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EP0483053B1 - Decontaminating agent and process for dissolving radioactively contaminated surfaces of metallic components - Google Patents

Decontaminating agent and process for dissolving radioactively contaminated surfaces of metallic components Download PDF

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EP0483053B1
EP0483053B1 EP91810731A EP91810731A EP0483053B1 EP 0483053 B1 EP0483053 B1 EP 0483053B1 EP 91810731 A EP91810731 A EP 91810731A EP 91810731 A EP91810731 A EP 91810731A EP 0483053 B1 EP0483053 B1 EP 0483053B1
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process according
contaminated
oxidant
lead
mixture
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EP0483053A1 (en
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Jozef Hanulik
Jean-Francois Equey
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Recytec SA
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
    • C23G1/10—Other heavy metals
    • 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

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  • the present invention relates to a method and a decontamination agent for dissolving oxidized or non-oxidized, radioactively contaminated surfaces of objects made of metal, according to the preamble of claim 1 or claim 22.
  • shielding stones are formed from lead or lead alloys, which are used to create entire walls around highly radioactive components. Heavily radioactive tubes are also covered with lead mats. Of course, these shielding stones, lead mats or lead plates can also be radioactively contaminated. They therefore have to be decontaminated from time to time. So far, this has been unsatisfactory.
  • the lead or lead-containing elements were scraped off on the surface or brushed manually, the contaminated scraped material was radioactively disposed of and the remaining, still slightly contaminated components were melted down.
  • a second variant was to provide the lead shielding stones or plates with a plastic covering that is renewed from time to time. The contaminated plastic cover was always disposed of by nuclear waste. Both variants led to a relatively large amount of nuclear waste to be disposed of.
  • the radioactive contaminated metallic components are placed in a fluoroboric acid bath and this is electrochemically regenerated and the metals are recovered while the regenerated fluoroboric acid is fed back into the process.
  • this method has proven to be too time-consuming that it can also only be used at elevated temperature and concentration.
  • the solubility of lead and other metals such as Ni, Cu, Hg, Ag or steel is also an extremely slow process in HBF4 acid at room temperature, which also takes place with the development of hydrogen H2.
  • This information relates to a reagent of 5% HBF4 with 0.5% H2O2 at a temperature of 25 ° C.
  • a first step (1) as shown in Figure 3, the contaminated components must be degreased. Then they are placed in a solution bath (2). This contains the reagent already described, consisting of a 5% HBF4 acid and 0.5% hydrogen peroxide.
  • the now decontaminated lead plates are removed from the solution bath (2).
  • the solution, which is now contaminated, is led (4) to an electrolysis bath by performing the electrolysis (5).
  • the contaminated lead or lead dioxide is now deposited on the anode or cathode.
  • the concentrated radioactive contaminated material (6) is now in a highly concentrated form and can now be disposed of in a nuclear manner in a known manner.
  • the remaining HBF4 acid is removed from the electrolysis cell (7). Now the return (9) of the HBF4 acid can take place in the solution bath (2). This is done with addition (8) of H2O2 until the desired concentration is reached again.
  • the process can be terminated by neutralizing the acid after the electrolysis has been carried out by adding calcium hydroxide or regenerating it on a cationic ion exchanger to the pure, uncontaminated acid. As is known, this produces a precipitate that can be filtered out or sedimented. The remaining, contaminated filter cake can solidify and be disposed of by nuclear waste. The remaining filtrate is free of activity and also no longer contains lead. It can therefore be disposed of without additional precautionary measures, for example by disposing of it in the waste water disposal system.

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  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
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Description

Die vorliegende Erfindung betrifft ein Verfahren sowie ein Dekontaminationsmittel zur Lösung von oxidierten oder nicht oxidierten, radioaktiv kontaminierten Oberflächen von Gegenständen aus Metall, gemäss Oberbegriff des Patentanspruches 1, bzw. des Patentanspruches 22.The present invention relates to a method and a decontamination agent for dissolving oxidized or non-oxidized, radioactively contaminated surfaces of objects made of metal, according to the preamble of claim 1 or claim 22.

An nuklearen Arbeitsplätzen werden Komponenten aus Blei oder bleienthaltenden Legierungen zur Abschirmung der radioaktiven Strahlung verwendet. Es ist bekannt, dass eine etwa 5 cm dicke Bleiplatte die radioaktive Strahlung um einen Faktor 10 reduziert. Deshalb bildet man aus Blei oder Bleilegierungen sogenannte Abschirmungssteine, mit denen ganze Mauern um hochradioaktive Bauteile erstellt werden. Stark radioaktiv strahlende Rohre werden auch mit Bleimatten ummantelt. Selbstverständlich können diese Abschirmungssteine, Bleimatten oder Bleiplatten ebenfalls radioaktiv kontaminiert sein. Sie müssen daher auch von Zeit zu Zeit dekontaminiert werden. Bisher geschah dies auf nicht zufriedenstellende Weise. Die Blei oder bleienthaltenden Elemente wurden oberflächlich abgekratzt oder manuell gebürstet, das kontaminierte abgekratzte Material radioaktiv entsorgt und die verbleibenden, immer noch leicht kontaminierten Komponenten eingeschmolzen.At nuclear workplaces, components made of lead or alloys containing lead are used to shield radioactive radiation. It is known that an approximately 5 cm thick lead plate reduces the radioactive radiation by a factor of 10. For this reason, so-called shielding stones are formed from lead or lead alloys, which are used to create entire walls around highly radioactive components. Heavily radioactive tubes are also covered with lead mats. Of course, these shielding stones, lead mats or lead plates can also be radioactively contaminated. They therefore have to be decontaminated from time to time. So far, this has been unsatisfactory. The lead or lead-containing elements were scraped off on the surface or brushed manually, the contaminated scraped material was radioactively disposed of and the remaining, still slightly contaminated components were melted down.

Das Resultat war unbefriedigend und führte zusätzlich zu einer Verschleppung der Radioaktivität. Die wiedergewonnenen Komponenten aus Blei oder bleihaltigen Legierungen konnten zwar wiederverwendet werden, wiesen aber von Anfang an eine erhöhte Radioaktivität auf. Eine zweite Variante bestand darin, die Bleiabschirmungs steine oder Platten mit einer Plastikumhüllung zu versehen, die von Zeit zu Zeit erneuert wird. Die kontaminierte Plastikumhüllung wurde jedesmal wieder nuklear entsorgt. Beide Varianten führten zu einer relativ grossen Menge an nuklear zu entsorgendem Abfall.The result was unsatisfactory and also led to a delay in radioactivity. The recovered components made of lead or lead-containing alloys could be reused, but showed increased radioactivity from the beginning. A second variant was to provide the lead shielding stones or plates with a plastic covering that is renewed from time to time. The contaminated plastic cover was always disposed of by nuclear waste. Both variants led to a relatively large amount of nuclear waste to be disposed of.

Bleikomponenten werden in diversen nuklearen Anwendungen eingesetzt. So beispielsweise in nuklearen Waffen, wo Bleikomponenten unter anderem als Reflektorschilder eingesetzt werden. Von Zeit zu Zeit müssen diese Bleikomponenten zur Aufrechterhaltung der Funktionstüchtigkeit der nuklearen Waffen erneuert und die Bleiabfälle dekontaminiert werden.Lead components are used in various nuclear applications. For example in nuclear weapons, where lead components are used, among other things, as reflector shields. From time to time, these lead components must be replaced to maintain the functionality of the nuclear weapons and the lead waste must be decontaminated.

Die gleiche Problematik, die bei Blei und Bleilegierungen auftritt, ist auch bei anderen Metallen relevant. So sind in Anlagen zur Herstellung von UF₆ in zivilen und militärischen Bereichen grosse Mengen von radioaktiv kontaminiertem Nickel vorhanden. Obwohl der Wert dieser Metalle gross ist, liess sich nur der geringste Teil zur Wiederverwertung gewinnen. Eine Anlage zur Herstellung von UF₆ enthält ca. 1′000 - 10′000 t reines Nickel. Ferner enthalten Wärmetauscher und Dampferzeugungsanlagen in Druckwasser-Reaktoren grosse Mengen von Nickel-Basislegierungen wie z.B. Inocel 600 mit einem Anteil von ca. 70% Ni. Aber auch Cu und Cu-Legierungen werden bei Wärmetauscher und Kondensatoren in nuklearen Anlagen verwendet.The same problem that occurs with lead and lead alloys is also relevant for other metals. In plants for the production of UF₆ in civil and military areas, there are large amounts of radioactive contaminated nickel. Although the value of these metals is great, only the smallest part could be won for recycling. A plant for the production of UF₆ contains approx. 1,000-10,000 t of pure nickel. Furthermore, heat exchangers and steam generating systems in pressurized water reactors contain large amounts of nickel-based alloys such as Inocel 600 with a share of approx. 70% Ni. However, Cu and Cu alloys are also used in heat exchangers and condensers in nuclear plants.

Aus der US-A-4828759 ist ein Verfahren zur Dekontamination radioaktiv kontaminierter metallischer Materialien bekannt.A method for the decontamination of radioactive contaminated metallic materials is known from US-A-4828759.

Die radioaktiv kontaminierten metallischen Komponenten werden in ein fluorobor-säurehaltiges Bad gegeben und dieses elektrochemisch regeneriert und die Metalle rückgewonnen, während die regenerierte Fluoroborsäure dem Prozess wieder zugeführt wird. Für die Dekontamination von Komponenten aus Blei und bleihaltigen Legierungen hat sich dieses Verfahren als zu zeitaufwendig erwiesen, dass zudem nur bei erhöhter Temperatur und Konzentration anwendbar ist. Die Löslichkeit von Blei und anderen Metallen wie Ni, Cu, Hg, Ag oder Stahl ist auch in HBF₄-Säure bei Raumtemperatur ein äusserst langsamer Prozess, der zudem unter Entwicklung von Wasserstoff H₂ abläuft.The radioactive contaminated metallic components are placed in a fluoroboric acid bath and this is electrochemically regenerated and the metals are recovered while the regenerated fluoroboric acid is fed back into the process. For the decontamination of components made of lead and lead-containing alloys, this method has proven to be too time-consuming that it can also only be used at elevated temperature and concentration. The solubility of lead and other metals such as Ni, Cu, Hg, Ag or steel is also an extremely slow process in HBF₄ acid at room temperature, which also takes place with the development of hydrogen H₂.

Es ist daher die Aufgabe der vorliegenden Erfindung, ein Verfahren sowie ein Dekontaminierungsmittel zu schaffen, das insbesondere zur Ablösung von oxidierten oder nicht oxidierten, radioaktiv kontaminierten Oberflächen von metallenen Gegenständen geeignet ist, und den Prozess der Ablösung gegenüber der Durchführung mit bekannten Verfahren erheblich beschleunigt und bei Raumtemperatur durchführbar macht.Diese Aufgabe löst ein Verfahren mit den Merkmalen des Patentanspruches 1, beziehungsweise ein Dekontaminationsmittel mit den Merkmalen des Patentanspruches 22.It is therefore the object of the present invention to provide a method and a decontamination agent which is particularly suitable for detaching oxidized or non-oxidized, radioactively contaminated surfaces from metal objects, and which considerably speeds up the detachment process compared to carrying out it using known methods and This object is achieved by a method having the features of claim 1, or a decontamination agent having the features of claim 22.

Die Erläuterung des erfindungsgemässen Verfahrens und des Dekontaminations mittels erfolgt in der nachfolgenden Beschreibung anhand der beigefügten Figuren. Es zeigt:

Fig. 1A + B
den Gewichtsverlust einer Bleiplatte in verschiedenen HBF₄ Konzentrationen in Funktion der Zeit A) unter Beifügung von 0,5 Vol % H₂O₂ und B) ohne Beifügung von H₂O₂;
Fig. 2A + B
zeigen wiederum den Gewichtsverlust einer Bleiplatte in 5%iger HBF₄ mit verschiedenen Konzentrationen von H₂O₂;
Fig. 3
eine schematische Darstellung des Ablaufs des erfindungsgemässen Verfahrens
Fig. 4
die Versuchsanordnung der Elektrolysezelle und die Reagenzgleichungen
Fig. 5
den Verlauf der hier durchgeführten Elektrolyse in Abhängigkeit der Stromdichte, namentlich A bei 30 mA/cm² und B bei 45 mA/cm²;
The method according to the invention and the decontamination are explained in the following description with reference to the attached figures. It shows:
1A + B
the weight loss of a lead plate in different HBF₄ concentrations as a function of time A) with the addition of 0.5 vol% H₂O₂ and B) without the addition of H₂O₂;
2A + B
again show the weight loss of a lead plate in 5% HBF₄ with different concentrations of H₂O₂;
Fig. 3
a schematic representation of the sequence of the inventive method
Fig. 4
the experimental setup of the electrolytic cell and the reagent equations
Fig. 5
the course of the electrolysis carried out here as a function of the current density, namely A at 30 mA / cm² and B at 45 mA / cm²;

Wenn im nachfolgenden Text von Reagenz gesprochen wird, so wird hierunter das erfindungsgemässe Dekontaminations mittel verstanden.If the text below speaks of reagent, this means the decontamination agent according to the invention.

Bei der Durchführung der nachfolgend beschriebenen Experimente wurde eine Bleiplatte mit der Dicke von 0,25 mm und einer Oberfläche von 2 x 88 cm² verwendet. Um zu vermeiden, dass die Bleiplatte mit einem schützenden Fettfilm überzogen ist, wurde diese jeweils vor dem Einbringen in die Lösung mit Aceton entfettet.A lead plate 0.25 mm thick and 2 x 88 cm² in surface area was used in the experiments described below. To prevent the lead plate from being coated with a protective grease film, it was degreased with acetone before it was introduced into the solution.

Bei der Verwendung der Fluoroborsäure HBF₄ wurde jeweils von einer 50%igen reinen Säure ausgegangen und die verschiedenen Verdünnungsgrade durch Zufügung von deionisiertem Wasser erreicht. Die Bleiplatte wurde vor und nach jedem Experiment gewogen. In einer ersten Versuchsreihe wurde der Gewichtsverlust einer genormten Bleiplatte der eingangs genannten Art in verschiedenen HBF₄-Konzentrationen in Abhängigkeit der Zeit ermittelt.When using the fluoroboric acid HBF₄, a 50% pure acid was assumed and the various degrees of dilution were achieved by adding deionized water. The lead plate was weighed before and after each experiment. In a first series of tests, the weight loss of a standardized lead plate of the type mentioned at the beginning in various HBF₄ concentrations was determined as a function of time.

Hierbei ergab sich das Bild gemäss der Figur 1B. Bei einer reinen HBF₄-Säure zeigten sich nach 200 Minuten bei den unterschiedlichen Konzentrationen zwischen 5 und 50% kaum relevante Unterschiede. Erst nach rund 400 Minuten zeigten sich unterschiedliche Gewichtsverluste an den Bleiplatten, wobei Bleiplatten, die höherkonzentrierter HBF₄-Säure ausgesetzt waren, einen grösseren Bleiverlust zeigten. Nach rund 200 Minuten betrug der Bleigewichtsverlust pro Platte bei allen Konzentrationen der HBF₄-Säure ungefähr 0,05 Gramm. Die gleichen Versuche wurden wiederholt unter Beigabe von 0,5 Vol % H₂O₂ wiederum in Abhängigkeit verschiedener Konzentrationen der HBF₄-Säure. Das nun sich zeigende Bild gemäss der Figur 1A zeigte eine stark verbesserte Bleiablösung an den Platten.This gave the picture according to FIG. 1B. With a pure HBF₄ acid, there were hardly any relevant differences after 200 minutes at the different concentrations between 5 and 50%. Only after around 400 minutes did different weight losses appear on the lead plates, with lead plates that were exposed to more concentrated HBF₄ acid showing a greater loss of lead. After approximately 200 minutes, the lead weight loss per plate was approximately 0.05 grams at all concentrations of HBF₄ acid. The same experiments were repeated with the addition of 0.5 vol% H₂O₂ again depending on different concentrations of HBF₄ acid. The picture now shown in FIG. 1A shows a greatly improved lead detachment on the plates.

Nach rund 100 Minuten wurde an allen Platten unabhängig der Konzentration der HBF₄-Säure ein Gewichtsverlust von rund 15 Gramm gemessen. Folglich zeigte sich, dass innert der halben Zeit die Bleiablösung sich um einen Faktor 300 erhöht hatte. Im Gegensatz zu den Versuchen ohne Zusatz von Hydrogenperoxyd zeigte sich, dass die Steigerung der Konzentration der HBF₄-Säure über 5% keine Resultatverbesserung brachte.After around 100 minutes, a weight loss of around 15 grams was measured on all plates regardless of the concentration of HBF₄ acid. As a result, it was found that within half the time the lead release had increased by a factor of 300. In contrast to the experiments without the addition of hydrogen peroxide, it was found that increasing the concentration of HBF₄ acid over 5% did not improve the results.

Es zeigte sich folglich, dass durch die Hinzufügung von 0,5 Vol % H₂O₂ der Aufbau der Oxydschicht sofort erfolgte und die Bleiauflösung schnell einsetzte. Die Auflösung war anfänglich schnell und wurde danach langsamer. Die Auflösung stoppte, wenn eine Konzentration von 55 Gramm-Blei pro Liter erreicht war.It was consequently shown that the addition of 0.5 vol% H₂O₂ caused the oxide layer to build up immediately and the lead dissolution started quickly. The resolution was initially fast and then slowed down. The dissolution stopped when a concentration of 55 grams of lead per liter was reached.

Analoge Beobachtungen haben sich nach Versuchen mit Ni, Cu, Ag, Hg und Stahl gezeigt. Hiernach wurden die bisher bei Raumtemperatur durchgeführten Versuche bei einer Temperatur von 60° C wiederholt. Auch hier zeigte sich wiederum, dass die Auflösungsrate sich durch die Zufügung von 0,5 % H₂O₂ scharf anstieg, doch eine erhöhte Bleilöslichkeit gegenüber der Durchführung der Versuche bei Raumtemperatur wurde nicht festgestellt.

Figure imgb0001
Analogous observations have been shown after experiments with Ni, Cu, Ag, Hg and steel. Thereafter, the experiments carried out at room temperature were repeated at a temperature of 60 ° C. Here, too, it was again shown that the dissolution rate increased sharply due to the addition of 0.5% H₂O₂, but an increased lead solubility compared to carrying out the tests at room temperature was not found.
Figure imgb0001

Diese Angaben beziehen sich auf ein Reagenz von 5% HBF₄ mit 0,5% H₂O₂ bei einer Temperatur von 25° C.This information relates to a reagent of 5% HBF₄ with 0.5% H₂O₂ at a temperature of 25 ° C.

Aus den bisherigen Experimenten ergibt sich somit, dass eine 5%ige HBF₄-Säure ein optimales Resultat ergibt.From the experiments so far, it follows that a 5% HBF₄ acid gives an optimal result.

Es wurde nun die Löslichkeitsrate von Blei in 5%iger HBF₄-Säure in Abhängigkeit der Konzentration des darin vorhandenen Hydrogenperoxydes ermittelt. Das Resultat zeigen die Figuren 2A und 2B. Bei steigender H₂O₂-Konzentration wurde ein ständiger Anstieg der Auflösungsgeschwindigkeit des Bleies festgestellt, und zwar innerhalb dem Bereich von 0 bis 2 Vol %.The solubility rate of lead in 5% HBF₄ acid has now been determined as a function of the concentration of the hydrogen peroxide present therein. Figures 2A and 2B show the result. With increasing H₂O₂ concentration, a constant increase in the rate of dissolution of the lead was found, namely within the range of 0 to 2 vol%.

In jedem Fall war die Bleiauflösung anfänglich schnell und nach 60 Minuten langsamer. Bei Hydrogenperoxyd-Konzentrationen zwischen 0,5 und 1,0% erreichte die Lösung gegen Ende des Prozesses eine maximale Bleikonzentration von 80 Gramm pro Liter. Bei dieser Konzentration bildete sich ein weisser Niederschlag in der Lösung und auf der Bleioberfläche. Bei höheren Konzentrationen von H₂O₂ verlief die Auflösungsreaktion stark exotherm. Bei der Versuchsanordnung mit 50 Milliliter Lösung begann diese sofort zu kochen, und fast gleichzeitig bildete sich ein weisser Niederschlag in der Lösung. Die maximale Bleikonzentration in einer 10%igen HBF₄-Lösung stellte sich bei etwa 120 Gramm pro Liter ein. Diese Konzentration ist zwar etwa 50% höher als die in den zuvor gemessenen Fällen, doch sind solche Auflösungsbedingungen bei einem Verfahren in industriellem Massstab nicht akzeptabel.In any case, the lead dissolution was initially fast and slower after 60 minutes. At hydrogen peroxide concentrations between 0.5 and 1.0%, the solution reached a maximum lead concentration of 80 grams per liter towards the end of the process. At this concentration, a white precipitate formed in the solution and on the lead surface. At higher concentrations of H₂O₂, the dissolution reaction was highly exothermic. In the test arrangement with 50 milliliters of solution, it started to boil immediately, and almost simultaneously a white precipitate formed in the solution. The maximum lead concentration in a 10% HBF₄ solution was around 120 grams per liter. While this concentration is about 50% higher than that in the previously measured cases, such dissolution conditions are not acceptable in an industrial scale process.

Aus der Gesamtheit der beschriebenen Versuche ergab sich, daß das bevorzugte Reagenz zur Auflösung der Oberflächen von oxidierten oder nicht oxidierten Bleiplatten am vorteilhaftesten mit einer Lösung bestehend aus einer 5%igen HBF₄-Säure mit einem Anteil von 0,5 Vol % Hydrogenperoxyd erfolgt. Mit dieser Lösung wurden die Versuche bezüglich dem Verfahren zur Dekontamination von radioaktiv kontaminierten Komponenten aus Blei oder bleienthaltenden Legierungen durchgeführt.From the totality of the experiments described, it was found that the preferred reagent for dissolving the surfaces of oxidized or non-oxidized lead plates is most advantageously carried out with a solution consisting of a 5% HBF₄ acid with a proportion of 0.5 vol% hydrogen peroxide. With this solution, the tests for the decontamination of radioactively contaminated components made of lead or lead-containing alloys were carried out.

Einige wenige Versuche, Hydrogenperoxid durch andere Oxidationsmittel zu ersetzen, haben sich als ebenfalls gangbare Lösungen erwiesen. So zeigten Versuche unter Verwendung von Permanganate-HBF₄-Lösungen auch annehmbare Resultate.A few attempts to replace hydrogen peroxide with other oxidizing agents have also proven to be viable solutions. Experiments using permanganate HBF₄ solutions also showed acceptable results.

Erstaunlicherweise die allerbesten Resultate ergaben sich bei der Kombination von verschiedenen Oxidationsmitteln zusammen mit einer 5%igen Fluoroborsäure. Insbesondere eine Mischung, bei der man der 5%igen Fluoroborsäure 0,5 bis 2% Hydrogen-Peroxid und 0,1 bis 2% Kaliumpermanganat beigab, führte dazu, dass die in der Tabelle bezüglich der Abtragungskinetik angegebenen Werte nochmals erheblich gesteigert werden konnten. Das Oxidationsmittel Kaliumpermanganat KMnO₄ oxidiert die Metalle resp. die Metalloxide und führt sie in eine in der Säure besonders gut lösliche Form über. Eine solche Lösung von Metallen und Metalloxide, welche die Radioaktivität beinhalten, ist beispielsweise: MnO₄⁻ + 2H₂O + 3e⁻ --------> MnO₂ + 4OH⁻

Figure imgb0002
Surprisingly, the very best results were obtained when various oxidizing agents were combined with a 5% fluoroboric acid. In particular, a mixture in which 0.5 to 2% hydrogen peroxide and 0.1 to 2% potassium permanganate were added to the 5% fluoroboric acid resulted in the values in the table relating to the removal kinetics being increased considerably. The oxidizing agent potassium permanganate KMnO₄ oxidizes the metals respectively. the metal oxides and converts them into a form that is particularly readily soluble in the acid. Such a solution of metals and metal oxides that contain the radioactivity is, for example: MnO₄⁻ + 2H₂O + 3e⁻ --------> MnO₂ + 4OH⁻
Figure imgb0002

Im Gegensatz zum bekannten AP-Citrox Dekontaminationsverfahren wird hier kein Mangatdioxid MnO₂ an der Metalloberfläche ausgeschieden.In contrast to the known AP-Citrox decontamination process, no manganese dioxide MnO₂ is excreted on the metal surface.

In einem ersten Schritt (1), wie in Figur 3 dargestellt, müssen die kontaminierten Komponenten entfettet werden. Hiernach werden sie in ein Lösungsbad (2) gegeben. Dieses enthält das bereits beschriebene Reagenz, bestehend aus einer 5%igen HBF₄-Säure und 0,5 % Hydrogenperoxyd.In a first step (1), as shown in Figure 3, the contaminated components must be degreased. Then they are placed in a solution bath (2). This contains the reagent already described, consisting of a 5% HBF₄ acid and 0.5% hydrogen peroxide.

Nachdem man die Reagenz abhängig von der notwendigen Abtragstiefe während ca. 60 Minuten auf die Bleiplatten hat einwirken lassen, entnimmt man (3) die nun dekontaminierten Bleiplatten dem Lösungsbad (2). Die Lösung, die nun kontaminiert ist, führt man (4) zu einem Elektrolysebad, indem man die Elektrolyse (5) durchführt. An der Anode bzw. Kathode lagern sich nun das kontaminierte Blei bzw. Bleidioxyd an. Das konzentrierte radioaktiv kontaminierte Material (6) liegt nun in hochkonzentrierter Form vor und kann nun auf bekannte Weise nuklear entsorgt werden. Die verbleibende HBF₄-Säure wird der Elektrolyse-Zelle entnommen (7). Nun kann die Rückführung (9) der HBF₄-Säure in das Lösungsbad (2) erfolgen. Dies geschieht unter Zufügung (8) von H₂O₂, bis die gewünschte Konzentration wieder erreicht ist. Sind sämtliche Komponenten dekontaminiert, so kann das Verfahren abgebrochen werden, indem man die Säure nach der Durchführung der Elektrolyse durch Zufügung von Kalzium-Hydroxyd neutralisiert oder an einem kationischen Ionentauscher bis zur reinen, nicht kontaminierten Säure regeneriert. Hierbei entsteht bekannterweise ein Niederschlag, den man ausfiltrieren oder sedimentieren kann. Der verbleibende, kontaminierte Filterkuchen lässt sich verfestigen und nuklear entsorgen. Das verbleibende Filtrat ist aktivitätsfrei und enthält auch kein Blei mehr. Es kann somit ohne zusätzliche Vorsichtsmassnahmen entsorgt werden, beispielsweise indem man es der Abwasserentsorgung zuführt.After allowing the reagent to act on the lead plates for approx. 60 minutes, depending on the necessary removal depth, (3) the now decontaminated lead plates are removed from the solution bath (2). The solution, which is now contaminated, is led (4) to an electrolysis bath by performing the electrolysis (5). The contaminated lead or lead dioxide is now deposited on the anode or cathode. The concentrated radioactive contaminated material (6) is now in a highly concentrated form and can now be disposed of in a nuclear manner in a known manner. The remaining HBF₄ acid is removed from the electrolysis cell (7). Now the return (9) of the HBF₄ acid can take place in the solution bath (2). This is done with addition (8) of H₂O₂ until the desired concentration is reached again. If all components have been decontaminated, the process can be terminated by neutralizing the acid after the electrolysis has been carried out by adding calcium hydroxide or regenerating it on a cationic ion exchanger to the pure, uncontaminated acid. As is known, this produces a precipitate that can be filtered out or sedimented. The remaining, contaminated filter cake can solidify and be disposed of by nuclear waste. The remaining filtrate is free of activity and also no longer contains lead. It can therefore be disposed of without additional precautionary measures, for example by disposing of it in the waste water disposal system.

In weiteren Versuchsreihen wurde ermittelt, bei welchen Bedingungen die Elektrolyse der 5%igen HBF₄-Säure durchgeführt werden soll, um eine möglichst effiziente Ausscheidung des Bleis bzw. des Bleioxydes zu erhalten.In further test series it was determined under which conditions the electrolysis of the 5% HBF₄ acid should be carried out in order to obtain the most efficient possible separation of the lead or the lead oxide.

Die Versuche wurden bei Raumtemperatur und bei Verwendung von rostfreiem Stahl an der Kathode und einer Grafitanode durchgeführt. Der Elektrolyt bestand aus einer 5%igen HBF₄-Säure mit einem Gehalt von ca. 30 Gramm pro Liter Pb2+. Der Elektrolyt wurde hergestellt durch die Lösung von Blei in einer 5%igen HBF₄-Säure mit einem Gehalt von 0,5% H₂O₂. Der anfängliche pH-Wert war etwa 0. Die Bleielektrolyse wurde gestartet bei einem Potential von ungefähr 2.0 Volt. Anfänglich bildeten sich Blasen an der Anodenoberfläche. Diese verschwanden, sobald sich Bleidioxyd gebildet hatte.The experiments were carried out at room temperature and when using stainless steel on the cathode and a graphite anode. The electrolyte consisted of a 5% HBF₄ acid with a content of approx. 30 grams per liter of Pb2 +. The electrolyte was produced by the solution of lead in a 5% HBF₄ acid with a content of 0.5% H₂O₂. The initial pH was approximately 0. Lead electrolysis was started at a potential of approximately 2.0 volts. Bubbles initially formed on the anode surface. These disappeared as soon as lead dioxide had formed.

Die Spannung blieb stabil während der Elektrolyse sowohl bei 30 wie auch bei 45 Milliampère pro cm² Stromdichte bis die Bleikonzentration etwa 5 Gramm pro Liter betrug. Von diesem Punkt weg begann die Spannung zu steigen, während gleichzeitig Blasenbildung inbesondere an der Anode beobachtet werden konnte. Hiermit einher ging eine rapide Verschlechterung der coulomb'schen Effizienz. Bei einer Dichte des Elektrolysestroms von 30 mA pro cm² betrug die coulomb'sche Effizienz etwas mehr als 80%, während bei einer Erhöhung der Stromdichte auf 45 mA pro cm² die coulomb'sche Effizienz bei annähernd 100% lag. Die coulomb'sche Effizienz ist davon abhängig, ob sie vor oder nach dem Zeitpunkt der Spannungserhöhung berechnet wird. Die Figur 5A zeigt zwei Beispiele der Bleielektrolyse. In beiden Fällen wurde der Strom auf einem festen Wert gehalten. Es wurde festgestellt, dass die Spannung stabil blieb solange wie die Bleikonzentration über 5 bis 6 Gramm pro Liter war.The voltage remained stable during the electrolysis at both 30 and 45 milliamps per cm² of current density until the lead concentration was about 5 grams per liter. From this point, the voltage began to rise, while bubble formation was observed at the anode in particular. This was accompanied by a rapid deterioration in Coulomb efficiency. With a density of the electrolysis current of 30 mA per cm² the coulomb efficiency was a little more than 80%, while with an increase of the current density to 45 mA per cm² the coulomb efficiency was approximately 100%. The coulombic efficiency depends on whether it is calculated before or after the time of the voltage increase. FIG. 5A shows two examples of lead electrolysis. In both cases the current was kept at a fixed value. The tension was found to remain stable as long as the lead concentration was over 5 to 6 grams per liter.

Sobald diese Konzentration erreicht war, begann die Spannung zu steigen, und die coulomb'sche Effizienz sank. Eine Steigerung der Spannung führte auch zur Bildung von Sauerstoffblasen an der Oberfläche der Anode. Es scheint somit vorteilhaft die Elektrolyse unter Spannungskontrolle durchzuführen, um die Sauerstoffentwicklung zu verhindern.As soon as this concentration was reached, the voltage began to rise and the Coulomb efficiency decreased. Increasing the voltage also led to the formation of oxygen bubbles on the surface of the anode. It therefore seems advantageous to carry out the electrolysis under voltage control in order to prevent the development of oxygen.

Aus den Versuchen ging hervor, dass die Auflösung von metallischem Blei in HBF₄-Säure von weniger als 50% bei einem Gehalt von weniger als 2 Vol % H₂O₂ eine erheblich verbesserte Auflösung bewirkte. Besonders gute Resultate wurden mit einer 5%igen HBF₄-Säure mit einem Gehalt von 0,5% H₂O₂ erzielt. In dieser Lösung liessen sich 35 Gramm Blei pro Liter in etwa 90 - 120 Minuten auflösen. Nach der Bleiauflösung wurde die Lösung ohne zusätzliche Modifikation direkt als Elektrolyt für die Bleirückgewinnung verwendet. Die Elektrolyse ergab an der Stahlkathode homogenes Blei und an der Graphitanode entsprechend Bleidioxyd PbO₂. Die coulomb'sche Effizienz war höher als 90% solange die Elektrolysespannung auf einem Potential gehalten wurde, bei der sich kaum eine O₂-Entwicklung zeigte.The experiments showed that the dissolution of metallic lead in HBF₄ acid of less than 50% with a content of less than 2 vol% H₂O₂ brought about a significantly improved resolution. Particularly good results were achieved with a 5% HBF₄ acid with a content of 0.5% H₂O₂. In this solution, 35 grams of lead per liter could be dissolved in about 90-120 minutes. After the lead dissolution, the solution was used directly as an electrolyte for lead recovery without additional modification. The electrolysis gave homogeneous lead on the steel cathode and lead dioxide PbO₂ on the graphite anode. The Coulomb efficiency was higher than 90% as long as the electrolysis voltage was kept at a potential at which there was hardly any O₂ development.

Bei der Verwendung eines Reagenz, das aus einer Mischung von 5%igem HBF₄ sowie 0,5 - 2% H₂O₂ und 0,1 - 2% KMnO₂ besteht, lassen sich verschiedene zusätzliche Anwendungsverfahren realisieren. Da bei der Verwendung dieser Reagenz lauter wasserlösliche Teile anfallen, können die dekontaminierten Metallteile schliesslich ganz einfach mit Wasser sauber gespült werden.When using a reagent consisting of a mixture of 5% HBF₄ as well as 0.5 - 2% H₂O₂ and 0.1 - 2% KMnO₂, various additional application methods can be realized. Since all water-soluble parts are produced when using this reagent, the decontaminated metal parts can finally be easily rinsed clean with water.

Ferner hat sich bei der hohen Geschwindigkeit der Auflösung gezeigt, daß dieses Reagenz auch direkt in ein geschlossenes Rohrsystem, beispielsweise einen Wärmetauscher in einem Kernkraftwerk, eingepumpt und in diesem während einigen Stunden umgewälzt werden kann und anschliessend das radioaktive Reagenz ausgepumpt und elektrolytisch regeneriert werden kann. Weil die Lösung vollständig wasserlöslich ist, kann danach das Rohrsystem mit Wasser durchgespült werden.Furthermore, the high speed of dissolution has shown that this reagent can also be pumped directly into a closed pipe system, for example a heat exchanger in a nuclear power plant, and can be circulated in this for a few hours and then the radioactive reagent can be pumped out and regenerated electrolytically. Because the solution is completely water-soluble, the pipe system can then be rinsed with water.

Eine Alternative besteht darin, dass man das Reagenz im Rohrsystem belässt, jedoch nach einiger Zeit über einen Ionentauscher führt, mit dem sich alle radioaktiven Anteile und die gelösten Metalle aus dem System entnehmen lassen. Die Reinigung mittels Ionentauscher ist an und für sich eine bekannte Technologie, die hier nicht weiter erörtert werden muss.An alternative is to leave the reagent in the pipe system, but after a while pass it through an ion exchanger, which can be used to remove all radioactive components and the dissolved metals from the system. The cleaning by means of ion exchangers is in itself a known technology which does not need to be discussed further here.

Eine mögliche Alternative besteht darin, dass man die zu dekontamierenden Teile erst einem Oxidationsmittel aussetzt und danach erst in ein reines HBF₄-Säurebad gibt, beziehungsweise mit HBF₄-Säure besprüht. Diese Vorgehensweise kann mehrmals wiederholt werden, bis die zu dekontaminierende Metalloberfläche eine Radioaktivität unterhalt der Freimessgrenze aufweist.A possible alternative is to first expose the parts to be decontaminated to an oxidizing agent and then to add them to a pure HBF₄ acid bath or spray them with HBF₄ acid. This procedure can be repeated several times until the metal surface to be decontaminated has radioactivity below the free measurement limit.

Schlussendlich ist es aber auch möglich, erst eine Oxidation mittels einem Oxidationsmittel durchzuführen und anschliessend erst das bereits vorher beschriebene Verfahren durchzuführen und die radioaktiv zu dekontaminierenden Metallteile in ein Reagenz aus HBF₄ und einem Oxidationsmittel zu geben.Ultimately, however, it is also possible to first carry out an oxidation using an oxidizing agent and then only to carry out the process already described above and to add the metal parts to be radioactively decontaminated to a reagent composed of HBF₄ and an oxidizing agent.

Claims (23)

  1. Process for dissolving radioactively contaminated surfaces of metal articles, the articles to be decontaminated being contacted with a decontaminating agent containing fluoroboric acid in aqueous solution and having a concentration of 0.05 to approximately 50 mole/litre and the contaminated articles or at least their surfaces are dissolved by the decontaminating agent and then the contaminated materials are disposed of in nuclear manner, characterized in that additionally the surfaces of the radioactively contaminated components are brought into an oxidized state with an oxidant having an increased, faster solubility in fluoroboric acid and then the known decontamination process stages are performed.
  2. Process according to claim 1, characterized in that hydrogen peroxide is used as the oxidant.
  3. Process according to claim 2, characterized in that hydrogen peroxide in a concentration of less than 20 vol. % is used as the oxidant.
  4. Process according to claim 1, characterized in that a mixture of hydrogen peroxide and a further oxidant is used as the oxidant.
  5. Process according to one of the claims 1 to 4, characterized in that the oxidant is firstly contacted with the surface of the radioactively contaminated metal components and then with the fluoroboric acid, before the further decontamination process stages are performed.
  6. Process according to claim 5, characterized in that the first two stages are repeated several times before performing the further decontamination stages.
  7. Process according to claim 5 or 6, characterized in that the surfaces of the radioactively contaminated metal components are alternately sprayed with the oxidant and the fluoroboric acid.
  8. Process according to claim 5 or 6, characterized in that the surfaces of the radioactively contaminated metal components are alternately immersed in an oxidant and in fluoroboric acid.
  9. Process according to claim 1, characterized in that the surfaces of the radioactively contaminated metal components are contacted with a mixture of preferably 5% fluoroboric acid and 0.5 vol. % hydrogen peroxide.
  10. Process according to claim 4, characterized in that the surface of the radioactively contaminated metal components is contacted with a mixture of preferably 5% fluoroboric acid, 0.5 to 2% hydrogen peroxide and 0.1 to 2% potassium permanganate.
  11. Process according to claim 1, characterized in that the surfaces of the radioactive metal components are firstly degreased.
  12. Process according to claim 1, characterized in that the radioactive metal components are dissolved at ambient temperature in a bath of fluoroboric acid and oxidant.
  13. Process according to claim 12, characterized in that a regenerative electrolysis of the contaminated mixture of fluoroboric acid and oxidant is performed at a temperature of preferably 25°C with a current density of 5 to 500 mA/cm².
  14. Process according to claim 13, characterized in that the regenerative electrolysis of the contaminated mixture is performed below a voltage, which leads to oxygen evolution.
  15. Process according to claim 12, characterized in that an electrolysis of the mixture of HBF₄ acid and oxidant is continued until the metal content is less than 0.1 g/litre and then the remaining HBF₄ acid is reused for repeating the process.
  16. Process according to claim 12, characterized in that after carrying out electrolysis, the acid is neutralized by adding calcium hydroxide Ca(OH)₂ and the resulting deposit is filtered off and/or sedimented and the remaining, contaminated filter cake is solidified and disposed of in nuclear manner, whereas the remaining, activity-free and lead-free filtrate is supplied to the sewage disposal system.
  17. Process according to claim 12, characterized in that the electrolysis of the mixture is performed until the lead content is less than 0.1 g/litre and then the solution still having a residual radioactivity is passed through a cation exchanger, so that an activity-free and lead-free 5% HBF₄ acid is obtained.
  18. Process according to claim 10, characterized in that the decontaminated metal parts are cleaned by water rinsing.
  19. Process according to claim 10 for decontaminating radioactively contaminated, closed metal pipe systems, characterized in that the mixture is pumped into the pipe system and circulated for a period of time and then, during a further period of time, the reagent is passed over an ion exchanger.
  20. Process according to claim 10 for decontaminating radioactively contaminated, closed metal pipe systems, characterized in that the mixture is pumped into the pipe system and circulated for a period of time and then the contaminated reagent is pumped out and the pipe system is rinsed with water.
  21. Process according to claim 20, characterized in that the pumped out reagent is electrolytically regenerated.
  22. Decontaminant-containing fluoroboric acid in aqueous solution with a concentration of 0.05 to approximately 50 mole/litre for dissolving radioactively contaminated, oxidized or non-oxidized surfaces of metal articles, characterized in that the decontaminating agent contains a mixture of two different oxidants, whereof at least one is hydrogen peroxide.
  23. Decontaminating agent according to claim 22, characterized in that the same preferably 5% fluoroboric acid contains 0.5 to 2% hydrogen peroxide H₂O₂ and 0.1 to 2% potassium permanganate KMnO₄.
EP91810731A 1990-10-26 1991-09-16 Decontaminating agent and process for dissolving radioactively contaminated surfaces of metallic components Expired - Lifetime EP0483053B1 (en)

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