EP1771865B1 - Method for treating ceramic contaminated with radiocarbon, in particular reactor graphite - Google Patents

Method for treating ceramic contaminated with radiocarbon, in particular reactor graphite Download PDF

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Publication number
EP1771865B1
EP1771865B1 EP05766947.5A EP05766947A EP1771865B1 EP 1771865 B1 EP1771865 B1 EP 1771865B1 EP 05766947 A EP05766947 A EP 05766947A EP 1771865 B1 EP1771865 B1 EP 1771865B1
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Prior art keywords
ceramic
radiocarbon
corrosion medium
process temperature
reaction
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French (fr)
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EP1771865A2 (en
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Johannes Fachinger
Tatjana Podruzhina
Werner Von Lensa
Kerstin Bundesamt für Strahlenschutz KÜHN
Reinhard Odoj
Heiner BRÜCHER
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Forschungszentrum Juelich GmbH
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Forschungszentrum Juelich GmbH
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/28—Treating solids
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/28—Treating solids
    • G21F9/30—Processing

Definitions

  • the invention relates to a method for treating a radio-carbon-contaminated ceramic, in particular reactor graphite.
  • Radiocarbon is the radioactive 14 carbon isotope of carbon. It is naturally produced by cosmic radiation in neutron radiation fields of nuclear reactors in small amounts as a fission product or by activation of the isotope 13 C occurring in natural carbon at 1.1% with an effective cross section of 0.0009 barn, but mainly by activation of nitrogen ( 14 N) in an n, p-reaction with a cross-section of 1.81 barn.
  • the isotope 17 O with only 0.038% in atmospheric oxygen can be converted to radiocarbon via a n, a reaction with a lower cross-section of 0.235 bam.
  • radiocarbon Because of its long physical half-life of 5,730 years and its good mountability in biological systems due to a substitution of 12 C or 13 C radiocarbon in carbon compounds with high biological half-life is radiocarbon a problematic contamination in radioactive waste represents and requires special safety precautions. On the other hand, it is also a valuable indicator of biological research because it is built into biological systems like natural carbon and can easily be tracked for radioactive decay.
  • Radio-carbon from ceramics in particular from nuclear waste, can therefore be used both for the decontamination of waste and for the recovery of valuable material for research.
  • ceramics may be mentioned: reactor graphite. Coal, SiC, Al 2 O 3 , MgO and composites containing ceramics, eg carbon fiber reinforced SiC.
  • a method of disposing of a radiotoxic contaminated article of graphite or carbon wherein a portion of the radiotoxic agents are removed by heating the article therefrom and supplied to a further disposal step, and wherein at least one closed layer is applied to the surface of the article by filling Pore with pyrolytic carbon by infiltration of hydrocarbons above 1000 ° C and / or formed by chemical reaction with a silicon compound to form silicon carbide sealing and / or diffusion-inhibiting. It is disclosed that the heating takes place in vacuum or under inert gas, to prevent the formation of carbon monoxide and carbon dioxide on heating by reactions with the atmospheric oxygen, which contain the existing radiocarbon and therefore may not escape uncontrolled.
  • This object is achieved in a method of the type mentioned in claim 1, characterized in that in a process temperature range by means of chemical reaction of at least one corrosion medium at least with the radiocarbon at least a volatile reaction gas is formed, wherein the amount of at least one corrosion medium, the process temperature and / or the process duration being such that the chemical reaction takes place substantially only on the surface of the ceramic, including pore surfaces, and within near-surface regions, and the at least one reaction gas is collected and fed to a separate treatment, such low process temperature being selected; that the corrosion medium can penetrate far into an existing pore system to partially oxidize the crystals on the inner surface.
  • the method considerably reduces the concentration of radiocarbon contamination. Although it is not possible to remove the entire radiocarbon from the treated ceramic by acting on the surfaces and the areas near the surface. However, even a distance of z. B. 50%, carried out with the method according to Measurements can be achieved, the usability of waste storage facilities would be able to double because the (end) storage capacities are linked to the total cumulative 14 C activity.
  • SectiondekontaminATORs graphite material can be supplied at sufficiently low residual contamination and a complete conversion to CO or CO 2 at higher temperatures of, for example, about 1000 ° C in air.
  • the concentration of radiocarbons in the collected reaction gases is significantly enriched in comparison to the natural occurrence, which is a good prerequisite for further use of radio carbon as a valuable material.
  • the treated ceramic can be corroded on its surface metered so that the inner regions remain as stable as possible.
  • the process according to the invention can also be carried out in such a way that oxygen is used as the corrosion medium.
  • oxygen when used, it reacts with carbon to form carbon monoxide or carbon dioxide, ie volatile carbon compounds.
  • the inventive method can also be carried out so that air is used as an oxygen supplier.
  • pure oxygen or oxygen may be used in admixture with other gases in a composition other than air.
  • the conversion into the abovementioned volatile carbon compounds already takes place at temperatures of about 500.degree. At these temperatures, the oxygen can penetrate far into an existing pore system to partially oxidize the crystals on the inner surface. At higher temperatures, however, a strong oxidation on the outside of the ceramic to be treated, since the pore diffusion is accelerated less by increasing the temperature than the chemical reaction and thus there is a depletion of the corrosion oxygen inside the pore system of the ceramic medium to be corroded.
  • the optimum temperature for the metered corrosion thus depends on the chemical reactivity of the corrosion medium, the diffusion rate in the pore system, which can be increased or controlled, for example by reducing the pressure or by adding inert inert gases, and the dimensions of the ceramic material to be corroded.
  • the process according to the invention can also be carried out so that water vapor is used as an oxygen supplier. It has proved to be advantageous, an inert gas To saturate at room temperature with water and then heat the water-inert gas mixture to process temperature.
  • the inventive method can also be carried out so that hydrogen is used as the corrosion medium.
  • reaction product with carbon in this case essentially CH 4 is formed.
  • the inventive method can also be carried out so that the ceramic is in a container, wherein the at least one corrosion medium is supplied controlled at a suitable process temperature and the reaction gas is withdrawn.
  • the at least one corrosion medium is adsorbed by the surface of the ceramic, including the pore surfaces, and then the ceramic is brought to process temperature. It may be advantageous to heat the ceramic under vacuum or in an inert gas atmosphere. How much the surfaces are loaded with the corrosion medium can be controlled, for example, by the chosen partial pressure and the loading time. The degree of loading should be chosen so that the amount of corrosion medium present is just sufficient to achieve the desired level of corrosion during heating. In this case, the removal of the reaction gases by evacuation or by purging with inert gas after the process at temperatures below the process temperature range or during the process can take place. In this procedure, near-surface carbon is reacted, which reacts chemically with the previously adsorbed corrosion medium. The proportion of radiocarbon in the separated carbon is higher in this method than in the treatment in a permanent atmosphere of the corrosion medium. However, this gain goes hand in hand with a decrease in total sales due to lower partial pressures.
  • the inventive method can also be carried out so that in a further step, the container is evacuated or the ceramic is purged with inert gas to withdraw the reaction gases, and then the process, starting with the adsorption of the at least one corrosion medium on the surface, at least one other Time is performed.
  • the process starting with the adsorption of the at least one corrosion medium on the surface, at least one other Time is performed.
  • a discontinuous process with several cycles is given, which on the one hand lead to longer treatment periods compared to the continuous process, but on the other hand can bring about increased amounts of radiocarbon in the reaction gases.
  • the inventive method can also be carried out so that before adsorbing the at least one corrosion medium metered corrosion by controlled addition of the at least one corrosion medium is carried out at such process temperature that at least a portion of closed pores is opened.
  • the first step in this process primarily serves to open the closed pores, it also already results in removal of a portion of the radio-carbon.
  • the opening of the closed pores can for example be done under a corrosive medium atmosphere, this treatment step can be carried out at elevated temperatures in a relatively short time, just enough to open the pores.
  • the corrosion too Pore opening can also be carried out with the aid of a previously adsorbed corrosion medium in vacuo or an inert gas atmosphere.
  • the process according to the invention can also be carried out in such a way that after the final removal of the reaction gases, the remaining residual ceramic is recycled, for example as nuclear graphite.
  • the method according to the invention can be carried out in such a way that the radiocarbon contained in the collected reaction gases is enriched. Subsequently, the radiocarbon can be recycled as a valuable material.
  • a cyclic process for the corrosion medium may be particularly advantageous when using steam as the oxygen supplier.
  • the cyclic process could look like this: In the corrosive process, carbon monoxide and hydrogen are produced as reaction products with the endothermic reaction of graphite with water vapor under appropriate process conditions.
  • the extracted and collected carbon monoxide now contains a significantly higher proportion of radiocarbon than the original ceramic. This proportion can now be further increased by enrichment processes.
  • solid carbon and water (steam) can be generated from the carbon monoxide in reaction with the hydrogen. The water can then again serve as a supplier for the corrosion medium oxygen.
  • carbon monoxide or CH 4 is preferably produced as the reaction gas.
  • Carbon monoxide and CH 4 have a lower weight than carbon dioxide. With these reaction gases, therefore, the given weight difference between radiocarbon and the stable isotopes of the carbon can be better utilized for enrichment of the radiocarbon.
  • the production of leach-resistant, non-combustible storage containers makes sense. This can e.g. by reaction of the radiocarbon-rich material to carbides, e.g. SiC, or rock-like carbonates happen.
  • the corrosion medium should be chosen so that the reaction gases are as directly as possible suitable for the further treatment steps.
  • FIG. 1 shows in a diagram the result of treatment of one of the AVR reactor (first High-temperature experimental reactor at Anlagenstechnik Anlagenlich; see VDI report 729, AVR - 20 Years of Operation, ISBN 3-18-090720-0, VDI-Verlag, Dusseldorf, 1989 )) originating graphite powder.
  • oxygen was used as a constituent of water.
  • first argon was saturated with water vapor at room temperature.
  • the graphite powder was heated in the steam-argon atmosphere to 1057 ° C and held at this temperature for 16 hours.
  • FIG. 1 represents the release of carbon during the treatment period.
  • Curve 1 shows the total mass loss of the graphite powder. This mass loss is expressed in percent by the left scale.
  • Curve 2 represents the percent release of radiocarbon with respect to the original radiocarbon content. Thus, after 16 hours, about 46% of the radiocarbon originally present in the graphite powder is released. Curve 3 plots the ratio between radiocarbon release in percent and the release of stable carbon isotopes in percent. As an example, the ratio after about 16 hours of treatment is shown below. As mentioned earlier, about 46% of the radiocarbon is removed. At the same time, the treatment released a little more than 16% of the stable carbon isotopes. The ratio of the percentages 46/16 gives a ratio of about 2.85. The ratio is on the right scale of the graph in FIG. 1 shown. The diagram clearly shows that at the beginning of the process the ratio of the yield of radiocarbon is higher than at later times. This confirms the predominant deposition of radiocarbon on the surface, including the pore surfaces.
  • graphite powder from the experimental reactor MERLIN was first stored in air so that the surfaces of the powder, including the pore surfaces, could adsorb oxygen. This material was then placed in a pure argon atmosphere, heated to 1057 ° C and held at this temperature for about 13.5 hours.
  • FIG. 2 shows the result of this treatment in one too FIG. 1 corresponding diagram. It can be seen that overall a much lower absolute release rate was achieved both with respect to the radiocarbon (curve 5) and the stable carbon isotopes (curve 4). However, according to curve 6, the ratio of the percentage release of the radiocarbon to the percentage release of the stable carbon isotopes is more than a factor of 10 higher. Accordingly, the percentage is also the radiocarbon-containing molecules in reaction gases significantly higher than in the treatment under the water-argon atmosphere. The corrosion alone by means of the adsorbed oxygen is particularly suitable when high proportions of radiocarbon in the reaction gases, for example for the recycling of the radio-carbon, to be achieved.

Description

Die Erfindung betrifft ein Verfahren zur Behandlung einer mit Radiokarbon kontaminierten Keramik, insbesondere Reaktorgraphit.The invention relates to a method for treating a radio-carbon-contaminated ceramic, in particular reactor graphite.

Radiokarbon ist das radioaktive Isotop 14C des Kohlenstoffs. Es entsteht außer auf natürliche Weise durch kosmische Strahlung in Neutronenstrahlungsfeldern von Kernreaktoren in geringen Mengen als Spaltprodukt oder durch Aktivierung des zu 1,1% in natürlichem Kohlenstoff vorkommenden Isotops 13C bei einem Wirkungsquerschnitt von 0,0009 barn, aber vorwiegend durch Aktivierung von Stickstoff (14N) in einer n,p-Reaktion mit einem Wirkungsquerschnitt von 1,81 barn. Außerdem kann das nur mit 0,038 % im Luftsauerstoff vorhandene Isotop 17O mit geringerem Wirkungsquerschnitt von 0,235 bam über eine n,a -Reaktion in Radiokarbon umgewandelt werden.Radiocarbon is the radioactive 14 carbon isotope of carbon. It is naturally produced by cosmic radiation in neutron radiation fields of nuclear reactors in small amounts as a fission product or by activation of the isotope 13 C occurring in natural carbon at 1.1% with an effective cross section of 0.0009 barn, but mainly by activation of nitrogen ( 14 N) in an n, p-reaction with a cross-section of 1.81 barn. In addition, the isotope 17 O with only 0.038% in atmospheric oxygen can be converted to radiocarbon via a n, a reaction with a lower cross-section of 0.235 bam.

Wegen seiner langen physikalischen Halbwertszeiten von 5.730 Jahren und seiner guten Einbaubarkeit in biologischen Systemen auf Grund einer Substitution von 12C oder 13C durch Radiokarbon in Kohlenstoffverbindungen mit einer hohen biologischen Halbwertszeit stellt Radiokarbon eine problematische Kontamination in radioaktiven Abfällen dar und verlangt besondere Sicherheitsvorkehrungen. Andererseits ist es jedoch auch ein wertvoller Indikator für die Forschung an biologischen Vorgängen, weil es sich in biologischen Systemen wie natürlicher Kohlenstoff einbaut und leicht wegen des radioaktiven Zerfalls als Marker verfolgt werden kann.Because of its long physical half-life of 5,730 years and its good mountability in biological systems due to a substitution of 12 C or 13 C radiocarbon in carbon compounds with high biological half-life is radiocarbon a problematic contamination in radioactive waste represents and requires special safety precautions. On the other hand, it is also a valuable indicator of biological research because it is built into biological systems like natural carbon and can easily be tracked for radioactive decay.

Eine Entfernung zumindest eines erheblichen Teils des Radiokarbons aus Keramiken, insbesondere aus kerntechnischen Abfällen, kann daher sowohl der Dekontamination der Abfälle als auch der Gewinnung eines Wertstoffes für die Forschung dienen. Als beispielhafte Keramiken seien genannt: Reaktorgraphit. Kohlestein, SiC, Al2O3, MgO sowie Verbundmaterialien, die Keramiken enthalten, z.B. kohlefaserverstärktes SiC.Removal of at least a substantial portion of the radio-carbon from ceramics, in particular from nuclear waste, can therefore be used both for the decontamination of waste and for the recovery of valuable material for research. As exemplary ceramics may be mentioned: reactor graphite. Coal, SiC, Al 2 O 3 , MgO and composites containing ceramics, eg carbon fiber reinforced SiC.

Besonders hohe Konzentrationen von Radiokarbon liegen in den meisten graphitischen Strukturen graphitmoderierter Reaktoren (MAGNOX-Reaktor (CO2-gekühlter Reaktortyp mit Natururan-Brennelementen mit Magnox-Hülle), AGR (Advanced Gas-cooled Reactor), HTR (Hochtemperatur-Reaktor), RBMK (wassergekühlter Kernreaktortyp russischer Bauart)), aber auch in den thermischen Säulen von Forschungsreaktoren (z. B. MERLIN; siehe ATW, Jahrgang 48, Heft 6, Juni 2003, Seiten 404-407) vor. Der Hauptanteil stammt dabei meist aus der Aktivierung von Stickstoff und Sauerstoff. Sauerstoff und Stickstoff lagern sich z. B. durch Luftzutritt an thermischen Säulen und Adsorption an. Bei der thermischen Zersetzung von stickstoffhaltigen Kunststoffen (z. B. Hexamethylentetramin als Binder) bei der Herstellung von Graphiten findet bevorzugt ein Einbau in Komgrenzen statt.Particularly high concentrations of radiocarbon are present in most graphitic structures of graphite-moderated reactors (MAGNOX reactor (CO 2 -cooled reactor type with natural uranium fuel elements with Magnox shell), AGR (Advanced Gas-cooled Reactor), HTR (High-temperature reactor), RBMK (water-cooled nuclear reactor type Russian)), but also in the thermal columns of research reactors (eg MERLIN, see ATW, Volume 48, Issue 6, June 2003, pages 404-407). The main part comes mostly from the activation of nitrogen and oxygen. Oxygen and nitrogen are stored z. B. by air access to thermal columns and adsorption. In the case of the thermal decomposition of nitrogen-containing plastics (for example hexamethylenetetramine as binder) in the production of graphites, incorporation into grain boundaries preferably takes place.

Aus der DE 197 37 891 C2 ist ein Verfahren zur Entsorgung eines mit Radiotoxika kontaminierten Gegenstandes aus Reaktorgraphit oder Kohlestein bekannt, bei dem ein Teil der Radiotoxika durch Aufheizen des Gegenstandes aus diesem entfernt und einem weiteren Entsorgungsschritt zugeführt wird und bei dem zumindest eine geschlossene Schicht an der Oberfläche des Gegenstandes durch Ausfüllen von Poren mit Pyrokohlenstoff mittels Infiltration von Kohlenwasserstoffen oberhalb 1000°C und/oder durch chemische Reaktion mit einer Siliziumverbindung unter Bildung von Siliziumcarbid dichtend und/oder diffusionshemmend ausgebildet wird. Dabei ist offenbart, dass das Aufheizen in Vakuum oder unter Schutzgas erfolgt, um zu verhindern, dass beim Erhitzen durch Reaktionen mit dem atmosphärischen Sauerstoff Kohlenmonoxid und Kohlendioxid entstehen, die das vorhandene Radiokarbon enthalten und daher nicht unkontrolliert entweichen dürfen. Beim Verfahren nach dem beschriebenen Stand der Technik sollen andere Toxika als Radiokarbon, z. B. an die keramische Struktur des Gegenstands gebundenes Tritium oder Cäsium entfernt werden. Die Bildung der geschlossenen Schicht an der Oberfläche des Gegenstandes soll insbesondere ein unerwünschtes Eindringen von Substanzen verhindern, mit denen die im Gegenstand verbliebenen Reste, unter anderem auch Radiokarbon, während der Zwischen- oder Endlagerung chemisch oder durch Lösung ausgetrieben werden könnten. Darüber hinaus ist jedoch ein wirksamer Schutz gegen Verbrennen und gegen die Diffusion der Toxika zur Oberfläche des Gegenstandes gegeben. Mit dem beschriebenen Verfahren wird somit der zu behandelnde Gegenstand nicht in erheblichem Umfange von der RadiokarbonKontamination befreit.From the DE 197 37 891 C2 A method of disposing of a radiotoxic contaminated article of graphite or carbon is known, wherein a portion of the radiotoxic agents are removed by heating the article therefrom and supplied to a further disposal step, and wherein at least one closed layer is applied to the surface of the article by filling Pore with pyrolytic carbon by infiltration of hydrocarbons above 1000 ° C and / or formed by chemical reaction with a silicon compound to form silicon carbide sealing and / or diffusion-inhibiting. It is disclosed that the heating takes place in vacuum or under inert gas, to prevent the formation of carbon monoxide and carbon dioxide on heating by reactions with the atmospheric oxygen, which contain the existing radiocarbon and therefore may not escape uncontrolled. In the method according to the described prior art, other toxicants than radiocarbon, z. For example, tritium or cesium bound to the ceramic structure of the article may be removed. The formation of the closed layer on the surface of the article is intended in particular to prevent undesired penetration of substances with which the residues remaining in the article, including radiocarbon, could be driven off chemically or by solution during the intermediate or final storage. In addition, however, there is effective protection against burning and diffusion of the toxicants to the surface of the article. With the described method, the object to be treated is thus not freed to a considerable extent from the radiocarbon contamination.

In der DE 197 37 891 C2 sind weitere Entsorgungsverfahren dargestellt, von denen aber keines eine wirkungsvolle Trennung des Radiokarbons von einer damit kontaminierten Keramik offenbart. Somit verbleibt gemäß dem Stand der Technik das Radiokarbon im zu entsorgenden Gegenstand oder gelangt - z. B. auf Grund einer Verbrennung von schwach kontaminiertem Material - in die Umwelt.In the DE 197 37 891 C2 further disposal methods are shown, but none of which discloses an effective separation of the radiocarbon from a ceramic contaminated therewith. Thus remains according to the prior art, the radiocarbon in the object to be disposed of or passes -. B. due to a combustion of weakly contaminated material - in the environment.

Es ist nun Aufgabe der vorliegenden Erfindung, ein Verfahren der eingangs genannten Art zur Verfügung zu stellen, bei dem Radiokarbon zu einem erheblichen Anteil aus einer kontaminierten Keramik entfernt werden kann und welches eine anschließende effektive entsorgende oder verwertende Weiterbehandlung des Radiokarbons erlaubt.It is an object of the present invention to provide a method of the type mentioned above, in which radiocarbon can be removed to a considerable extent from a contaminated ceramic and which allows a subsequent effective disposal or recycling further treatment of the radiocarbon.

Diese Aufgabe wird bei einem Verfahren der eingangs genannten Art gemäß Anspruch 1 dadurch gelöst, dass in einem Prozesstemperaturbereich mittels chemischer Reaktion mindestens eines Korrosionsmediums zumindest mit dem Radiokarbon mindestens ein flüchtiges Reaktionsgas gebildet wird, wobei die Menge des mindestens einen Korrosionsmediums, die Prozesstemperatur und/oder die Prozessdauer derart gewählt werden, dass die chemische Reaktion im Wesentlichen lediglich an der Oberfläche der Keramik, einschließlich von Porenoberflächen, und innerhalb oberflächennaher Bereiche stattfindet, und das mindestens eine Reaktionsgas aufgefangen und einer gesonderten Behandlung zugeführt wird, wobei eine derart geringe Prozeßtemperatur gewählt wird, dass das Korrosionsmedium weit in ein vorhandenes Porensystem eindringen kann, um die Kristalle an der inneren Oberfläche partiell zu oxidieren.This object is achieved in a method of the type mentioned in claim 1, characterized in that in a process temperature range by means of chemical reaction of at least one corrosion medium at least with the radiocarbon at least a volatile reaction gas is formed, wherein the amount of at least one corrosion medium, the process temperature and / or the process duration being such that the chemical reaction takes place substantially only on the surface of the ceramic, including pore surfaces, and within near-surface regions, and the at least one reaction gas is collected and fed to a separate treatment, such low process temperature being selected; that the corrosion medium can penetrate far into an existing pore system to partially oxidize the crystals on the inner surface.

Diese Verfahrensweise beruht auf der Erkenntnis, dass ein signifikanter Teil des Radiokarbons auf den Oberflächen der Graphitkristalle oder im Binder sitzt und bei den üblichen Betriebstemperaturen gegebenenfalls auch nur in oberflächennahe Kristallbereiche oder Korngrenzen hinein diffundiert. Zuvor ging die Fachwelt davon aus, dass Radiokarbon nahezu vollständig auf regulären Gitterplätzen der betroffenen Keramik eingebaut ist und sich damit einer selektiven Entfernung weitgehend entzieht. Es wird zudem inzwischen angenommen, dass der bei der Herstellung technischer Graphit verwendete organisch-chemische Binder bei der Herstellung nicht vollständig graphitiert, weshalb das dort entstandene Radiokarbon unter bestimmten Bedingungen ebenfalls leichter korrodiert werden kann als dies bei regulären Graphitkristallen der Fall ist.This procedure is based on the finding that a significant part of the radiocarbon sits on the surfaces of the graphite crystals or in the binder and optionally also diffuses into the near-surface crystal regions or grain boundaries at the usual operating temperatures. Previously, the experts assumed that radiocarbon is almost completely installed on regular lattice sites of the affected ceramic and thus largely eludes selective removal. It is also now believed that the organic-chemical binder used in the production of engineering graphite is not completely graphitized during production, and therefore the radiocarbon formed there may under certain conditions also be more easily corroded than is the case with regular graphite crystals.

Das erfindungsgemäße Verfahren bringt eine Reihe von erheblichen Vorteilen mit sich:

  • Das Verfahren kann bei relativ geringen Temperaturen durchgeführt werden, so dass eine stärkere Einbindung des Radiokarbons, z. B. durch Diffundieren von oberflächennahem Radiokarbon in das Kristallgitter hinein oder durch eine Nachgraphitierung verhindert wird.
The process according to the invention has a number of considerable advantages:
  • The process can be carried out at relatively low temperatures, so that a stronger involvement of the radio-carbon, z. B. is prevented by diffusing near-surface radiocarbon into the crystal lattice or by a Nachgraphitierung.

Zum einen kann durch das Verfahren die Konzentration der Radiokarbonkontamination erheblich verringert werden. Mit der Einwirkung auf die Oberflächen und die oberflächennahen Bereiche kann zwar nicht das gesamte Radiokarbon aus der behandelten Keramik entfernt werden. Jedoch selbst eine Entfernung von z. B. 50 %, die mit dem Verfahren gemäß durchgeführter Messungen erreichbar sind, würde die Nutzbarkeit von Abfall-Lagern verdoppeln können, weil die (End-)Lagerkapazitäten an die gesamte kumulierte 14C-Aktivität gekoppelt sind. Teildekontaminiertes Graphitmaterial kann bei hinreichend niedriger Restkontamination auch einer vollständigen Umwandlung in CO oder CO2 bei höheren Temperaturen von z.B. über 1000° C in Luft zugeführt werden.On the one hand, the method considerably reduces the concentration of radiocarbon contamination. Although it is not possible to remove the entire radiocarbon from the treated ceramic by acting on the surfaces and the areas near the surface. However, even a distance of z. B. 50%, carried out with the method according to Measurements can be achieved, the usability of waste storage facilities would be able to double because the (end) storage capacities are linked to the total cumulative 14 C activity. Teildekontaminiertes graphite material can be supplied at sufficiently low residual contamination and a complete conversion to CO or CO 2 at higher temperatures of, for example, about 1000 ° C in air.

Zum anderen ist die Konzentration des Radiokarbons in den aufgefangenen Reaktionsgasen im Vergleich zum natürlichen Vorkommen deutlich angereichert, was eine gute Voraussetzung für eine Weiterverwertung des Radiokarbons als Wertstoff ist.On the other hand, the concentration of radiocarbons in the collected reaction gases is significantly enriched in comparison to the natural occurrence, which is a good prerequisite for further use of radio carbon as a valuable material.

Mit dem erfindungsgemäßen Verfahren kann die behandelte Keramik auf ihrer Oberfläche derart dosiert korrodiert werden, dass die inneren Bereiche möglichst stabil bleiben.With the method according to the invention, the treated ceramic can be corroded on its surface metered so that the inner regions remain as stable as possible.

Das erfindungsgemäße Verfahren kann auch so ausgeführt werden, dass als Korrosionsmedium Sauerstoff eingesetzt wird. Beim Einsatz von Sauerstoff reagiert dieser mit Kohlenstoff zu Kohlenmonoxid oder Kohlendioxid, also flüchtigen Kohlenstoffverbindungen.The process according to the invention can also be carried out in such a way that oxygen is used as the corrosion medium. When oxygen is used, it reacts with carbon to form carbon monoxide or carbon dioxide, ie volatile carbon compounds.

Dabei kann das erfindungsgemäße Verfahren auch so ausgeführt werden, dass Luft als Sauerstofflieferant verwendet wird. Alternativ kann auch reiner Sauerstoff oder Sauerstoff im Gemisch mit anderen Gasen in einer von der Luft verschiedenen Zusammensetzung eingesetzt werden. Die Umsetzung in die vorgenannten flüchtigen Kohlenstoffverbindungen geschieht bereits bei Temperaturen von etwa 500°C. Bei diesen Temperaturen kann der Sauerstoff weit in ein vorhandenes Porensystem eindringen, um die Kristalle an der inneren Oberfläche partiell zu oxidieren. Bei höheren Temperaturen setzt hingegen eine starke Oxidation an der Außenseite der zu behandelnden Keramik ein, da die Porendiffusion weniger stark durch Temperaturerhöhung beschleunigt wird als die chemische Reaktion und es damit zu einer Verarmung am Korrosionssauerstoff im Inneren des Porensystems des zu korrodierenden keramischen Mediums kommt. Die optimale Temperatur für die dosierte Korrosion hängt damit von der chemischen Reaktivität des Korrosionsmediums, der Diffusionsrate im Porensystem, welche zum Beispiel durch Druckverminderung oder durch Zugabe leichter Inertgase vergrößert oder kontrolliert werden kann, und den Dimensionen des zu korrodierenden keramischen Materials ab.In this case, the inventive method can also be carried out so that air is used as an oxygen supplier. Alternatively, pure oxygen or oxygen may be used in admixture with other gases in a composition other than air. The conversion into the abovementioned volatile carbon compounds already takes place at temperatures of about 500.degree. At these temperatures, the oxygen can penetrate far into an existing pore system to partially oxidize the crystals on the inner surface. At higher temperatures, however, a strong oxidation on the outside of the ceramic to be treated, since the pore diffusion is accelerated less by increasing the temperature than the chemical reaction and thus there is a depletion of the corrosion oxygen inside the pore system of the ceramic medium to be corroded. The optimum temperature for the metered corrosion thus depends on the chemical reactivity of the corrosion medium, the diffusion rate in the pore system, which can be increased or controlled, for example by reducing the pressure or by adding inert inert gases, and the dimensions of the ceramic material to be corroded.

Das erfindungsgemäße Verfahren kann auch so ausgeführt werden, dass Wasserdampf als Sauerstofflieferant verwendet wird. Hierbei hat es sich als vorteilhaft erwiesen, ein Inertgas bei Raumtemperatur mit Wasser zu sättigen und das Wasser-Inertgas-Gemisch dann auf Prozesstemperatur aufzuheizen.The process according to the invention can also be carried out so that water vapor is used as an oxygen supplier. It has proved to be advantageous, an inert gas To saturate at room temperature with water and then heat the water-inert gas mixture to process temperature.

Das erfindungsgemäße Verfahren kann auch so ausgeführt werden, dass als Korrosionsmedium Wasserstoff eingesetzt wird. Als Reaktionsprodukt mit Kohlenstoff wird in diesem Fall im Wesentlichen CH4 gebildet.The inventive method can also be carried out so that hydrogen is used as the corrosion medium. As reaction product with carbon, in this case essentially CH 4 is formed.

Grundsätzlich kommen als Korrosionsmedien alle Gase oder Dämpfe in Betracht, die mit Kohlenstoff reagieren und in der Lage sind, das oberflächennah gebundene Radiokarbon in gasförmige Reaktionsprodukte zu überführen.Basically come as corrosion media all gases or vapors into consideration, which react with carbon and are able to convert the near-surface bound radiocarbon into gaseous reaction products.

Es kann auch vorteilhaft sein, das erfindungsgemäße Verfahren so auszuführen, dass die Keramik vor dem Starten der chemischen Reaktion zerkleinert, insbesondere gemahlen, wird. Kleine Kristalldimensionen können eine Erweiterung des nutzbaren Temperaturbereichs mit sich bringen: Zum einen sind wegen der größeren Oberfläche niedrigere Prozesstemperaturen möglich. Andererseits verringern kleine Kristalldimensionen das Maß der notwendigen Diffusion des Korrosionsmediums. Bei höheren Prozesstemperaturen kommt es daher im Vergleich zu größeren Kristalldimensionen nur im verminderten Maße zu der oben beschriebenen Verarmung des Korrosionsmediums in den inneren Poren, d.h. die obere Grenze des nutzbaren Prozesstemperaturbereichs verschiebt sich weiter nach oben. Ein zu starkes Zerkleinern, welches die Kristalle zerstört, ist jedoch zu vermeiden, da hierdurch die ursprünglichen Oberflächen zerstört werden und der Vorteil der erhöhten Konzentration des Radiokarbons an der Oberfläche verloren gehen kann. Der Anteil der natürlichen und stabilen Kohlenstoffisotope 12C und 13C in den Reaktionsprodukten würde steigen. Dieser unerwünschte Effekt würde auch bei nicht zu starkem Mahlen, aber zu hohen Temperaturen auftreten.It may also be advantageous to carry out the method according to the invention in such a way that the ceramic is comminuted, in particular ground, before starting the chemical reaction. Small crystal dimensions can lead to an extension of the usable temperature range: on the one hand, lower process temperatures are possible due to the larger surface area. On the other hand, small crystal dimensions reduce the degree of necessary diffusion of the corrosion medium. At higher process temperatures, therefore, in comparison to larger crystal dimensions, the depletion of the corrosion medium in the inner pores described above occurs only to a lesser extent, ie the upper limit of the usable process temperature range shifts further upwards. Too much comminution, which destroys the crystals, is to be avoided, however, as this may destroy the original surfaces and may lose the benefit of the increased radioactive carbon concentration on the surface. The proportion of natural and stable carbon isotopes 12 C and 13 C in the reaction products would increase. This undesirable effect would occur even if not too strong grinding, but too high temperatures.

Das erfindungsgemäße Verfahren kann auch so ausgeführt werden, dass sich die Keramik in einem Behälter befindet, wobei das mindestens eine Korrosionsmedium bei geeigneter Prozesstemperatur kontrolliert zugeführt und das Reaktionsgas abgezogen wird.The inventive method can also be carried out so that the ceramic is in a container, wherein the at least one corrosion medium is supplied controlled at a suitable process temperature and the reaction gas is withdrawn.

Auf diese Art und Weise kann ein kontinuierlicher Prozess durchgeführt werden, bei dem die gewünschte Reduzierung des Radiokarbongehalts in der Keramik in einem einzigen Aufheizzyklus erreicht werden kann.In this way, a continuous process can be performed in which the desired reduction in radio carbon content in the ceramic can be achieved in a single heating cycle.

Weiterhin kann es vorteilhaft sein, das erfindungsgemäße Verfahren so auszuführen, dass das mindestens eine Korrosionsmedium von der Oberfläche der Keramik, einschließlich der Porenoberflächen, adsorbiert wird und anschließend die Keramik auf Prozesstemperatur gebracht wird. Dabei kann es vorteilhaft sein, die Keramik unter Vakuum oder in einer Inertgasatmosphäre aufzuheizen. Wie stark die Oberflächen mit dem Korrosionsmedium beladen werden, kann zum Beispiel über den gewählten Partialdruck sowie die Beladungsdauer kontrolliert werden. Der Beladungsgrad sollte dabei so gewählt werden, dass die vorhandene Menge des Korrosionsmediums gerade ausreicht, den gewünschten Korrosionsgrad beim Aufheizen zu erreichen. Dabei kann das Abziehen der Reaktionsgase durch Evakuierung oder auch durch Spülung mit Inertgas nach dem Prozess bei Temperaturen unterhalb des Prozesstemperaturbereichs oder auch während des Prozesses erfolgen. Bei dieser Verfahrensweise wird oberflächennaher Kohlenstoff umgesetzt, der mit dem zuvor adsorbierten Korrosionsmedium chemisch reagiert. Der Anteil des Radiokarbons am abgetrennten Kohlenstoff ist bei diesem Verfahren höher als bei der Behandlung in einer dauerhaften Atmosphäre des Korrosionsmediums. Allerdings geht dieser Gewinn einher mit einer Erniedrigung des Gesamtumsatzes auf Grund der geringeren Partialdrücke.Furthermore, it may be advantageous to carry out the method according to the invention such that the at least one corrosion medium is adsorbed by the surface of the ceramic, including the pore surfaces, and then the ceramic is brought to process temperature. It may be advantageous to heat the ceramic under vacuum or in an inert gas atmosphere. How much the surfaces are loaded with the corrosion medium can be controlled, for example, by the chosen partial pressure and the loading time. The degree of loading should be chosen so that the amount of corrosion medium present is just sufficient to achieve the desired level of corrosion during heating. In this case, the removal of the reaction gases by evacuation or by purging with inert gas after the process at temperatures below the process temperature range or during the process can take place. In this procedure, near-surface carbon is reacted, which reacts chemically with the previously adsorbed corrosion medium. The proportion of radiocarbon in the separated carbon is higher in this method than in the treatment in a permanent atmosphere of the corrosion medium. However, this gain goes hand in hand with a decrease in total sales due to lower partial pressures.

Das erfindungsgemäße Verfahren kann auch so ausgeführt werden, dass in einem weiteren Schritt der Behälter evakuiert oder die Keramik mit Inertgas gespült wird, um die Reaktionsgase abzuziehen, und anschließend der Prozess, beginnend mit dem Adsorbieren des mindestens einen Korrosionsmediums auf der Oberfläche, mindestens ein weiteres Mal durchgeführt wird. Auf diese Weise ist ein diskontinuierlicher Prozess mit mehreren Zyklen gegeben, der einerseits im Vergleich zum kontinuierlichen Verfahren zu längeren Behandlungsdauern führen, andererseits aber erhöhte Anteilen an Radiokarbon in den Reaktionsgasen mit sich bringen kann.The inventive method can also be carried out so that in a further step, the container is evacuated or the ceramic is purged with inert gas to withdraw the reaction gases, and then the process, starting with the adsorption of the at least one corrosion medium on the surface, at least one other Time is performed. In this way, a discontinuous process with several cycles is given, which on the one hand lead to longer treatment periods compared to the continuous process, but on the other hand can bring about increased amounts of radiocarbon in the reaction gases.

Das erfindungsgemäße Verfahren kann auch so ausgeführt werden, dass vor dem Adsorbieren des mindestens einen Korrosionsmediums eine dosierte Korrosion mittels kontrollierter Zugabe des mindestens einen Korrosionsmediums derart bei Prozesstemperatur durchgeführt wird, dass zumindest ein Teil geschlossener Poren geöffnet wird. Der erste Schritt in diesem Verfahren dient zwar vorrangig dem Öffnen der geschlossenen Poren, führt jedoch ebenfalls bereits zu einem Entfernen eines Teils des Radiokarbons. Das Öffnen der geschlossenen Poren kann beispielsweise unter einer Korrosionsmediumatmosphäre geschehen, wobei dieser Behandlungsschritt bei erhöhten Temperaturen in einer relativ kurzen Zeit durchgeführt werden kann, die gerade zum Öffnen der Poren ausreicht. Die Korrosion zu Porenöffnung kann aber auch mit Hilfe eines zuvor adsorbierten Korrosionsmediums im Vakuum oder einer Inertgasatmosphäre durchgeführt werden.The inventive method can also be carried out so that before adsorbing the at least one corrosion medium metered corrosion by controlled addition of the at least one corrosion medium is carried out at such process temperature that at least a portion of closed pores is opened. Although the first step in this process primarily serves to open the closed pores, it also already results in removal of a portion of the radio-carbon. The opening of the closed pores can for example be done under a corrosive medium atmosphere, this treatment step can be carried out at elevated temperatures in a relatively short time, just enough to open the pores. The corrosion too Pore opening can also be carried out with the aid of a previously adsorbed corrosion medium in vacuo or an inert gas atmosphere.

Das erfindungsgemäße Verfahren kann auch so ausgeführt werden, dass nach letztmaligem Abziehen der Reaktionsgase die verbliebene Restkeramik wiederverwertet wird, zum Beispiel als Nukleargraphit.The process according to the invention can also be carried out in such a way that after the final removal of the reaction gases, the remaining residual ceramic is recycled, for example as nuclear graphite.

Weiterhin kann das erfindungsgemäße Verfahren so ausgeführt werden, dass das in den aufgefangenen Reaktionsgasen enthaltene Radiokarbon angereichert wird. Anschließend kann das Radiokarbon als Wertstoff einer Wiederverwertung zugeführt werden. Sofern aus dem extrahierten Radiokarbon wieder ein Festkörper, z.B. in Form von Graphit, erzeugt werden soll, kann insbesondere bei Verwendung von Wasserdampf als Sauerstofflieferant ein Kreisprozess für das Korrosionsmedium vorteilhaft sein. Der Kreisprozess könnte wie folgt aussehen: Beim Korrosionsprozess entstehen bei entsprechenden Prozessbedingungen mit der endothermen Reaktion von Graphit mit Wasserdampf als Reaktionsprodukte Kohlenmonoxid und Wasserstoff. Im extrahierten und aufgefangenen Kohlenmonoxid ist nun ein gegenüber der ursprünglichen Keramik deutlich erhöhter Anteil an Radiokarbon enthalten. Dieser Anteil kann nun durch Anreicherungsprozesse weiter erhöht werden. In einem weiteren Schritt kann aus dem Kohlenmonoxid in Reaktion mit dem Wasserstoff fester Kohlenstoff und Wasser(dampf) erzeugt werden. Das Wasser kann dann wieder als Lieferant für das Korrosionsmedium Sauerstoff dienen.Furthermore, the method according to the invention can be carried out in such a way that the radiocarbon contained in the collected reaction gases is enriched. Subsequently, the radiocarbon can be recycled as a valuable material. If from the extracted radiocarbon again a solid, e.g. in the form of graphite, a cyclic process for the corrosion medium may be particularly advantageous when using steam as the oxygen supplier. The cyclic process could look like this: In the corrosive process, carbon monoxide and hydrogen are produced as reaction products with the endothermic reaction of graphite with water vapor under appropriate process conditions. The extracted and collected carbon monoxide now contains a significantly higher proportion of radiocarbon than the original ceramic. This proportion can now be further increased by enrichment processes. In a further step, solid carbon and water (steam) can be generated from the carbon monoxide in reaction with the hydrogen. The water can then again serve as a supplier for the corrosion medium oxygen.

Dabei kann es vorteilhaft sein, das erfindungsgemäße Verfahren so auszuführen, dass als Reaktionsgas bevorzugt Kohlenmonoxid oder CH4 erzeugt wird. Kohlenmonoxid und CH4 haben ein geringeres Gewicht als Kohlendioxid. Mit diesen Reaktionsgasen kann daher der gegebene Gewichtsunterschied zwischen Radiokarbon und den stabilen Isotopen des Kohlenstoffs besser für eine Anreicherung des Radiokarbons ausgenutzt werden.It may be advantageous to carry out the process according to the invention so that carbon monoxide or CH 4 is preferably produced as the reaction gas. Carbon monoxide and CH 4 have a lower weight than carbon dioxide. With these reaction gases, therefore, the given weight difference between radiocarbon and the stable isotopes of the carbon can be better utilized for enrichment of the radiocarbon.

Falls das extrahierte, Radiokarbon enthaltende Material für lange Zeit sicher gelagert werden soll, ist die Herstellung auslaugbeständiger, nicht brennbarer Lagergebinde sinnvoll. Dies kann z.B. durch Reaktion des radiokarbonreichen Materials zu Karbiden, z.B. SiC, oder gesteinsähnlichen Karbonaten geschehen. Das Korrosionsmedium sollte so gewählt werden, dass die Reaktionsgase möglichst direkt für die weiteren Behandlungsschritte geeignet sind.If the extracted radiocarbon-containing material is to be stored safely for a long time, the production of leach-resistant, non-combustible storage containers makes sense. This can e.g. by reaction of the radiocarbon-rich material to carbides, e.g. SiC, or rock-like carbonates happen. The corrosion medium should be chosen so that the reaction gases are as directly as possible suitable for the further treatment steps.

Im Folgenden werden zwei Ausführungsbeispiele des erfindungsgemäßen Verfahrens dargestellt.In the following two embodiments of the method according to the invention are shown.

Figur 1 zeigt in einem Diagramm das Ergebnis einer Behandlung eines aus dem AVR-Reaktor (erster Hochtemperatur-Versuchs-Reaktor im Forschungszentrum Jülich; siehe VDI-Bericht 729, AVR - 20 Jahre Betrieb, ISBN 3-18-090720-0, VDI-Verlag, Düsseldorf, 1989 )) stammenden Graphitpulvers. Als Korrosionsmedium wurde Sauerstoff als Bestandteil von Wasser eingesetzt. Hierzu wurde zunächst Argon bei Raumtemperatur mit Wasserdampf gesättigt. Anschließend wurde das Graphitpulver in der Wasserdampf Argon-Atmosphäre auf 1057°C aufgeheizt und bei dieser Temperatur 16 Stunden gehalten. Figur 1 stellt.die Freisetzung des Kohlenstoffs während des Behandlungszeitraumes dar. Kurve 1 zeigt den Gesamtmassenverlust des Graphitpulvers. Dieser Massenverlust ist durch die linke Skala in Prozent ausgedrückt. Kurve 2 stellt die prozentuale Freisetzung an Radiokarbon in Bezug auf den ursprünglichen Radiokarbongehalt dar. Demzufolge sind nach 16 Stunden etwa 46% des ursprünglich im Graphitpulver vorhandenen Radiokarbons freigesetzt. Durch Kurve 3 ist das Verhältnis zwischen der Radiokarbonfreisetzung in Prozent und der Freisetzung der stabilen Kohlenstoffisotope in Prozent wiedergegeben. Als Beispiel ist im Folgenden das Verhältnis nach etwa 16 Stunden Behandlungsdauer dargestellt. Wie bereits erwähnt sind etwa 46% des Radiokarbons entfernt. Zum gleichen Zeitpunkt wurden durch die Behandlung ein wenig mehr als 16% der stabilen Kohlenstoffisotope freigesetzt. Das Verhältnis der Prozentzahlen 46/16 ergibt ein Verhältnis von etwa 2.85. Das Verhältnis ist auf der rechten Skala des Diagramms in Figur 1 dargestellt. Das Diagramm macht deutlich, dass zu Beginn des Verfahrens im Verhältnis die Ausbeute an Radiokarbon höher ist als zu späteren Zeitpunkten. Dies bestätigt die vorwiegende Anlagerung des Radiokarbons auf der Oberfläche, einschließlich der Porenoberflächen. FIG. 1 shows in a diagram the result of treatment of one of the AVR reactor (first High-temperature experimental reactor at Forschungszentrum Jülich; see VDI report 729, AVR - 20 Years of Operation, ISBN 3-18-090720-0, VDI-Verlag, Dusseldorf, 1989 )) originating graphite powder. As a corrosion medium, oxygen was used as a constituent of water. For this purpose, first argon was saturated with water vapor at room temperature. Subsequently, the graphite powder was heated in the steam-argon atmosphere to 1057 ° C and held at this temperature for 16 hours. FIG. 1 represents the release of carbon during the treatment period. Curve 1 shows the total mass loss of the graphite powder. This mass loss is expressed in percent by the left scale. Curve 2 represents the percent release of radiocarbon with respect to the original radiocarbon content. Thus, after 16 hours, about 46% of the radiocarbon originally present in the graphite powder is released. Curve 3 plots the ratio between radiocarbon release in percent and the release of stable carbon isotopes in percent. As an example, the ratio after about 16 hours of treatment is shown below. As mentioned earlier, about 46% of the radiocarbon is removed. At the same time, the treatment released a little more than 16% of the stable carbon isotopes. The ratio of the percentages 46/16 gives a ratio of about 2.85. The ratio is on the right scale of the graph in FIG. 1 shown. The diagram clearly shows that at the beginning of the process the ratio of the yield of radiocarbon is higher than at later times. This confirms the predominant deposition of radiocarbon on the surface, including the pore surfaces.

In einer alternativen Verfahrensweise wurde Graphitpulver aus dem Versuchsreaktor MERLIN zunächst in Luft gelagert, so dass die Oberflächen des Pulvers, einschließlich der Porenoberflächen, Sauerstoff adsorbieren konnten. Dieses Material wurde anschließend in eine reine Argon-Atmosphäre gebracht, auf 1057°C aufgeheizt und bei dieser Temperatur etwa 13,5 Stunden gehalten.In an alternative procedure, graphite powder from the experimental reactor MERLIN was first stored in air so that the surfaces of the powder, including the pore surfaces, could adsorb oxygen. This material was then placed in a pure argon atmosphere, heated to 1057 ° C and held at this temperature for about 13.5 hours.

Figur 2 zeigt das Ergebnis dieser Behandlung in einem zu Figur 1 entsprechenden Diagramm. Es ist aus ersichtlich, dass insgesamt eine wesentlich niedrigere absolute Freisetzungsrate sowohl bezüglich des Radiokarbons (Kurve 5) als auch bezüglich der stabilen Kohlenstoffisotope (Kurve 4) erzielt wurde. Allerdings ist gemäß Kurve 6 das Verhältnis der prozentualen Freisetzung des Radiokarbons zur prozentualen Freisetzung der stabilen Kohlenstoffisotope um mehr als den Faktor 10 höher. Demnach ist auch der prozentuale Anteil der radiokarbonhaltigen Moleküle bei Reaktionsgasen deutlich höher als bei der Behandlung unter der Wasser-Argon-Atmosphäre. Die Korrosion allein mittels des adsorbierten Sauerstoffs bietet sich insbesondere dann an, wenn hohe Anteile an Radiokarbon in den Reaktionsgasen, zum Beispiel für die Wiederverwertung des Radiokarbons, erreicht werden sollen. FIG. 2 shows the result of this treatment in one too FIG. 1 corresponding diagram. It can be seen that overall a much lower absolute release rate was achieved both with respect to the radiocarbon (curve 5) and the stable carbon isotopes (curve 4). However, according to curve 6, the ratio of the percentage release of the radiocarbon to the percentage release of the stable carbon isotopes is more than a factor of 10 higher. Accordingly, the percentage is also the radiocarbon-containing molecules in reaction gases significantly higher than in the treatment under the water-argon atmosphere. The corrosion alone by means of the adsorbed oxygen is particularly suitable when high proportions of radiocarbon in the reaction gases, for example for the recycling of the radio-carbon, to be achieved.

Claims (14)

  1. Method for the treatment of a carbon-containing ceramic contaminated with radiocarbon in which at least a part of the radiocarbon is removed from the ceramic and the removed part is collected, wherein
    a. the method is used for the at least partial concentration-reducing removal of radiocarbon from a carbon content of the ceramic, wherein
    b. the quantity of the at least one corrosion medium, the process temperature and/or the duration of the process are chosen such that the chemical reaction substantially only takes place on the outer and inner surface of the ceramic, including pore surfaces,
    c. within a process temperature range, at least one volatile reaction gas is formed by means of chemical reaction of at least one corrosion medium at least with the radiocarbon,
    d. the at least one reaction gas is collected and passed on for separate treatment,
    characterised in that
    e. such a low process temperature is chosen that the corrosion medium can penetrate deep into an existing pore system in order to partially oxidise the crystals on the inner surface.
  2. Method according to claim 1, characterised in that oxygen is used as corrosion medium.
  3. Method according to claim 2, characterised in that air is used as oxygen supplier.
  4. Method according to claim 2, characterised in that water vapour is used as oxygen supplier.
  5. Method according to one of the claims 1 to 4, characterised in that hydrogen is used as corrosion medium.
  6. Method according to one of the claims 1 to 5, characterised in that the ceramic is crushed, in particular ground, before starting the chemical reaction.
  7. Method according to one of the claims 1 to 6, characterised in that the ceramic is contained in a vessel, wherein the at least one corrosion medium is added in a controlled manner at a suitable process temperature and the reaction gas drawn off.
  8. Method according to one of the claims 1 to 6, characterised in that the at least one corrosion medium is adsorbed by the surface of the ceramic, including the pore surfaces, and the ceramic is then brought to process temperature.
  9. Method according to claim 8, characterised in that the ceramic is then brought to process temperature under a vacuum or in an inert gas atmosphere.
  10. Method according to claim 9, characterised in that, in a further step, the vessel is evacuated or the ceramic is flushed with inert gas in order to draw off the reaction gases and the process is then carried out at least one further time, beginning with the adsorption of the at least one corrosion medium on the surface.
  11. Method according to claim 9 or 10, characterised in that, before the absorption of the at least one corrosion medium, a regulated corrosion is carried out at process temperature by means of the controlled addition of the at least one corrosion medium such that at least some closed pores are opened.
  12. Method according to one of the claims 1 to 11, characterised in that, after the reaction gases are drawn off for the last time, the remaining residual ceramic is recycled, for example as nuclear graphite.
  13. Method according to one of the claims 1 to 12, characterised in that the radiocarbon contained in the collected reaction gases is enriched.
  14. Method according to claim 13, characterised in that carbon monoxide or CH4 is preferably generated as reaction gas.
EP05766947.5A 2004-07-28 2005-07-12 Method for treating ceramic contaminated with radiocarbon, in particular reactor graphite Not-in-force EP1771865B1 (en)

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DE10148146B4 (en) * 2001-09-28 2009-08-27 Forschungszentrum Jülich GmbH A method of disposing of a reactor of at least one radiotoxic contaminated article of graphite and / or coal

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DE102004036631A1 (en) 2006-03-23
EP1771865A2 (en) 2007-04-11
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WO2006012830A3 (en) 2006-05-11
DE102004036631B4 (en) 2013-02-21

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