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
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions

Definitions

• the tenacious magnetite film containing included radioactive contaminants which forms on stainless steel heat exchange surfaces of nuclear reactors is removed by a two step treatment.
• the first step utilizes a hot, alkaline, aqueous solution of potassium permanganate.
• the second utilizes a hot aqueous solution of oxalic acid, dibasic ammonium citrate, ferric sulfate or nitrate and diethyl thiourea.
• the invention relates to a method of and a composition for the removal of radioactive contamination from metal surfaces. It is effective for removing the extremely tenacious radioactive film which forms on stainless steel surfaces on long exposure to hot Water containing radioisotopes. It is also effective for removing the less tenacious radioactive films formed on carbon steel, zircaloy, brass, bronze and other metals. At the same time there is no objectionable corrosion to any of these metals.
• the principal object of the invention is the decontamination of nuclear reactor cooling systems composed primarily of stainless steel.
• the radioactive corrosion films characteristic of recirculating water-cooled nuclear reactors must be periodically removed to permit contact maintenance and continuity of operation. Before these systems can be cleaned, procedures and processes must be developed which are suitable for use in the system. These processes must meet certain criteria which are discussed in the following paragraphs.
• a decontamination reagent must dissolve the radioactive corrosion film and remove it from the system.
• Large nuclear plants are no exception to other types of plants; they are built with inherent low velocity areas and other traps where particulate material will settle out. The particulates in these areas must be dissolved for successful removal. Therefore, a successful decontamination reagent must dissolve as well as remove the radioactive corrosion film because if it is only removed from the piping surfaces and not dissolved, it will settle out in the low velocity areas and traps.
• a successful decontamination reagent must remove and dissolve radioactive films formed during extended periods of continuous operation (up to at least two or three years). From the limited data available in the AEC literature, it is probable that cleaning will not be required oftener unless under unusual circumstances or demands. It is desirous, in power reactor operation, to keep the down time at a minimum and possibly reach five years of continuous operation before cleaning. Therefore, the removal of these long term films is an essential requirement.
• a successful decontamination reagent must not be excessively corrosive to the materials of construction in the primary system.
• the reactor system will be constructed of primarily one or two materials, but there will be small quantities of many other types of materials in the system. These lesser materials will be found in such places as valves and sampling devices. All of these materials must be compatible with the reagent if they are in either direct or indirect contact with the solution, this is particularly true if the components are in a critical location, e.g., a drain valve plug, seat or stem.
• the film which forms on stainless steel surfaces in the cooling systems in water cooled nuclear reactors appears to be primarily magnetite mixed with oxides of nickel and chromium. Radioactive ions present in the water are included in or adsorbed on this film so that they cannot be removed without removing the film itself. It is known in the art to decontaminate stainless steel nuclear reactor cooling systems by treatment with alkaline potassium permanganate followed by oxalic acid. However, previously known oxalic acid containing solutions have tended to deposit a secondary film on the surfaces. Sometimes the secondary film takes the form of a precipitate settling out in the low velocity regions and dead legs of the cooling system. This secondary film contains a considerable amount of radioactivity and its formation partially nullifies the decontamination.
• composition at present is as follows:
• the primary cooling system is composed principally of type 304 stainless steel.
• Corrosion tests were then conducted on samples of various metals.
• One corrosion test was conducted with the RDW-3 solution at 80 C. for 120 hours; the total corrosion incurred by the carbon steel samples exposed 3 was 0.22 mil and by the stainless steel samples was 0.01 mil.
• a pale yellow film was deposited on the carbon steel samples when the test was terminated; the solution was a clear yellow color with no precipitates present.
• a method of removing a tenacious magnetite film containing included radioactive contaminants from a nuclear reactor cooling system composed primarily of stainless steel, which system has been subject to extended circulation of hot water during recator operation which method comprises:

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Food Science & Technology (AREA)
• Physics & Mathematics (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=24180661

Family Applications (1)

Country Status (9)

Cited By (27)

Families Citing this family (2)

Citations (4)

• 1966
  • 1966-04-28 US US546489A patent/US3496017A/en not_active Expired - Lifetime
• 1967
  • 1967-03-13 GB GB11681/67A patent/GB1130068A/en not_active Expired
  • 1967-03-21 IL IL27663A patent/IL27663A/en unknown
  • 1967-03-23 SE SE4166/67A patent/SE321130B/xx unknown
  • 1967-04-03 CH CH473167A patent/CH468697A/de unknown
  • 1967-04-06 DE DE19671621670 patent/DE1621670A1/de active Pending
  • 1967-04-11 ES ES339132A patent/ES339132A1/es not_active Expired
  • 1967-04-13 BE BE696994D patent/BE696994A/xx unknown
  • 1967-04-27 NO NO167918A patent/NO122687B/no unknown

Patent Citations (4)

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