Slurry and decontamination method

Abstract

This invention provides a low-cost blast decontamination method for removing radioactive isotopes adhering to the surface of objects to be decontaminated, and also provides a slurry and other materials that prevent the slurry and radioactive isotopes from scattering as dust or mist. [Solution] The slurry contains a decontamination agent and an abrasive, the decontamination agent containing a thioglycolate, a thickening agent, and a holding carrier corresponding to a radioactive isotope, and the viscosity of the slurry is 10 to 100 mPa·s.

Description

Technical Field

[0001] This invention relates to decontamination treatment.

Background Art

[0002] Wastes generated in nuclear power plants are classified into low-level radioactive wastes (L1, L2, L3), materials that do not need to be treated as radioactive substances (clearance materials), and wastes that are not radioactive wastes (NR) according to their radioactivity levels, and need to be disposed of according to their radioactivity levels. Among low-level radioactive wastes, if L3 wastes with the lowest radioactivity level can be sufficiently decontaminated to become clearance materials, they can be reused and disposed of in the same way as general materials.

[0003] Conventionally, there is blast decontamination as a method for decontaminating radioactive wastes. Generally, blast decontamination is divided into dry blast decontamination and wet blast decontamination. The currently mainstream dry blast decontamination is a process of scraping off radioactive isotopes on the surface of radioactive wastes by injecting a slurry from a nozzle with compressed air (blasting). However, since the slurry and radioactive isotopes become dust and scatter in the air, the working environment is poor and there are concerns about adverse effects on workers. On the other hand, wet blast decontamination injects a liquid slurry from a nozzle with compressed air, but since the slurry and radioactive isotopes become fog and scatter in the air, there are concerns about adverse effects on workers similar to those of dry blast decontamination.

[0004] The technology of Patent Document 1 is to perform blast treatment in a blast box to improve the environment of the decontamination work and recover the slurry. Therefore, it has a blast head with a blast nozzle for ejecting the slurry and a suction hose for sucking the slurry, and controls the intake of outside air into the blast box as the slurry is ejected.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[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 slurry and the like that can decontaminate radioactive isotopes adhering to the surface of an object to be decontaminated at low cost using blast decontamination, and that the slurry and radioactive isotopes are less likely to be scattered as dust or mist. [Means for solving the problem]

[0008] The slurry according to the present invention, which solves the above problems, is a gel-like slurry for blast decontamination of radioactive isotopes attached to an object to be decontaminated, wherein the slurry comprises a decontamination agent and an abrasive, the decontamination agent comprises water, a thioglycolate, a thickener, and a holding carrier corresponding to the radioactive isotope, and the viscosity of the slurry is 10 to 100 mPa·s.

[0009] Furthermore, the slurry according to the present invention is characterized by further containing sodium bicarbonate.

[0010] Furthermore, in the slurry according to the present invention, a portion of the sodium bicarbonate is dissolved, and at least a portion of the abrasive material is the undissolved sodium bicarbonate.

[0011] Furthermore, in the slurry according to the present invention, the thickening agent is characterized by being at least one of locust bean gum, xanthan gum, guar gum, tara gum, carrageenan, gelatin, cellulose derivative, tremel gum, and konjac powder.

[0012] Furthermore, in the slurry according to the present invention, the retaining carrier is characterized by being at least one of manganese(II, III) oxide, manganese(IV) dioxide, cobalt(II, III) oxide, strontium halide, europium(III) chloride, cesium halide, cesium hydroxide, and cesium sulfate.

[0013] Furthermore, the slurry according to the present invention is characterized in that the decontamination agent further comprises at least one of β-ionone or vanillin.

[0014] Furthermore, the slurry according to the present invention is characterized in that the decontamination agent further comprises an amphoteric surfactant.

[0015] Furthermore, the decontamination method according to the present invention is a decontamination method for blast decontaminating radioactive isotopes attached to an object to be decontaminated, and includes a removal step of spraying a slurry onto the object to be decontaminated to remove the radioactive isotopes, wherein the slurry comprises a decontamination agent and an abrasive, the decontamination agent comprises water, a thioglycolate, a thickener, and a holding carrier corresponding to the radioactive isotope, and the viscosity of the slurry is 10 to 100 mPa·s.

[0016] Furthermore, in the decontamination method according to the present invention, the slurry is characterized in that it further contains sodium bicarbonate.

[0017] Furthermore, in the decontamination method according to the present invention, a portion of the sodium bicarbonate is dissolved, and at least a portion of the abrasive material is the undissolved sodium bicarbonate.

[0018] Furthermore, in the decontamination method according to the present invention, the thickening agent is characterized by being at least one of locust bean gum, xanthan gum, guar gum, tara gum, carrageenan, gelatin, cellulose derivatives, tremel gum, and konjac powder.

[0019] In addition, in the decontamination method according to the present invention, the holding carrier is at least one of manganese (II, III) oxide, manganese (IV) dioxide, cobalt (II, III) oxide, strontium halide, europium (III) chloride, cesium halide, cesium hydroxide, and cesium sulfate.

[0020] In addition, in the decontamination method according to the present invention, the decontamination agent further includes at least one of β-ionone or vanillin.

[0021] In addition, in the decontamination method according to the present invention, the decontamination agent further includes an amphoteric surfactant.

Advantages of the Invention

[0022] According to the slurry of the present invention, by blasting the decontamination target, the radioisotopes attached to the decontamination target are separated from the decontamination target by the action of thioglycolate and the holding carrier, taken into the gel-like slurry, and held by the holding carrier. Moreover, due to its viscosity, it is possible to suppress the slurry and radioisotopes from scattering as dust or mist when blasted.

Brief Description of the Drawings

[0023] [Figure 1] It is a diagram showing an example of a holding carrier corresponding to a radioisotope. [Figure 2] It is a diagram showing an example of the components of the slurry according to the present embodiment. [Figure 3] It is a graph showing the relationship between the viscosity of the gel-like slurry and the concentration of the guar gum aqueous solution. [Figure 4] It is a table showing the relationship between the viscosity of the gel-like slurry and the concentration of the guar gum aqueous solution.

Embodiments for Carrying Out the Invention

[0024] The slurry according to the present embodiment will be described below.

[0025] The slurry according to this embodiment is a gel-like slurry for removing radioactive isotopes attached to an object to be decontaminated, and comprises a decontamination agent and an abrasive. The decontamination agent contains the components (a) to (d) listed below. The viscosity of the slurry is 10 to 100 mPa·s. (a) water (b) Thioglycolate (c) Thickening agent (d) Holding carriers corresponding to radioactive isotopes

[0026] (a) water Water is the solvent for the decontamination agent. Note that the aqueous solution of thioglycolate in which (b) thioglycolate is dissolved can be prepared as (a) water and (b) thioglycolate.

[0027] (b) Thioglycolate The thioglycolate is not particularly limited, and conventionally known types can be appropriately selected and used, for example, ammonium thioglycolate or sodium thioglycolate can be selected. The content of the thioglycolate is not particularly limited, but it is preferably 1 mol / L to 3 mol / L relative to the total decontamination agent. The thioglycolate reduces and separates radioactive isotopes attached to the object to be decontaminated.

[0028] (c) Thickening agent The thickening agent is not particularly limited, and conventionally known thickening agents can be appropriately selected and used. For example, at least one of the following thickening agents can be selected: locust bean gum, xanthan gum, guar gum, tara gum, carrageenan, gelatin, cellulose derivatives, tremel gum, konjac powder, etc. By adjusting the content of the thickening agent, the viscosity of the slurry can be adjusted to 10 to 100 mPa·s.

[0029] (d) Holding carriers corresponding to radioactive isotopes Radioactive isotopes behave differently from ordinary non-radioactive isotopes in the radiocolloid state due to their physicochemical properties. Therefore, to facilitate the separation of radioactive isotopes (i.e., to separate them from the object to be decontaminated and to retain the separated radioactive isotopes in the slurry), a retaining carrier corresponding to the radioactive isotope is included. As the retaining carrier, a chemical substance consisting of a stable isotope with the same chemical form as the chemical substance containing the radioactive isotope attached to the object to be decontaminated, or a stable isotope of another atom similar to the radioactive isotope in question, can be used. The retaining carrier included in the decontamination agent is appropriately selected according to the radioactive isotope attached to the object to be decontaminated. For example, a retaining carrier corresponding to the radioactive isotope is selected as shown in Figure 1. Note that Figure 1 shows an example of a retaining carrier, and conventionally known retaining carriers can be selected according to the radioactive isotope. In addition, multiple types of retaining carriers may be included. This means that even if radioactive isotopes attached to the object to be decontaminated cannot be identified, if a corresponding holding carrier is present, the separation of the radioactive isotope becomes easier due to the action of the holding carrier.

[0030] The content of the retaining carrier is not particularly limited, but it is preferably, for example, 0.005 wt% to 0.05 wt% relative to the total amount of the decontamination agent.

[0031] In the decontamination agent according to this embodiment, in addition to (a) to (d) above, other components described below may be included. When including other components, multiple other components may be included in combination, and any combination can be selected.

[0032] Various colorants may be added to the decontamination agent for the purpose of coloring it to a desired color.

[0033] Furthermore, sodium bicarbonate may be included. Generally, blast decontamination requires degreasing as a pretreatment, but by including sodium bicarbonate, the slurry becomes weakly alkaline, thus eliminating the need for degreasing as a pretreatment. In other words, by including sodium bicarbonate, the degreasing and decontamination treatments can be performed at the same time. It should be noted that many conventional decontamination agents are acidic, and mixing them with sodium bicarbonate makes them neutral, thus losing the intended acidic effect. However, the thioglycolate contained in the decontamination agent of this embodiment is neutral, so it can be mixed with sodium bicarbonate, and the decontamination effect is not reduced by mixing with sodium bicarbonate.

[0034] Furthermore, surfactants (for example, amphoteric surfactants such as sodium cocoamphoacetate (Softazolin® CH-R), cocamidopropyl betaine (Softazolin® CPB-R), and lauramidopropyl betaine (Softazolin® LPB-R)) may be included. The amount of surfactant added should be, for example, 0.02 wt% to 0.05 wt% of the total decontamination agent. Amphoteric surfactants such as Softazolin® CPB-R act on substances that do not normally mix, such as oil and water, and can mix oily and watery substances. This ability allows them to remove oil adhering to pollutants, improving the cleaning effect. In addition, amphoteric surfactants can capture odor-causing components and dissolve them in water, improving the deodorizing effect.

[0035] Furthermore, since thioglycolate salts exhibit malodorous and irritating odors, at least one of β-ionone or vanillin may be included as a deodorant to mitigate or eliminate these odors. The amount of deodorant is preferably, for example, 0.08 wt% to 0.2 wt% of the total decontamination agent. β-ionone has a deodorant effect that suppresses the rotten egg odor of ammonium thioglycolate by inhibiting human olfactory receptors that respond to volatile sulfur compounds and their response.

[0036] Vanillin is soluble in water, but β-ionone is not. Therefore, when adding β-ionone, it is preferable to add a surfactant to emulsify or disperse it. Furthermore, as mentioned above, surfactants have the effect of removing oil adhering to pollutants and also deodorizing, so it is preferable to add them even when β-ionone or vanillin are not included.

[0037] Next, the abrasive material will be described. Conventional abrasive materials used for slurry abrasives can be employed. For example, polygonal brown fused alumina, white fused alumina, black silicon carbide, zircon grid, etc., can be used. The abrasive material removes the oxide film from the surface of the object to be decontaminated, thereby improving the decontamination effect.

[0038] Furthermore, sodium bicarbonate that is not dissolved in the slurry can also be used as an abrasive. Sodium bicarbonate dissolves in water and exhibits weak alkalinity. It is also known that when an aqueous solution is heated to above 60°C, the sodium bicarbonate in the solution decomposes and produces carbon dioxide. The solubility of sodium bicarbonate (g / 100g of water) can be approximated by the following equation (1).

[0039] Solubility of sodium bicarbonate = -8 × 10 -6 x 3 +0.0015x 2 +0.0986x+7.0025 (1) formula

[0040] In equation (1), x is the water temperature (°C). The usable range for equation (1) is (0°C ≤ x ≤ 50°C).

[0041] For example, since the solubility of sodium bicarbonate in water at 20°C is 9.5g / 100g of water, if 100g of sodium bicarbonate is added to 220g of water (at 20°C), 20.9g of sodium bicarbonate will dissolve in the 220g of water, and 79.1g of sodium bicarbonate will remain in the aqueous solution. When sodium bicarbonate is included in a slurry, if 100g of sodium bicarbonate is added to 220g of decontamination agent, a portion of the sodium bicarbonate (20.9g) will dissolve in the decontamination agent, and the remaining 79.1g of sodium bicarbonate will function as at least part of the abrasive. In other words, it is possible to include an amount of sodium bicarbonate that does not dissolve in the decontamination agent, and use the undissolved sodium bicarbonate as an abrasive. At this time, it is also possible to further include the aforementioned brown fused alumina, white fused alumina, black silicon carbide, zircon grid, etc., as abrasives, or it is also possible to use only the undissolved sodium bicarbonate as an abrasive without including these. Furthermore, a portion of the dissolved sodium bicarbonate (20.9g) makes the slurry (decontamination agent) weakly alkaline, which is useful for cleaning, such as degreasing, the objects to be decontaminated. In addition, the undissolved sodium bicarbonate, acting as an abrasive, removes the oxide film from the surface of the objects to be decontaminated, thereby improving the decontamination effect.

[0042] Next, we will explain the viscosity of the gel-like slurry. The gel-like slurry has a higher viscosity than the liquid slurry conventionally used in wet blast decontamination, in order to prevent the slurry and radioactive isotopes from scattering as dust or mist during blast decontamination. Specifically, the viscosity of the gel-like slurry should be 10 to 100 mPa·s.

[0043] Figures 3 and 4 are graphs and tables showing the relationship between slurry viscosity and guar gum aqueous solution concentration when guar gum is used as a thickening agent. As mentioned above, to achieve a slurry viscosity of 10-100 mPa·s, guar gum aqueous solution should be added at a concentration of 0.19-0.40%.

[0044] If the abrasive particles are large (small particle size), the viscosity of the slurry will increase. In this case, the viscosity of the slurry should be adjusted to 10-100 mPa·s by reducing the concentration of the thickener. When using undissolved sodium bicarbonate as an abrasive, since sodium bicarbonate has a large particle size of about 200 μm, adding 100 g to 220 g of decontamination agent will maintain the viscosity of the slurry at 10-100 mPa·s. On the other hand, adding white alumina (particle size 1500, particle size 8 μm) will increase the viscosity of the slurry, exceeding 10-100 mPa·s, so the viscosity of the slurry should be adjusted by reducing the concentration of the thickener. Furthermore, when incorporating ceramics such as alumina as an abrasive, using particles in the range of 60 (particle size 300 μm) to 800 (particle size 14 μm) can suppress the increase in viscosity, making it easier to adjust the viscosity of the slurry to 10-100 mPa·s.

[0045] Next, a decontamination method for blast decontamination of radioactive isotopes attached to an object to be decontaminated will be described. The decontamination method according to this embodiment includes a removal step of spraying (blasting) the slurry described above according to this embodiment onto the object to be decontaminated to remove radioactive isotopes. Specifically, a wet blasting device is used to spray the gel-like slurry according to this embodiment at high speed onto the object to be decontaminated. The wet blasting device is a device that sprays slurry at high speed using compressed air from a dedicated spray nozzle, and conventionally known devices can be used in the decontamination method according to this embodiment.

[0046] According to the decontamination method of this embodiment, by blasting the object to be decontaminated, radioactive isotopes attached to the object are separated from the object by the action of the thioglycolate and the retaining carrier, incorporated into a gel-like slurry, and held in place by the retaining carrier. Furthermore, due to its viscosity, it is possible to suppress the scattering of the slurry and radioactive isotopes as dust or mist when blasted.

[0047] Furthermore, when the object to be decontaminated is stainless steel containing chromium, simply bringing the object into contact with thioglycolate is ineffective because the chromium oxide film on the stainless steel surface interferes with decontamination. However, by blasting the object with a slurry containing sodium bicarbonate as an abrasive, the chromium oxide film can be broken down, and at the same time, the radioactive isotopes on the stainless steel surface can be decontaminated by the thioglycolate.

[0048] Furthermore, since the decontaminated object will still have a gel-like slurry remaining after decontamination, the next step can be taken by removing the slurry with a suction device or drying it with a laser as a post-treatment.

[0049] Next, an example of the slurry according to this embodiment will be described using Figure 2. The slurry of this embodiment contains the following components. (a) Ammonium thioglycolate solution: 119g (i) Water: 100g (c) Softazoline (registered trademark) CPB-R: 0.5ml (e)β-ionone: 0.5ml (O) Guar gum: 0.53g (c) Cobalt(II,III) oxide: 0.01g (Ki) Sodium bicarbonate: 100g It contains.

[0050] The method for generating the slurry in this embodiment will be described below.

[0051] (i) Put 100g of water into a 250ml wide-mouthed PE bottle. (ii) Add 0.53 g of guar gum to (i) and stir until dissolved, then allow to swell. (iii) Add 119 g of ammonium thioglycolate solution to (ii). (iv) Add 0.5 ml of β-ionone and 0.5 ml of softazoline® CPB-R to (iii). (v) Add 0.01 g of cobalt(II,III) oxide to (iv). (vi) Add 100g of sodium bicarbonate to (v).

[0052] As mentioned above, the solubility of sodium bicarbonate is 9.5 g / 100 g of water. Therefore, when 100 g of sodium bicarbonate is added to 219 g of solution (at 20°C), 20.8 g of sodium bicarbonate dissolves in the 219 g solution, and 79.2 g of sodium bicarbonate remains in the solution, functioning as an abrasive.

[0053] Adding softazolin® CPB-R and β-ionone to an ammonium thioglycolate solution suppresses the characteristic rotten egg odor of ammonium thioglycolate, changing it to a violet scent. Furthermore, the addition of softazolin® CPB-R and β-ionone does not reduce the decontamination effect.

[0054] Adding sodium bicarbonate to ammonium thioglycolate solution does not reduce the decontamination effect.

[0055] By adding 0.01 g of cobalt(II,III) oxide, the cobalt(II,III) oxide functions as a retaining carrier and a fungicide.

Claims

1. A gel-like slurry for blast decontamination of radioactive isotopes attached to objects to be decontaminated, The slurry comprises a decontamination agent and an abrasive, The aforementioned decontamination agent is Water and, Thioglycolate and Thickening agent, A holding carrier corresponding to the aforementioned radioactive isotope, Includes, The slurry is characterized by having a viscosity of 10 to 100 mPa·s.

2. The slurry according to claim 1, A slurry characterized by further containing sodium bicarbonate.

3. The slurry according to claim 2, The aforementioned sodium bicarbonate partially dissolves, A slurry characterized in that at least a portion of the abrasive material is the undissolved sodium bicarbonate.

4. A slurry according to any one of claims 1 to 3, The slurry is characterized in that the thickening agent is at least one of locust bean gum, xanthan gum, guar gum, tara gum, carrageenan, gelatin, cellulose derivative, tremel gum, and konjac powder.

5. A slurry according to any one of claims 1 to 3, The slurry is characterized in that the retaining carrier is at least one of manganese(II, III) oxide, manganese(IV) dioxide, cobalt(II, III) oxide, strontium halide, europium(III) chloride, cesium halide, cesium hydroxide, and cesium sulfate.

6. A slurry according to any one of claims 1 to 3, The aforementioned decontamination agent is a slurry characterized by further comprising at least one of β-ionone or vanillin.

7. A slurry according to any one of claims 1 to 3, The aforementioned decontamination agent is a slurry characterized by further comprising an amphoteric surfactant.

8. A decontamination method that uses blast decontamination to remove radioactive isotopes attached to an object to be decontaminated, The process includes a removal step of spraying a slurry onto the object to be decontaminated to remove the radioactive isotope, The slurry comprises a decontamination agent and an abrasive, The aforementioned decontamination agent is Water and, Thioglycolate and Thickening agent, A holding carrier corresponding to the aforementioned radioactive isotope, Includes, A decontamination method characterized in that the viscosity of the slurry is 10 to 100 mPa·s.

9. A decontamination method according to claim 8, The decontamination method is characterized in that the slurry further contains sodium bicarbonate.

10. A decontamination method according to claim 9, The aforementioned sodium bicarbonate partially dissolves, A decontamination method characterized in that at least a portion of the abrasive material is the undissolved sodium bicarbonate.

11. A decontamination method according to any one of claims 8 to 10, A decontamination method characterized in that the thickening agent is at least one of locust bean gum, xanthan gum, guar gum, tara gum, carrageenan, gelatin, cellulose derivative, tremel gum, and konjac powder.

12. A decontamination method according to any one of claims 8 to 10, A decontamination method characterized in that the retaining carrier is at least one of manganese(II) chloride, manganese(II, III) oxide, manganese(IV) dioxide, cobalt(II, III) oxide, strontium halide, strontium chloride, cesium chloride, europium(III) chloride, cesium halide, cesium hydroxide, and cesium sulfate.

13. A decontamination method according to any one of claims 8 to 10, A decontamination method characterized in that the decontamination agent further comprises at least one of β-ionone or vanillin.

14. A decontamination method according to any one of claims 8 to 10, A decontamination method characterized by further comprising an amphoteric surfactant as the decontamination agent.

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