CA2265413A1 - A method for complex decontamination of metal surfaces with deep and surface contamination and of liquid radioactive wastes - Google Patents
A method for complex decontamination of metal surfaces with deep and surface contamination and of liquid radioactive wastes Download PDFInfo
- Publication number
- CA2265413A1 CA2265413A1 CA002265413A CA2265413A CA2265413A1 CA 2265413 A1 CA2265413 A1 CA 2265413A1 CA 002265413 A CA002265413 A CA 002265413A CA 2265413 A CA2265413 A CA 2265413A CA 2265413 A1 CA2265413 A1 CA 2265413A1
- Authority
- CA
- Canada
- Prior art keywords
- per
- decontamination
- radionuclides
- solution
- electrolyte
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
- G21F9/002—Decontamination of the surface of objects with chemical or electrochemical processes
- G21F9/004—Decontamination of the surface of objects with chemical or electrochemical processes of metallic surfaces
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
- C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/04—Treating liquids
- G21F9/06—Processing
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/28—Treating solids
Abstract
Essence of the invention consists in electrochemical destruction of oxide films, situated on metal surface and impeding the diffusion of radionuclides deeply contaminating metal, and in intensification of their transfer from depth to surface at the expense of potential, applied to the metal surface, with subsequent interaction of radionuclides with humus substances which make up main component of decontaminating solution. In aqueous solutions humus substances dissociate with formation of negatively charged matrix interacting with radionuclides on the surface being decontaminated, followed by formation of insoluble substances, thus removing radionuclides from the formed liquid radioactive wastes.
Description
METHOD FOR COMPLEX DECONTAMINATION OF METAL SURFACES
WITH DEEP AND SURFACE CONTAMINATION AND OF LIQUID
RADIOACTIVE WASTES
The invention refers to electrochemical decontamination of contaminated metal surfaces, for example, components of nuclear power plants, and is based on contacting the surface being decontaminated with a special electrolytic solution. Decontamination is carried out with the help of a system of electrodes, which is followed by treatment of the used solution.
In the process of operation of nuclear power plants, as well as plants for mining and processing of rare earth elements, deep and surface contamination of equipment, contacting radioactive substances, takes place. In the case of complicated deep contamination chemical methods for decontamination by means of aggressive media such as those disclosed in Russian Patent No. 1,830,149, c1.G21 F9/00, 1993 or Russian Patent No. 2,017,244, cl.
G21 F9/36, 1994 are very expensive and ecologically hazardous for personnel. Electropolishing method such as those disclosed in Russian Patent No. 2,009,557, c1.G21 F9/34, 1994 or German Patent No.
3,343,396, c1.G21 F9/30, 1985 used for such purposes, consist in removal of a rather thick layer from the metal surface, thickness of which depends on the depth of radionuclides diffusion layer.
This results in considerable consumption of power and change of dimensions of objects being decontaminated.
The objective ofthe invention is to provide a method and compound for decontamination of radioactive contaminated metal objects by means of electrochemical destruction of oxide films impeding diffusion of radionuclides to metal surface. After the destruction of oxide films the positive potential, applied to the object being decontaminated, promotes movement of radionuclides to the surface. Deep contamination presents in fact a more complex case of surface decontamination. In fact, destruction and removal of oxide films transforms deep contamination into surface contamination. (see. A. D. Zimon, U.K. Pikalov, Decontamination, Izdat (Publishing House), Moscow, 1994 p. 40,96.) Humus substances have been found to be effective means for decontamination of metals with contaminated surfaces and they are added to the electrolytic compound for intensification of the decontamination process.
Anions of humus substances, added to electrolyte composition, interact with canons of radionuclides situated on the surface being decontamination. Electrochemical processes lead al so to changes in chemical structure of humus substances and result in formation of fractions with still higher decontaminating effect.
In the method of the present invention, a solution of liquid radioactive wastes is obtained electrolytically in decontamination of metal objects. A resulting insoluble residue consists of humic acids and positive radionuclides (for example, such as Cs, Sr, Co, Mn, Fe, Ni, Ce). Thus, in this case, humic acid plays the role of a flocculent. For intensification of decomposition and reduction of content of radionuclides down to a required level, the introduction of a humus substances suspension may be repeated with the use of special additives. For example, for removal of radioactive cesium it is necessary to add to the solution a microquantity of potassium ferrocyanide which, being adsorbed on colloidal particles of humus substances, additionally bonds cesium ions by transforming them into an insoluble state. In case the proposed method, it is not necessary to prepare adsorbents in advance, as their formation and the absorption of radionuclides in the solution proceed simultaneously. Iron salts may be used as flocculants for treatment of liquid wastes for final removal of multivalent radionuclides from liquid wastes. In case of decontamination of iron containing objects (steel, pig iron) by the proposed method the solution is saturated by iron ions in the process of decontamination at the expense of dissolution of oxide films and partially surface itself, which considerably decreases the amount of reagent used.
The residue of organic substances containing radionuclides formed according to the present invention is preferably ashed with the aim of reducing the amount of solid radioactive wastes isolated from the solution. Decontaminated aqueous solution may be used repeatedly.
The invention is explained by the following examples:
Example 1 Part of deeply contaminated 10 X 10 cm steel plate, which had been in a durable contact with uranium concentrate and was unamenable to decontamination by submersion into regular decontaminating solutions based on surfactant and organic acids, was subject to decontamination by the proposed method. The object being tested served as anode while a titanium plate was used as cathode, and alkaline suspension of humus substances with sodium sulfate additives was used as an electrolyte. After two hours off decontamination ~3-activity reduced 10 times, and y-activity reduced from 1000 ,uR/h to the background after three hours.
WITH DEEP AND SURFACE CONTAMINATION AND OF LIQUID
RADIOACTIVE WASTES
The invention refers to electrochemical decontamination of contaminated metal surfaces, for example, components of nuclear power plants, and is based on contacting the surface being decontaminated with a special electrolytic solution. Decontamination is carried out with the help of a system of electrodes, which is followed by treatment of the used solution.
In the process of operation of nuclear power plants, as well as plants for mining and processing of rare earth elements, deep and surface contamination of equipment, contacting radioactive substances, takes place. In the case of complicated deep contamination chemical methods for decontamination by means of aggressive media such as those disclosed in Russian Patent No. 1,830,149, c1.G21 F9/00, 1993 or Russian Patent No. 2,017,244, cl.
G21 F9/36, 1994 are very expensive and ecologically hazardous for personnel. Electropolishing method such as those disclosed in Russian Patent No. 2,009,557, c1.G21 F9/34, 1994 or German Patent No.
3,343,396, c1.G21 F9/30, 1985 used for such purposes, consist in removal of a rather thick layer from the metal surface, thickness of which depends on the depth of radionuclides diffusion layer.
This results in considerable consumption of power and change of dimensions of objects being decontaminated.
The objective ofthe invention is to provide a method and compound for decontamination of radioactive contaminated metal objects by means of electrochemical destruction of oxide films impeding diffusion of radionuclides to metal surface. After the destruction of oxide films the positive potential, applied to the object being decontaminated, promotes movement of radionuclides to the surface. Deep contamination presents in fact a more complex case of surface decontamination. In fact, destruction and removal of oxide films transforms deep contamination into surface contamination. (see. A. D. Zimon, U.K. Pikalov, Decontamination, Izdat (Publishing House), Moscow, 1994 p. 40,96.) Humus substances have been found to be effective means for decontamination of metals with contaminated surfaces and they are added to the electrolytic compound for intensification of the decontamination process.
Anions of humus substances, added to electrolyte composition, interact with canons of radionuclides situated on the surface being decontamination. Electrochemical processes lead al so to changes in chemical structure of humus substances and result in formation of fractions with still higher decontaminating effect.
In the method of the present invention, a solution of liquid radioactive wastes is obtained electrolytically in decontamination of metal objects. A resulting insoluble residue consists of humic acids and positive radionuclides (for example, such as Cs, Sr, Co, Mn, Fe, Ni, Ce). Thus, in this case, humic acid plays the role of a flocculent. For intensification of decomposition and reduction of content of radionuclides down to a required level, the introduction of a humus substances suspension may be repeated with the use of special additives. For example, for removal of radioactive cesium it is necessary to add to the solution a microquantity of potassium ferrocyanide which, being adsorbed on colloidal particles of humus substances, additionally bonds cesium ions by transforming them into an insoluble state. In case the proposed method, it is not necessary to prepare adsorbents in advance, as their formation and the absorption of radionuclides in the solution proceed simultaneously. Iron salts may be used as flocculants for treatment of liquid wastes for final removal of multivalent radionuclides from liquid wastes. In case of decontamination of iron containing objects (steel, pig iron) by the proposed method the solution is saturated by iron ions in the process of decontamination at the expense of dissolution of oxide films and partially surface itself, which considerably decreases the amount of reagent used.
The residue of organic substances containing radionuclides formed according to the present invention is preferably ashed with the aim of reducing the amount of solid radioactive wastes isolated from the solution. Decontaminated aqueous solution may be used repeatedly.
The invention is explained by the following examples:
Example 1 Part of deeply contaminated 10 X 10 cm steel plate, which had been in a durable contact with uranium concentrate and was unamenable to decontamination by submersion into regular decontaminating solutions based on surfactant and organic acids, was subject to decontamination by the proposed method. The object being tested served as anode while a titanium plate was used as cathode, and alkaline suspension of humus substances with sodium sulfate additives was used as an electrolyte. After two hours off decontamination ~3-activity reduced 10 times, and y-activity reduced from 1000 ,uR/h to the background after three hours.
Example 2 Samples of steam generator pipe and of pipeline of autonomous pump circuit made of 1 X 18H9T and 08X 18H 1 OT (Russian standard) steel, correspondingly, were decontamination by the proposed method. During 20 years of operation they were in contact with a heat carrier of the primary circuit which had the following parameters: temperature :260°C, specific activity:
106 Bq/1 and pH approximately 6.5, which promoted the formation of a solid oxide film with radionuclides sorbed in it.
Decontamination results are given in Table 1.
'table 1 Results of gamma-spectrometric measurement Name of Sample Initial Specific Specific ActivityDecontamination Gravity after activity for Co-60,decontamination, Factor Bq/cmz Bq/cmz Steam Generator 8.1 E + S 1. I E + 2 733 Pipe Pipe of autonomous4.4E + 5 1.6E + 2 272 circuit Ferrous metal pipes with the level of contamination about 400 ~cR/h were decontaminated by the method described in Example 1. y-activity reduced to background after 10 minutes of decontamination.
106 Bq/1 and pH approximately 6.5, which promoted the formation of a solid oxide film with radionuclides sorbed in it.
Decontamination results are given in Table 1.
'table 1 Results of gamma-spectrometric measurement Name of Sample Initial Specific Specific ActivityDecontamination Gravity after activity for Co-60,decontamination, Factor Bq/cmz Bq/cmz Steam Generator 8.1 E + S 1. I E + 2 733 Pipe Pipe of autonomous4.4E + 5 1.6E + 2 272 circuit Ferrous metal pipes with the level of contamination about 400 ~cR/h were decontaminated by the method described in Example 1. y-activity reduced to background after 10 minutes of decontamination.
Part of a lead screen with the level of contamination about 150 ,uR/h, which had been used for biological protection at nuclear power plant, was decontaminated by the above-described method. Radioactivity was reduced down to the background after 5 minutes.
A working piece of the primary circuit of nuclear reactor (a return valve), which had (3-radiation activity of 3000 particles/cmz min, was subject to decontamination by the above-mentioned method. After two and a half hours of decontamination, the decontamination factor made up approximately 400.
Decontamination of liquid radioactive wastes, obtained by the above-mentioned method, was carried out in the following way. Solution containing up to 0.1 g of potassium ferrocyanide was added to 1.0 litre of the solution being decontaminated, then the mixture was stirred and, by means of introduction of a mineral acid, solution pH was reduced down to coagulation of humus acids. The formed complex residue, mainly containing radioactive cesium and other radionuclides, was separated and iron sulphate solution was added to acid filtrate. Then, by means of adding alkali, pH was increased up to formation of flocculent, thus multivalent radionuclides were finally removed from the solution.
Liquid radioactive wastes, not containing humus substances, e.g., trap water or liquid radioactive wastes from special storage, may be also utilized by the proposed method by means of their alkalization (if necessary) and introduction of humus substances with subsequent utilization according to the scheme given in Example 6. In this case, liquid radioactive wastes from a special storage were decontaminated by the given method.
Results obtained in Examples 6 and 7 are given in Table 2.
Table 2 Results of decontamination of Liquid Radioactive Wastes SAMPLE Contents of Radionuclides, Bq/1 A total Cs-137 Co-60 Sr-90 Initial liquid radioactive 1.3E+4 9.3E+3 2.OE+3 6.OE+2 wastes (Example 6) 4.8E+2 7.4 3.3E+2 9.3 After decontamination Initial liquid radioactive 9.3E+4 4.8E+4 l .0E+3 2.2E+4 wastes (Example 7) 5.2E+2 1.3E+2 56 9.3 After decontamination Permissible concentration 5.6E+2 2.OE+3 14.8 of radionuclides in potable water Note: contamination levels for Mn-54 and Ru-106 are not given as in initial liquid radioactive wastes they were found to be within the permissible concentration of radionuclides in potable water.
A working piece of the primary circuit of nuclear reactor (a return valve), which had (3-radiation activity of 3000 particles/cmz min, was subject to decontamination by the above-mentioned method. After two and a half hours of decontamination, the decontamination factor made up approximately 400.
Decontamination of liquid radioactive wastes, obtained by the above-mentioned method, was carried out in the following way. Solution containing up to 0.1 g of potassium ferrocyanide was added to 1.0 litre of the solution being decontaminated, then the mixture was stirred and, by means of introduction of a mineral acid, solution pH was reduced down to coagulation of humus acids. The formed complex residue, mainly containing radioactive cesium and other radionuclides, was separated and iron sulphate solution was added to acid filtrate. Then, by means of adding alkali, pH was increased up to formation of flocculent, thus multivalent radionuclides were finally removed from the solution.
Liquid radioactive wastes, not containing humus substances, e.g., trap water or liquid radioactive wastes from special storage, may be also utilized by the proposed method by means of their alkalization (if necessary) and introduction of humus substances with subsequent utilization according to the scheme given in Example 6. In this case, liquid radioactive wastes from a special storage were decontaminated by the given method.
Results obtained in Examples 6 and 7 are given in Table 2.
Table 2 Results of decontamination of Liquid Radioactive Wastes SAMPLE Contents of Radionuclides, Bq/1 A total Cs-137 Co-60 Sr-90 Initial liquid radioactive 1.3E+4 9.3E+3 2.OE+3 6.OE+2 wastes (Example 6) 4.8E+2 7.4 3.3E+2 9.3 After decontamination Initial liquid radioactive 9.3E+4 4.8E+4 l .0E+3 2.2E+4 wastes (Example 7) 5.2E+2 1.3E+2 56 9.3 After decontamination Permissible concentration 5.6E+2 2.OE+3 14.8 of radionuclides in potable water Note: contamination levels for Mn-54 and Ru-106 are not given as in initial liquid radioactive wastes they were found to be within the permissible concentration of radionuclides in potable water.
Claims (8)
1. A method for decontamination of metal surfaces with deep and surface radioactive contamination, based on electrochemical effect of a special electrolyte solution on the surface being decontaminated, characterized in that, that with the purpose of destruction of oxide films on metal surface and release of radioactive substances from inner layers and their subsequent transfer into the solution, an electrode couple is used in electrolyte medium containing alkaline suspension of humus substances, serving as complex formers of radionuclides thereby simplifying the utilization of used liquid radioactive wastes by means of obtaining and separating the formed solid radioactive residue, and its ashing.
2. A method as per claim 1 characterized in that solutions of alkaline metals salts are used in the capacity of electrolyte.
3. A method as per claim 1 characterized in that hydroxides or carbonates of alkaline metals are used as alkalization agents.
4. A method as per claims 1 - 3 characterized in that, that with the purpose of increasing the decontamination efficiency, the electrolyte temperature is increased above ambient temperature.
5. A method as per claims 1 - 4 characterized in that, that with the purpose of increasing the decontamination efficiency, the electrolyte solution is pre-electrolyzed.
6. A method as per claims 1 - 5 characterized in that that potassium ferro-cyanide is additionally introduced into the solution with the purpose of increasing the efficiency of decontamintion of formed liquid radioactive wastes.
7. A method as per claims 1 - 6 characterized in that that iron salts are introduced into the solution and pH is increased up to formation of flocculent with the purpose of increasing the efficiency of removal of two and more valent radionuclides.
8. A method as per claim 7 characterized in that that chlorides and sulphate are used in the capacity of iron salts.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002265413A CA2265413A1 (en) | 1999-03-15 | 1999-03-15 | A method for complex decontamination of metal surfaces with deep and surface contamination and of liquid radioactive wastes |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002265413A CA2265413A1 (en) | 1999-03-15 | 1999-03-15 | A method for complex decontamination of metal surfaces with deep and surface contamination and of liquid radioactive wastes |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2265413A1 true CA2265413A1 (en) | 2000-09-15 |
Family
ID=29588563
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002265413A Abandoned CA2265413A1 (en) | 1999-03-15 | 1999-03-15 | A method for complex decontamination of metal surfaces with deep and surface contamination and of liquid radioactive wastes |
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| Country | Link |
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| CA (1) | CA2265413A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3792936A4 (en) * | 2018-05-11 | 2023-01-04 | Joint Stock Company "Rosenergoatom" | Assembly for the electrochemical decontamination of metallic radioactive waste |
-
1999
- 1999-03-15 CA CA002265413A patent/CA2265413A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3792936A4 (en) * | 2018-05-11 | 2023-01-04 | Joint Stock Company "Rosenergoatom" | Assembly for the electrochemical decontamination of metallic radioactive waste |
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |