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

Definitions

• the present invention relates to a method by which r active coatings on the walls of the primary heating system nuclear reactors of the pressurized water type can be remo More specifically, the invention relates to the decontamin ion of in acid insoluble or sparingly. soluble corrosion pr ducts from these primary system surfaces.
• invention is a development and simpli ication of the techn that includes a first step wherein the contaminated surfac contacted with an oxidation agent, for oxidation of the in le products to acid-soluble oxidation products, whereupon subsequent step the oxidized products are dissolved and re by . means of an acidic decontamination solution.
• Corrosion products stemming from the primary heating system, which to a major extent comprises the tubes and pi lines of the steam generators, are conveyed into the react core where they are deposited on the fuel elements.
• the corrosion products which are n radioactive after the neutron irradiation, are liberated f the fuel elements and are subsequently deposited on the pa of the primary system in contact with water which lie outs the reactor core. Then the radioactive corrosion products rise to radiation fields outside the core and thereby to radiation doses to the operational personnel.
• the decontamin ion factor (Df) is defined in the following way: nf - ra at ⁇ on ⁇ e -'- c ⁇ ⁇ e f° re decontamination radiation field after decontamination
• radioactive solutions of chemicals from this pro- cess have either been purified by ion exchangers or been treated in special evaporators.
• the greatest disadvantage the APAC process is the large volumes of waste occurring in the form of radioactive ion exchangemasses or evaporator residues.
• dizing agents permanganate in an alkaline or nitric acidic enviro ment (in the latter case the pH is about 2.5) - .
• potassium hexacyanoferrate in an alkaline environme
• almos exclusively organic acids citric or oxalic acids and ammon salts of these
• EDTA ethylenediaminetetraacetic acid
• the conditions (reducing, high pH) prevailing in a pressurized water reactor are such that the oxide layers fo ed will to a large extent have relatively high contents of chromium, partially together with nickel, in the form of ox or spinel phases. To have these oxide layers dissolved at al in organic acids, it is thus necessary to carry out the pre-treatment in an oxidizing environment. At present the completely dominating oxidation agent in this respect is permanganate.
• the reaction sequence for the oxidation step is substantially as follows: 3MnO ⁇ + Cr 3+ + 8H 7 0 "* «- 3Mn 2+ + 5Cr0 4 2" + 16H +
• the contami nated surfaces are brought into contact with the above-ment ned oxidation agent in an aqueously based form and with an acidic pH, i.e. a pH below 7.
• an acidic pH i.e. a pH below 7.
• the oxidation agent is present in the form of an aqueous solution of cerium nitrate and chromic acid, and ozone prefe ⁇ rably in a saturated solution and dispersed form.
• the oxidation ag can however be utilized in the form of a two-phase ozone ga
• a particularly ferable embodiment of the method in accordance with the in ion thus means that the decontamination is carried out at temperature or lower, i.e. at a temperature below about 25 and preferably below 20 C.
• very favourable effect relation to the known art are obtained in the decontaminat already at a temperature below about 60°C.
• the decontamination according to the invention means the contaminated surfaces are contacted with the acidic so ion with the new oxidation agent for a period of time su ficient to oxidize insoluble oxides, so as to make these soluble in the same solution.
• the period of time required each individual case is of course easily determined by one skilled in the art against the background of utilized conc trations of oxidation reagents, utilized treatment tempera res etc.
• a water-soluble cerium salt has oxidizing properties only when the cerium ion is present in its highest oxidati stage, viz. Ce , while the pH of the solution is preferab about 1.
• Ce(5)nitrate which in contact with the ozone is immediatel oxidized to Ce(4)nitrate.
• the origin of the chromic acid is preferably dosed chromium trioxide, and the ozone is suitably utilized in t form of an ozone-enriched oxygen gas or air.
• concentrations or proportions of the chemicals i cluded in the oxidation agent are determined by one skille in the art from case to case, so as to obtain the desired results, inter alia depending on the materials which are t be decontaminated and the desired decontamination effect, generally the concentrations are usually within the range 0.01-50 g/1, preferably 0.5-2 g/1, of the cerium nitrate, within the range of 0.01-50 g/1, preferably 0.05-0.2 g/1, the chromic acid and within the range of 0.001-1 g/1, pre ⁇ ferably 0.005-0.015 g/1 of the ozone.
• the water-based or aqueous oxidation agent has pre ' fe ably been made acidic by nitric acid, preferably to a pH o about 1.
• the method in accordance with the invention is gener utilizable for the decontamination of all those different types of materials which are present in these connections.
• the invention has been found to give extremely go results in the decontamination of chromium (III) oxide fro a chromium-nickel-iron alloy, such a decontamination there fore representing an especially preferable embodiment of t invention.
• the three samples were exposed in parallel in a 100 glass container in an aqueous solution containing 12 g/1 boric acid, 1.5 g/1 of Ce(3)nitrate and 0.1 g/1 of .CrO, i nitric acid at a pH of about 1.4.
• Oxygen gas with about 2 percent by volume of ozone was bubbled into the same con ⁇ tainer at a rate of about 0.1 1/min.
• the temperature was 20°C and the exposure time was hours.

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• Engineering & Computer Science (AREA)
• Food Science & Technology (AREA)
• General Engineering & Computer Science (AREA)
• General Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Electrochemistry (AREA)
• High Energy & Nuclear Physics (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Treatment Of Water By Oxidation Or Reduction (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Detergent Compositions (AREA)
• Apparatus For Disinfection Or Sterilisation (AREA)

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• 1984
  • 1984-03-09 SE SE8401336A patent/SE451915B/sv not_active IP Right Cessation
• 1985
  • 1985-02-05 EP EP85900825A patent/EP0174317B1/en not_active Expired
  • 1985-02-05 KR KR1019850700286A patent/KR850700284A/ko not_active Withdrawn
  • 1985-02-05 JP JP60500671A patent/JPS61501338A/ja active Granted
  • 1985-02-05 DE DE8585900825T patent/DE3566591D1/de not_active Expired
  • 1985-02-05 WO PCT/SE1985/000052 patent/WO1985004279A1/en not_active Ceased
  • 1985-02-05 US US06/789,958 patent/US4704235A/en not_active Expired - Lifetime
  • 1985-02-25 ES ES540671A patent/ES8700784A1/es not_active Expired

Patent Citations (2)

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