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
• • 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
  • G21F9/12—Processing by absorption; by adsorption; by ion-exchange
• • 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
• • 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
  • G21F9/30—Processing

Definitions

• the invention relates to a method for surface decontamination of components of the coolant circuit of a pressurized water reactor.
• the core of the coolant circuit is a reactor pressure vessel in which nuclear fuel-containing fuel elements are arranged.
• At the reactor pressure vessel several cooling loops are usually connected, each with a coolant pump and a steam generator.
• the nuclides are dispersed by the coolant flow throughout the coolant system and are stored in oxide layers that form on the surfaces of coolant system components during operation. With too ⁇ participating operating time, the amount of Tarlager- th activated nuclides summed so that the radioactivity or the dose rate increases on the components of the coolant system.
• the oxide layers contain depending on the type of a component
• the alloy used is iron oxide with di- and trivalent iron and oxides of other metals, especially chromium and nickel, which are present as alloying constituents in the above-mentioned steels. Nickel is always present in divalent form (Ni 2+ ), chromium in trivalent (Cr 3+ ) form.
• the oxide layer is first treated oxidatively in the case of components containing chromium, for example in the case of a pressurized water reactor (oxidation step), and then the oxide layer is dissolved under acidic conditions in a so-called decontamination step with the aid of an acid, which is referred to below as decontamination or deconic acid.
• the metal ions which pass from the oxide layer into the solution can then be removed from the solution by passing it through an ion exchanger.
• Excess oxidizing agent of the oxidation step is neutralized or reduced in a reduction step by adding a reducing agent.
• the dissolution of the oxide layer or the dissolution of metal ions in the decontamination step thus takes place in the absence of an oxidizing agent.
• the reduction of excess Oxidizing agent may be an independent treatment step, wherein the cleaning solution is a reducing agent serving for the purpose of reduction, for example, ascorbic acid, citric acid or hydrogen peroxide for the reduction of manganese ions manganese and manganese added.
• the reduction of excess oxidizing agent can also take place in the context of the decontamination step, wherein in addition to Reduk ⁇ tion means a dissolution of the oxide layer causing decontamination or acid is used, which is capable of excess oxidant, such as the frequently used permanganate ion and to reduce the resulting ent ⁇ wholesomeen Braunstein.
• the oxidative treatment of the oxide layer is required to solve difficult because chromium III oxide and trivalent chromium-containing mixed oxides, especially spinel in the coming eligible for Dekonta ⁇ mination acids.
• the oxide layer is first treated with an aqueous solution of an oxidizing agent such as Ce 4+ , HMnO 4 , H 2 S 2 O 8 , ⁇ 4 , ⁇ 4 with acid or alkali or O 3.
• an oxidizing agent such as Ce 4+ , HMnO 4 , H 2 S 2 O 8 , ⁇ 4 , ⁇ 4 with acid or alkali or O 3.
• Deconic acid is oxalic acid because it dissolves the oxide layers to be removed from component surfaces.
• oxalic acid with divalent metal ⁇ ions such as Ni 2+, Fe 2+, Co 2+, Cu 2+ sparingly soluble oxalate forms precipitates which are divided published in the entire coolant system, and on the inner surfaces of pipes and of Depositing components, for example from steam generators.
• the precipitates complicate the entire procedural ⁇ rens die entry.
• organic constituents of a solution by treatment with an oxidation are often onsstoff and UV irradiation to carbon dioxide and water vice converts ⁇ and thus removed from the solution. By the low blows ⁇ but the solution becomes cloudy, which limits the effectiveness of UV irradiation significantly reduced. It also comes to
• Re-contamination is especially high for components with a high surface to volume ratio. This is especially the case with steam generators which have a very large number of small diameter exchanger tubes.
• Another disadvantage of the use of oxalic acid is that oxalate precipitates filter devices, such as an ion exchanger upstream filter and sieve plates or the Clogging filter from circulation pumps can clog.
• a further disadvantage is finally, if one described above, is repeated from oxidation step and Dekontön existing treatmen ⁇ development cycle, ie when a
• the oxalate in solution, that is not bound in the form of a precipitate, the oxalate can be destroyed in a simple manner, such as before the cleaning solution is passed into an ion exchanger in a simple and cost- effective manner, for example with the aid of UV light ie converted to carbon dioxide and water.
• turbidity caused by an oxalate precipitate interferes with the monitoring of the process, for example with photometry.
• a decontamination process which is subdivided into two process stages.
• a treatment ⁇ cycle is performed at least, of an oxidation step, a reductive ⁇ tion step, and a subsequent first De- Contamination step includes.
• a treatment cycle can be carried out only once or even several times.
• the component having a wêt- membered cleaning solution is treated comprising an oxidizing agent whose oxidizing power sufficient to convert in the oxide layer contained ⁇ trivalent chromium to hexavalent chromium.
• this step increases the solubility of an oxide layer present on the component.
• the component is treated with a solution containing a reducing agent to reduce excess oxidizing agent from the oxidation step.
• the component is treated with an aqueous solution which contains exclusively or predominantly, ie more than 50 mol%, at least one decontamination acid which is mixed with metal ions contained in the solution, in particular bivalent metal ions such as Ni-II, Fe. II, Co II and Mn II no sparingly soluble Never ⁇ Dersch would forms, as is the case with oxalic acid.
• a Dekont yarn which does not form a sparingly soluble precipitates with tri- and higher valent acids, but in the normally used for a Dekontaminati ⁇ on the present kind of acids, such as formic acid and glyoxylic acid, is the case.
• a Dekontaminati ⁇ on the present kind of acids, such as formic acid and glyoxylic acid.
• Base metal of the component derived metal ions passed through an ion exchanger can be carried out together or at the same time as white ⁇ ter has already been explained above.
• the reduction step and decontamination step can be carried out together or at the same time as white ⁇ ter has already been explained above.
• In the first stage of the procedure can be applied to the proposed
• a method according to the invention thus offers the possibility of preventing or at least greatly reducing the formation of sparingly soluble precipitates without thereby impairing the effectiveness of decontamination.
• the method can be carried out so that is first performed in the first process stage at least one treatment cycle and in the subsequent second process step, the component surface without a prior oxidation of the second Dekont Republic performed, the oxide ⁇ layer of the component is treated with oxalic acid ,
• the oxide layer is treated approximately with the above-mentioned oxidizing agents and only then is the oxide layer dissolution carried out with oxalic acid.
• a reduction step as described above, is required.
• an organic acid is used because its organic constituent, insofar as it consists of carbon, hydrogen and oxygen, converts into carbon dioxide and water and thus can be removed virtually without residue, since the carbon dioxide escapes as gas from the solution.
• the removal of the organic constituents takes place in a manner known per se by irradiating the solution mixed with an oxidizing agent, such as hydrogen peroxide, with UV light.
• an oxidizing agent such as hydrogen peroxide
• an acid with max. used two carbon atoms.
• the decomposition of such an acid to carbon dioxide and water is faster than the decomposition of three or more carbon atoms containing acids, so that time, energy and oxidizing agent, ultimately cost can be saved.
• inorganic acids such as HN03, H2S04 HBF4 and suitable, non-complexing monocarboxylic acids, formic acid, acetic acid, and Monohydroxyessigklare Dihydroxyessigklare and com ⁇ plexnduende acids such as EDTA, nitrilotriacetic acid and
• Tartronic acid Tartronic acid.
• Formic acid and glyoxylic acid have proven to be suitable with regard to waste prevention, with the best decontamination factors being achieved when only glyoxylic acid is used in the first process stage.
• These acids form a soluble salt with the metal ions, in particular with the nickel of the oxide layer.
• glycine containing a nitrogen atom or inorganic acids is not.
• EXAMPLES be the efficacy of the proposed method to test experiments with samples from the primary circuit of a pressurized water ⁇ water reactor performed (see Table 1).
• the samples are immersed in a container in a cleaning solution having a volume of 1 liter and a temperature of about 90 ° C.
• a cleaning solution having a volume of 1 liter and a temperature of about 90 ° C.
• WEI ter has been described above, the dissolved-out metal ions of an oxide layer removed in a decontamination ⁇ method with an ion exchanger from the cleaning solution.
• no ion exchange the respective cleaning solution at the end of a treatment cycle (oxidation and Dekont suits) is carried out in the experiments, but ver ⁇ designed and replaced with a new cleaning solution.
• the acidic range pH about 2, worked.
• Each treatment cycle includes an oxidation step and a decontamination step.
• the exposure time is 16 hours.
• not oxalic acid is used for the decontamination step, acid and / or glyoxylic acid used (see Tables 1-3).
• excess oxidant (HMnO 4) is neutralized by addition of an appropriate amount of reducing agent and then the acid used in the decontamination step is added.
• the reaction time of the acid in the decontamination step is in each case 5 hours.
• Decont cycles of the first process stage with this acid is gearbei ⁇ tet.
• decontamination steps of the first stage are also suitable for inorganic acids.
• an experiment is carried out in which a sample from the primary circuit of a pressurized water reactor with a size corresponding to the above samples one from oxidation step and
• Decontamination step was subjected to existing cycle. At a Volume of the cleaning solution of 600 ml and a temperature of about 95 ° C was first carried out an oxidation of the existing on the sample oxide layer with HMn04 (300 ppm) in a period of 20 hours. After this step, the existing remainder of the oxidizing agent is neutralized with a mixture of water ⁇ peroxide and nitric acid, the former being required to dissolve from the HMn04 forming manganese in the oxidation step (Mn02). This is followed by a 5-hour decontamination step in which the nitric acid (HNO 3) already contained in solution acts as deconic acid, ie to dissolve the oxide layer present on the sample. After the decontamination step, the gamma activity of the sample drops to a value of 2.18E + 4Bq. Compared with the initial activity of the sample of 6.88E + 4Bq, this means one

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

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• 2009
  • 2009-12-04 DE DE102009047524A patent/DE102009047524A1/de not_active Withdrawn
• 2010
  • 2010-12-01 CA CA2755288A patent/CA2755288A1/en not_active Abandoned
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  • 2010-12-01 WO PCT/EP2010/068602 patent/WO2011067271A1/de active Application Filing
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