Decontamination methods

Abstract

To provide a novel decontamination method that enables low-cost removal of radioactive substances attached to a surface of a decontamination target object.SOLUTION: A decontamination method disclosed herein comprises applying a gel-type decontamination agent to a surface of a decontamination target object having radioactive substances attached thereto, drying and solidifying the applied gel-type decontamination agent, and peeling off the solidified decontamination agent together with the radioactive substances from the decontamination target object.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to decontamination treatment.

Background Art

[0002] Wastes generated in nuclear power plants are classified according to radioactivity level into low-level radioactive waste (L1, L2, L3), materials that do not need to be handled as radioactive substances (clearance materials), and non-radioactive waste (NR), and must be disposed of according to their radioactivity level. For L3 waste, which has the lowest radioactivity level among low-level radioactive wastes, if it can be sufficiently decontaminated into clearance materials, it can be reused and disposed of in the same manner as ordinary materials.

[0003] Conventionally, air blasting has been used as one decontamination method for radioactive waste. Air blast treatment is a process in which a blast material is injected from a nozzle onto radioactive waste using compressed air to scrape off radioactive materials from the surface of the radioactive waste. However, during the treatment process, the blast material and radioactive materials scatter into the air, resulting in a poor working environment, and there are concerns about adverse effects on workers.

[0004] The technology of Patent Document 1 performs blasting treatment in a blast box to recover the blast material in order to improve the working environment for decontamination work. The technology comprises a blast head having a blast nozzle that emits blast material, and a suction hose that sucks the blast material, and controls the intake of outside air into the blast box as the blast material is emitted.

Prior Art Literature

Patent Literature

[0005]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0006] However, there are concerns that the device described in Patent Document 1 will have high production and maintenance costs due to its complex configuration.

[0007] Therefore, the object of this invention is to provide a new decontamination method that can remove radioactive materials adhering to the surface of an object to be decontaminated at low cost. [Means for solving the problem]

[0008] This invention was made to achieve the above objective and is characterized by the following:

[0009] The invention described in claim 1 is a decontamination method for removing radioactive material adhering to the surface of an object to be decontaminated, comprising: a coating step of applying a gel-like decontamination agent to the surface of the object to be decontaminated to which the radioactive material is adhering; a solidification step of drying and solidifying the applied gel-like decontamination agent; and a peeling step of peeling the solidified decontamination agent together with the radioactive material from the object to be decontaminated. The decontamination agent comprises at least one of locust bean gum, xanthan gum, guar gum, tara gum, carrageenan, gelatin, cellulose derivatives, tremel gum, and konjac powder, and a thioglycolate. It is characterized by [something].

[0010] The invention described in claim 2 is a decontamination method according to claim 1, further comprising an ultrasonic step of irradiating the surface of the object to be decontaminated, to which the gel-like decontamination agent has been applied, between the coating step and the solidification step.

[0013] Claim 3 The invention described in the claim 1 The decontamination method described above, wherein the decontamination agent further comprises a surfactant.

[0014] Claim 4 The invention described in claim 1 or The decontamination method described in 3, wherein the decontamination agent further comprises at least one of β-ionone or vanillin.

[0015] Claim 5 The invention described is Claim 1 orThe decontamination method according to 3, wherein the decontamination agent further contains at least one of cobalt oxide, cobalt phosphate, and cobalt aluminate. The invention described in claim 6 is a decontamination method described in claim 4, characterized in that the decontamination agent further comprises at least one of cobalt oxide, cobalt phosphate, and cobalt aluminate.

[0018] Claim 7 The invention described in, wherein the decontamination method according to claim 1 or 3, wherein the decontamination agent further contains borax. Effects of the Invention

[0019] According to the present invention, radioactive substances are adsorbed by the decontamination agent, and the decontamination agent and the radioactive substances are peeled off from the object to be decontaminated. Therefore, radioactive substances can be removed from the object to be decontaminated without being scattered unlike blasting treatment. As a result, for example, L3 waste can be leveled down to clearance waste, which can be reused or disposed of as it is. Brief Description of the Drawings

[0020] [Figure 1] (A) is a diagram showing a state where a gel-like decontamination agent is applied to an object to be decontaminated, (B) is a diagram showing a state where ultrasonic waves are irradiated to the surface of the decontamination object coated with the gel-like decontamination agent, and (C) is a diagram showing a state where radioactive substances are peeled off from the decontamination object together with the decontamination agent. [Figure 2] It is a diagram showing a flowchart of the decontamination method according to the present embodiment. [Figure 3] It is a diagram showing an example of components of the decontamination agent used in an experiment of the decontamination method according to the present embodiment. Mode for Carrying Out the Invention

[0021] Embodiments of the present invention will be described with reference to the drawings.

[0022] In this embodiment, decontamination of a decontamination target object 1 having radioactive substances 2 attached to the surface is performed as shown in FIG. 1(A), by applying a gel-like decontamination agent 11 to the surface of the decontamination target object 1, as shown in FIG. 1(B), irradiating the surface of the decontamination target object 1 coated with the gel-like decontamination agent 11 with ultrasonic waves 13, drying and solidifying the gel-like decontamination agent 11, and then peeling the solidified decontamination agent 11 from the decontamination target object 1 together with the radioactive substances 2, as shown in FIG. 1(C). That is, the radioactive substances 2 attached to the surface of the decontamination target object 1 are removed by the decontamination agent 11, just like removing dust attached to the surface of clothing with adhesive tape. As a result, the radioactive substances 2 are separated from the decontamination target object 1, and the separated radioactive substances 2 are retained by the decontamination agent 11 without scattering.

[0023] Here, the decontamination agent 11 of the present embodiment will be described. The decontamination agent 11 contains at least one of thickeners for gelatinizing the decontamination agent 11, the thickeners including locust bean gum, xanthan gum, guar gum, tara gum, carrageenan, gelatin, cellulose derivatives, tremel gum and konjac flour .

[0024] Note that the decontamination agent 11 may further contain at least one of borax as a crosslinking agent for various thickeners such as guar gum, tara gum and konjac flour, and reducing monosaccharides / oligosaccharides. For example, borax has an effect of promoting a crosslinking reaction linking between guar gum molecules to increase the rigidity of the gel-like decontamination agent 11. However, when borax is added to guar gum, while the rigidity of the gel-like decontamination agent 11 is increased, the fluidity thereof is reduced. Therefore, by further adding reducing monosaccharides / oligosaccharides, both the rigidity and fluidity of the gel-like decontamination agent 11 can be improved.

[0025] The decontamination agent 11 can be produced, for example, by adding 0.5 g of guar gum to 50 ml of water, stirring, and allowing the mixture to stand to swell, then adding borax sugar solution (containing 10 wt% of borax and 13 wt% of fructose) and stirring the mixture.

[0026] The viscosity of the decontamination agent 11 produced in this manner can be adjusted by changing the amount of reducing monosaccharides and oligosaccharides added.

[0027] Furthermore, the decontamination agent 11 may include a mixture of roasted bean gum and xanthan gum as an example of how to make the decontamination agent 11 gel-like. By adjusting the ratio of roasted bean gum to xanthan gum in the range of 2:8 to 7:3, the gel strength can be approximately 150 g / cm². 2 The above can be achieved, and if the ratio is 5 parts roasted bean gum to 5 parts xanthan gum, the gel strength will be approximately 300 g / cm². 2 This can be done. In this way, the gel strength of the decontamination agent 11 can be adjusted by the combination and mixing ratio of various thickeners. The gel strength of the decontamination agent 11 is 150 g / cm³. 2 ~300g / cm 2 It is preferable to do so.

[0028] The amount of the thickening agent should be, for example, 0.5 wt% to 1.5 wt% of the total amount of the decontamination agent 11.

[0029] The decontamination agent 11 can be applied to the surface of the object 1 to be decontaminated, which is contaminated with radioactive material 2, and then removed to decontaminate the object 1. Furthermore, by incorporating the radioactive material 2 into the gel, it is possible to prevent the radioactive material 2 from scattering and contaminating the surrounding area, and disposal is also made easier.

[0030] Next, the ultrasonic generator 12 will be described. A commercially available ultrasonic generator 12 can be used; for example, the plastic welder (SONAC-200) from Honda Electronics Co., Ltd. can be used. The frequency of the ultrasonic waves 13 can be set in the range of 15kHz to 28kHz.

[0031] Next, the decontamination method of this embodiment will be explained using the flowchart in Figure 2.

[0032] First, the gel-like decontamination agent 11 is applied to the surface of the object to be decontaminated 1, which has radioactive material 2 attached to its surface (step S11: an example of the "application process").

[0033] Next, ultrasonic waves 13 are irradiated onto the surface of the object to be decontaminated 1 to which the gel-like decontamination agent 11 has been applied (step S12: an example of the "ultrasonic process"). This makes it easier for the radioactive material 2 to be peeled off from the surface of the object to be decontaminated 1 in step S14.

[0034] Next, the gel-like decontamination agent 11 applied to the object to be decontaminated 1 is dried and solidified (step S13: an example of the "solidification process"). Methods for drying and solidifying the gel-like decontamination agent 11 include, for example, applying a heat gun, irradiating with microwaves, or heating with high frequency. Furthermore, to improve drying efficiency, air may be blown into the system to lower the humidity inside the system.

[0035] Next, the solidified decontamination agent 11 is detached from the object to be decontaminated 1 together with the radioactive material 2 (step S14: an example of the "detachment process"). For example, the detachment is achieved by grasping one end of the decontamination agent 11 that has adsorbed the radioactive material 2 with a tool and pulling it off.

[0036] Furthermore, the purpose of drying the decontamination agent 11 in step S13 is to allow it to be detached together with the radioactive material 2 in step S14, so it is not necessary to solidify it completely through drying. In other words, it is sufficient for the decontamination agent 11, which has adsorbed the radioactive material 2, to be solidified to the extent that it does not tear when picked up and pulled. Alternatively, instead of drying and solidifying, or in addition to this, a crosslinking accelerator (such as borax or reducing monosaccharides / oligosaccharides) that increases the gel strength of the gel-like decontamination agent 11 may be applied to or added to the decontamination agent 11.

[0037] As described above, the decontamination method of this embodiment is a decontamination method for removing radioactive material 2 adhering to the surface of an object to be decontaminated 1, and includes: step S11 (an example of a "coating step") of applying a gel-like decontamination agent 11 to the surface of the object to be decontaminated 1 to which the radioactive material 2 is adhering; step S12 (an example of an "ultrasonic step") of irradiating the surface of the object to be decontaminated 1 to which the gel-like decontamination agent 11 has been applied with ultrasonic waves 13; step S13 (an example of a "solidification step") of drying and solidifying the applied gel-like decontamination agent 11; and step S14 (an example of a "peeling step") of peeling off the solidified decontamination agent 11 together with the radioactive material 2 from the object to be decontaminated 1.

[0038] Therefore, according to the decontamination method of this embodiment, the decontamination agent 11 adsorbs the radioactive material 2, and the decontamination agent 11 and the radioactive material 2 are separated from the object to be decontaminated 1. Thus, the radioactive material 2 can be removed from the object to be decontaminated 1 without the radioactive material 2 being scattered, as in blast treatment. As a result, for example, L3 waste can be reduced to a clearance level, which can then be reused or disposed of as is.

[0039] If the radioactive material 2 is hydrophilic, for example, and can be incorporated directly into the gel-like decontamination agent 11 without irradiation by ultrasonic waves 13, step S12 may be skipped. On the other hand, if the radioactive material 2 is hydrophobic (such as oil), it is preferable to lift the radioactive material 2 from the object to be decontaminated 1 by irradiation with ultrasonic waves 13, as in the decontamination method of this embodiment, and then incorporate it into the gel-like decontamination agent 11.

[0040] Furthermore, if the radioactive material 2 is rusted on the surface of the object to be decontaminated 1, or if the surface of the object to be decontaminated 1 is radioactive, a thioglycolate such as ammonium thioglycolate or sodium thioglycolate may be added to the gel-like decontamination agent 11. The amount of thioglycolate added should be, for example, 0.3 mol / L to 1 mol / L relative to the total amount of decontamination agent 11. The thioglycolate reduces the radioactive material 2 and radioactive materials attached to the object to be decontaminated 1, making them easier to incorporate into the gel-like decontamination agent 11.

[0041] In addition, a surfactant (for example, an amphoteric surfactant such as sodium cocoamphoacetate (Softazolin® CH-R), cocamidopropyl betaine (Softazolin® CPB-R), or lauramidopropyl betaine) may be added to the decontamination agent 11 along with the thioglycolate. The amount of surfactant added should be, for example, 0.02 wt% to 0.05 wt% of the total amount of the decontamination agent 11.

[0042] Furthermore, since thioglycolate salts exhibit a malodorous and irritating odor, it is preferable to further add at least one of β-ionone or vanillin to mitigate or eliminate this odor. When adding only β-ionone, the amount added should be, for example, 0.08 wt% to 0.2 wt% of the total decontamination agent 11. When adding only vanillin, the amount added should be, for example, 0.08 wt% to 0.2 wt% of the total decontamination agent 11. When adding both β-ionone and vanillin, the amount added should be, for example, 0.08 wt% to 0.2 wt% of the total decontamination agent 11.

[0043] Furthermore, since the decontamination agent 11 contains a thickening agent that is prone to mold growth, at least one of cobalt oxide, cobalt phosphate, and cobalt aluminate may be added to the decontamination agent 11 for the purpose of preventing mold growth. When only cobalt oxide is added, the amount added should be, for example, 0.05 wt% to 0.2 wt% of the total amount of the decontamination agent 11. When only cobalt phosphate is added, the amount added should be, for example, 0.05 wt% to 0.2 wt% of the total amount of the decontamination agent 11. When only cobalt aluminate is added, the amount added should be, for example, 0.05 wt% to 0.2 wt% of the total amount of the decontamination agent 11. This improves the mold resistance of the decontamination agent 11.

[0044] Furthermore, if the radioactive material 2 attached to the object to be decontaminated 1 contains cobalt 60, it may not be completely incorporated into the decontamination agent 11 and may remain on the surface of the object to be decontaminated 1. In this case, by adding a cobalt compound with a structure similar to cobalt 60 to the decontamination agent 11, the cobalt compound acts as a retaining carrier, allowing the cobalt 60 to be incorporated into the decontamination agent 11. In other words, by adding at least one of cobalt oxide, cobalt phosphate, and cobalt aluminate, these will act as antifungal agents and retaining carriers.

[0045] Next, an example of the decontamination agent 11 used in the experiment of the decontamination method of this embodiment, shown in Figure 3, will be described. The decontamination agent 11 in the experimental example is a mixture of a thickener, a decontamination liquid, and an antifungal agent (retaining carrier).

[0046] The thickening agent consists of two solutions: one in which 2g of locust bean gum is dissolved in 200g of water, and the other in which 1.65g of xanthan gum is dissolved in 125g of water.

[0047] The decontamination solution consists of 49.2 g of 55% aqueous solution of ammonium thioglycolate, 41.0 g of water, 0.4 g of 30% aqueous solution of softazoline CPB-R, and 0.4 g of β-ionone.

[0048] The total mass of the mixture of these thickeners and decontamination solution is 419.65 g. The mass percentage concentration (%) of each component is as follows: Locust bean gum: 0.48% Xanthan gum: 0.39% Ammonium thioglycolate: 6.4% Softazoline CPB-R: 0.03% β-ionone: 0.10% When adding other thioglycolate salts such as sodium thioglycolate instead of ammonium thioglycolate, it is preferable to add an amount of thioglycolate salt that results in a molar concentration of 0.6 mol / L.

[0049] Decontamination agent 11 is prepared by adding 0.10 wt% or less of cobalt oxide as an antifungal agent (retaining carrier) to a mixture of these thickeners and the decontamination liquid.

[0050] As described above, the decontamination agent 11 may consist of at least one of the following as a thickener: locust bean gum, xanthan gum, guar gum, tara gum, carrageenan, gelatin, cellulose derivative, tremel gum, and konjac powder; a thioglycolate; a surfactant; at least one of β-ionone or vanillin as a deodorant; and at least one of the following as an antifungal agent (retaining carrier): cobalt oxide, cobalt phosphate, and cobalt aluminate. Here, let the thickener be "A", the thioglycolate be "B", the surfactant be "C", the deodorant be "D", and the antifungal agent (retaining carrier) be "E". An example of a combination of components for the decontamination agent 11 is shown below. However, the combination of components for the decontamination agent 11 is not limited to these, and any combination that is significant as a decontamination agent 11 can be adopted. • "A only" · "A + B" · "A+B+C" · "A+B+D" • "A+B+C+D" • "A+E" · "A+B+E" · "A+B+C+E" • "A+B+D+E" • "A+B+C+D+E" [Explanation of symbols]

[0051] 1: Objects to be decontaminated 2:Radioactive material 11: Decontamination agent 12: Ultrasonic generator 13: Ultrasound

Claims

1. A decontamination method for removing radioactive materials attached to the surface of an object to be decontaminated, A coating step of applying a gel-like decontamination agent to the surface of the object to be decontaminated to which the radioactive material is attached, The process involves drying and solidifying the applied gel-like decontamination agent, A peeling step in which the solidified decontamination agent is peeled off from the object to be decontaminated together with the radioactive material, Includes, The aforementioned decontamination agent is At least one of locust bean gum, xanthan gum, guar gum, tara gum, carrageenan, gelatin, cellulose derivative, tremel gum, and konjac powder, Thioglycolate and A decontamination method characterized by including [a certain component].

2. A decontamination method according to claim 1, A decontamination method characterized by further comprising an ultrasonic step of irradiating the surface of the object to be decontaminated, to which the gel-like decontamination agent has been applied, between the coating step and the solidification step.

3. A decontamination method according to claim 1, The decontamination method is characterized by further comprising a surfactant as the decontamination agent.

4. A decontamination method according to claim 1 or 3, A decontamination method characterized in that the decontamination agent further comprises at least one of β-ionone or vanillin.

5. A decontamination method according to claim 1 or 3, A decontamination method characterized in that the decontamination agent further comprises at least one of cobalt oxide, cobalt phosphate, and cobalt aluminate.

6. A decontamination method according to claim 4, A decontamination method characterized in that the decontamination agent further comprises at least one of cobalt oxide, cobalt phosphate, and cobalt aluminate.

7. A decontamination method according to claim 1 or 3, The decontamination method is characterized in that the decontamination agent further contains borax.

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