Classifications

• • 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
  • C25F1/02—Pickling; Descaling
  • C25F1/04—Pickling; Descaling in solution
• • 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
  • C25F1/02—Pickling; Descaling
  • C25F1/04—Pickling; Descaling in solution
  • C25F1/06—Iron or steel
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F3/00—Electrolytic etching or polishing
  • C25F3/02—Etching
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F3/00—Electrolytic etching or polishing
  • C25F3/02—Etching
  • C25F3/06—Etching of iron or steel
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F7/00—Constructional parts, or assemblies thereof, of cells for electrolytic removal of material from objects; Servicing or operating
  • C25F7/02—Regeneration of process liquids
• • 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
  • G21F9/28—Treating solids

Definitions

• manganese are to be managed as waste and to store.
• the amount of manganese to be used in decontamination must be reduced to the minimum necessary.
• Another disadvantage of manganese is its relative instability in aqueous solution necessitating the use of generally reducing stabilizing products at the end of treatment to avoid any uncontrolled precipitation.
• These stabilizing agents can be: organic like the alkaline gluconate
• the deposition of MnO 2 by precipitation on the surface to be decontaminated is minimized or even completely avoided. Therefore, throughout the treatment, the oxidizing capacity of manganese VII is kept constant without requiring the use of large initial amounts of this oxidant or an additional supply of manganese during treatment. Finally, the process of the present invention is remarkable because it can be used to decontaminate a metal surface, but also to erode by oxidation any metal surface that radioelements are or not fixed on this surface.
• the method according to the present invention is capable of being implemented on any metal surface whatever its size and shape.
• the surface to be eroded or decontaminated is a metal wall including an internal circuit, a pipe, a nuclear reactor, an apparatus of an irradiated nuclear fuel reprocessing plant and a primary circuit of nuclear reactor cooled with water under pressure.
• the inventors have realized that the fact of applying to the metal surface to be eroded or decontaminated, an electrical potential more anode than the corrosion potential of said surface and this intermittently avoids the electrolysis of the electrolyte and in particular a gassing of hydrogen during the process according to the present invention.
• the acid and especially the nitric acid that may contain the oxidizing solution S placed in contact with the surface to be eroded or decontaminated is present at a concentration of between 0.01 and 10 mol / l, especially between 0.05 and 5. moles / L, in particular between 0.1 and 3.5 mol / L and, more particularly, between 0.5 and 2 mol / L of oxidizing solution S.
• the manganese VII is reduced to manganese II. It is therefore necessary to regenerate it. Any reaction involving a more oxidizing compound than the manganese VII is usable for this regeneration.
• the process of catalytic erosion or decontamination of a metal surface according to the present invention is carried out in the presence of ozone.
• said process is carried out under ozone sweep.
• ozone is used, in the context of the present invention, to regenerate manganese VII from manganese II.
• the gas comprising ozone is introduced into the solution S of the process according to the invention by means of two gas-liquid contact members which can be, on the one hand, transfer air-lift, natural submergence or vacuum, and / or, on the other hand, air-lift brewing.
• mixture means a mixture comprising two or three forms of manganese with different degrees of oxidation.
• an originality of the process according to the invention consists in the fact that the manganese can be introduced primitively into the solution S indifferently in the form of Mn II, Mn IV or Mn VII. It is then converted into Mn VII, a majority species in the electrolyte and under the conditions used in the process according to the invention.
• the skilled person will adapt, without inventive effort, the conditions including temperature, pH, potential applied during the polarization of the metal surface to be eroded or decontaminated.
• the transformation of manganese VII (Mn ⁇ 4 ⁇ ) of manganese II (Mn 2+) or IV manganese (MnO 2) can be obtained through the use of ozone in nitric acid and, under the conditions such defined for the regeneration of Mn VII from Mn II.
• the process according to the present invention may comprise a subsequent step of stabilizing manganese VII to manganese II, a form that is completely stable in an aqueous medium.
• a “subsequent step” is meant, in the context of the present invention, a step implemented after the oxidative erosion or the decontamination of the metal surface in the presence of oxidizing solution containing manganese VII and the polarization of said surface is considered sufficient. The skilled person will determine the appropriate time to implement this stabilization without inventive effort. Any known step for stabilizing manganese VII to manganese II may be used within the scope of the present invention.
• this stabilization step is an optional step, unlike decontamination processes of the state of the art.
• an agent of stabilization such as reducing stabilizers.
• Any stabilizing agent, organic or inorganic, known can be used.
• the latter may be chosen from alkaline gluconate, ascorbic acid, citric acid, EDTA, dehydroascorbic acid, ascorbic acid, aldols, reducing sugars, sodium hydroxide and hydrogen peroxide. .
• the reducing stabilizing agent used in the process according to the invention is hydrogen peroxide (H 2 O 2).
• H 2 O 2 hydrogen peroxide
• this reducing compound stabilizes manganese VII in the form of Mn II.
• the oxygenated water decomposes into water, the operation does not add any other substance to the solution S.
• the manganese can be again brought to valence VII by resumption of ozone injection, which makes the stabilization operation reversible.
• the process of the present invention may have at least 2, in particular at least 3, in particular at least 5 and, more particularly, at least 10 oxidation / stabilization cycles.
• the stabilization step of the method according to the invention is not mandatory.
• the skilled person will be able to judge if he is necessary or not to implement it. Indeed, it can be interesting to keep the manganese in the form of IV manganese, especially to precipitate decontamination effluents and, therefore, submit them to a pre-decontamination.
• the method of oxidative erosion or decontamination of a metal surface according to the present invention may, in addition, comprise at least one prior step of one (or more) rinsing (s) advantageously non-corrosive (s) to eliminate contamination labile and / or major deposits adhering to the metal surface. Such a step is carried out before the oxidation step.
• rinsing advantageously non-corrosive
• Those skilled in the art know different solutions that can be used for this or these different rinses.
• the method of oxidative erosion or decontamination of a metal surface advantageously comprises the following steps of: a) optionally, subjecting the metal surface to be eroded or decontaminated to at least one non-corrosive rinse ; b) dissolving manganese such as manganese II, manganese IV, manganese VII; c) optionally, contacting the solution obtained in step (b) with ozone, in particular according to the previously envisaged embodiments; d) contacting said metal surface to be eroded or decontaminated with the solution obtained after step (b) or possibly after step (c); e) polarizing said metal surface to be eroded or decontaminated, in contact with the solution obtained after step (b) or possibly after step (c), at an electrical potential that is more anodic than the corrosion potential of said surface, in particular according to the forms of implementation previously envisaged; f) optionally, stabilize the manganese VII contained in said manganese II solution, in particular according to the embodiments previously envisaged (ie stopping the
• step (e) above) are carried out at a temperature above 0 ° C., in particular between 0 and 85 ° C., in particular between 10 and 65 ° C. and, more particularly, between 20 and 50 ° C. even
• the steps (b) and (d) as well as the possible steps (a), (c) and (f) may each and independently of each other be carried out at a temperature greater than 0 ° C., in particular between 0 ° C. and 85 ° C, in particular between 10 and 65 ° C and, more particularly, between 20 and 50 ° C.
• step (e) above is carried out for a time of between 1 and 72 hours, in particular between 6 and 48 hours and, in particular, between 12 and 36 hours.
• the whole process that is to say the steps (b), (d) and (e) with the possible steps (a),
• the oxidizing treatment step employing manganese VII may be carried out according to any of the methods known to those skilled in the art using manganese VII as a corrosion engine and in particular any of the methods described in the patent applications [2-4].
• the various embodiments already described for the use of hydrogen peroxide as a reducing agent also apply to the reducing treatment stage of the process of the invention mutatis mutandis.
• the present invention also relates to a device that can be implemented in certain aspects of the process according to the present invention and especially in the context of a process involving, on the one hand, the polarization of the surface to be eroded or decontaminated and on the other hand, a sweep with nitrogen.
• Such a device comprises:
• the means already described for introducing ozone into a solution can be used for the device according to the present invention.
• These means comprise at least one element and, advantageously, at least two elements chosen from transfer air-lift, with natural submergence or under vacuum; brewing air-lift and plunging piping for introducing liquid or gaseous reagent.
• the means adapted to bias a metal surface advantageously comprise a current generator or DC voltage, means adapted to electrically connect said metal surface to said generator and means adapted to control and control said generator to ensure intermittent polarization from said surface to the desired potential.
• the device according to the present invention may, in addition, comprise means adapted to the production of ozone and, optionally, means adapted to the introduction into a solution of a stabilizing agent such as hydrogen peroxide.
• a stabilizing agent such as hydrogen peroxide
• Mn VII oxidation state manganese is the engine of the corrosion reaction for the oxidation of the metal such as stainless steel AISI 316L (M °) constituting the installation.
• the reaction used in a nitric acid medium is: n Mn VII + 5 M 0 O n Mn II + 5 M + n with 2 ⁇ n ⁇ 6)
• Manganese (Mn VII) can oxidize the various elements constituting the metal such as stainless steel AISI 316L such as:
• This regeneration is carried out using ozone according to the following reaction: 5 O 3 + 2 Mn 11 + 10 H + O 5 O 2 + 2 Mn VI 1 + 5 H 2 O
• FIG. 2 shows the influence of the nitric acid concentration on the corrosion current density of AISI 304L stainless steel at different initial concentrations of Mn II at a temperature of 37 ° C.
• the aim of the study is to present the optimal operating conditions allowing to limit the formation of manganese oxide IV (MnO2) and thus to obtain maximum corrosion of AISI 304L stainless steel with a minimal addition of manganese in the nitric acid medium maintained under a constant sweep of ozone (oxygen or air ozone).
• MnO2 manganese oxide IV
• ozone oxygen or air ozone
• the ozone flow rate is fixed at 1.5 g / hr / 1 and the S / V ratio at 34 m- 1 .
• the polarization curves are plotted for different initial concentrations of Mn II [Mn 2+ ] with a fixed nitric acid concentration of 0.5 M.
• the initial Mn II concentrations used in this experiment are 0, 25, 50, 100, 150 and 200 mg / L, respectively.
• the corrosion current density of the stainless steel is determined graphically (by the plateau value of the cathodic diffusion current limit) as a function of the initial concentration of Mn II [Mn 2+ ]. The results are reported in FIG. 1.
• the corrosion current density of AISI 304L stainless steel increases linearly with the initial concentration of Mn II in solution ([Mn II]).
• the nitric acid concentrations are generally greater than 0.5 M and can reach 2.5 M. Under these conditions, the corrosion rate of the stainless steel at 37 ° C. varies differently depending on the initial concentration in Mn II. The results comparing the two acidities are reported in FIG. 2. For the two different concentrations of nitric acid, the corrosion current density increases overall with the initial Mn II concentration. However, with a 2.5 M nitric acid concentration, the corrosion current density remains constant above an initial Mn II concentration of 100 mg / L. Thus, for initial concentrations of Mn II greater than or equal to 100 mg / L, the corrosion current density of the stainless steel for a 0.5 M nitric acid concentration becomes higher than that obtained with a concentration of 2.5M nitric acid
• the evolutions of the corrosion current density of AISI 304L stainless steel as a function of the temperature and the initial Mn II concentration are comparable to those observed with a 0.5 M nitric acid concentration and for a temperature of 37 ° C.
• the corrosion current density increases with the initial Mn II concentration, but in a different way depending on the temperature.
• the corrosion rate of stainless steel is disadvantaged by raising the temperature to 60 ° C. At this latter temperature, the black deposit of MnO 2 is much greater than in all other cases. It increases again with the increase of nitric acid concentration.
• the temperature is a kinetic factor that promotes the rate of formation of MnO 2 and this leads (at 60 ° C.) to a reduction in the corrosion rate of the stainless steel with respect to the temperatures of 25 ° C. and 37 ° C. At 25 ° C, the formation of manganese oxide remains negligible but the temperature is not high enough to allow corrosion of stainless steel comparable to that observed at 37 ° C.
• the corrosion rate of stainless steel increases with the initial concentration of Mn II in the range 0-200 mg / L for a concentration of nitric acid of 0.5 M and medium ozone (air or oxygen ozone).
• the reactor study assesses the corrosion rate of AISI 304L stainless steel under actual decontamination conditions and examines the conditions to avoid MnO 2 formation.
• the oxidizing solution is transferred to the second reactor (reactor 2) where the AISI 304L stainless steel plates are already arranged with a Surface / Volume ratio of 64 m -1 . constant and continuous ozone is maintained during the experiments to ensure the regeneration of the Mn VII
• the temperature of the electrolyte in the reactor 2 is kept constant with the aid of a thermostat and the jacket provided on this reactor.
• a saturated calomel reference electrode and a platinum electrode are used throughout the electrochemical measurements.
• the corrosion rate of the stainless steel expressed in ⁇ m / h as a function of the initial Mn II concentration is reported in FIG. 4. The results are obtained after 24 hours of etching and with a 0.5 M nitric acid medium at 37 ° C. ° C.
• the attack speed is proportional to the Mn II concentration.
• Mn II concentration For an initial concentration of Mn II in solution equal to 100 mg / L, the average corrosion rate of the stainless steel after 24 hours is 0.07 ⁇ m / h. This value is already sufficient to ensure surface decontamination of facilities. 11.3.
• the polarization resistance increases by 2000 ohm. cm 2 to 8000 ohm. cm 2 over time.
• This phenomenon reflects the formation of an MnO 2 deposit at the surface of the stainless steel. This deposit causes a slowing down of the corrosion rate of the stainless steel during
• the present inventors propose to apply a potential slightly higher than the corrosion potential (e abandonment ) of stainless steel.
• This maintenance of the steel to a more anodic potential only for role to provoke the dissolution of the deposit of MnO2.
• the corrosion rate of the metal does not need to be modified by this potential change because the oxidizing medium is already very efficient. It is the maintenance of its effectiveness that must be ensured for 24 hours.
• the rate of corrosion also increases with the application of a higher potential but this is not the goal. It suffices that the corrosion rate remains constant during the duration of the decontamination treatment with a minimum of disturbance. Thus, according to these results, and in particular under the experimental conditions used, it is preferable to apply intermittently a potential of + 0.1 V / E drop .
• Table 1 summarizes the mass losses of stainless steel plates after corrosion.
• Patent Application FR 2 792 763 (French Atomic Energy Commission) published on October 27, 2000.

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