the temperature of the chemical decontamination treatment liquid in this step is such that the second chemical decontamination treatment part (step group S200) is reheated quickly in the oxidation step (step S201) and the second reduction step (step S202). In order to carry out efficiently, it is preferable that it is high to some extent.

  From the above circumstances, in this step, the temperature of the chemical decontamination treatment liquid is usually slightly lower than that of the chemical decontamination treatment liquid in the first reduction step (step S101), usually 70 ° C to 90 ° C, preferably 75 to 85 ° C.

  In addition, the temperature of the chemical decontamination treatment liquid in this step can be easily set to the above temperature range by not performing heating with the heater 33, for example. That is, if heating with the heater 33 is not performed in this step, the temperature of the chemical decontamination treatment liquid naturally decreases from the high temperature of 80 ° C. to 100 ° C. in the first reduction step, and usually 70 ° C. to 90 ° C. Preferably, it becomes 75 to 85 degreeC.

  The pH of the chemical decontamination treatment liquid in this step is usually 4 or more, preferably 4-8.

The chemical decontamination treatment liquid that has undergone this step substantially does not contain a reducing agent, but usually contains impurity ions such as radioactive iron ions Fe ²⁺ , Fe ³⁺ , cobalt ions Co ²⁺ , nickel ions Ni ²⁺ . The chemical decontamination processing liquid that has finished this process is discharged from the decontamination agent decomposing apparatus 62.

  The chemical decontamination treatment liquid discharged from the decontamination agent decomposing apparatus 62 is usually passed through a cation exchange resin tower (ion exchange resin tower) 63 and an anion exchange resin tower (ion exchange resin tower) 64. In the cation exchange resin tower (ion exchange resin tower) 63 and the anion exchange resin tower (ion exchange resin tower) 64, the first purification step is performed.

(First purification process)
The first purification step (step S103) is a step of removing impurity ions in the chemical decontamination treatment liquid after the first reducing agent decomposition step.

Specifically, the chemical decontamination treatment liquid after the first reducing agent decomposing step used in this step is usually derived from the oxide film to be removed, which is discharged from the decontamination agent decomposing apparatus 62. It contains cationic impurity ions (impurity cations) such as iron ions Fe ²⁺ , Fe ³⁺ , cobalt ions Co ²⁺ and nickel ions Ni ²⁺ . In addition, the chemical decontamination treatment liquid after the first reducing agent decomposition step is an anionic impurity ion such as oxalate ion C ₂ O ₄ ²⁻ derived from the reducing agent used in the first reduction step (step S101). (Impurity anion) may be contained.

  The chemical decontamination treatment liquid containing impurity ions is passed through a cation exchange resin tower (ion exchange resin tower) 63 and an anion exchange resin tower (ion exchange resin tower) 64 to remove impurity ions.

Specifically, when the chemical decontamination treatment liquid contains impurity cations such as iron ions Fe ²⁺ , Fe ³⁺ , cobalt ions Co ²⁺ , nickel ions Ni ²⁺ , the chemical decontamination treatment liquid is added to the cation exchange resin tower 63. When the water is passed, impurity cations in the chemical decontamination treatment liquid are removed by ion exchange.

Further, when the chemical decontamination treatment liquid contains an impurity anion such as oxalate ion C ₂ O ₄ ^2−, when the chemical decontamination treatment liquid is passed through the anion exchange resin tower 64, the chemical decontamination treatment liquid contains Impurity anions are removed by ion exchange.

The temperature of the chemical decontamination treatment liquid in this step is usually 70 ° C to 90 ° C, preferably 75 ° C to 85 ° C.
In order to increase the ion exchange efficiency of impurity ions in this step, the temperature of the chemical decontamination treatment liquid is preferably low.

  On the other hand, in the oxidation process (step S201) and the second reduction process (step S202) of the second chemical decontamination process part (step group S200), which is a subsequent process of this process, the solubility of the removal target oxide film is increased. Therefore, the temperature of the chemical decontamination treatment liquid is preferably high. For this reason, the temperature of the chemical decontamination treatment liquid in this step is such that the second chemical decontamination treatment part (step group S200) is reheated quickly in the oxidation step (step S201) and the second reduction step (step S202). In order to carry out efficiently, it is preferable that it is high to some extent.

  From the above circumstances, in this step, the temperature of the chemical decontamination treatment liquid is slightly lower than that of the chemical decontamination treatment solution in the first reduction step (step S101), and the chemical removal in the first reducing agent decomposition step (step S102). The temperature is about 70 ° C to 90 ° C, preferably 75 ° C to 85 ° C, which is the same temperature as the dyeing solution.

  The temperature of the chemical decontamination treatment liquid in this step naturally decreases, for example, by controlling such as not heating with the heater 33, so that the temperature within the above temperature range can be easily set.

  The pH of the chemical decontamination treatment liquid in this step is usually 4 or more, preferably 4-8.

  The chemical decontamination treatment liquid after this step (first purification step) that has been passed through and discharged through the cation exchange resin tower 63 and the anion exchange resin tower 64 is a chemical decontamination treatment liquid that has been purified by removing impurity ions. become.

[Second chemical decontamination part]
The second chemical decontamination processing part (step group S200) uses the chemical decontamination processing liquid obtained by adding an oxidizing agent to the chemical decontamination processing liquid after the purification process of the first chemical decontamination processing part, to thereby remove the target oxidation. An oxidation process (step S201) for subjecting the film to oxidative decontamination, and a chemical decontamination treatment liquid obtained by adding a reducing agent to the chemical decontamination treatment liquid after the oxidation process, and reducing the decontamination treatment of the oxide film to be removed. This is a process including a second reducing process (step S202) and a second reducing agent decomposing process (step S203) for decomposing the reducing agent in the chemical decontamination processing liquid after the second reducing process.

(Oxidation process)
In the oxidation step (step S201), the removal target oxide film is subjected to oxidative decontamination treatment using a chemical decontamination treatment solution obtained by adding an oxidizing agent to the chemical decontamination treatment solution after the purification step of the first chemical decontamination treatment portion. It is a process.
As an oxidizing agent used at this process, permanganate or this aqueous solution, and ozone are mentioned, for example.

  When the oxidant is a solid or liquid such as permanganate, the oxidant is, for example, a chemical decontamination treatment liquid stored in the chemical tank 30 or water newly charged in the chemical tank 30. As a result, a chemical decontamination treatment liquid containing an oxidizing agent is prepared in the chemical liquid tank 30. Examples of the chemical decontamination treatment liquid containing an oxidizing agent include an aqueous permanganate solution in which an oxidizing agent is dissolved in pure water.

  The chemical decontamination treatment liquid containing an oxidizing agent such as permanganate in the chemical liquid tank 30 is supplied to the reactor coolant recirculation system 3 via the decontamination treatment liquid main circulation line 21, and the reactor coolant recycle is performed. The oxide film to be removed from the circulation system 3 is subjected to oxidative decontamination treatment.

  Specifically, a chemical decontamination process including an oxidizing agent such as permanganate in the chemical tank 30 in the state where the valve 91 shown in FIG. 1 of the reactor recirculation piping 4 is closed and the valve 92 is opened. The liquid is fed to the decontamination processing liquid main circulation line 21 by the chemical liquid line pump 32, and further supplied to the branch pipe 9 of the reactor recirculation system pipe 4 by the chemical decontamination processing liquid circulation pump 22.

  When the oxidizing agent is ozone, ozone is generated by the ozone generator 50 and then supplied to the chemical decontamination liquid in the decontamination liquid main circulation line 21 via the mixer 51. As a result, a chemical decontamination treatment liquid containing ozone is prepared in the decontamination treatment liquid main circulation line 21.

  The chemical decontamination treatment liquid containing ozone in the decontamination treatment liquid main circulation line 21 is supplied to the reactor coolant recirculation system 3 through the decontamination treatment liquid main circulation line 21, and the reactor coolant recirculation system. Oxidation decontamination treatment of the oxide film to be removed 3

  Specifically, the chemical decontamination treatment liquid containing ozone in the decontamination treatment liquid main circulation line 21 in the state where the valve 91 of the reactor recirculation piping 4 is closed and the valve 92 is opened is the chemical decontamination treatment. The liquid circulation pump 22 supplies the branch pipe 9 of the reactor recirculation system pipe 4.

  In any case where the oxidant is a solid or liquid such as permanganate and the oxidant is ozone, the chemistry containing the oxidant supplied from the branch pipe 9 to the reactor recirculation system pipe 4 The decontamination processing liquid is, for example, in the reactor recirculation system pipe 4, the recirculation pump 5, the PLR vertical pipe 6, the PLR horizontal pipe 7, and the PLR riser pipe 8 in the same manner as in the first reduction process (step S <b> 101). It is filled. Then, the oxide film to be removed attached to the surface of the metal material such as the reactor recirculation pipe 4 is decontaminated by contacting with a chemical decontamination treatment liquid containing an oxidizing agent.

The oxide film to be removed is made of, for example, hematite, chromium oxide, nickel ferrite (NiFe ₂ O ₄ ) or the like containing a radioactive substance. For example, chromium oxide in the oxide film to be removed is oxidized and dissolved to be dichromate ions Cr ₂ O ₇ ^{2− when in contact} with a chemical decontamination treatment liquid containing an oxidant and decontaminated.

The temperature of the chemical decontamination treatment liquid in this step is usually adjusted to a high temperature of 80 ° C to 100 ° C in order to enhance the solubility of the removal target oxide film.
Adjustment of the temperature of the chemical decontamination solution in this step is usually performed by controlling the heating of the heater 33.

  In addition, when the oxidizing agent is ozone, the chemical decontamination treatment liquid containing the oxidizing agent (ozone) is prepared using the ozone generator 50 and the mixer 51. It is not necessary to use the chemical tank 30 for the preparation. However, even when the oxidizing agent is ozone, the chemical liquid tank 30 and the heater 33 provided in the chemical liquid tank 30 are usually used to adjust the temperature of the chemical decontamination treatment liquid containing ozone.

The chemical decontamination treatment liquid after this step (oxidation step) usually contains radioactive impurity ions such as dichromate ion Cr ₂ O ₇ ²⁻ . Moreover, the chemical decontamination processing liquid after this process may contain the remaining oxidizing agent.

  The chemical decontamination treatment liquid that has finished this step is returned to the decontamination treatment liquid main circulation line 21 from the reactor recirculation system piping 4 of the reactor coolant recirculation system 3. In addition, the chemical decontamination processing liquid which finished this process is between a part of the reactor recirculation system piping 4 of the reactor coolant recirculation system 3 and the decontamination processing liquid main circulation line 21 as necessary. It may be circulated in a loop.

(Second reduction process)
The second reduction step (step S202) is a step of subjecting the oxide film to be removed to reduction decontamination treatment using a chemical decontamination treatment solution obtained by adding a reducing agent to the chemical decontamination treatment solution after the oxidation step.

  The second reduction process (step S202) is the same as the first reduction process (step S101) of the first chemical decontamination process part (step group S100) except that the composition of the chemical decontamination process liquid is slightly different. It is.

Specifically, the chemical decontamination treatment liquid containing the reducing agent in the first reduction step (step S101) does not substantially contain impurity ions or oxidizing agents, whereas the reducing agent in the second reduction step (step S202). The chemical decontamination treatment liquid to which is added is usually a composition of the chemical decontamination treatment liquid in that it contains impurity ions, an oxidant and the like which are decontaminated with an oxidant such as dichromate ion Cr ₂ O ₇ ^2−. Is slightly different. In addition, even if the chemical decontamination treatment liquid used in this step contains an oxidizing agent, the action of the oxidizing agent is offset by the action of the reducing agent added in this step, so that no particular problem occurs.

  Since the second reduction process (step S202) and the first reduction process (step S101) are the same except for the composition of the chemical decontamination treatment liquid, description of the configuration and operation of the second reduction process is omitted or simplified. Turn into.

Type of reducing agent used in the second reduction step, method for preparing a chemical decontamination treatment liquid containing a reducing agent, and a metal material such as a reactor recirculation piping 4 using a chemical decontamination treatment liquid containing a reducing agent The decontamination action of the removal target oxide film is the same as in the first reduction step.
The temperature of the chemical decontamination treatment liquid in this step is usually adjusted to a high temperature of 80 ° C to 100 ° C in order to enhance the solubility of the removal target oxide film.
Adjustment of the temperature of the chemical decontamination solution in this step is usually performed by controlling the heating of the heater 33.

  The pH of the chemical decontamination solution in this step is usually 1 to 3, preferably about 1.5 to 2.5.

In this step, for example, radioactive iron ions Fe ²⁺ , Fe ³⁺ , cobalt ions Co ²⁺ and nickel ions Ni ²⁺ are eluted from the oxide film to be removed by decontamination using a chemical decontamination treatment solution with a reducing agent added. To do. Since the chemical decontamination treatment liquid after the oxidation process used in this step contains impurity ions such as dichromate ion Cr ₂ O ₇ ²⁻ from the beginning, the chemical decontamination treatment liquid after this step is iron Impurity ions such as ions Fe ²⁺ , Fe ³⁺ , cobalt ions Co ²⁺ , nickel ions Ni ²⁺ , and dichromate ions Cr ₂ O ₇ ²⁻ are included.

(Second reducing agent decomposition step)
The second reducing agent decomposing step (step S203) is a step of decomposing the reducing agent in the chemical decontamination treatment liquid after the second reducing step.

  The second reducing agent decomposition step (step S203) is a chemical decontamination treatment liquid used in the process compared to the first reducing agent decomposition step (step S102) of the first chemical decontamination processing portion (step group S100). The composition is the same except that the composition is slightly different.

Specifically, the chemical decontamination treatment liquid after the first reduction process (step S101), which is the chemical decontamination treatment liquid at the start of the first reducing agent decomposition process (step S102), is dichromate ion Cr ₂ O. ₇ Second reduction step which is a chemical decontamination treatment liquid at the start of the second reductant decomposition step (step S203) while it does not substantially contain impurity ions decontaminated with an oxidizing agent such as ^2- The chemical decontamination treatment liquid after (Step S202) usually has a slight composition of chemical decontamination treatment liquid in that it contains impurity ions decontaminated with an oxidizing agent such as dichromate ion Cr ₂ O ₇ ^2−. Different.

  Since the second reducing agent decomposition step (step S203) and the first reducing agent decomposition step (step S102) are the same except for the composition of the chemical decontamination treatment liquid, the configuration and action of the second reducing agent decomposition step. The description of is omitted or simplified.

  The temperature of the chemical decontamination treatment liquid in this step is usually 70 ° C to 90 ° C, preferably 75 ° C to 85 ° C. The reason for this is the same as the reason why the temperature of the chemical decontamination treatment liquid in the first reducing agent decomposition step (step S102) is usually 70 ° C to 90 ° C, preferably 75 ° C to 85 ° C, and thus the description thereof is omitted. .

  The pH of the chemical decontamination treatment liquid in this step is usually 4 or more, preferably 4-8.

The chemical decontamination treatment liquid that has undergone this step is substantially free of a reducing agent, but is usually radioactive, iron ions Fe ²⁺ , Fe ³⁺ , cobalt ions Co ²⁺ , nickel ions Ni ^2+, and dichromate ions Cr _2. Impurity ions such as O ₇ ²⁻ are included. The chemical decontamination processing liquid that has finished this process is discharged from the decontamination agent decomposing apparatus 62.

  The chemical decontamination processing liquid discharged from the decontaminating agent decomposing apparatus 62 is supplied to the final purification process (step S301) or the oxidation process (step S201) of the second chemical decontamination processing part (step group S200).

  When the chemical decontamination processing liquid discharged from the decontamination agent decomposing apparatus 62 is used for the oxidation step (step S201) of the second chemical decontamination processing part (step group S200), the second chemical decontamination processing described above. The step (step group S200), that is, the step group including the oxidation step (step S201), the second reduction step (step S202), and the second reducing agent decomposition step (step S203) is repeated.

[Final purification process]
The final purification step (step S301) is a step of removing impurity ions in the chemical decontamination processing liquid after the end of the second chemical decontamination processing portion (step group S200).

  The composition of the chemical decontamination treatment liquid used in the final purification process (step S301) is slightly different from that of the first purification process (step S103) of the first chemical decontamination process portion (step group S100). Other than that, it is the same.

Specifically, the chemical decontamination treatment liquid after the first reducing agent decomposition step (step S102), which is the chemical decontamination treatment liquid at the start of the first purification step (step S103), is dichromate ion Cr ₂ O. ₇ The second reducing agent decomposition process which is a chemical decontamination treatment liquid at the start of the process of the first purification process (step S103) while it does not substantially contain impurity ions decontaminated with an oxidizing agent such as ^2- The chemical decontamination treatment liquid after (Step S203) usually has a slight composition of chemical decontamination treatment liquid in that it contains impurity ions decontaminated with an oxidizing agent such as dichromate ion Cr ₂ O ₇ ^2−. Different.

  Since the final purification process (step S301) and the first purification process (step S103) are the same except for the composition of the chemical decontamination treatment liquid, description of the configuration and operation of the final purification process is omitted or simplified. .

Specifically, the chemical decontamination treatment liquid after the second chemical decontamination treatment part (step group S200), which is the starting material of this process, is the chemical decontamination treatment liquid discharged from the decontamination agent decomposing apparatus 62. Usually, it contains cationic impurity ions (impurity cations) such as iron ions Fe ²⁺ , Fe ³⁺ , cobalt ions Co ²⁺ and nickel ions Ni ²⁺ derived from the oxide film to be removed. In addition, the chemical decontamination treatment liquid after the second chemical decontamination treatment part is oxalic acid derived from the reducing agent used in the second reduction step (step S202) of the second chemical decontamination treatment part (step group S200). It may contain anionic impurity ions (impurity anions) such as the ions C ₂ O ₄ ²⁻ .

  The chemical decontamination treatment liquid containing the impurity ions is passed through the cation exchange resin tower (ion exchange resin tower) 63 and the anion exchange resin tower (ion exchange resin tower) 64 as in the first purification step (step S103). As a result, impurity ions are removed.

Specifically, when the chemical decontamination treatment liquid contains impurity cations such as iron ions Fe ²⁺ , Fe ³⁺ , nickel ions Ni ²⁺ , cobalt ions Co ²⁺ , the chemical decontamination treatment liquid is added to the cation exchange resin tower 63. When the water is passed, impurity cations in the chemical decontamination treatment liquid are removed by ion exchange.

When the chemical decontamination treatment liquid contains impurity anions such as dichromate ion Cr ₂ O ₇ ²⁻ and oxalate ion C ₂ O ₄ ²⁻ , the chemical decontamination treatment liquid is added to the anion exchange resin tower 64. When the water is passed, the impurity anions in the chemical decontamination treatment liquid are removed by ion exchange.

The temperature of the chemical decontamination treatment liquid in this step is usually 50 ° C to 80 ° C, preferably 50 ° C to 70 ° C. The temperature of the chemical decontamination treatment liquid in this step is preferably within this range because the ion exchange efficiency of impurity ions in this step is high.
The temperature of the chemical decontamination treatment liquid in this step can be easily adjusted by, for example, not heating the chemical decontamination treatment liquid with the heater 33.

  In addition, since the temperature of the chemical decontamination process liquid of a 1st purification process (step S103) is 70 to 90 degreeC normally, Preferably it is 75 to 85 degreeC, Therefore The temperature of the chemical decontamination process liquid of this process is more. Low. This is because, in the case of the first purification process, there is a heating process such as an oxidation process (step S201) or a second reduction process (step S202) of the second chemical decontamination processing part (step group S200) later. In the present process, it is necessary not to reduce the temperature excessively in consideration of the reheating of the chemical decontamination liquid in the subsequent oxidation process (step S201) or the second reduction process (step S202). It is because it is not necessary to consider reheating of the chemical decontamination treatment liquid in the subsequent process because there is no process to heat later.

  The temperature of the chemical decontamination treatment liquid in this step naturally decreases, for example, by controlling such as not heating with the heater 33, so that the temperature within the above temperature range can be easily set.

  The pH of the chemical decontamination treatment liquid in this step is usually 4 or more, preferably 4-8.

  The chemical decontamination treatment liquid that is passed through the cation exchange resin tower 63 and the anion exchange resin tower 64 and discharged is a chemical decontamination treatment liquid that has been purified by removing impurity ions.

[Process where chemical decontamination solution contains microbubbles]
In the decontamination method according to the present invention, the chemical decontamination treatment liquid used in at least one step selected from the chemical decontamination treatment includes microbubbles.

  That is, the decontamination method according to the present invention includes a first reduction process (step S101), a first reducing agent decomposition process (step S102), a first purification process (step S103), an oxidation process (step S201), and a second reduction process. The chemical decontamination liquid used in at least one process selected from the process (step S202), the second reducing agent decomposition process (step S203), and the final purification process (step S301) includes microbubbles.

  When the chemical decontamination treatment liquid contains microbubbles, in addition to the chemical decontamination effect of the oxide film to be removed, the physical decontamination effect of the oxide film to be removed by microbubbles is also exhibited, thereby improving the decontamination effect. Therefore, it is preferable.

  The physical decontamination using micro bubbles will be described.

  The microbubbles used in the present invention, that is, microbubbles having a bubble diameter equal to or smaller than the critical bubble diameter, cause a crushing phenomenon in the chemical decontamination treatment liquid. In this crushing phenomenon, it is said that, in the microbubbles, the pressure in the bubbles rapidly increases due to the reduction of the bubbles, and the temperature in the bubbles rapidly increases due to the adiabatic compression action. As a result, when the bubbles disappear, a region of several thousand degrees and several thousand atmospheres microscopically appears in the bubble extinguishing part, and this region of several thousand degrees and several thousand atmospheres generates a strong impact force on the surrounding medium. It is said to let you. The decontamination method using the decontamination apparatus 10 uses this strong impact force to peel off and remove the removal target oxide film on the surface of the reactor coolant recirculation system 3 that is the decontamination target part. is there. Note that the phenomenon in which a strong impact force is generated in the surrounding medium by the crushing phenomenon of microbubbles is considered to be the same phenomenon as the generation and collapse of cavitation due to ultrasonic vibration.

Physical decontamination using microbubbles does not dissolve the oxide film to be removed like chemical decontamination, but peels the oxide film to be removed from the metal material using the impact force when the bubbles disappear. It is. Therefore, physical decontamination using microbubbles is effective even when the oxide film to be removed is a chemically difficult substance such as nickel ferrite (NiFe ₂ O ₄ ) and chemical decontamination is not effective. There is an advantage that decontamination is possible.

  In physical decontamination using microbubbles, the impact force (destructive force) when the microbubbles disappear is affected by the temperature of the chemical decontamination treatment liquid containing the microbubbles. The relationship between the temperature of the chemical decontamination treatment liquid and the destructive force caused by microbubbles will be described with reference to the drawings.

  FIG. 3 is a graph showing the influence of water temperature on the destructive force caused by bubbles generated in water by cavitation caused by ultrasonic vibration. The horizontal axis of FIG. 3 is the water temperature of cavitation. The vertical axis in FIG. 3 is the relative value of the cavitation breaking force, and is an index indicating the breaking force that bubbles generated in water by cavitation have on the object.

  As shown in FIG. 3, the destructive force due to bubbles generated by cavitation is maximum when the water temperature is around 60 ° C., and the destructive force decreases as the temperature increases or decreases from around 60 ° C. Specifically, the breaking force due to bubbles is 91 at 50 ° C., 100 at 60 ° C., 87 at 70 ° C., 66 at 75 ° C., 40 at 80 ° C., 20 at 85 ° C., and 4 at 90 ° C. Thus, from the viewpoint of the magnitude of the destructive force caused by the microbubbles, the temperature of the chemical decontamination treatment liquid is preferably around 60 ° C.

  On the other hand, the suitable temperature of the chemical decontamination treatment liquid varies depending on the circumstances of each process as described above.

  Specifically, in the decontamination process such as the first reduction process (step S101), the oxidation process (step S201), and the second reduction process (step S202), the temperature of the chemical decontamination treatment liquid is usually 80 ° C. to 100 ° C. ° C. In this temperature range, for example, when the temperature of the chemical decontamination treatment liquid is 90 ° C., the destructive force due to bubbles is 4 from FIG. Hereinafter, the decontamination processes such as the first reduction process (step S101), the oxidation process (step S201), and the second reduction process (step S202) are referred to as “chemical decontamination treatment liquid high temperature process”.

  In the decontaminating agent decomposing step such as the first reducing agent decomposing step (step S102) and the second reducing agent decomposing step (step S203), and the first purification step (step S103), the temperature of the chemical decontamination treatment liquid is Usually, it is 70 ° C to 90 ° C, preferably 75 ° C to 85 ° C. In this temperature range, for example, when the temperature of the chemical decontamination treatment liquid is 70 ° C. and 80 ° C., the destructive force due to the bubbles is 87 and 40, respectively, from FIG. Hereinafter, the decontaminating agent decomposing steps such as the first reducing agent decomposing step (step S102) and the second reducing agent decomposing step (step S203) and the first purifying step (step S103) are referred to as “chemical decontamination treatment liquid intermediate temperature step”. "

  Further, in the final purification step (step S301), the temperature of the chemical decontamination treatment liquid is usually 50 ° C to 80 ° C, preferably 50 ° C to 70 ° C. In this temperature range, for example, when the temperature of the chemical decontamination treatment liquid is 50 ° C. and 60 ° C., the destructive force due to the bubbles is 91 and 100, respectively, from FIG. Hereinafter, the final purification process (step S301) is referred to as “chemical decontamination liquid low temperature process”.

  For this reason, in view of FIG. 3 and the suitable temperature of the chemical decontamination treatment liquid in each step, the chemical decontamination treatment liquid has the greatest destructive force due to microbubbles and is most suitable for performing physical decontamination with microbubbles. Examples of the process include a chemical decontamination treatment liquid low temperature process, that is, a final purification process (step S301) that is usually a process in which the temperature of the chemical decontamination treatment liquid is the lowest.

  Further, the destructive force of the chemical decontamination treatment liquid due to microbubbles is large after the chemical decontamination treatment liquid low-temperature process, that is, the final purification process (step S301), and the physics due to microbubbles after the final purification process (step S301). A process suitable for performing decontamination is a chemical decontamination treatment liquid intermediate temperature process, that is, a process in which the temperature of the chemical decontamination treatment liquid is usually slightly higher than the final purification process (step S301). A decontaminating agent decomposing step such as a decomposing agent decomposing step (step S102) and a second reducing agent decomposing step (step S203), and a first purification step (step S103) can be mentioned.

  Further, the destructive power of the chemical decontamination treatment liquid due to microbubbles is a decontamination agent such as a chemical decontamination treatment liquid intermediate temperature process, that is, a first reducing agent decomposition process (step S102) and a second reducing agent decomposition process (step S203). As a process that is smaller than the decomposition process and the first purification process (step S103) and is usually not very suitable for performing physical decontamination with microbubbles, a chemical decontamination solution high-temperature process, that is, usually chemical decontamination. The first reduction process (step S101), the oxidation process (step S201), and the second reduction process (step), in which the temperature of the treatment liquid is higher than the chemical decontamination treatment liquid low temperature process and the chemical decontamination treatment liquid intermediate temperature process. Decontamination process such as S202).

  Note that the chemical decontamination liquid intermediate temperature process such as the first reducing agent decomposition process (step S102) has a destructive force due to microbubbles compared to the chemical decontamination liquid high temperature process such as the first reduction process (step S101). Since it is about 10 times larger, it is a process suitable for physical decontamination with microbubbles.

  For example, the temperature of the chemical decontamination treatment liquid in the high temperature process of the chemical decontamination treatment liquid such as the first reduction process (step S101) is normally about 90 ° C., but when it is 90 ° C., the destructive force due to microbubbles is 4 from FIG. It is. On the other hand, the temperature of the chemical decontamination treatment liquid in the chemical decontamination treatment liquid intermediate temperature step such as the first reducing agent decomposition step (step S102) is usually about 80 ° C., but if it is 80 ° C., it is due to microbubbles from FIG. Destructive power is 40.

  Therefore, the destructive force due to the microbubbles in the chemical decontamination treatment liquid intermediate temperature process such as the first reducing agent decomposition process (step S102) is due to the microbubbles in the chemical decontamination treatment liquid high temperature process such as the first reduction process (step S101). This process is 10 times larger than the destructive force, and is a process that is sufficiently suitable for physical decontamination using microbubbles.

  For this reason, in the decontamination method according to the present invention, the first reducing agent decomposition step (step S102), the second reducing agent decomposition step (step S203), and the first purification step (step), which are chemical decontamination treatment liquid intermediate temperature steps. S103), and the chemical decontamination liquid used in at least one process selected from the final purification process (step S301) which is a low temperature chemical decontamination process liquid contains microbubbles, the decontamination effect due to the microbubbles is large. Therefore, it is preferable.

  Moreover, the temperature of the chemical decontamination processing liquid containing microbubbles becomes like this. Preferably it is 80 degrees C or less, More preferably, it is 50 to 80 degreeC, More preferably, it is 50 to 70 degreeC. This is because when the temperature of the chemical decontamination treatment liquid is 80 ° C. or lower, the destructive force due to microbubbles is greater than when the temperature exceeds 80 ° C.

  The chemical decontamination treatment liquid containing microbubbles in this temperature range includes the first reducing agent decomposition process (step S102), the second reducing agent decomposition process (step S203), and the intermediate temperature process of the chemical decontamination treatment liquid. Although it is preferable that it is a chemical decontamination treatment liquid used in at least one process selected from one purification process (step S103) and a final purification process (step S301) which is a low temperature chemical decontamination treatment liquid process, It is not limited to the chemical decontamination processing liquid used.

  As a process in which a chemical decontamination treatment liquid containing microbubbles in the above temperature range other than these is used, for example, a first reduction process (step S101) which is a chemical decontamination treatment liquid high temperature process, an oxidation process (step S201), And a decontamination process such as a second reduction process (step S202). Hereinafter, decontamination processes, such as a 1st reduction process (Step S101), an oxidation process (Step S201), and a 2nd reduction process (Step S202), are mentioned.

  Thus, in the decontamination method according to the present invention, the temperature of the process in which the chemical decontamination treatment liquid containing microbubbles is used is important. However, the temperature of the chemical decontamination treatment liquid is determined by circumstances such as the decontamination process and the purification process of the chemical decontamination process, and it is not easy to change the temperature of the chemical decontamination treatment liquid. For this reason, when the decontamination method according to the present invention is used, a process having a temperature suitable for including microbubbles in the chemical decontamination treatment liquid is selected as described above, and the chemical decontamination is performed in this process. It is preferable to include microbubbles in the treatment liquid because it is efficient.

  In the decontamination method according to the present invention, if the chemical decontamination treatment liquid contains microbubbles made of oxygen in the oxidation step (step S201), the amount of dissolved oxygen in the chemical decontamination treatment liquid increases and the chemical decontamination treatment liquid increases. It is preferable because the entire dyeing treatment liquid is in an oxidative atmosphere and an extremely strong oxidative state can be locally produced in the chemical decontamination treatment liquid, so that the oxidation effect is enhanced and the oxidative decontamination capability is improved.

  That is, if the chemical decontamination treatment liquid contains microbubbles made of oxygen, the oxygen in the microbubbles dissolves very efficiently in the chemical decontamination treatment liquid due to the disappearance of the microbubbles, and dissolved oxygen in the chemical decontamination treatment liquid The amount can be increased. For example, when oxygen bubbles are supplied to the chemical decontamination solution at room temperature, the dissolved oxygen concentration becomes about 1.5 times the normal saturation concentration.

  Also, if the chemical decontamination treatment liquid contains microbubbles made of oxygen, OH radicals are generated in the chemical decontamination treatment liquid due to the energy at the time of the collapse of the microbubbles, and are extremely strong locally in the chemical decontamination treatment liquid. An oxidative state can be created.

  As described above, when the chemical decontamination treatment liquid includes microbubbles made of oxygen in the oxidation step (step S201), in addition to the physical decontamination effect due to the microbubbles, the oxidation effect of the chemical decontamination treatment liquid is increased and oxidation is performed. Decontamination capability can also be improved.

  Note that the oxidation step (step S201) is a chemical decontamination treatment liquid high temperature step, and since the temperature of the chemical decontamination treatment solution is usually high, the physical decontamination effect due to microbubbles is not large. However, if microbubbles made of oxygen are contained in the chemical decontamination treatment liquid, the oxidation effect of the chemical decontamination treatment liquid is increased and the oxidative decontamination ability is improved, which is generally preferable.

  In this oxidation step (step S201), the chemical decontamination treatment liquid contains microbubbles made of oxygen. The first reduction step (step S101), the first reducing agent decomposition step (step S102), and the first purification step (step S103), chemical removal used in at least one step selected from an oxidation step (step S201), a second reduction step (step S202), a second reducing agent decomposition step (step S203), and a final purification step (step S301). It can be used together with the fact that the dyeing solution contains microbubbles made of a gas not limited to oxygen. When used together, it is preferable because a physical decontamination effect by microbubbles made of a gas not limited to oxygen and an oxidative decontamination effect and physical decontamination effect by microbubbles made of oxygen can be expressed.

[Zeta potential and pH of microbubbles]
In order to effectively decontaminate the oxide film to be removed using the microbubbles in the chemical decontamination liquid, the microbubbles in the chemical decontamination liquid are in contact with the chemical decontamination liquid. It is preferable to exist on the surface of the oxide film or in the vicinity thereof. This is because physical decontamination due to the crushing phenomenon of microbubbles, and oxidative decontamination and physical decontamination with microbubbles containing oxygen are highly effective in decontamination when performed on or near the surface of the oxide film to be removed.

  As a method of causing microbubbles in the chemical decontamination treatment liquid to be present on or near the surface of the oxide film to be removed that is in contact with the chemical decontamination treatment liquid, the microbubbles in the chemical decontamination treatment liquid are chemically decontaminated. There is a method in which the microbubbles are electrically attracted to or adsorbed on the surface of the oxide film to be removed while having a charge having a sign opposite to that of the zeta potential of the oxide film to be removed in contact with the treatment liquid.

  As a method of making the microbubbles in the chemical decontamination treatment liquid have a charge with the sign opposite to the zeta potential of the oxide film to be removed that has come into contact with the chemical decontamination treatment liquid, the pH of the chemical decontamination treatment liquid is set. A method of setting the zeta potential of the microbubbles in the chemical decontamination treatment liquid to a negative potential and adsorbing the negatively charged microbubbles to the target oxide film to be removed within the pH range can be mentioned. .

  The relationship between the pH of the chemical decontamination solution and the zeta potential of the oxide film to be removed and the microbubbles will be described with reference to the drawings.

FIG. 4 is a graph showing the relationship between the pH of the chemical decontamination solution and the zeta potential of metal oxides and microbubbles corresponding to the oxide film to be removed. Here, hematite and nickel ferrite (NiFe ₂ O ₄ ), which are considered to be attached to and generated on the inner surface of the reactor recirculation pipe 4, were used as the metal oxide as a measurement sample. Moreover, as a chemical decontamination processing liquid, what added the pH adjuster to the pure water suitably was used. As the pH adjuster, dilute hydrochloric acid and sodium hydroxide aqueous solution were used. Furthermore, the microbubbles were microbubbles made of air.

  As shown in FIG. 4, it can be seen that the hematite, nickel ferrite, and microbubbles all show a positive zeta potential when the pH decreases, and a negative zeta potential when the pH increases.

  Specifically, the isoelectric points of microbubbles, hematite, and nickel ferrite are pH 4.5, pH 6.3, and pH 6.7, respectively, and all of microbubbles, hematite, and nickel ferrite have a pH of It can be seen that the zeta potential is positive if it is smaller than the isoelectric point and negative if the pH is higher than the isoelectric point.

  Here, in the range of pH 4.5 to 6.3, the zeta potential of microbubbles is negative, whereas the zeta potential of hematite is positive. Further, in the range of pH 4.5 to 6.7, the zeta potential of the microbubbles is negative, whereas the zeta potential of nickel ferrite is positive.

  For this reason, when the pH of the chemical decontamination treatment liquid is normally in the range of pH 4.5 to 6.5, preferably pH 4.5 to 6.3, the chemical decontamination treatment liquid has a negative charge. The microbubbles are preferred because they are easily attracted by being attracted electrically to the removal target oxide film made of hematite, nickel ferrite or the like having a positive charge.

  FIG. 5 is an explanatory view schematically showing the action of decontamination with microbubbles in a state where the microbubbles have a charge opposite to the zeta potential of the oxide film to be removed. In FIG. 5, the state in which the lump of the oxide film 72 to be removed attached to the surface of the metal pipe 71 is peeled off from the surface of the metal pipe 71 over time by the action of the microbubbles 74 is shown in the order of the passage of time. P1, P2, P3, P4, and P5.

  First, in a state where the microbubbles 74 do not exist in the vicinity of the removal target oxide film 72, such as a state where the chemical decontamination treatment liquid 73 does not include the microbubbles 74, a lump of the removal target oxide film 72 is a metal pipe. It adheres to the surface of 71 (P1).

  Next, when there is a microbubble 74 having a charge opposite to the zeta potential of the removal target oxide film 72 in the vicinity of the removal target oxide film 72 in the chemical decontamination treatment liquid 73, the microbubble 74 is Adsorbed on the surface of the oxide film 72 to be removed (P2).

  The microbubbles 74 adsorbed on the surface of the removal target oxide film 72 are gradually reduced and finally disappeared, and the removal target oxide film 72 is peeled off from the surface of the metal pipe 71 due to a collapse phenomenon or the like when the bubbles disappear. Even after the microbubbles 74 adsorbed on the surface of the removal target oxide film 72 disappear, new microbubbles 74 existing in the chemical decontamination treatment liquid 73 are sequentially adsorbed on the surface of the removal target oxide film 72. The peeling action of the oxide film 72 to be removed by the microbubbles 74 is continuously performed (P3, P4). As described above, the adsorption and disappearance of the microbubbles 74 are repeated on the surface of the removal target oxide film 72, and the removal target oxide film 72 is gradually peeled off from the surface of the metal pipe 71.

  When the removal target oxide film 72 is completely peeled from the surface of the metal pipe 71, the peeled and floated removal target oxide film 72 is taken into the chemical decontamination treatment liquid 73, and the decontamination of the removal target oxide film 72 is completed ( P5).

  In the first reduction step and the second reduction step, since the pH of the chemical decontamination treatment liquid is usually as low as 1 to 3, both the charge of the microbubbles 74 and the zeta potential of the oxide film 72 to be removed become positive. Cheap. That is, in these steps, the charge of the microbubbles 74 is less likely to be opposite to the zeta potential of the removal target oxide film 72 in contact with the chemical decontamination liquid 73. For this reason, in the first reduction process and the second reduction process, the microbubbles 74 in the chemical decontamination treatment liquid 73 are difficult to be adsorbed on the surface of the oxide film 72 to be removed.

  However, in the latter stage of the first reducing agent decomposition step and the second reducing agent decomposition step, and in the first purification step and the final purification step, the pH of the chemical decontamination treatment liquid is usually 4 or more, so the charge of the microbubbles 74 Becomes negative, and the zeta potential of the oxide film 72 to be removed tends to become positive. That is, in these steps, the charge of the microbubbles 74 tends to be opposite to the zeta potential of the oxide film 72 to be removed that is in contact with the chemical decontamination solution 73. For this reason, in the first reducing agent decomposition step, the second reducing agent decomposition step, the first purification step, and the final purification step, the microbubbles 74 in the chemical decontamination treatment liquid 73 are adsorbed on the surface of the oxide film 72 to be removed. It becomes easy.

[Difference in decontamination effect with and without microbubbles]
In order to confirm the difference in the decontamination effect between the case where the chemical decontamination treatment liquid contains microbubbles and the case where it does not contain, a decontamination test was performed using a test piece. As the contaminated metal test piece, a test piece in which a nickel ferrite (NiFe ₂ O ₄ ) film that hardly chemically dissolves on the surface of a stainless steel metal material was used was used.

  The test conditions for the decontamination test were two cases, one when the chemical decontamination solution did not contain microbubbles and the other. An experimental example in which the chemical decontamination liquid does not contain microbubbles throughout the entire process is referred to as Experimental Example 1. An experimental example in which the chemical decontamination treatment liquid includes a process including microbubbles is referred to as Experimental Example 2.

  Experimental Example 1 and Experimental Example 2 have the same test conditions except that the chemical decontamination solution contains microbubbles.

  In addition, since Experimental Example 1 and Experimental Example 2 are simple tests using a contaminated metal test piece, a reducing agent decomposition step such as a first reducing agent decomposition step or a final purification step of the decontamination method according to the present invention. Instead of the purification step, a cleaning step such as a first cleaning step was performed.

  The experimental procedure common to Experimental Example 1 and Experimental Example 2 is as follows. Specifically, the following three cycles of steps were performed.

(First cycle)
In the first cycle, the following first reduction step and first cleaning step were performed.
<First reduction process>
First, a 95 ° C. oxalic acid aqueous solution containing 2000 ppm of oxalic acid was prepared as a reducing decontamination solution, and a contaminated metal test piece was immersed in this oxalic acid aqueous solution for 5 hours.
<First cleaning step>
Next, the contaminated metal specimen was washed with pure water.

(2nd cycle)
In the second cycle, the following second oxidation step, second reduction step, and second cleaning step were performed.
<Second oxidation step>
First, as an oxidizing decontamination solution, 80 ° C. ozone water containing 3 ppm of ozone was prepared, and a contaminated metal test piece was immersed in this ozone water for 2 hours.
<Second reduction process>
Next, the same process as the 1st reduction process of the 1st cycle was performed.
<Second cleaning step>
Furthermore, the same process as the 1st washing process of the 1st cycle was performed.

(3rd cycle)
In the third cycle, the same steps (second oxidation step, second reduction step, and second cleaning step) as in the second cycle were performed. These steps are referred to as a third oxidation step, a third reduction step, and a third cleaning step.

  The above is the experimental procedure common to Experimental Example 1 and Experimental Example 2. For each of Experimental Example 1 and Experimental Example 2, two similar test pieces A and B were prepared, and the test was performed twice. Tests of test pieces A and B of Experimental Example 1 are referred to as Experimental Example 1-A and Experimental Example 1-B, respectively, and tests of Test Pieces A and B of Experimental Example 2 are referred to as Experimental Example 2-A and Experimental Example 2-B, respectively. .

  Experimental Example 2 was the same as Experimental Example 1 except that ultrasonic cleaning using a cavitation effect was performed for 5 minutes using a 45 kHz ultrasonic wave in the third cleaning step of the third cycle. Ultrasonic cleaning using this cavitation effect mimics the effect of microbubbles.

  FIG. 6 is a graph showing the difference in decontamination effect depending on the presence or absence of microbubbles. The vertical axis | shaft of FIG. 6 shows a decontamination coefficient. In FIG. 6, in Experimental Example 1-A and Experimental Example 1-B, data are also shown for decontamination coefficients at the end of one cycle and at the end of two cycles in addition to the decontamination coefficients at the end of three cycles.

  As shown in FIG. 6, the decontamination coefficients at the end of the two cycles of Experimental Example 1-A and Experimental Example 1-B in which the chemical decontamination treatment liquid does not contain microbubbles are both 2, and the chemical decontamination treatment liquid contains microbubbles. Including Experimental Example 2-A and Experimental Example 2-B were found to have decontamination factors of about 300 and about 1000.

  From the results of Experimental Example 1 and Experimental Example 2, when chemical decontamination processing liquid contains microbubbles during chemical decontamination, the chemical decontamination processing liquid does not contain microbubbles significantly. It was found that the decontamination efficiency was high.

<Effect>
According to the decontamination apparatus and the decontamination method according to this embodiment, the decontamination work period can be shortened because the decontamination effect is high.

  In the decontamination method, as shown in FIG. 2, the chemical decontamination process includes a first reduction process (step S101), a first reducing agent decomposition process (step S102), and a first purification process (step S103). ), Oxidation step (step S201), second reduction step (step S202), second reducing agent decomposition step (step S203), and final purification step (step S301). .

  However, in the decontamination method of the present invention, such a chemical decontamination process is replaced with a chemical decontamination process including all the processes from the first reduction process (step S101) to the final purification process (step S301). The decontamination method may include a decontamination process, a decontamination agent decomposition process, and a purification process. Hereinafter, the decontamination method including the decontamination step, the decontamination agent decomposition step, and the purification step is referred to as “simplified decontamination method”.

  Here, the decontamination step means a step of decontamination treatment of the oxide film to be removed with a chemical decontamination treatment liquid containing a reducing or oxidizing decontamination agent. The decontamination process includes, for example, at least one of a first reduction process (step S101), a second reduction process (step S202), and an oxidation process (step S201).

  The decontamination agent decomposition step means a step of decomposing the reducing or oxidizing decontamination agent in the chemical decontamination treatment liquid after the decontamination step. The decontaminating agent decomposition step includes, for example, at least one of a first reducing agent decomposition step (step S102) and a second reducing agent decomposition step (step S203).

  Further, the purification step means a step of removing impurity ions in the chemical decontamination treatment liquid after the decontamination agent decomposition step. The purification process includes, for example, at least one of a first purification process (step S103) and a final purification process (step S301).

  In the simplified decontamination method, the chemical decontamination treatment liquid used in at least one step selected from the decontamination step, the decontamination agent decomposition step, and the purification step includes microbubbles. When the chemical decontamination treatment liquid contains microbubbles, in addition to the chemical decontamination effect of the oxide film to be removed, the physical decontamination effect of the oxide film to be removed by microbubbles is also exhibited, thereby improving the decontamination effect. Therefore, it is preferable.

  In the simplified decontamination method, if the chemical decontamination treatment liquid used in at least one step selected from the decontamination agent decomposition step and the purification step contains microbubbles, the decontamination effect by the microbubbles is large. Therefore, it is preferable.

  That is, the decontaminating agent decomposition step is a chemical decontamination treatment liquid intermediate temperature step as described above, and the purification step is a chemical decontamination treatment solution low temperature step as described above. This is preferable because the temperature is relatively low and the decontamination effect due to microbubbles is large.

  Furthermore, in the simplified decontamination method, when the decontamination process is an oxidation process (step S201), if the chemical decontamination treatment liquid used in this oxidation process contains microbubbles made of oxygen, the chemical decontamination process The amount of dissolved oxygen in the treatment liquid becomes high and the entire chemical decontamination treatment liquid is made an oxidative atmosphere, and an extremely strong oxidative state can be created locally in the chemical decontamination treatment liquid, so that the oxidation effect becomes high. The oxidative decontamination capability is preferable.

(Second Embodiment)
FIG. 7 is a schematic configuration diagram showing a second embodiment of the decontamination apparatus according to the present invention. A decontamination apparatus 10A shown in FIG. 7 is a decontamination apparatus that decontaminates the reactor coolant recirculation system 3 of the nuclear power plant 1A having a boiling water reactor (BWR).

  A nuclear power plant 1A shown in FIG. 7 is the same as the nuclear power plant 1 shown in FIG. 1 except that a decontamination device 10A is used instead of the decontamination device 10.

  Further, the decontamination apparatus 10A shown as the second embodiment in FIG. 7 is more specific than the decontamination apparatus 10 shown as the first embodiment in FIG. This is the same except that the microbubble generator 40A having a simple structure is used.

  For this reason, the same symbol is attached to the same member between the decontamination apparatus 10A shown as the second embodiment in FIG. 7 and the decontamination apparatus 10 shown as the first embodiment in FIG. Explanation of members and actions is omitted or simplified.

<Microbubble generator>
The micro-bubble generator 40A is a pressurized micro-bubble generator, and is provided in a chemical circulation line 41 that takes out the chemical decontamination processing liquid in the chemical tank 30 out of the chemical tank 30 and returns it to the chemical tank 30 for chemical treatment. A gas dissolving device 45 that dissolves a gas in the decontamination treatment liquid to supersaturation, and a nozzle 46 that ejects the chemical decontamination treatment liquid in which the gas is supersaturated into the chemical decontamination treatment liquid in the chemical tank 30 are included. .

  Specifically, in the microbubble generator 40A, the gas tank 42 for injecting gas into the chemical decontamination treatment liquid in the chemical liquid circulation line 41 via the gas injection line 43, and the gas in the chemical liquid circulation line 41 are injected. The chemical circulation line pump 44 for pressurizing the chemical decontamination treatment liquid, and the chemical decontamination treatment liquid into which gas has been injected and pressurized are introduced into the tank, and gas is introduced into the chemical decontamination treatment liquid in the tank. A gas dissolution tank (gas dissolution apparatus) 45 that dissolves in supersaturation and a nozzle 46 that ejects the chemical decontamination treatment liquid in which the gas in the chemical circulation line 41 is dissolved into the chemical decontamination treatment liquid in the chemical liquid tank 30 are included. .

  As the gas dissolution tank 45, a known gas dissolution tank can be used. For example, a tank in which the gas is dissolved in the chemical decontamination treatment liquid by introducing the chemical decontamination treatment liquid in the chemical circulation line 41 into which the gas has been injected and pressurized is introduced from the bottom of the tank.

  As the nozzle 46, a known nozzle that ejects gas into the liquid can be used.

<Action>
Next, the operation of the decontamination apparatus 10A will be described with reference to FIG.

  The decontamination apparatus 10A shown as the second embodiment in FIG. 7 is more specific in place of the microbubble generator 40 than the decontamination apparatus 10 shown as the first embodiment in FIG. The operation is the same except that the microbubble generator 40A is used. Therefore, hereinafter, only the action of generating the microbubbles by the microbubble generator 40A will be described.

  In the decontamination method of the present invention, the procedure for including microbubbles in the chemical decontamination treatment liquid by the pressure dissolution type generation method using the microbubble generator 40A which is a pressurization type microbubble generator is as follows. It is.

  First, the chemical liquid circulation line pump 44 is operated in a state where the chemical decontamination processing liquid is stored in the chemical liquid tank 30, and the chemical decontamination processing liquid is circulated between the chemical liquid tank 30 and the chemical liquid circulation line 41.

  Next, gas is injected into the chemical solution circulation line 41 from the gas tank 42 via the gas injection line 43. The gas to be injected is air, oxygen, or the like, and is a gas of a desired type as a gas constituting the microbubbles. For example, when microbubbles are included in the chemical decontamination solution in the first reducing agent decomposition step (step S102), the first purification step (step S103), etc., air is used, and chemical decontamination is performed in the oxidation step (step S201). When microbubbles are included in the treatment liquid, oxygen is used.

  The chemical decontamination processing liquid into which the gas in the chemical solution circulation line 41 is injected is pressurized by the chemical solution circulation line pump 44 and introduced into the gas dissolution tank 45. In the gas dissolution tank 45, the gas is dissolved in the chemical decontamination solution so as to be supersaturated.

  The chemical decontamination processing liquid dissolved so that the gas is supersaturated is discharged or ejected from the nozzle 46 provided in the chemical liquid tank 30 into the chemical decontamination processing liquid in the chemical liquid tank 30 via the chemical liquid circulation line 41. Is done. Since the chemical decontamination processing liquid discharged or ejected from the nozzle 46 is dissolved so that the gas becomes supersaturated, the pressure in the chemical liquid tank 30 is released, so that the supersaturated gas is contained in the chemical liquid tank 30. In the chemical decontamination treatment liquid, microbubbles are generated and a microbubble flow 87 is formed.

  FIG. 8 is a graph showing the bubble diameter distribution of the microbubbles generated in the second embodiment 10A of the decontamination apparatus according to the present invention. Specifically, it is a graph showing the bubble diameter distribution of the microbubbles generated in the chemical decontamination processing liquid in the chemical tank 30 using the microbubble generator 40A.

  As shown in FIG. 8, in the microbubbles generated in the chemical decontamination treatment liquid using the microbubble generator 40A which is a pressurized microbubble generator, a two-peak type in which two bubble diameter peaks exist. The distribution of was shown. Specifically, a two-peak type distribution in which a narrow peak having a peak value at a bubble diameter of 12 μm and a broad peak widely distributed over a bubble diameter of 40 μm to 56 μm is shown.

  Although the cause is not clear, in general, microbubbles having a two-peak distribution are seen when high concentration microbubbles are generated. For this reason, even if the bubble diameter distribution is a two-peak type, since it is considered that microbubbles are generated at a high concentration, the microbubble generator 40A is suitable as the microbubble generator of the present invention.

  The peak value of the bubble diameter of the narrow peak is as very small as 12 μm, and the range of the bubble diameter of the broad peak is 40 μm to 56 μm, which is a critical bubble diameter of 65 μm or less. For this reason, even if the bubble diameter distribution is a two-peak type, it is considered that the impact force due to the crushing phenomenon of the microbubbles is sufficiently large and the microbubbles have a sufficiently long floating time. Is suitable as a microbubble generator of the present invention.

<Effect>
According to the decontamination apparatus and the decontamination method according to the present embodiment, it is possible to generate very small microbubbles having a peak value of the bubble diameter of about 12 μm at a high concentration, and thus the decontamination according to the first embodiment. The decontamination effect is higher than that of the apparatus and the decontamination method, and the decontamination work period can be further shortened.

(Third embodiment)
FIG. 9 is a schematic configuration diagram showing a microbubble generator used in the third embodiment of the decontamination apparatus according to the present invention. A decontamination apparatus 10B shown in FIG. 9 is a decontamination apparatus for decontaminating the reactor coolant recirculation system 3 of the nuclear power plant 1B having a boiling water reactor (BWR).

  The nuclear power plant 1B shown in FIG. 9 is the same as the nuclear power plant 1 shown in FIG. 1 except that a decontamination device 10B is used instead of the decontamination device 10.

  Further, the decontamination apparatus 10B shown as the third embodiment in FIG. 9 is more specific than the decontamination apparatus 10 shown as the first embodiment in FIG. This is the same except that a microbubble generator 40B having a simple configuration is used.

  For this reason, the same code | symbol is attached | subjected to the same member between the decontamination apparatus 10B shown as 3rd Embodiment in FIG. 9, and the decontamination apparatus 10 shown as 1st Embodiment in FIG. Explanation of members and actions is omitted or simplified.

<Microbubble generator>
The microbubble generator 40B is a swirling flow type microbubble generator, which forms a two-phase swirl flow of a chemical decontamination treatment liquid and a gas, and uses this two-phase swirl flow as a chemical decontamination treatment liquid in the chemical tank 30. Drain inside.

  FIG. 10 is a cross-sectional view schematically showing a microbubble generator 40B used in the third embodiment 10B of the decontamination apparatus according to the present invention. FIG. 10 shows a state in which the microbubble generator 40 </ b> B is disposed in the bulk chemical decontamination processing liquid 86 in the chemical tank 30. In FIGS. 10 and 9, the direction of the microbubble generator 40 </ b> B is shown in reverse left and right.

  As shown in FIG. 10, the microbubble generator 40B includes a liquid channel 88 through which a liquid supplied from the outside flows in the swirl type microbubble generator main body 80, and a gas channel through which a gas supplied from outside flows. 89 and a fixed swirl plate 82 as a swirl flow generating mechanism disposed in the liquid flow path 88.

  Here, the swirl flow generation mechanism is a swirl flow, that is, a flow that moves in the flow direction of the flow channel while rotating when viewed from the cross section of the flow channel. Means a mechanism to change. An example of the fixed turning plate 82 is a fixed fan.

  In addition, a device (not shown), for example, a pump, for supplying a liquid to the liquid channel 88 of the microbubble generator 40B is provided outside the microbubble generator 40B.

<Action>
Next, the operation of the decontamination apparatus 10B will be described with reference to FIG. 9 and FIG.

  A decontamination apparatus 10B shown as the third embodiment in FIG. 9 is more specific in place of the microbubble generator 40 than the decontamination apparatus 10 shown as the first embodiment in FIG. The operations other than using the microbubble generator 40B are the same. For this reason, only the action of generating microbubbles by the microbubble generator 40B will be described below.

  In the decontamination method of the present invention, the procedure for including microbubbles in the chemical decontamination treatment liquid by the swirling flow type generating method using the microbubble generating apparatus 40B which is a swirling flow type microbubble generating apparatus is as follows. It is.

  First, the microbubble generator 40B is disposed in the chemical decontamination processing liquid 86 in the chemical tank 30, and the chemical decontamination processing liquid is supplied into the liquid flow path 88 using a pump or the like (not shown). The chemical decontamination liquid supplied into the liquid flow path 88 forms a linear liquid flow 81 in the liquid flow path 88. When the linear liquid flow 81 of the chemical decontamination processing liquid in the liquid flow path 88 hits a fixed swirl plate 82 disposed in the liquid flow path 88 as a swirl flow generation mechanism, As a result, a high-speed swirl flow is generated, and a negative pressure cavity is formed at the center of the high-speed swirl flow.

  Next, when a gas 83 such as air or oxygen is introduced into the chemical decontamination solution near the fixed swirl plate 82 in the liquid channel 88 from the outside through the gas channel 89, the gas is generated in the chemical decontamination solution. A tornado-shaped air bubble 84 includes a chemical decontamination treatment liquid in which a high-speed swirling flow of the chemical decontamination treatment liquid is entrained in a negative pressure cavity and a gas constituting the negative pressure cavity. The two-phase swirl flow 85 is formed.

  Here, as the gas 83 to be introduced, for example, air is used when the chemical decontamination treatment liquid includes microbubbles in the first reducing agent decomposition step (step S102), the first purification step (step S103), and the like. Oxygen is used when microbubbles are included in the chemical decontamination solution in the oxidation step (step S201).

  Further, when the two-phase swirl flow 85 in the liquid flow path 88 is discharged from the microbubble generator 40B into the chemical decontamination treatment liquid 86 in the chemical tank 30, a microbubble flow 87 is formed in the chemical decontamination treatment liquid 86. Is done.

  That is, since the bulk chemical decontamination treatment liquid 86 in the chemical liquid tank 30 does not flow or flows slowly, the two-phase swirl flow 85 in the liquid flow path 88 is converted into the chemical decontamination treatment liquid in the chemical liquid tank 30. When released into the gas flow 86, a large speed difference is generated between the two-phase swirl flow 85 and the chemical decontamination treatment liquid 86, so that a shear force is generated between the two-phase swirl flow 85 and the chemical decontamination treatment liquid 86. Arise. The two-phase swirl flow 85 is broken by this shearing force, and the gas contained in the two-phase swirl flow 85 is cut and crushed apart to generate microbubbles in the chemical decontamination liquid. When the chemical decontamination processing liquid containing microbubbles is released from the microbubble generator 40B, a microbubble flow 87 is formed in the chemical decontamination processing liquid 86 in the chemical tank 30.

  FIG. 11 is a graph showing the bubble diameter distribution of the microbubbles generated in the third embodiment 10B of the decontamination apparatus according to the present invention. Specifically, it is a graph showing the bubble diameter distribution of the microbubbles generated in the chemical decontamination treatment liquid in the chemical tank 30 using the microbubble generator 40B.

  As shown in FIG. 11, in the microbubbles generated in the chemical decontamination processing liquid using the microbubble generator 40B which is a swirling flow microbubble generator, one peak having one bubble diameter peak exists. The type distribution was shown. Specifically, a clean mountain-shaped distribution having a peak value at a bubble diameter of 28 μm and gently descending from the peak value to the lower limit side and the upper limit side of the bubble diameter was shown. As described above, when the microbubble generator 40B is used, sufficiently microbubbles can be generated in the chemical decontamination treatment liquid.

  As shown in FIG. 11, the peak value of the bubble diameter of the microbubbles generated by the microbubble generator 40B is 28 μm, and the bubble diameter of the microbubbles generated by the microbubble generator 40A is small as shown in FIG. The peak value is 12 μm. That is, the center of the bubble diameter of the microbubble generated by the microbubble generator 40B is slightly larger than the microbubble generated by the microbubble generator 40A.

  Therefore, judging only from the viewpoint of the bubble diameter of the microbubbles, the microbubble generator 40A, which is the pressurization type microbubble generator shown in FIG. 8, is the swirl type microbubble generator shown in FIG. It seems to be superior to the microbubble generator 40B.

  However, since the microbubble generator 40B is a swirl type microbubble generator, the gas pressure in the generated microbubbles is lower than the microbubbles generated by the microbubble generator 40A. That is, in the microbubble generator 40B which is a swirling flow type microbubble generator, the microbubbles are generated from the gas constituting the negative pressure cavity formed at the center of the high-speed swirling flow of the chemical decontamination treatment liquid. The pressure of the gas in the microbubbles is low.

  And since the microbubble with the low pressure of this internal gas tends to shrink | contract in a chemical decontamination processing liquid, it becomes a microbubble with a large shrinkage | contraction and crushing effect. Therefore, judging from the viewpoint of the pressure of the gas inside the microbubbles, the microbubble generator 40B, which is the swirl type microbubble generator shown in FIG. 11, is more suitable for the pressurized microbubble generator shown in FIG. This is superior to the microbubble generator 40A, and is suitable.

  Thus, the microbubble generator 40B, which is a swirl type microbubble generator, and the microbubble generator 40A, which is a pressurization type microbubble generator, are different in terms of the size of the microbubbles and the size of the microbubbles. Both have excellent aspects in terms of internal gas pressure, and both are suitable as microbubble generators.

<Effect>
According to the decontamination apparatus and the decontamination method according to the present embodiment, since the pressure of the gas inside the microbubbles is low and the microbubbles having a large contraction and collapse effect can be generated, the first embodiment is concerned. The decontamination effect is higher than that of the decontamination apparatus and decontamination method, and the decontamination work period can be further shortened.

  In the decontamination apparatus according to the first to third embodiments and the decontamination method using the decontamination apparatus, the metal material is a nuclear power plant 1 having a boiling water reactor (BWR). The example which is a structural member of the reactor coolant recirculation system 3 was shown.

  However, in the decontamination apparatus of the present invention and the decontamination method using this decontamination apparatus, the metal material is a constituent member of a nuclear reactor power plant having a pressurized water reactor (PWR), or a radioactive coolant recirculation system. It may be a component used in a material handling facility.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1, 1A, 1B Nuclear power plant 3 Reactor coolant recirculation system (decontamination target part)
4 Recirculation system piping 5 Recirculation pump 6 PLR vertical pipe 7 PLR horizontal pipe 8 PLR riser pipe 9 Branch pipe 10, 10A, 10B Decontamination equipment 20 Chemical decontamination treatment system 21 Decontamination liquid main circulation line Dyeing solution piping)
22 Chemical Decontamination Treatment Liquid Circulation Pump 30 Chemical Liquid Tank 31 Chemical Liquid Line 32 Chemical Liquid Line Pump 33 Heater 34 Chemical Liquid Heating Line Pump 35 Chemical Liquid Heating Line 40 Microbubble Generator 40A Pressurized Microbubble Generator 40B Swirling Flow Microbubble Generator ( Microbubble generator)
41 Chemical liquid circulation line 42 Gas tank 43 Gas injection line 44 Chemical liquid circulation line pump 45 Gas dissolution tank (gas dissolution apparatus)
46 Nozzle 50 Ozone generator 51 Mixer 52 Ozone supply line 61 Decontamination agent decomposition / ion exchange line 62 Decontamination agent decomposition device 63 Cation exchange resin tower (ion exchange resin tower)
64 Anion exchange resin tower (ion exchange resin tower)
65 Decontamination Decomposition / Ion Exchange Line Pump 71 Metal Piping (Metal Piping for Decontamination Target)
72a, 72b, 72c, 72d, 72e Removal target oxide film 73 Chemical decontamination treatment liquid 74 Microbubbles 80 Swirl flow type microbubble generator main body 81 Liquid flow 82 Fixed swirl plate (swirl flow generating mechanism)
83 Gas 84 Bubble 85 Two-phase swirl flow 86 Bulk liquid (chemical decontamination solution)
87 Microbubble flow 88 Liquid flow path 89 Gas flow path 91, 92 Valve 93 Decontamination liquid outlet S100 First chemical decontamination processing part S101 First reduction process S102 First reductant decomposition process S103 First purification process S200 Second Chemical decontamination process part S201 Oxidation process S202 2nd reduction process S203 2nd reducing agent decomposition | disassembly process S301 Final purification process

Claims (15)

In the decontamination method in which the removal target oxide film is removed by chemical decontamination treatment by bringing the chemical decontamination treatment liquid into contact with the removal target oxide film consisting of an oxide film containing a radioactive substance and adhering to the surface of the metal material.
The chemical decontamination treatment includes a decontamination process for decontaminating the oxide film to be removed with a chemical decontamination treatment liquid containing a decontamination agent, and a decontamination agent in the chemical decontamination treatment liquid after the decontamination process. A decontamination decomposition step for decomposing, and a purification step for removing impurity ions in the chemical decontamination treatment liquid after this decontamination decomposition step,
A decontamination method, wherein the chemical decontamination treatment liquid used in at least one step selected from the decontamination step, the decontamination agent decomposition step, and the purification step contains microbubbles. The decontamination method according to claim 1, wherein the chemical decontamination treatment liquid used in at least one step selected from the decontamination agent decomposition step and the purification step contains microbubbles. 3. The decontamination method according to claim 1, wherein when the decontamination step includes an oxidation step, the chemical decontamination treatment liquid used in the oxidation step includes microbubbles made of oxygen. The chemical decontamination process includes a first chemical decontamination process part, a second chemical decontamination process part performed after the first chemical decontamination process part, and a final purification process performed after the second chemical decontamination process part. And processing including
The first chemical decontamination process part includes a first reduction process in which the removal target oxide film is subjected to a reduction decontamination process using a chemical decontamination process liquid containing a reducing agent, and a chemical decontamination process after the first reduction process. A first reducing agent decomposing step for decomposing the reducing agent in the liquid, and a first purification step for removing impurity ions in the chemical decontamination processing liquid after the first reducing agent decomposing step,
The second chemical decontamination treatment part oxidizes and deoxidizes the oxide film to be removed using a chemical decontamination treatment liquid obtained by adding an oxidizing agent to the chemical decontamination treatment liquid after the purification step of the first chemical decontamination treatment part. An oxidation step for dyeing treatment, a second reduction step for reducing and decontaminating the oxide film to be removed using a chemical decontamination treatment liquid obtained by adding a reducing agent to the chemical decontamination treatment liquid after the oxidation step, 2 is a treatment having a second reducing agent decomposition step for decomposing the reducing agent in the chemical decontamination treatment liquid after the reduction step,
The second chemical decontamination treatment part is repeated once or twice or more,
The final purification step is a step of removing impurity ions in the chemical decontamination treatment liquid after the end of the second chemical decontamination treatment part,
The decontamination method according to claim 1, wherein the chemical decontamination treatment liquid used in at least one step selected from the chemical decontamination treatment includes microbubbles. The chemical decontamination treatment liquid used in at least one step selected from the first reducing agent decomposition step, the second reducing agent decomposition step, the first purification step, and the final purification step contains microbubbles. The decontamination method according to claim 4, wherein the method is decontamination. The decontamination method according to claim 4 or 5, wherein the chemical decontamination treatment liquid used in the oxidation step includes microbubbles made of oxygen. The decontamination method according to any one of claims 1 to 6, wherein the metal material is a constituent member used in a nuclear power plant or a radioactive material handling facility. The decontamination method according to claim 7, wherein the constituent member is a constituent member of a coolant recirculation system of a nuclear power plant. The decontamination method according to any one of claims 1 to 8, wherein the temperature of the chemical decontamination treatment liquid containing microbubbles is 80 ° C or lower. 10. The decontamination method according to claim 1, wherein the microbubbles in the chemical decontamination treatment liquid have an average cell diameter of 65 μm or less. The microbubble in the said chemical decontamination processing liquid has the electric charge of the code | symbol opposite to the zeta potential of the oxide film to be removed which contacted the said chemical decontamination processing liquid. The decontamination method according to item 1. The decontamination method according to claim 1, wherein the oxide film to be removed is a hardly soluble oxide film mainly containing nickel ferrite. The microbubbles in the chemical decontamination treatment liquid are obtained by using a pressure dissolution type generation method or a swirl flow type generation method. Decontamination method. Chemical decontamination treatment is performed by bringing the chemical decontamination treatment solution supplied from the chemical decontamination treatment system into contact with the metal decontamination target site where the oxide film to be removed consisting of an oxide film containing radioactive substances is attached to the surface. A decontamination device for removing the oxide film to be removed by
The chemical decontamination system is
A decontamination liquid pipe for supplying a chemical decontamination liquid to the decontamination target site;
A chemical tank for supplying chemical decontamination liquid to this decontamination liquid pipe,
A microbubble generator for generating microbubbles in the chemical decontamination treatment liquid in the chemical tank,
A decontamination apparatus comprising: The microbubble generator includes a gas dissolving device that dissolves the gas in a chemical decontamination treatment liquid and a chemical decontamination treatment liquid in which the gas is dissolved in supersaturation in the chemical decontamination treatment liquid in the chemical solution tank. A pressurized micro-bubble generating device comprising a nozzle to be ejected, or a two-phase swirling flow containing a chemical decontamination treatment liquid and gas is formed, and this two-phase swirling flow is introduced into the chemical decontamination treatment liquid in the chemical tank. The decontamination apparatus according to claim 14, wherein the decontamination apparatus is a swirling flow type microbubble generator for discharging.

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