EP1968075A1 - Method for decontaminating an oxidised surface of a component or a system of a nuclear plant - Google Patents

Method for decontaminating an oxidised surface of a component or a system of a nuclear plant Download PDF

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EP1968075A1
EP1968075A1 EP08009058A EP08009058A EP1968075A1 EP 1968075 A1 EP1968075 A1 EP 1968075A1 EP 08009058 A EP08009058 A EP 08009058A EP 08009058 A EP08009058 A EP 08009058A EP 1968075 A1 EP1968075 A1 EP 1968075A1
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Prior art keywords
oxide layer
water
treated
marked
oxidation
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German (de)
French (fr)
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EP1968075B1 (en
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Horst-Otto Bertholdt
Terezinha Claudete Dr. Maciel
Franz Dr. Strohmer
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Areva GmbH
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Areva NP GmbH
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    • GPHYSICS
    • G21NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21FPROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/28Treating solids
    • GPHYSICS
    • G21NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21FPROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/001Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
    • G21F9/002Decontamination of the surface of objects with chemical or electrochemical processes
    • GPHYSICS
    • G21NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21FPROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/001Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
    • G21F9/002Decontamination of the surface of objects with chemical or electrochemical processes
    • G21F9/004Decontamination of the surface of objects with chemical or electrochemical processes of metallic surfaces

Definitions

  • the invention relates to a method for decontamination of an oxide layer having surface of a component or a system of a nuclear facility.
  • an oxidation layer forms on system and component surfaces which must be removed in order, for example, to minimize the radiation exposure of the personnel in the case of revision work.
  • Austenitic chromium-nickel steel for example, with 72% iron, 18% chromium and 10% nickel comes into consideration as material for a system or a component.
  • Oxidation on the surfaces forms oxide layers with spinel-like structures of the general formula AB 2 O 4 .
  • the chromium is always present in trivalent, nickel always in divalent and iron in both the two- and trivalent form in the oxide structure. Such oxide layers are chemically almost insoluble.
  • the mentioned pre-oxidation of the oxide layer is conventionally in acidic solution with potassium permanganate and nitric acid or in alkaline solution with potassium permanganate and sodium hydroxide.
  • EP 0 160 831 B1 known process is carried out in the acidic range and used instead of potassium permanganate permanganic acid.
  • the said processes have the disadvantage that during the oxidation treatment manganese dioxide (MnO 2 ) is formed, which deposits on the oxide layer to be treated and inhibits the passage of the oxidant (permanganate ion) into the oxide layer.
  • MnO 2 manganese dioxide
  • the oxide layer can not be completely oxidized in one step. Rather, acting as a diffusion barrier manganese dioxide layers must be removed by intermediate reduction treatments. Normally, three to five such reduction treatments are required, which is associated with a correspondingly high expenditure of time.
  • Another disadvantage of the known methods is the large amount of secondary waste, which is mainly due to the removal of manganese by means of ion exchanger
  • This object is achieved in a method according to claim 1, characterized in that the oxidation of the oxide layer with gaseous nitrogen oxide (NO x ) is performed.
  • NO x gaseous nitrogen oxide
  • Such a procedure initially achieves the advantage that the oxidizing agent can be applied to the oxide layer at a considerably higher concentration than is the case with an aqueous solution with its limited solubility for the oxidizing agent.
  • nitric oxide is less stable in aqueous solution than in the gas phase.
  • an oxidant in aqueous solution such as the primary coolant of a light water reactor, usually finds a variety of reactants, so that a portion of the oxidizing agent is consumed on its way from the feed point to the oxide layer.
  • the required oxidation reactions in particular the conversion of chromium-III to chromium-VI, would take place slowly. Therefore, it is advantageous if a water film is maintained on the oxide layer during the treatment.
  • the nitrogen oxide (NO x ) finds in the oxide film covering the water film or in water-filled pores of the oxide layer, the aqueous conditions required for the course of the oxidative reactions.
  • the oxide layer is still moistened or moistened with water, so a water film already exists, so this may need to be maintained only during the gas phase oxidation.
  • a water film is preferably generated or maintained by means of water vapor.
  • an elevated temperature can be achieved to be required.
  • heat is supplied to the surface of a system or a component or the oxide layer present on it, which takes place for example with the aid of an external heating device or preferably with the aid of superheated steam or hot air.
  • the desired water film is also formed on the oxide layer at the same time.
  • ozone is used as the oxidizing agent.
  • ozone is converted to oxygen, which can be supplied to the exhaust air system of a nuclear installation without further aftertreatment.
  • Ozone is also much more stable in the gas phase than in the aqueous phase. Solubility problems as in the aqueous phase, especially at higher temperatures, do not occur.
  • the ozone gas can thus be introduced in high doses to a water-wetted oxide layer, so that the oxidation of the oxide layer, in particular the oxidation of chromium-III to chromium-VI proceeds faster, especially when working at higher temperatures.
  • Ozone has an oxidation potential of 2.08 V in an acidic solution, but only 1.25 V in a basic solution.
  • acidic conditions are created in the water film wetting the oxide layer, which occurs in particular due to the metered addition of nitrogen oxides can.
  • ozone as an oxidizing agent, a pH of 1 to 2 is maintained.
  • the acidification of the water film is preferably carried out with the aid of gaseous acid anhydrides. These form acids under water accumulation in the water film.
  • the acid anhydrides have an oxidizing effect, they can simultaneously be used as the oxidizing agent, as is the case in a preferred process variant described below.
  • the running oxidation reactions can be accelerated by using elevated temperatures.
  • a temperature range of 40-70 ° C has been found to be particularly advantageous. From 40 ° C, the oxidation reactions take place in the oxide layer at an acceptable rate. However, a temperature increase is only useful up to about 70 ° C, since at higher temperatures, the decomposition of ozone in the gas phase increases significantly.
  • the duration for the oxidation treatment of the oxide layer can be influenced not only by the temperature but also by the concentration of the oxidizing agent. In the case of ozone, acceptable conversion rates, optimum ratios at concentrations of 100 to 120 g / Nm 3 , are achieved within the abovementioned temperature range only from about 5 g / Nm 3 .
  • mixtures of various nitrogen oxides such as NO, NO 2 , N 2 O and N 2 O 4 are used for the oxidation.
  • the oxidation effect can be increased by using elevated temperatures, with such an increase from about 80 ° C is noticeable.
  • the best effectiveness is achieved when working in a temperature range of about 110 ° C to about 180 ° C.
  • the oxidation effect can also, as in the case of ozone, be influenced by the concentration of nitrogen oxides.
  • An NO x concentration of less than 0.5 g / Nm 3 is hardly effective.
  • work is carried out at NO x concentrations of 10 to 50 g / Nm 3 .
  • a rinse is that of the above-described Way treated oxide layer, for example, with deionized appropriate.
  • an oxide layer is subjected to steam after the oxidation treatment, wherein a condensation of the water vapor takes place at the oxide layer.
  • this treatment in or adheres to the oxide layers or component surfaces adhering activity, such as in particulate form or in dissolved or colloidal form in the condensate and is removed with this from the surfaces. This effect is clearly noticeable at water vapor temperatures above 100 ° C.
  • Another advantage of this approach is the comparatively small amount of accumulating condensate.
  • Excess water vapor that is, which has not been condensed on the treated surfaces, is removed from the system to be cleaned or a container in which an oxidative treatment has been carried out and condensed. Together with the condensate draining from a component surface, it is passed over a cation exchanger. In this way, the condensate is released from the activity and can be disposed of easily.
  • a further treatment may be expedient in advance, especially if nitrate ions are contained which originate from the oxidative treatment of an oxide layer or an acidification of a water film with nitrogen oxides.
  • the nitrates are preferably removed from the condensate by reacting with a reducing agent, in particular with hydrazine, to form gaseous nitrogen. It is expedient to set a molar ratio of nitrate to hydrazine of 1: 0.5 to 2: 5.
  • the attached figure shows a flow chart for a decontamination process.
  • the system 1 to be decontaminated for example the primary circuit of a pressurized water system, is first emptied. In the decontamination of a component, such as a primary system pipeline, this is arranged in a container. Such a container would correspond in the flow chart to the system 1.
  • a decontamination circuit 2 is connected to the system 1 and the container. This is gas-tight. Before commissioning, the decontamination circuit 2 and the system are checked for leaks, for example by evacuation.
  • the entire system, ie system 1 and decontamination circuit 2 is heated up.
  • a feed station 3 for hot air and / or superheated steam is arranged in the decontamination circuit 2.
  • a pump 5 is further provided to fill the system 1 with the appropriate gaseous medium and this, as long as necessary, to circulate in the entire system.
  • the system With the help of hot air or superheated steam, the system is brought to the intended process temperature, in the case of ozone to 50-70 ° C.
  • steam is added via the feed station 3. Separating or condensing water is separated at the system outlet 6 by means of a liquid separator 7 and removed from the decontamination circuit 2 with the aid of a condensate line 8.
  • the water film wetting the oxide layer to be oxidized is acidified.
  • 2 gaseous nitrogen oxides or finely atomized nitric acid are added at a feed station 9 of the decontamination cycle.
  • the nitrogen oxides dissolve in the water to form the corresponding acids, such as to form nitric or nitrous acid.
  • the metered amounts of NO x or nitric acid / nitrous acid are chosen so that in the water film a pH of about 1 to 2 sets.
  • the system 1 is supplied with ozone at a concentration of preferably 100 to 120 g via a feed stadium 10 / Nm 3 continuously supplied with in-service pump 5. If necessary, there is a continuous feed of NO x (or HNO 3 ) to maintain the acidic conditions in the water film and hot air or superheated steam to maintain the set temperature parallel to the ozone feed.
  • NO x or HNO 3
  • part of the gas / vapor mixture present in the decontamination cycle 2 is discharged, so that fresh ozone gas and, if appropriate, other auxiliary substances such as NOx can be metered in, the discharged quantity corresponding to the metered amount of gas.
  • the discharge takes place via a scrubber for the separation of NO x / HNO 3 / HNO 2 and then via a catalyst 12, in which a conversion of ozone to oxygen takes place.
  • the ozone-free, optionally still containing water vapor oxygen-air mixture is fed to the exhaust system of the power plant.
  • the ozone concentration is measured at the system return 13 by means of measuring probes (not shown).
  • a temperature monitoring is carried out with appropriate, arranged in the area of the system 1 sensors.
  • the amount of metered NO x is a function of the amount of water vapor supplied. Per Nm 3 of water vapor is supplied at least 0.1 g of NO x, thereby ensuring a pH of the water film of ⁇ 2.
  • the oxide layer is acted upon by steam and ensured that the component surfaces or an oxide layer located thereon a Temperature of below 100 ° C, so that the water vapor can condense it.
  • activity present in or on the oxide layer is removed by this treatment.
  • the respective surfaces of acid residues mainly so rinsed by nitrates.
  • aqueous solution containing nitrate and radioactive cations there is thus an aqueous solution containing nitrate and radioactive cations.
  • the nitrate is converted to gaseous nitrogen with the aid of a reducing agent, the best results of which were achieved with hydrazine, and thus removed from the condensate solution.
  • a stoichiometric amount of hydrazine is preferably used, ie a molar ratio of nitrate to hydrazine of 2: 5 is set.
  • the active cations are removed by passing the solution through a cation exchanger.
  • the rinsing of an oxidatively treated oxide layer can also be done by filling the system 1 with deionized water.
  • the displaced gas is passed over the catalyst 12 while the residual ozone therein is reduced to O 2 and, as already mentioned above, fed to the exhaust system of the nuclear power plant.
  • the nitrate ions present on the surface of the components to be decontaminated or of the oxide layer still present there, which have been formed by metering in nitric acid or by oxidation of NO x are taken up by the deionate and remain during the subsequent treatment to dissolve the oxide coating the decontamination solution.
  • an organic complexing acid preferably oxalic acid, approximately corresponding to one in EP 0 160 831 B1 described method at a temperature of for example 95 ° C added. It will circulated the decontamination solution by means of the pump 5 in the decontamination circuit 2, wherein via a shunt (not shown), a part of the solution passed through ion exchange resins and cations dissolved out of the oxide layer are bound to the exchange resins. Finally, at the end of decontamination, an oxidative decomposition of the organic acid by means of UV irradiation to carbon dioxide and water, approximately corresponding to that in the EP patent 0 753 196 B1 described method.
  • a gas phase oxidation was carried out on a pipe section of a primary system pipeline.
  • the pipeline originated from a pressurized water system with more than 25 years of service operation and was provided with an inner cladding made of austenitic Fe-Cr-Ni steel (DIN 1.4551). Accordingly, dense and difficult to dissolve was the oxide formation present on the pipe inner surface.
  • the oxide layer of Inconel 600 steam generator pipes which had been in power operation for 22 years, was preoxidized with ozone in the gas phase. Comparative tests with permanganate as the oxidizing agent were carried out in each case for the first and second laboratory tests.

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  • High Energy & Nuclear Physics (AREA)
  • General Engineering & Computer Science (AREA)
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  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
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Abstract

Decontaminating the surface involves treating the oxide layer with a gaseous oxidant such as ozone or nitric oxide. When treating the oxide layer a water film is maintained and a water-soluble oxidant is used. Hot air, hot steam or an external heating device can be used to supply heat to the surface. Following the oxidation treatment the oxide layer can be treated with an aqueous solution of an organic acid.

Description

Die Erfindung betrifft ein Verfahren zur Dekontamination einer eine Oxidschicht aufweisenden Oberfläche einer Komponente oder eines Systems einer kerntechnischen Anlage. Während des Betriebs eines Leichtwasserreaktors bildet sich auf System- und Komponentenoberflächen eine Oxidationsschicht, die entfernt werden muss, um beispielsweise im Falle von Revisionsarbeiten die Strahlenbelastung des Personals möglichst gering zu halten. Als Material für ein System bzw. eine Komponente kommt vor allen Dingen austenitischer Chrom-Nickel-Stahl beispielsweise mit 72% Eisen, 18% Chrom und 10% Nickel in Frage. Durch Oxidation bilden sich auf den Oberflächen Oxidschichten mit spinellartigen Strukturen der allgemeinen Formel AB2O4. Das Chrom kommt dabei immer in dreiwertiger, Nickel immer in zweiwertiger und Eisen sowohl in zwei- als auch in dreiwertiger Form in der Oxidstruktur vor. Derartige Oxidschichten sind chemisch nahezu unlöslich. Der Entfernung bzw. Auflösung einer Oxidschicht im Rahmen eines Dekontaminationsverfahrens geht somit stets ein Oxidationsschritt voraus, bei dem das dreiwertig gebundenen Chrom in sechswertiges Chrom überführt wird. Dabei wird die kompakte Spinellstruktur zerstört und es bilden sich Eisen-,Chrom- und Nickeloxide, die in organischen und mineralischen Säuren leicht löslich sind. Herkömmlicherweise schließt sich daher an einen Oxidationsschritt eine Behandlung mit einer Säure, insbesondere mit einer komplexierenden Säure, etwa Oxalsäure an.The invention relates to a method for decontamination of an oxide layer having surface of a component or a system of a nuclear facility. During operation of a light water reactor, an oxidation layer forms on system and component surfaces which must be removed in order, for example, to minimize the radiation exposure of the personnel in the case of revision work. Austenitic chromium-nickel steel, for example, with 72% iron, 18% chromium and 10% nickel comes into consideration as material for a system or a component. Oxidation on the surfaces forms oxide layers with spinel-like structures of the general formula AB 2 O 4 . The chromium is always present in trivalent, nickel always in divalent and iron in both the two- and trivalent form in the oxide structure. Such oxide layers are chemically almost insoluble. The removal or dissolution of an oxide layer in the context of a decontamination process thus always precedes an oxidation step in which the trivalent chromium is converted into hexavalent chromium. In the process, the compact spinel structure is destroyed and iron, chromium and nickel oxides are formed which are readily soluble in organic and mineral acids. Conventionally, therefore, an oxidation step is followed by treatment with an acid, in particular with a complexing acid, such as oxalic acid.

Die erwähnte Voroxidation der Oxidschicht wird herkömmlicherweise in saurer Lösung mit Kaliumpermanganat und Salpetersäure oder in alkalischer Lösung mit Kaliumpermanganat und Natriumhydroxid durchgeführt. Bei einem aus EP 0 160 831 B1 bekannten Verfahren wird im sauren Bereich gearbeitet und anstelle von Kaliumpermanganat Permangansäure eingesetzt. Die genannten Verfahren haben den Nachteil, dass sich während der Oxidationsbehandlung Braunstein (MnO2) bildet, der sich auf der zu behandelnden Oxidschicht absetzt und den Übertritt des Oxidationsmittels (Permanganat-Ion) in die Oxidschicht hemmt. Bei herkömmlichen Verfahren kann daher die Oxidschicht nicht in einem Schritt vollständig aufoxidiert werden. Vielmehr müssen als Diffusionssperre wirkende Braunsteinschichten durch zwischengeschaltete Reduktionsbehandlungen entfernt werden. Normalerweise sind drei bis fünf solcher Reduktionsbehandlungen erforderlich, was mit entsprechend hohem Zeitaufwand verbunden ist. Ein weiterer Nachteil der bekannten Verfahren ist die große Menge an Sekundärabfall, die sich vor allem durch die Entfernung des Mangans mittels Ionentauscher ergibt.The mentioned pre-oxidation of the oxide layer is conventionally in acidic solution with potassium permanganate and nitric acid or in alkaline solution with potassium permanganate and sodium hydroxide. At one off EP 0 160 831 B1 known process is carried out in the acidic range and used instead of potassium permanganate permanganic acid. The said processes have the disadvantage that during the oxidation treatment manganese dioxide (MnO 2 ) is formed, which deposits on the oxide layer to be treated and inhibits the passage of the oxidant (permanganate ion) into the oxide layer. In conventional methods, therefore, the oxide layer can not be completely oxidized in one step. Rather, acting as a diffusion barrier manganese dioxide layers must be removed by intermediate reduction treatments. Normally, three to five such reduction treatments are required, which is associated with a correspondingly high expenditure of time. Another disadvantage of the known methods is the large amount of secondary waste, which is mainly due to the removal of manganese by means of ion exchangers.

Neben der Permanganatoxidation wird in der Literatur die Oxidation mittels Ozon in wässriger saurer Lösung unter Zusatz von Chromaten, Nitraten oder Cer-IV-Salzen beschrieben. Die Oxidation mit Ozon unter den genannten Bedingungen erfordert Prozesstemperaturen im Bereich von 40-60°. Unter diesen Bedingungen ist jedoch die Löslichkeit und die thermische Beständigkeit des Ozons relativ gering, so dass es nahezu unmöglich ist, an einer Oxidschicht Ozonkonzentrationen zu erzeugen, die ausreichend hoch sind, um die Spinellstruktur der Oxidschicht in akzeptabler Zeit aufzubrechen. Außerdem ist die Einbringung von Ozon in große Wasservolumina technisch aufwendig. Daher hat sich, trotz ihrer Nachteile, die Oxidation mit Permanganat bzw. Permangansäure weltweit durchgesetzt.In addition to the permanganate oxidation in the literature, the oxidation by means of ozone in aqueous acidic solution with the addition of chromates, nitrates or cerium-IV salts is described. The oxidation with ozone under the conditions mentioned requires process temperatures in the range of 40-60 °. Under these conditions, however, the solubility and thermal stability of ozone is relatively low, so that it is almost impossible to produce ozone concentrations on an oxide layer which are sufficiently high to break up the spinel structure of the oxide layer in an acceptable time. In addition, the introduction of ozone in large volumes of water is technically complex. Therefore, despite its disadvantages, oxidation with permanganate or permanganic acid has become established worldwide.

Davon ausgehend ist es die Aufgabe der Erfindung, ein Verfahren zur Dekontamination einer eine Oxidschicht aufweisenden Oberfläche einer Komponente oder eines Systems einer kerntechnischen Anlage vorzuschlagen, welches wirksam arbeitet und insbesondere einstufig durchführbar ist.On this basis, it is the object of the invention to provide a method for the decontamination of an oxide layer having a surface of a component or a system of nuclear To propose plant, which works effectively and is particularly feasible in one stage.

Diese Aufgabe wird bei einem Verfahren nach Anspruch 1 dadurch gelöst, dass die Oxidation der Oxidschicht mit gasförmigen Stickoxid (NOx) durchgeführt wird. Durch eine derartige Verfahrensweise wird zunächst der Vorteil erzielt, dass das Oxidationsmittel mit einer erheblich höheren Konzentration auf die Oxidschicht appliziert werden kann, als dies bei einer wässrigen Lösung mit ihrer begrenzten Lösefähigkeit für das Oxidationsmittel der Fall ist. Außerdem ist Stickoxid in wässriger Lösung weniger beständig als in der Gasphase. Hinzu kommt noch, dass ein Oxidationsmittel in wässriger Lösung, etwa dem Primärkühlmittel eines Leichtwasserreaktors, in der Regel eine Vielzahl von Reaktionspartnern findet, so dass ein Teil des Oxidationsmittels auf seinem Weg von der Einspeisestelle zur Oxidschicht verbraucht wird.This object is achieved in a method according to claim 1, characterized in that the oxidation of the oxide layer with gaseous nitrogen oxide (NO x ) is performed. Such a procedure initially achieves the advantage that the oxidizing agent can be applied to the oxide layer at a considerably higher concentration than is the case with an aqueous solution with its limited solubility for the oxidizing agent. In addition, nitric oxide is less stable in aqueous solution than in the gas phase. In addition, an oxidant in aqueous solution, such as the primary coolant of a light water reactor, usually finds a variety of reactants, so that a portion of the oxidizing agent is consumed on its way from the feed point to the oxide layer.

Bei völlig trockener Oxidschicht würden die erforderlichen Oxidationsreaktionen, insbesondere die Umwandlung von Chrom-III zu Chrom-VI, langsam ablaufen. Daher ist es vorteilhaft, wenn während der Behandlung auf der Oxidschicht ein Wasserfilm aufrechterhalten wird. Das Stickoxid (NOx) findet dann in dem die Oxidschicht bedeckenden Wasserfilm bzw. in mit Wasser gefüllten Poren der Oxidschicht die zum Ablaufen der oxidativen Umsetzungen erforderlichen wässrigen Bedingungen vor. Für den Fall, dass ein vorher mit Wasser gefülltes System entleert und anschließend die Gasphasenoxidation durchgeführt wird, ist die Oxidschicht noch mit Wasser benetzt bzw. durchfeuchtet, ein Wasserfilm also schon vorhanden, so dass dieser gegebenenfalls während der Gasphasenoxidation nur noch aufrechterhalten werden muss. Ein Wasserfilm wird vorzugsweise mit Hilfe von Wasserdampf erzeugt bzw. aufrechterhalten.With a completely dry oxide layer, the required oxidation reactions, in particular the conversion of chromium-III to chromium-VI, would take place slowly. Therefore, it is advantageous if a water film is maintained on the oxide layer during the treatment. The nitrogen oxide (NO x ) then finds in the oxide film covering the water film or in water-filled pores of the oxide layer, the aqueous conditions required for the course of the oxidative reactions. In the event that emptied a previously filled with water system and then the gas phase oxidation is carried out, the oxide layer is still moistened or moistened with water, so a water film already exists, so this may need to be maintained only during the gas phase oxidation. A water film is preferably generated or maintained by means of water vapor.

Damit die gewünschten Oxidationsreaktionen in ökonomisch vertretbaren Zeiträumen ablaufen, kann eine erhöhte Temperatur erforderlich sein. Bei einer weiteren bevorzugten Verfahrensvariante ist daher vorgesehen, dass der Oberfläche eines Systems oder einer Komponente bzw. der auf ihr vorhandenen Oxidschicht Wärme zugeführt wird, was etwa mit Hilfe einer externen Heizeinrichtung oder vorzugsweise mit Hilfe von Heißdampf oder Heißluft erfolgt. Im erstgenannten Fall entsteht gleichzeitig auch der gewünschte Wasserfilm auf der Oxidschicht.For the desired oxidation reactions to take place in economically justifiable periods, an elevated temperature can be achieved to be required. In a further preferred variant of the method it is therefore provided that heat is supplied to the surface of a system or a component or the oxide layer present on it, which takes place for example with the aid of an external heating device or preferably with the aid of superheated steam or hot air. In the former case, the desired water film is also formed on the oxide layer at the same time.

Bei einer weiteren besonders bevorzugten Verfahrensvariante wird als Oxidationsmittel Ozon verwendet. Bei den in oder an der Oxidschicht ablaufenden Redox-Reaktionen wird Ozon zu Sauerstoff umgesetzt, der ohne weitere Nachbehandlung dem Abluftsystem einer kerntechnisches Anlage zugeführt werden kann. Ozon ist außerdem in der Gasphase wesentlich beständiger als in der wässrigen Phase. Löslichkeitsprobleme wie in der wässrigen Phase, insbesondere bei höheren Temperaturen, treten nicht auf. Das Ozongas kann somit in hohen Dosen an eine wasserbenetzte Oxidschicht herangeführt werden, so dass die Oxidation der Oxidschicht, insbesondere die Oxidation von Chrom-III zu Chrom-VI schneller vonstatten geht, insbesondere wenn bei höheren Temperaturen gearbeitet wird.In a further particularly preferred process variant, ozone is used as the oxidizing agent. In the case of the redox reactions taking place in or on the oxide layer, ozone is converted to oxygen, which can be supplied to the exhaust air system of a nuclear installation without further aftertreatment. Ozone is also much more stable in the gas phase than in the aqueous phase. Solubility problems as in the aqueous phase, especially at higher temperatures, do not occur. The ozone gas can thus be introduced in high doses to a water-wetted oxide layer, so that the oxidation of the oxide layer, in particular the oxidation of chromium-III to chromium-VI proceeds faster, especially when working at higher temperatures.

Nicht nur Ozon, sondern auch andere Oxidationsmittel haben in saurer Lösung ein höheres Oxidationspotential als in alkalischer Lösung. Ozon beispielsweise hat in saurer Lösung ein Oxidationspotential von 2,08 V, in basischer Lösung dagegen nur von 1,25 V. Bei einer weiteren bevorzugten Verfahrensvariante werden daher in dem die Oxidschicht benetzenden Wasserfilm saure Bedingungen geschaffen, was insbesondere durch die Zudosierung von Stickoxiden geschehen kann. Insbesondere im Falle von Ozon als Oxidationsmittel wird ein pH-Wert von 1 bis 2 eingehalten. Das Ansäuern des Wasserfilms erfolgt vorzugsweise mit Hilfe von gasförmigen Säureanhydriden. Diese bilden unter Wasseranlagerung im Wasserfilm Säuren.Not only ozone, but also other oxidants have a higher oxidation potential in acidic solution than in alkaline solution. Ozone, for example, has an oxidation potential of 2.08 V in an acidic solution, but only 1.25 V in a basic solution. In a further preferred process variant, acidic conditions are created in the water film wetting the oxide layer, which occurs in particular due to the metered addition of nitrogen oxides can. In particular, in the case of ozone as an oxidizing agent, a pH of 1 to 2 is maintained. The acidification of the water film is preferably carried out with the aid of gaseous acid anhydrides. These form acids under water accumulation in the water film.

Wenn die Säureanhydride oxidierend wirken, können sie gleichzeitig als Oxidationsmittel eingesetzt werden, wie dies bei einer weiter unten beschriebenen bevorzugten Verfahrensvariante der Fall ist.If the acid anhydrides have an oxidizing effect, they can simultaneously be used as the oxidizing agent, as is the case in a preferred process variant described below.

Wie bereits erwähnt wurde, können die ablaufenden Oxidationsreaktionen durch Anwendung erhöhter Temperaturen beschleunigt werden. Im Falle der Oxidation mit Ozon hat sich ein Temperaturbereich von 40-70°C als besonders vorteilhaft herausgestellt. Ab 40 °C laufen die Oxidationsreaktionen in der Oxidschicht mit akzeptabler Geschwindigkeit ab. Eine Temperatursteigerung ist jedoch nur bis etwa 70 °C zweckmäßig, da bei höheren Temperaturen der Zerfall des Ozons in der Gasphase merklich zunimmt. Die Dauer für die Oxidationsbehandlung der Oxidschicht kann außer durch die Temperatur auch durch die Konzentration des Oxidationsmittels beeinflusst werden. Im Fall von Ozon werden innerhalb des o.g. Temperaturbereichs erst ab etwa 5 g/Nm3 akzeptable Umsatzraten, optimale Verhältnisse bei Konzentrationen von 100 bis 120 g/Nm3 erreicht.As already mentioned, the running oxidation reactions can be accelerated by using elevated temperatures. In the case of oxidation with ozone, a temperature range of 40-70 ° C has been found to be particularly advantageous. From 40 ° C, the oxidation reactions take place in the oxide layer at an acceptable rate. However, a temperature increase is only useful up to about 70 ° C, since at higher temperatures, the decomposition of ozone in the gas phase increases significantly. The duration for the oxidation treatment of the oxide layer can be influenced not only by the temperature but also by the concentration of the oxidizing agent. In the case of ozone, acceptable conversion rates, optimum ratios at concentrations of 100 to 120 g / Nm 3 , are achieved within the abovementioned temperature range only from about 5 g / Nm 3 .

Bei einer weiteren bevorzugten Verfahrensvariante werden zur Oxidation Gemische verschiedener Stickstoffoxide wie NO, NO2, N2O und N2O4 eingesetzt. Auch bei Verwendung von Stickoxiden kann die Oxidationswirkung durch Anwendung erhöhter Temperaturen gesteigert werden, wobei eine solche Steigerung ab etwa 80 °C spürbar ist. Die beste Effektivität wird erreicht, wenn in einem Temperaturbereich von etwa 110 °C bis etwa 180 °C gearbeitet wird. Die Oxidationswirkung kann außerdem, wie im Falle von Ozon auch, durch die Konzentration der Stickoxide beeinflusst werden. Eine NOx-Konzentration von weniger als 0,5 g/Nm3 ist kaum wirksam. Vorzugsweise wird bei NOx-Konzentrationen von 10 bis 50 g/Nm3 gearbeitet.In a further preferred process variant, mixtures of various nitrogen oxides such as NO, NO 2 , N 2 O and N 2 O 4 are used for the oxidation. Even when using nitrogen oxides, the oxidation effect can be increased by using elevated temperatures, with such an increase from about 80 ° C is noticeable. The best effectiveness is achieved when working in a temperature range of about 110 ° C to about 180 ° C. The oxidation effect can also, as in the case of ozone, be influenced by the concentration of nitrogen oxides. An NO x concentration of less than 0.5 g / Nm 3 is hardly effective. Preferably, work is carried out at NO x concentrations of 10 to 50 g / Nm 3 .

Bevor nach Abschluss der Oxidationsbehandlung eine Auflösung der auf einer Bauteiloberfläche vorhandenen Oxidschicht eingeleitet wird, ist eine Spülung der auf die oben geschilderte Art und Weise behandelten Oxidschicht, beispielsweise mit Deionat zweckmäßig. Bei einer bevorzugten Verfahrensvariante wird jedoch eine Oxidschicht im Anschluss an die Oxidationsbehandlung mit Wasserdampf beaufschlagt wird, wobei an der Oxidschicht eine Kondensation des Wasserdampfes erfolgt. Damit Wasserdampf kondensieren kann ist gegebenenfalls eine Abkühlung der Bauteiloberflächen bzw. einer auf ihnen vorhandenen Oxidschicht auf eine Temperatur unterhalb 100 °C erforderlich. Es hat sich überraschenderweise gezeigt, dass durch diese Behandlung in oder an den Oxidschichten oder Bauteiloberflächen anhaftende Aktivität, etwa in Partikelform oder in gelöster oder kolloidaler Form in das Kondensat übertritt und mit diesem von den Oberflächen entfernt wird. Dieser Effekt macht sich bei Wasserdampf-Temperaturen oberhalb von 100 °C deutlich bemerkbar. Ein weiterer Vorteil dieser Vorgehensweise ist die vergleichsweise geringe Menge an anfallender Kondensatflüssigkeit.Before a dissolution of the oxide layer present on a component surface is initiated after completion of the oxidation treatment, a rinse is that of the above-described Way treated oxide layer, for example, with deionized appropriate. In a preferred variant of the method, however, an oxide layer is subjected to steam after the oxidation treatment, wherein a condensation of the water vapor takes place at the oxide layer. In order for water vapor to condense, it may be necessary to cool the component surfaces or an oxide layer on them to a temperature below 100 ° C. It has surprisingly been found that by this treatment in or adheres to the oxide layers or component surfaces adhering activity, such as in particulate form or in dissolved or colloidal form in the condensate and is removed with this from the surfaces. This effect is clearly noticeable at water vapor temperatures above 100 ° C. Another advantage of this approach is the comparatively small amount of accumulating condensate.

Überschüssiger Wasserdampf, also solcher der nicht an den behandelten Oberflächen kondensiert ist, wird aus dem zu reinigenden System oder einem Behälter, in dem eine oxidative Behandlung durchgeführt wurde, entfernt und kondensiert. Zusammen mit dem von einer Bauteiloberfläche ablaufenden Kondensat wird es über einen Kationentauscher geführt wird. Auf diese Weise wird das Kondensat von der Aktivität befreit und kann problemlos entsorgt werden. Vorher kann allerdings eine weitere Behandlung zweckmäßig sein, insbesondere wenn Nitrationen enthalten sind, die aus der oxidativen Behandlung einer Oxidschicht oder einer Ansäuerung eines Wasserfilms mit Stickoxiden stammen. Die Nitrate werden vorzugsweise dadurch aus dem Kondensat entfernt, dass sie mit einem Reduktionsmittel, insbesondere mit Hydrazin zu gasförmigen Stickstoff umgesetzt werden. Dabei wird zweckmäßigerweise ein Molverhältnis von Nitrat zu Hydrazin von 1:0,5 bis 2:5 eingestellt.Excess water vapor, that is, which has not been condensed on the treated surfaces, is removed from the system to be cleaned or a container in which an oxidative treatment has been carried out and condensed. Together with the condensate draining from a component surface, it is passed over a cation exchanger. In this way, the condensate is released from the activity and can be disposed of easily. However, a further treatment may be expedient in advance, especially if nitrate ions are contained which originate from the oxidative treatment of an oxide layer or an acidification of a water film with nitrogen oxides. The nitrates are preferably removed from the condensate by reacting with a reducing agent, in particular with hydrazine, to form gaseous nitrogen. It is expedient to set a molar ratio of nitrate to hydrazine of 1: 0.5 to 2: 5.

Die beigefügte Abbildung zeigt ein Flussdiagramm für ein Dekontaminationsverfahren. Das zu dekontaminierende System 1, beispielsweise der Primärkreis einer Druckwasseranlage wird zunächst entleert. Bei der Dekontamination eines Bauteils, beispielsweise einer Primärsystem-Rohrleitung, wird dieses in einem Behälter angeordnet. Ein solcher Behälter würde im Flussdiagramm dem System 1 entsprechen. An das System 1 bzw. den Behälter ist ein Dekontaminationskreislauf 2 angeschlossen. Dieser ist gasdicht ausgeführt. Vor der Inbetriebnahme erfolgt eine Prüfung des Dekontaminationskreislaufs 2 und des Systems auf Dichtigkeit beispielsweise durch Evakuieren. Als nächster Schritt wird die gesamte Anlage also System 1 und Dekontaminationskreislauf 2 aufgeheizt. Zu diesem Zweck ist in den Dekontaminationskreislauf 2 eine Einspeisestadion 3 für Heißluft und/oder Heißdampf angeordnet. Die Zuführung von Luft bzw. Dampf erfolgt über eine Zuleitung 4. Im Dekontaminationskreislauf 2 ist weiterhin eine Pumpe 5 vorhanden, um das System 1 mit dem entsprechenden gasförmigen Medium zu füllen und dieses, solange erforderlich, in der gesamten Anlage umzuwälzen. Mit Hilfe heißer Luft oder Heißdampf wird das System auf die vorgesehene Prozesstemperatur, im Falle von Ozon auf 50-70°C gebracht. Zur Erzeugung eines Wasserfilms auf der Oxidschicht des Systems 1 bzw. einer in einem Behälter vorhandenen Systemkomponente wird über die Einspeisestadion 3 Wasserdampf zudosiert. Sich abscheidendes oder kondensierendes Wasser wird am Systemausgang 6 mit Hilfe eines Flüssigkeitsabscheiders 7 abgetrennt und mit Hilfe einer Kondensatleitung 8 aus dem Dekontaminationskreislauf 2 entfernt. Zur Beschleunigung der CrIII/CrVI-Oxidation wird der die zu oxidierende Oxidschicht benetzende Wasserfilm angesäuert. Dazu werden an einer Einspeisestadion 9 des Dekontaminationskreislaufes 2 gasförmige Stickoxide oder fein vernebelte Salpetersäure zudosiert. Die Stickoxide lösen sich im Wasser unter Bildung der entsprechenden Säuren, etwa unter Bildung von Salpeter- oder salpetriger Säure. Die zudosierten Mengen an NOx bzw. Salpetersäure/salpetriger Säure werden so gewählt, dass sich im Wasserfilm ein pH-Wert von etwa 1 bis 2 einstellt. Sobald die erforderlichen Prozessparameter, also gewünschte Temperatur des Systems bzw. eines auf einer Oberfläche vorhandenen Oxidfilms, Vorhandensein eines Wasserfilms und Säuregrad des Wasserfilms, erreicht sind, wird dem System 1 über eine Einspeisestadion 10 Ozon mit einer Konzentration im Bereich von vorzugsweise 100 bis 120 g/Nm3 bei in Betrieb befindlicher Pumpe 5 kontinuierlich zugeführt. Soweit erforderlich, erfolgt parallel zur Ozoneinspeisung eine kontinuierliche Einspeisung von NOx (oder auch HNO3) zur Aufrechterhaltung der sauren Bedingungen im Wasserfilm und Heißluft oder Heißdampf zur Aufrechterhaltung der Solltemperatur. Am Systemaustritt 6 wird ein Teil des sich im Dekontaminationskreislauf 2 befindlichen Gas/Dampfgemisches ausgeleitet, damit frisches Ozongas und gegebenenfalls sonstige Hilfsstoffe wie NOx zudosiert werden können, wobei die ausgeleitete Menge der zudosierten Gasmenge entspricht. Die Ausleitung erfolgt über einen Gaswäscher zur Abscheidung von NOx/HNO3/HNO2 und anschließend über einen Katalysator 12, in welchem eine Umwandlung von Ozon zu Sauerstoff erfolgt. Die ozonfreie, gegebenenfalls noch Wasserdampf enthaltende Sauerstoff-Luftmischung wird dem Abluftsystem des Kraftwerkes zugeführt. Während der Oxidationsbehandlung wird am Systemrücklauf 13 mit Hilfe von Messsonden (nicht dargestellt) die Ozonkonzentration gemessen. Eine Temperaturüberwachung erfolgt mit entsprechenden, im Bereich des Systems 1 angeordneten Messfühlern. Die Menge des zudosierten NOx erfolgt in Abhängigkeit von der zugeführten Wasserdampfmenge. Pro Nm3 Wasserdampf wird mindestens 0,1g NOx zugeführt und dadurch ein pH des Wasserfilms von <2 gewährleistet.The attached figure shows a flow chart for a decontamination process. The system 1 to be decontaminated, for example the primary circuit of a pressurized water system, is first emptied. In the decontamination of a component, such as a primary system pipeline, this is arranged in a container. Such a container would correspond in the flow chart to the system 1. To the system 1 and the container, a decontamination circuit 2 is connected. This is gas-tight. Before commissioning, the decontamination circuit 2 and the system are checked for leaks, for example by evacuation. As a next step, the entire system, ie system 1 and decontamination circuit 2, is heated up. For this purpose, a feed station 3 for hot air and / or superheated steam is arranged in the decontamination circuit 2. The supply of air or steam via a supply line 4. In the decontamination circuit 2, a pump 5 is further provided to fill the system 1 with the appropriate gaseous medium and this, as long as necessary, to circulate in the entire system. With the help of hot air or superheated steam, the system is brought to the intended process temperature, in the case of ozone to 50-70 ° C. To generate a water film on the oxide layer of the system 1 or a system component present in a container, steam is added via the feed station 3. Separating or condensing water is separated at the system outlet 6 by means of a liquid separator 7 and removed from the decontamination circuit 2 with the aid of a condensate line 8. To accelerate the CrIII / CrVI oxidation, the water film wetting the oxide layer to be oxidized is acidified. For this purpose, 2 gaseous nitrogen oxides or finely atomized nitric acid are added at a feed station 9 of the decontamination cycle. The nitrogen oxides dissolve in the water to form the corresponding acids, such as to form nitric or nitrous acid. The metered amounts of NO x or nitric acid / nitrous acid are chosen so that in the water film a pH of about 1 to 2 sets. As soon as the required process parameters, ie the desired temperature of the system or of an oxide film present on a surface, presence of a water film and acidity of the water film, are reached, the system 1 is supplied with ozone at a concentration of preferably 100 to 120 g via a feed stadium 10 / Nm 3 continuously supplied with in-service pump 5. If necessary, there is a continuous feed of NO x (or HNO 3 ) to maintain the acidic conditions in the water film and hot air or superheated steam to maintain the set temperature parallel to the ozone feed. At the system outlet 6, part of the gas / vapor mixture present in the decontamination cycle 2 is discharged, so that fresh ozone gas and, if appropriate, other auxiliary substances such as NOx can be metered in, the discharged quantity corresponding to the metered amount of gas. The discharge takes place via a scrubber for the separation of NO x / HNO 3 / HNO 2 and then via a catalyst 12, in which a conversion of ozone to oxygen takes place. The ozone-free, optionally still containing water vapor oxygen-air mixture is fed to the exhaust system of the power plant. During the oxidation treatment, the ozone concentration is measured at the system return 13 by means of measuring probes (not shown). A temperature monitoring is carried out with appropriate, arranged in the area of the system 1 sensors. The amount of metered NO x is a function of the amount of water vapor supplied. Per Nm 3 of water vapor is supplied at least 0.1 g of NO x, thereby ensuring a pH of the water film of <2.

Wenn das in einer Oxidschicht vorhandene Cr-III in Cr-VI zumindest in einem wesentlichen Umfang umgewandelt ist, werden Ozon-, NOx-, Heißlufteinspeisung abgestellt und ein Spülschritt eingeleitet. Vorzugsweise wird dazu die Oxidschicht mit Wasserdampf beaufschlagt und dafür Sorge getragen, dass die Bauteilflächen bzw. eine sich darauf befindliche Oxidschicht eine Temperatur von unter 100 °C aufweisen, damit der Wasserdampf daran kondensieren kann. Wie bereits weiter oben erwähnt, wird durch diese Behandlung in oder an der Oxidschicht vorhandene Aktivität entfernt. Außerdem werden die jeweiligen Oberflächen von Säureresten, hauptsächlich also von Nitraten freigespült. Diese sind bei der oxidativen Behandlung eines Oxidfilms oder bei der Ansäuerung eines auf einer Oxidschicht vorhandenen Oxidfilms aus den dazu verwendeten Stickoxiden durch Reaktion mit Wasser entstanden. Nach dem mit Wasserdampf durchgeführten Spülschritt liegt somit eine wässrige Nitrat und radioaktive Kationen enthaltende Lösung vor. Zunächst wird das Nitrat mit Hilfe eines Reduktionsmittels, die besten Ergebnisse wurden mit Hydrazin erzielt, zu gasförmigen Stickstoff umgewandelt, und damit aus der Kondensatlösung entfernt. Um das Nitrat vollständig zu entfernen wird vorzugsweise eine stöchimetrische Menge an Hydrazin eingesetzt, d.h. es wird ein Molverhältnis von Nitrat zu Hydrazin von 2:5 eingestellt. Als nächstes werden die aktiven Kationen entfernt, indem die Lösung über einen Kationenaustauscher geführt wird.When the Cr-III is present in an oxide layer converted to Cr VI, at least to a substantial extent, ozone, NO x will be - hot-air feed is stopped and started by a rinsing step. Preferably, the oxide layer is acted upon by steam and ensured that the component surfaces or an oxide layer located thereon a Temperature of below 100 ° C, so that the water vapor can condense it. As already mentioned above, activity present in or on the oxide layer is removed by this treatment. In addition, the respective surfaces of acid residues, mainly so rinsed by nitrates. These have arisen during the oxidative treatment of an oxide film or during the acidification of an oxide film present on an oxide film from the nitrogen oxides used for this purpose by reaction with water. After the rinsing step carried out with water vapor, there is thus an aqueous solution containing nitrate and radioactive cations. First of all, the nitrate is converted to gaseous nitrogen with the aid of a reducing agent, the best results of which were achieved with hydrazine, and thus removed from the condensate solution. In order to completely remove the nitrate, a stoichiometric amount of hydrazine is preferably used, ie a molar ratio of nitrate to hydrazine of 2: 5 is set. Next, the active cations are removed by passing the solution through a cation exchanger.

Natürlich kann die Spülung einer oxidativ behandelten Oxidschicht auch erfolgen, indem das System 1 mit Deionat aufgefüllt wird. Beim Auffüllen wird das verdrängte Gas über den Katalysator 12 geführt und dabei das sich darin befindliche Rest-Ozon zu O2 reduziert und, wie weiter oben schon erwähnt dem Abluftsystem des Kernkraftwerkes zugeführt. Die auf der Oberfläche der zu dekontaminierenden Bauteile bzw. der dort noch vorhandenen Oxidschicht vorliegenden Nitrationen, die durch Zudosierung von Salpetersäure oder durch Oxidation von NOx entstanden sind, werden vom Deionat aufgenommen und verbleiben während der sich nun anschließenden zum Auflösen der Oxidschicht dienenden Behandlung in der Dekontaminationslösung. Dieser wird zu dem genannten Zwecke eine organische komplexierende Säure, vorzugsweise Oxalsäure, etwa entsprechend einem in EP 0 160 831 B1 beschriebenen Verfahren bei einer Temperatur von beispielsweise 95°C zugesetzt. Dabei wird die Dekontaminationslösung mit Hilfe der Pumpe 5 im Dekontaminationskreislauf 2 umgewälzt, wobei über einen Nebenschluss (nicht dargestellt) ein Teil der Lösung über Ionentauscherharze geführt und aus der Oxidschicht herausgelöste Kationen an den Austauscherharzen gebunden werden. Am Ende der Dekontamination erfolgt schließlich noch eine oxidative Zersetzung der organischen Säure mittels einer UV-Bestrahlung zu Kohlendioxid und Wasser, etwa entsprechend dem in dem EP-Patent 0 753 196 B1 beschriebenen Verfahren.Of course, the rinsing of an oxidatively treated oxide layer can also be done by filling the system 1 with deionized water. When filling the displaced gas is passed over the catalyst 12 while the residual ozone therein is reduced to O 2 and, as already mentioned above, fed to the exhaust system of the nuclear power plant. The nitrate ions present on the surface of the components to be decontaminated or of the oxide layer still present there, which have been formed by metering in nitric acid or by oxidation of NO x , are taken up by the deionate and remain during the subsequent treatment to dissolve the oxide coating the decontamination solution. This is for the purpose mentioned, an organic complexing acid, preferably oxalic acid, approximately corresponding to one in EP 0 160 831 B1 described method at a temperature of for example 95 ° C added. It will circulated the decontamination solution by means of the pump 5 in the decontamination circuit 2, wherein via a shunt (not shown), a part of the solution passed through ion exchange resins and cations dissolved out of the oxide layer are bound to the exchange resins. Finally, at the end of decontamination, an oxidative decomposition of the organic acid by means of UV irradiation to carbon dioxide and water, approximately corresponding to that in the EP patent 0 753 196 B1 described method.

In einem Laborversuch wurde eine Gasphasenoxidation an einem Rohrstück einer Primärsystemrohrleitung durchgeführt. Dazu wurde ein dem beigefügten Flussdiagramm entsprechender Versuchsaufbau verwendet. Die Rohrleitung stammte aus einer Druckwasseranlage mit mehr als 25 Jahren Leistungsbetrieb und war mit einer Innenplattierung aus austenitischen Fe-Cr-Ni-Stahl (DIN 1.4551) versehen. Dementsprechend dicht und schwer löslich war die auf der Rohrinnenfläche vorhandene Oxidformation In einem zweiten Laborversuch wurde die Oxidschicht von aus Inconel 600 bestehenden Dampferzeugerrohren, die 22 Jahre im Leistungsbetrieb waren, mit Ozon in der Gasphase voroxidiert. Sowohl zum ersten als auch zum zweiten Laborversuch wurden jeweils Vergleichsversuche mit Permanganat als Oxidationsmittel durchgeführt. In weiteren Versuchen wurden Originalproben aus einer Druckwasseranlage, die sich 3 Jahre lang im Leistungsbetrieb befanden, ausschließlich einer NOx-GasphasenOxidation unterzogen. Die Ergebnisse sind in den nachfolgenden Tabellen 1, 2 und 3 zusammengefasst. Unter dem in den Tabellen angegebenen Begriff "Zyklus" ist 1 Voroxidations- und 1 Dekontaminationsschritt zu verstehen. Tabelle 1: Dekontamination einer austenitischen Fe/Cr/Ni-Stahlplattierung (DIN 1.4551) aus einer Primärrohrleitung eines Druckwasserreaktors Dekontaminationsverfahren Voroxidations-schritt Summe der Behandlungszeit [h] Dekontaminationsschritt Summe der Behandlungszeit [h] DF Dekontverfahren auf Basis Permanganat + Oxalsäure
3 Zyklen, Temp. 90-95°C
40-60 20 10-17
Dekontverfahren auf Basis Ozon/NOx-Gasphase
1 Zyklus, Temp. 50-55°C
12 6 300-400
Tabelle 2: Dekontamination von DWR/Dampferzeugerrohren aus Inconel 600 Dekontaminationsverfahren Voroxidations-schritt Summe der Behandlungszeit [h] Dekontaminationsschritt Summe der Behandlungszeit [h] DF Dekontverfahren auf Basis Permanganat + Oxalsäure
3 Zyklen, Temp. 90-95°C
40-60 20 3-8
Dekontverfahren auf Basis Ozon/NOx-Gasphase
1 Zyklus, Temp. 50-55°C
6 6 30-60
Tabelle 3 Original Probe aus einer DWR Anlage (Werkstoff Nr. 1.4550, 3 Jahre Leistungsbetrieb Dekontaminationsverfahren Behandlungsdauer gesamt DF Dekontverfahren auf Basis Permanganat + Oxalsäure
3 Zyklen, Temp. 90-95°C
36 Stunden 20-35
NOxBehandlung
1 Zyklus, Temp. 150-160°C
12 Stunden 100-280
In a laboratory experiment, a gas phase oxidation was carried out on a pipe section of a primary system pipeline. For this purpose, a test setup corresponding to the attached flow chart was used. The pipeline originated from a pressurized water system with more than 25 years of service operation and was provided with an inner cladding made of austenitic Fe-Cr-Ni steel (DIN 1.4551). Accordingly, dense and difficult to dissolve was the oxide formation present on the pipe inner surface. In a second laboratory experiment, the oxide layer of Inconel 600 steam generator pipes, which had been in power operation for 22 years, was preoxidized with ozone in the gas phase. Comparative tests with permanganate as the oxidizing agent were carried out in each case for the first and second laboratory tests. In further experiments, original samples from a pressurized water plant, which were in power operation for 3 years, were subjected exclusively to NO x gas phase oxidation. The results are summarized in Tables 1, 2 and 3 below. The term "cycle" given in the tables refers to 1 pre-oxidation and 1 decontamination step. Table 1: Decontamination of austenitic Fe / Cr / Ni steel plating (DIN 1.4551) from a primary pipeline of a pressurized water reactor decontamination procedures Pre-oxidation step Sum of treatment time [h] Decontamination step Sum of treatment time [h] DF Decontamination based on permanganate + oxalic acid
3 cycles, temp. 90-95 ° C
40-60 20 10-17
Decontamination based on ozone / NO x gas phase
1 cycle, temp. 50-55 ° C
12 6 300-400
decontamination procedures Pre-oxidation step Sum of treatment time [h] Decontamination step Sum of treatment time [h] DF Decontamination based on permanganate + oxalic acid
3 cycles, temp. 90-95 ° C
40-60 20 3-8
Decontamination based on ozone / NO x gas phase
1 cycle, temp. 50-55 ° C
6 6 30-60
decontamination procedures Total treatment time DF Decontamination based on permanganate + oxalic acid
3 cycles, temp. 90-95 ° C
36 hours 20-35
NO x treatment
1 cycle, temp. 150-160 ° C
12 hours 100-280

Es ist erkennbar, dass für die Gasphasenoxidation mit Ozon eine wesentlich geringere Behandlungszeit bei niedrigerer Temperatur erforderlich war als bei einer Voroxidation mit Permanganat. Überraschenderweise hat sich auch gezeigt, dass die sich der Voroxidation anschließende Dekontaminationsphase, bei der also die vorbehandelte Oxidschicht mit Hilfe von Oxalsäure abgelöst wurde, ebenfalls in wesentlich kürzerer Zeit durchgeführt werden konnte. Als weiteres überraschendes Ergebnis wurde festgestellt, dass bei einer erfindungsgemäßen Vorgehensweise wesentlich höhere Dekontaminationsfaktoren (DF) erreicht werden können. Da die Nachbehandlung bei den Versuchen und ihren entsprechenden Vergleichsversuchen jeweils gleich war, kann dieses Ergebnis nur als Auswirkung der Voroxidation in der Gasphase interpretiert werden. Diese schließt einen Oxidfilm offenbar in einer Weise auf, die das nachfolgende Auflösen der Oxidschicht mit Oxal- oder auch einer anderen komplexierenden organischen Säure erheblich begünstigt.It can be seen that a much lower treatment time was required for the gas phase oxidation with ozone than with a pre-oxidation with permanganate. Surprisingly, it has also been found that the decontamination phase subsequent to the pre-oxidation, in which the pretreated oxide layer was thus removed with the aid of oxalic acid, could likewise be carried out in a much shorter time. As a further surprising result, it was found that in a procedure according to the invention significantly higher decontamination factors (DF) can be achieved. Since the aftertreatment was the same in the experiments and their corresponding comparative experiments, this result can only be interpreted as an effect of the pre-oxidation in the gas phase. This apparently includes an oxide film in a manner that significantly favors subsequent dissolution of the oxide layer with oxalic or other complexing organic acid.

Vergleichbare Ergebnisse (siehe Tabelle 3) wurden bei einer ausschließlich mit NOx als Oxidationsmittel arbeitenden Voroxidation erreicht.Comparable results (see Table 3) were achieved with pre-oxidation using only NO x as the oxidant.

Claims (20)

Verfahren zur Dekontamination einer eine Oxidschicht aufweisenden Oberfläche einer Komponente oder eines Systems einer kerntechnischen Anlage, bei dem die Oxidschicht mit gasförmigem Stickoxid (NOx) als Oxidationsmittel behandelt wird.A method of decontaminating an oxide layer surface of a component or system of a nuclear facility, wherein the oxide layer is treated with gaseous nitric oxide (NO x ) as the oxidant. Verfahren nach Anspruch 1,
dadurch gekennzeichnet,
dass während der Behandlung auf der Oxidschicht ein Wasserfilm aufrechterhalten und ein wasserlösliches Oxidationsmittel verwendet wird.
Method according to claim 1,
characterized,
that during the treatment on the oxide layer a film of water is maintained and a water-soluble oxidizing agent is used.
Verfahren nach Anspruch 2,
dadurch gekennzeichnet,
dass der Wasserfilm mit Hilfe von Wasserdampf erzeugt wird.
Method according to claim 2,
characterized,
that the water film is generated by means of water vapor.
Verfahren nach einem der vorhergehenden Ansprüche,
dadurch gekennzeichnet,
dass der Oberfläche bzw. der auf ihr vorhandenen Oxidschicht Wärme zugeführt wird.
Method according to one of the preceding claims,
characterized,
that the surface or supplied to their existing oxide layer heat.
Verfahren nach Anspruch 4,
dadurch gekennzeichnet,
dass die Wärmezufuhr mit Hilfe von Heißdampf oder Heißluft erfolgt.
Method according to claim 4,
characterized,
that the heat is supplied by means of superheated steam or hot air.
Verfahren nach Anspruch 4,
dadurch gekennzeichnet,
dass die Wärmezufuhr mit Hilfe einer externen Heizeinrichtung erfolgt.
Method according to claim 4,
characterized,
that the heat is supplied by means of an external heater.
Verfahren nach einem der vorstehenden Ansprüche,
dadurch gekennzeichnet,
dass die zu behandelnde Oberfläche auf eine Temperatur von mindestens 80 °C, aufgeheizt wird.
Method according to one of the preceding claims,
characterized,
that the surface to be treated to a temperature of at least 80 ° C, heated.
Verfahren nach Anspruch 7,
gekennzeichnet durch
eine Temperatur von 110°C bis 180°C.
Method according to claim 7,
marked by
a temperature of 110 ° C to 180 ° C.
Verfahren nach einem der vorstehenden Ansprüche,
dadurch gekennzeichnet,
dass während der Behandlung eine NOx-Konzentration von mindestens 1 g/Nm3 eingehalten wird.
Method according to one of the preceding claims,
characterized,
that is maintained during the treatment, a NOx concentration of at least 1 g / Nm 3.
Verfahren nach Anspruch 9,
gekennzeichnet durch
eine NOx-Konzentration von 10 bis 50 g/Nm3.
Method according to claim 9,
marked by
a NO x concentration of 10 to 50 g / Nm 3 .
Verfahren nach einem der vorhergehenden Ansprüche,
dadurch gekennzeichnet,
dass im Anschluss an die Oxidationsbehandlung die behandelten Oberflächen mit Wasserdampf behandelt werden, wobei an den Oberflächen eine Kondensation des Wasserdampfes erfolgt.
Method according to one of the preceding claims,
characterized,
in that , following the oxidation treatment, the treated surfaces are treated with water vapor, condensation of the water vapor taking place on the surfaces.
Verfahren nach Anspruch 11,
gekennzeichnet durch
eine Temperatur des Wasserdampfes von größer 100 °C
Method according to claim 11,
marked by
a temperature of the water vapor of greater than 100 ° C.
Verfahren nach Anspruch 12,
dadurch gekennzeichnet,
dass überschüssiger Wasserdampf kondensiert wird.
Method according to claim 12,
characterized,
that excess water vapor is condensed.
Verfahren nach Anspruch 12 oder 13,
dadurch gekennzeichnet,
dass das Kondensat über einen Kationentauscher geführt wird.
Method according to claim 12 or 13,
characterized,
that the condensate is passed over a cation exchanger.
Verfahren nach Anspruch 12, 13 oder 14,
dadurch gekennzeichnet,
dass das Kondensat zur Entfernung von darin enthaltenem Nitrat mit einem Reduktionsmittel behandelt wird.
Method according to claim 12, 13 or 14,
characterized,
that the condensate is treated with a reducing agent to remove nitrate contained therein.
Verfahren nach Anspruch 15,
dadurch gekennzeichnet,
dass als Reduktionsmittel Hydrazin eingesetzt wird.
Method according to claim 15,
characterized,
that hydrazine is used as the reducing agent.
Verfahren nach Anspruch 16,
gekennzeichnet durch
ein Molverhältnis von Nitrat zu Hydrazin von mindestens 1 zu 0,5.
Method according to claim 16,
marked by
a molar ratio of nitrate to hydrazine of at least 1 to 0.5.
Verfahren nach Anspruch 17,
gekennzeichnet durch
ein Molverhältnis von Nitrat zu Hydrazin von 1:0,5 bis 2:5.
Method according to claim 17,
marked by
a molar ratio of nitrate to hydrazine of 1: 0.5 to 2: 5.
Verfahren nach einem der vorhergehenden Ansprüche,
dadurch gekennzeichnet,
dass im Anschluss an die Oxidationsbehandlung die Oxidschicht mit einer wässrigen Lösung einer organischen Säure behandelt wird.
Method according to one of the preceding claims,
characterized,
that after the oxidation treatment, the oxide layer is treated with an aqueous solution of an organic acid.
Verfahren nach Anspruch 19,
gekennzeichnet durch
die Verwendung von Oxalsäure.
Method according to claim 19,
marked by
the use of oxalic acid.
EP08009058A 2005-11-29 2006-11-15 Method for decontaminating an oxidised surface of a component or a system of a nuclear plant Active EP1968075B1 (en)

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