EP0224510B1 - Process for decontaminating radioactively contaminated metalic or cement-containing materials - Google Patents

Process for decontaminating radioactively contaminated metalic or cement-containing materials Download PDF

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EP0224510B1
EP0224510B1 EP86903176A EP86903176A EP0224510B1 EP 0224510 B1 EP0224510 B1 EP 0224510B1 EP 86903176 A EP86903176 A EP 86903176A EP 86903176 A EP86903176 A EP 86903176A EP 0224510 B1 EP0224510 B1 EP 0224510B1
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decontamination
process according
acid
solution
separated
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German (de)
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EP0224510A1 (en
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Jozef Hanulik
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Recytec SA
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Recytec SA
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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
    • G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
    • G21F9/002—Decontamination of the surface of objects with chemical or electrochemical processes

Definitions

  • US Pat. No. 3,873,362 describes a similar two-stage decontamination process in which hydrogen peroxide is preferably used in the first stage for oxidation and aqueous solutions of mixtures of mineral acids (sulfuric acid and / or nitric acid) and complex-forming substances such as oxalic acid in the reducing second stage of the process , Citric acid or formic acid can be used.
  • the contaminated metal surface is treated with a cerium salt solution containing at least one cerium IV salt and a water-containing solvent.
  • a cerium salt solution containing at least one cerium IV salt and a water-containing solvent.
  • Another decontamination process is described in EP application, publication no. 00 73 366, in which an aqueous solution of formic acid and / or acetic acid and a reducing agent, in particular formaldehyde and / or acetyldehyde, is used as the decontamination agent.
  • This method has a particular advantage in that there is a comparatively low need for chemicals and in the disposal of the used decontamination solution, an amount of radioactive substances corresponding to the volume of the removed surface layers.
  • the basic concept is based on the fact that the activity in the contaminated surface layer decreases with the extent to which the surface layer itself is detached by the decontamination solution.
  • the depth of penetration of active material into the surface layer can be determined or measured before decontamination, which then results in the thickness of the surface layer to be removed in order to achieve a certain final decontamination state.
  • GB-A-891'670 decontamination is carried out using hydrofluoric acid.
  • a rolled layer is to be removed from a metal, in particular silicon iron.
  • the contaminated metal is added to an aqueous solution of fluoroborate, so that hydrolysis produces hydrofluoric acid to remove the layer and volatile boric acid.
  • hydrofluoric acid is very aggressive, so a neutral salt is added to reduce the attack on the metal.
  • boric acid In the primary water circuit of pressurized water reactors there is a concentration of boric acid of up to 3000 ppm. During the operation of such reactors, smaller amounts of the liquid mentioned fall than Waste. In addition to boric acid, this waste also contains contaminants such as cobalt compounds, as well as solid contaminants such as rust residues, fabric fibers, dust, etc. In certain cases, this waste can even be treated to the extent that it is in the form of a solid material.
  • the device for performing the present method ( Figure 1) has a container for holding the objects to be decontaminated.
  • the duration of treatment of objects in the receptacle 1 is chosen so that the objects are free of radioactivity after the end of the process. Such objects are then removed from the receptacle 1 and can then either be reused or sent to the scrap.
  • a decontamination solution is introduced into the receptacle 1, which acts on the surface of the objects in such a way that the contaminated surface layer is dissolved and removed.
  • the decontamination solution in container 1 can form a bath in which the objects are located, or the decontamination solution is sprayed into container 1.
  • a circulating device 2 with a pump can be assigned to the receiving container 1. This makes it possible to achieve a long treatment time for the objects with a relatively small amount of the decontamination solution.
  • An evaporator 3 is connected to the receptacle 1 via a line 4. In the evaporator 3, more volatile components of a concentrated solution are separated from less volatile components thereof. Vaporizable components are fed to an absorber 6 through a further line 5.
  • the bottom products from the evaporator 3 are transferred to a reduction device 7, in which they are reduced to metallic iron, chromium, nickel, lead, etc. However, there is also the possibility of feeding the solid, evaporated products to the chemical industry or the scrap without reducing them for further use as chemical metal compounds.
  • the reduction device 7 is connected via a line 9 to the absorber 6, through which HF is led from the reduction device 7 to the absorber 6.
  • the hydrogen required for the reduction of metal compounds can be fed to the reduction device 7 through a line 10 from the dissolver 1.
  • An electrolytic cell 12 can be connected to the receptacle 1 via a line 13, through which the concentrated solution is pumped out of the receptacle 1 into the cell 12.
  • BF 4 ions are recombined to HBF 4 at the anode.
  • HBF 4 is fed to the receptacle 1 through a further line 14.
  • HBF 4 which is fed to the receptacle 1 via a line 15, likewise arises in the already mentioned absorber 6.
  • the quality of the surface of the treated objects can be influenced during and / or after decontamination by surface-active substances. Wetting agents such as soaps, water permeability inhibitors such as formaldehyde, etc. come into consideration as such substances.
  • the high absorption capacity of the decontamination agent or the decontamination solution - 1 liter can dissolve up to 220 grams of stainless steel at 90 ° C - allows high area-related decontamination performance. Such a high absorption capacity allows to decontaminate approx. 30 m 2 of the surface with only 1 liter of decontamination solution with a removal of 1 micrometer. In the dissolver 1 you can reach a concentration of up to 220 grams of stainless steel per liter at 90 ° C. This concentrated solution is pumped into the electrolytic cell 12, where metal is on the cathode is excreted, while at the anode BF 4 ions recombine to HBF 4 . This solution is returned to the decontamination process.
  • iron-containing Fe (BF 4 ) 2 concentrate is discussed as an example. This concentrate also contains radioactivity, but this does not affect the chemical balance. Detached stainless steel, nickel-based alloys and other contaminated materials are to be treated analogously. The following equation applies to the direct disposal of iron concentrates:
  • Iron, chromium, nickel or copper is removed electrolytically from the iron-containing concentrate and then mixed with cement.
  • the electrolysis proceeds as follows:
  • the object of the present invention is to eliminate the mentioned but also further disadvantages of the prior art in the field of decontamination. This object is achieved according to the invention in the method of the type mentioned at the outset, as defined in the characterizing part of claim 1.
  • the masonry surface is misted / moistened with HBF 4 ⁇ and / or H 2 SiF 6 ⁇ acid.
  • the chemical reaction between the carbonates in the masonry and the acids produces gaseous C0 2 .
  • the gas bubbles form a foam with the acid, which is an excellent flotation agent for the contaminants.
  • the foam is then suctioned off with the activity.
  • Fluorine ions from the fluorocomplexes of the acids react with the calcium present and form an insoluble, voluminous precipitate of CaF 2 , which clogs the pores on the surface.
  • the impregnation of the masonry described massively impedes the transport of activity into the interior of the material. With radium-contaminated concrete, decofactors between 10 and 15 were achieved during decontamination.
  • the device for carrying out the present method contains a reaction container 1, in which contaminated boric acid is converted into an easily evaporable boron compound ( Figure 2).
  • Contaminated boric acid is introduced into the reaction vessel 1 through a first line 2. It is usually a liquid that, in addition to boric acid, also water, contaminants such as Cobalt compounds, as well as impurities, e.g. Contains rust, fabric fibers, dust, etc.
  • a chemical substance is supplied to the reaction vessel 1, which causes the conversion mentioned. It can be gaseous fluorine or hydrofluoric acid. Hydrofluoric acid can be used either in the form of liquid or in the form of gas.
  • a pump 4 is connected to the reaction container 2 and conveys the reaction product from the reaction vessel 1 into a distillation device 5 of a type known per se.
  • the speed of the introduction of the two components mentioned through lines 2 and 3 in the Reaction container 1 and the rate at which the reaction product is withdrawn from the reaction container 1 are selected such that the material supplied is given sufficient time for the reaction to proceed to completion.
  • the sump that remains in the distillation device 5 is removed from it and conditioned for disposal.
  • the sump is first neutralized in a further vessel 6, for example with calcium hydroxide.
  • the neutralized sump material can only be dried and then immediately deposited. However, it can also be solidified with cement or bitumen and only then deposited.
  • the thermal energy required for the distillation in the device 5 is advantageously taken from liquid or gaseous media.
  • the distillation is advantageously carried out under reduced pressure because the temperatures in the device 5 are then relatively low and at such temperatures virtually no pyrolysis can take place.
  • the HBF 4 acid obtained during the distillation is led out of the distillation device 5 through a line 6.
  • This acid can be used as a fully regenerable decontamination agent as described in a Swiss patent application no. 2238/85 by the same applicant, or the acid can be sold to the chemical industry, where it can be used, for example, in electroplating.
  • the borofluoric acid which is obtained during the distillation, does not end up in the repository for radioactive material, but can be sold to the chemical industry, for example, and thus can be used further.
  • the swamp because it now has a smaller volume, can be disposed of without incurring great costs.
  • the present process is based on the knowledge that, in contrast to H 3 B0 3 , borofluoric acid HBF 4 can be distilled and can thus be separated from the contaminants, such as, for example, from Co-60 Cs nuclides.
  • the borofluoric acid can be separated into fractions of different densities during distillation.
  • the principle reactions on which the present method is based are as follows:
  • the HBF 4 acid obtained may also contain traces of activity (in single-stage distillation) because it can be used as a completely regenerable decontamination agent for components made from DWR and SWR.
  • the option for an inactive use is when carrying out a multi-stage distillation.
  • Contaminated surface layers are decontaminated by treatment with an aqueous fluorobase-containing decontamination solution.
  • the aqueous solution contains 0.05 to 50 moles of decontamination agent per liter, the decontamination agent preferably being at least one substance from the group of hexafluorosilicate acids, fluoroboric acid and their salts.
  • the decontamination solution provides the necessary decontamination factors, particularly on DWR, SWR, high-temperature alloys and masonry.
  • the used decontamination solution can be recycled into the decontamination process after regeneration.
  • the decontamination agent (HBF 4 acid) is advantageously produced from contaminated boric acid from DWR waste with the help of fluoric or hydrofluoric acid.
  • the HBF 4 acid thus produced is separated from the contaminants and impurities by the distillation.

Abstract

The contaminated surface layers of a material are decontaminated by treatment with an aqueous decontamination fluorine-based solution containing from 0.05 to 50 moles of decontamination agent per litre, the decontamination agent being preferably a substance selected from the group comprising hexafluorosilicate acid, fluoroboric acid and salts thereof. The decontamination solution has a very high efficiency which is particularly necessary for pressure water reactors, boiling water reactors, high temperature alloys and masonry works. The decontamination agent (HBF4 acid) is appropriately produced by using fluoric acid or hydrogen fluoride and from contaminated boric acid from pressure water reactor waste. The HBF4 acid thus obtained is separated from contaminants and other impurities by distillation. The spent decontamination solution may be recycled in the decontamination process after regeneration.

Description

Früher wurden die radioaktive kontaminierten Oberflächenschichten von Reaktor-Kühlkreisläufen häufig mittels wässriger Mineralsäurelösungen abgetragen. Eine solche Dekontaminationslösung mit 20% Salpetersäure und 3% Fluorwasserstoffsäure ist beispielsweise in "Kernenergie", 11. Jhg. 1968, pp. 285 angegeben. Da wegen der Aggressivität solcher Mineralsäurelösungen der Abtragungsvorgang nur schwer zu steuern ist, besteht die Gefahr, dass das reine Metall unterhalb der kontaminierten Oberflächenschicht korrodiert und so Schwachstellen entstehen können, die zu Leckbildung neigen, was unter allen Umständen ausgeschlossen sein muss. Von den zur Behebung solcher und anderer Mängel später entwickelten Dekontaminationsverfahren dürfte das bekannteste das sogenannte "AP-Citrox"-Verfahren sein ("Kernenergie", 11. Jh. 1968, pp. 285), bei dem die kontaminierte Oberfläche zuerst mit einer oxidierenden alkalischen Permanganatlösung zur Vorbereitung der Auflösung und danach mit einer reduzierenden wässrigen Lösung von dibasischen Ammoniumcitrat behandelt wird.In the past, the radioactive, contaminated surface layers of reactor cooling circuits were often removed using aqueous mineral acid solutions. Such a decontamination solution with 20% nitric acid and 3% hydrofluoric acid is described, for example, in "Nuclear Energy", 11th century. 1968, pp. 285 specified. Since the removal process is difficult to control due to the aggressiveness of such mineral acid solutions, there is a risk that the pure metal corrodes underneath the contaminated surface layer and thus weak spots can develop which tend to leak, which must be excluded under all circumstances. Of the decontamination processes developed later to remedy such and other shortcomings, the best known is probably the so-called "AP-Citrox" process ("Nuclear Energy", 11th century 1968, pp. 285), in which the contaminated surface is first treated with an oxidizing alkaline Permanganate solution to prepare for dissolution and then treated with a reducing aqueous solution of dibasic ammonium citrate.

In der US-PS 3 873 362 ist ein ähnliches zweistufiges Dekontaminationsverfahren beschrieben, bei dem zum Oxydieren in der ersten Stufe vorzugsweise Wasserstoffperoxid und in der reduzierenden zweiten Prozessstufe wässrige Lösungen von Mischungen aus Mineralsäuren (Schwefelsäure und/oder Salpetersäure) und komplexbildenden Stoffen, wie Oxalsäure, Zitronensäure oder Ameisensäure, verwendet werden.US Pat. No. 3,873,362 describes a similar two-stage decontamination process in which hydrogen peroxide is preferably used in the first stage for oxidation and aqueous solutions of mixtures of mineral acids (sulfuric acid and / or nitric acid) and complex-forming substances such as oxalic acid in the reducing second stage of the process , Citric acid or formic acid can be used.

Nach einem anderen bekannten Dekontaminationsverfahren (DE-PS 27 14 245) wird die kontaminierte Metalloberfläche mit einer mindestens ein Cer-IV-Salz und ein wasserhaltiges Lösungsmittel enthaltenden Cersalzlösung behandelt. Ein weiteres Dekontaminationsverfahren ist in der EP-Anmeldung, Veröffentlichungs Nr. 00 73 366, beschrieben, bei dem als Dekontaminationsmittel eine wässrige Lösung aus Ameisensäure und/oder Essigsäure und aus einem Reduktionsmittel, insbesondere Formaldehyd und/ oder Acetyldehyd, zum Einsatz kommt. Bei diesem Verfahren sind von besonderem Vorteil ein verhältnismässig geringer Bedarf an Chemikalien und bei der Entsorgung der gebrauchten Dekontaminationslösung eine etwa dem Volumen der abgetragenen Oberflächenschichten entsprechende Menge anfallender radioaktiver Stoffe.According to another known decontamination method (DE-PS 27 14 245), the contaminated metal surface is treated with a cerium salt solution containing at least one cerium IV salt and a water-containing solvent. Another decontamination process is described in EP application, publication no. 00 73 366, in which an aqueous solution of formic acid and / or acetic acid and a reducing agent, in particular formaldehyde and / or acetyldehyde, is used as the decontamination agent. This method has a particular advantage in that there is a comparatively low need for chemicals and in the disposal of the used decontamination solution, an amount of radioactive substances corresponding to the volume of the removed surface layers.

Bei den naßchemischen Dekontaminationsverfahren, von denen oben einige kurz beschrieben sind, beruht das Grundkonzept darauf, dass die Aktivität in der kontaminierten Oberflächenschicht mit dem Maße abnimmt, wie die Oberflächenschicht selbst durch die Dekontaminationslösung abgelöst wird. Die Eindringtiefe von aktivem Material in die Oberflächenschicht kann vor der Dekontamination bestimmt oder gemessen werden, woraus sich dann die für die Erreichung eines bestimmten Dekontaminations-Endzustandes die Dicke der jeweils abzutragenden Oberflächenschicht ergibt.In the wet chemical decontamination process, some of which are briefly described above, the basic concept is based on the fact that the activity in the contaminated surface layer decreases with the extent to which the surface layer itself is detached by the decontamination solution. The depth of penetration of active material into the surface layer can be determined or measured before decontamination, which then results in the thickness of the surface layer to be removed in order to achieve a certain final decontamination state.

In der GB-A-891'670 wird eine Dekontamination mittels Flußsäure durchgeführt. Gemäss jener Erfindung soll von einem Metall, insbesondere Siliziumeisen eine Walzschicht entfernt werden. Hierzu wird das kontaminierte Metall einer wässrigen Lösung von Fluorborat zugegeben, so dass bei der Hydrolyse Flusssäure zur Entfernung der Schicht, sowie flüchtige Borsäure entsteht. Da Flußsäure bekanntlich sehr aggressiv ist, wird zusätzlich ein neutrales Salz beigegeben, um den Angriff auf das Metall zu verringern.In GB-A-891'670, decontamination is carried out using hydrofluoric acid. According to that invention, a rolled layer is to be removed from a metal, in particular silicon iron. For this purpose, the contaminated metal is added to an aqueous solution of fluoroborate, so that hydrolysis produces hydrofluoric acid to remove the layer and volatile boric acid. As is well known, hydrofluoric acid is very aggressive, so a neutral salt is added to reduce the attack on the metal.

Der Angriff von Flußsäure auf eine Metalloberfläche ist unregelmässig. Damit verbleiben bei der Dekontamination nicht dekontaminierte Inseln, die nach wie vor radioaktiv sind.The attack of hydrofluoric acid on a metal surface is irregular. This leaves islands that are not decontaminated during decontamination and are still radioactive.

Flußsäure hat jedoch noch weiter wesentliche Nachteile:

  • a) HF gehört der Giftklasse 1 an und die geforderte Arbeitshygiene kann bei den hier erforderlichen Arbeitsprozessen kaum eingehalten werden.
  • b) Bezüglich der Löslichkeit von Metallen hat die Flußsäure eine Kapazität von cirka 10-20 g/I, während die Fluoroborsäure eine Kapazität von cirka 200-300 g/I aufweist.
  • c) Die Regeneration von HF ist schwieriger als diejenige von Fluoroborsäure, weil die elektrische Leitfähigkeit von HF niedriger ist und somit ein größerer Energieaufwand erforderlich ist als bei Fluoroborsäure. Die Regeneration des Dekontaminationsmittels ist jedoch für die Entsorgung von radioaktiven Abfällen eine wichtige Voraussetzung um die Abfallmenge zu reduzieren.
However, hydrofluoric acid has other major disadvantages:
  • a) HF belongs to poison class 1 and the required occupational hygiene can hardly be complied with in the work processes required here.
  • b) With regard to the solubility of metals, the hydrofluoric acid has a capacity of approximately 10-20 g / l, while the fluoroboric acid has a capacity of approximately 200-300 g / l.
  • c) The regeneration of HF is more difficult than that of fluoroboric acid because the electrical conductivity of HF is lower and therefore more energy is required than with fluoroboric acid. The regeneration of the decontamination agent is an important prerequisite for the disposal of radioactive waste in order to reduce the amount of waste.

Dekontaminationstests an verschiedenen metallischen Reaktorbaustoffen haben nun einen Wiederspruch zur obigen Annahme, dass der Betrag der Restaktivität allein eine Funktion der Dicke der abgetragenen Oberflächenschicht ist, aufgezeigt. Für verschiedene Dekontaminationslösungen ergaben sich bei gleichem, gravimetrisch bestimmtem Schichtabtrag unterschiedliche Dekontaminationsfaktoren. Untersuchungen mit einem Raster-Elektromikroskop haben gezeigt, dass sich auf der dekontaminierten Metalloberfläche Feststoffschichten oder Feststoffinseln gebildet haben, in denen aktives Material angereichert ist, und die als unerwünschte Beiprodukte der jeweiligen Abtragungsreaktionen anzusehen sind. solche Abweichungen sind insbesondere bei silicium- und gegebenenfalls aluminiumhaltigen Werkstoffen zu beobachten, also etwa bei rostfreien Stählen und Hochtemperatur-Werkstoffen, wie sie z.B. bei heliumgekühlten Hochtemperaturreaktoren Verwendung finden, und auch niedrig legierten Stählen. Abgesehen von einer unerwünschte hohen Restaktivität wird durch die unregelmässige Abtragung derartiger Oberflächenschichten auch die Ueberwachung und Steuerung des Dekontaminationsprozesses selbst schwierig, so dass eine zuverlässige Dekontamination nicht mehr gewährleistet ist und auch mit den eingangs erwähnten Korrosionsschäden zu rechnen ist.Decontamination tests on various metallic reactor building materials have now contradicted the above assumption that the amount of residual activity is solely a function of the thickness of the removed surface layer. Different decontamination factors resulted for different decontamination solutions with the same, gravimetrically determined layer removal. Investigations with a scanning electromicroscope have shown that solid layers or solid islands, in which active material is enriched, have formed on the decontaminated metal surface and which are to be regarded as undesirable by-products of the respective ablation reactions. Such deviations can be observed in particular in the case of materials containing silicon and possibly aluminum, for example in the case of stainless steels and high-temperature materials, such as those e.g. used in helium-cooled high-temperature reactors, and also in low-alloy steels. Apart from an undesirable high residual activity, the irregular removal of such surface layers also makes it difficult to monitor and control the decontamination process itself, so that reliable decontamination is no longer guaranteed and the corrosion damage mentioned at the outset can also be expected.

Im Primärwasserkreislauf von Druckwasserreaktoren befindet sich Borsäure in Konzentration bis zu 3000 ppm. Während des Betriebes solcher Reaktoren fallen kleinere Mengen der genannten Flüssigkeit als Abfall an. Dieser Abfall enthält neben Borsäure noch Kontaminanten wie z.B. Kobaltverbindungen, sowie feste Verunreinigungen, wie z.B. Rostreste, Stofffasern, Staub, usw. Dieser Abfall kann in bestimmten Fällen sogar so weit behandelt werden, dass.er in Form eines festen Materials vorliegt.In the primary water circuit of pressurized water reactors there is a concentration of boric acid of up to 3000 ppm. During the operation of such reactors, smaller amounts of the liquid mentioned fall than Waste. In addition to boric acid, this waste also contains contaminants such as cobalt compounds, as well as solid contaminants such as rust residues, fabric fibers, dust, etc. In certain cases, this waste can even be treated to the extent that it is in the form of a solid material.

Meistens wurde der Abfall bisher auf ca. 16 Gew.% durch Eindampfen aufkonzentriert, wobei dieser Konzentrat dann eine Aktivität von 0,1 bis 3 Ci/m3 und bis zu 1 g/I an Feststoffen (28'000 ppm Bor) aufweist. Ein solches Konzentrat wird mit Zement verfestigt (siehe z.B. Nagra: Technischer Bericht 84-09). Eine Menge von 123 kg Konzentratlösung/200 Liter Matrix, mit einem Raumgewicht 1.89 Mg/m3 d.h. 123 kg (=114 Liter mit einer Dichte von 1,08 Mg/m3) wird in 378 kg schwerer Matrix verfestigt. Die Konzentratmengen können in einem Jahr bis zu 10 m3 pro Kernkraftwerk erreichen. Zur Aufnahme dieser Menge von Konzentrat benötigt man, gemäss obigen Annahmen, etwa 88 Fässer, wobei das Volumen des jeweiligen Fasses etwa 200 Liter beträgt. Bei einem Preis von sFr. 5'000.- je Faß, inklusiv Entsorgung, ergibt sich ein Betrag von sFr. 440'000.- für die Entsorgung der jährlich anfallenden Menge von Abfall.Most of the waste has so far been concentrated to about 16% by weight by evaporation, this concentrate then having an activity of 0.1 to 3 Ci / m 3 and up to 1 g / l of solids (28,000 ppm boron). Such a concentrate is solidified with cement (see eg Nagra: Technical Report 84-09). A quantity of 123 kg concentrate solution / 200 liters matrix, with a density of 1.89 mg / m 3 ie 123 kg (= 114 liters with a density of 1.08 mg / m 3 ) is solidified in a 378 kg heavy matrix. The concentrate quantities can reach up to 10 m 3 per nuclear power plant in one year. According to the above assumptions, about 88 barrels are required to take up this amount of concentrate, the volume of each barrel being about 200 liters. At a price of sFr. 5'000.- per barrel, including disposal, there is an amount of SFr. 440,000.- for the disposal of the annual amount of waste.

Es ist die Aufgabe der vorliegenden Erfindung ein Verfahren zur Dekontamination radioaktiv kontaminierter, metallischer oder zementhaltiger Werkstoffe zu schaffen, welches geschilderte Nachteile meidet, wirtschaftlicher arbeitet und die Menge der nuklear zu entsorgenden Abfälle reduziert. Gelöst wird diese Aufgabe durch das Verfahren gemäß Anspruch 1.It is the object of the present invention to provide a process for the decontamination of radioactive contaminated, metallic or cement-containing materials, which avoids the disadvantages described, works more economically and reduces the amount of nuclear waste to be disposed of. This object is achieved by the method according to claim 1.

Die Einrichtung zur Durchführung des vorliegenden Verfahrens (Bild 1) weist einen Behälter zur Aufnahme der zu dekontaminierenden Gegenstände auf. Die Behandlungsdauer von Gegenständen im Aufnahmebehälter 1 wird so gewählt, daß die Gegenstände nach der Beendigung des Verfahrens von Radioaktivität frei sind. Solche Gegenstände werden dann dem Aufnahmebehälter 1 entnommen und sie können anschliessend entweder wiederverwendet oder dem Schrott zugeführt werden.The device for performing the present method (Figure 1) has a container for holding the objects to be decontaminated. The duration of treatment of objects in the receptacle 1 is chosen so that the objects are free of radioactivity after the end of the process. Such objects are then removed from the receptacle 1 and can then either be reused or sent to the scrap.

In den Aufnahmebehälter 1 wird eine Dekontaminationslösung eingeführt, welche auf die Oberfläche der Gegenstände derart einwirkt, daß die kontaminierte Oberflächenschicht aufgelöst und abgetragen wird. Die Dekontaminationslösung im Behälter 1 kann ein Bad bilden, in welchem sich die Gegenstände befinden, oder die Dekontaminationslösung wird in den Behälter 1 eingesprüht.A decontamination solution is introduced into the receptacle 1, which acts on the surface of the objects in such a way that the contaminated surface layer is dissolved and removed. The decontamination solution in container 1 can form a bath in which the objects are located, or the decontamination solution is sprayed into container 1.

Dem Aufnahmebehälter 1 kann eine Umwälzvorrichtung 2 mit einer Pumpe zugeordnet sein. Dies ermöglicht, mit einer verhältnissmässig kleinen Menge der Dekontaminationslösung eine lange Behandlungsdauer der Gegenstände zu erreichen. An den Aufnahmebehälter 1 ist ein Verdampfer 3 über eine Leitung 4 angeschlossen. Im Verdampfer 3 werden flüchtiqere Komponenten einer konzentrierten Lösung von weniger flüchtigen Komponenten derselben getrennt. Verdampfbare Komponenten werden durch eine weitere Leitung 5 einem Absorber 6 zugeführt. Die Sumfpprodukte aud dem Verdampfer 3 werden in eine Reduktionsvorrichtung 7 übergeführt, in welcher sie zu metallischem Eisen, Chrom, Nickel, Blei usw. reduziert werden. Es besteht jedoch auch die Möglichkeit, die festen, eingedampften Produkte ohne Reduktion derselben zur Weiterverwendung als chemische Metallverbindungen der chemischen Industrie oder dem Schrott zuzuführen. Die Reduktionsvorrichtung 7 ist über eine Leitung 9 an den Absorber 6 angeschlossen, durch welche HF von der Reduktionsvorrichtung 7 zum Absorber 6 geführt wird. Den für die Reduktion von Metallverbindungen erforderlichen Wasserstoff kann man der Reduktionsvorrichtung 7 durch eine Leitung 10 aus dem Auflöser 1 zuführen.A circulating device 2 with a pump can be assigned to the receiving container 1. This makes it possible to achieve a long treatment time for the objects with a relatively small amount of the decontamination solution. An evaporator 3 is connected to the receptacle 1 via a line 4. In the evaporator 3, more volatile components of a concentrated solution are separated from less volatile components thereof. Vaporizable components are fed to an absorber 6 through a further line 5. The bottom products from the evaporator 3 are transferred to a reduction device 7, in which they are reduced to metallic iron, chromium, nickel, lead, etc. However, there is also the possibility of feeding the solid, evaporated products to the chemical industry or the scrap without reducing them for further use as chemical metal compounds. The reduction device 7 is connected via a line 9 to the absorber 6, through which HF is led from the reduction device 7 to the absorber 6. The hydrogen required for the reduction of metal compounds can be fed to the reduction device 7 through a line 10 from the dissolver 1.

An den Aufnahmebehälter 1 kann eine elektrolytische Zelle 12 über eine Leitung 13 angeschlossen sein, durch welche die konzentrierte Lösung aus dem Aufnahmebehälter 1 in die Zelle 12 umgepumpt wird. Während des Betriebes dieser Zelle 12 wird an der Anode BF4- Ionen zu HBF4 rekombinieren. HBF4 wird durch eine weitere Leitung 14 dem Aufnahmebehälter 1 zugeführt. Im bereits erwähnten Absorber 6 entsteht ebenfalls HBF4, welche über eine Leitung 15 dem Aufnahmebehälter 1 zugeführt wird. Die Qualität der Oberfläche der behandelten Gegenstände kann während und/oder nach der Dekontamination durch oberflächenwirksame Stoffe beeinflusst werden. Als solche Stoffe kommen Netzmittel, wie z.B. Seifen, Wasserpermeabilitätsinhibitoren, wie z.B. Formaldehyd, usw. in Frage.An electrolytic cell 12 can be connected to the receptacle 1 via a line 13, through which the concentrated solution is pumped out of the receptacle 1 into the cell 12. During the operation of this cell 12, BF 4 ions are recombined to HBF 4 at the anode. HBF 4 is fed to the receptacle 1 through a further line 14. HBF 4 , which is fed to the receptacle 1 via a line 15, likewise arises in the already mentioned absorber 6. The quality of the surface of the treated objects can be influenced during and / or after decontamination by surface-active substances. Wetting agents such as soaps, water permeability inhibitors such as formaldehyde, etc. come into consideration as such substances.

Die starke Ueberlegenheit des hier beschriebenen Verfahrens gegenüber den Verfahren des Standes der Technik beruht in beinahe universaller Verwendbarkeit dieses Verfahrens, in ausserordentlich grosser Aufnahmekapazität von HBF4 für die behandelten Materialien und in der totalen Regenerierbarkeit der Dekontaminationslösung, so daß eine ausserordentlich kleine Menge von sekundären Anfällen entsteht.The strong superiority of the method described here over the methods of the prior art resides in the almost universal usability of this method, in the extraordinarily large absorption capacity of HBF 4 for the treated materials and in the total regenerability of the decontamination solution, so that an extraordinarily small amount of secondary attacks arises.

Dekomtinationswirkung (Tabelle 1)Decompression effect (Table 1)

Es wurden Versuche durchgeführt mit Materialien des Primärkreislaufes von Siedewasserreaktoren und mit Dampferzeugermaterial aus einem Druckwasserreaktor mit jeweils starker Magnetschicht. Die Materialien hatten Aktivitäten von ca. 10 IlCi/cm2 Cobalt-60.

Figure imgb0001
Experiments were carried out with materials from the primary circuit of boiling water reactors and with steam generator material from a pressurized water reactor, each with a strong magnetic layer. The materials had activities of approximately 10 Il Ci / cm 2 Cobalt-60.
Figure imgb0001

Korrosionsverhalten (Tabelle 2)Corrosion behavior (table 2)

Die Abtragungskinetik von rostfreiem Stahl und Nickelbasislegierungen wurde bei 80, 90 und 100°C untersucht.

Figure imgb0002
The removal kinetics of stainless steel and nickel-based alloys were examined at 80, 90 and 100 ° C.
Figure imgb0002

Am Prozeßanfang steht der Auflöser 1 (Berieselunganlage), in welchen die zu dekontaminierenden Gegenstände zur Freidekontamination oder zur Freimessung in ein Bad gelegt oder durch ein Sprühverfahren besprüht werden. Der zweite Teil des Prozesses besteht aus Verdampfen in einem Verdampfer 3. Im Verdampfer 3 werden konzentrierte Lösungen mit ca. 200 Gramm rostfreiem Stahl pro Liter, bei erhöhten Temperaturen, bei Normaldruck oder unter Druck eingeengt und bis auf feste FeF2 bzw. analoge Fluoride anderer Metalle getrocknet. BF3, B2O3 · BF3, HBF4, H20 und Dehydrate der Borsäure werden abgedampft, abgesaugt und im nächsten Teil der Anlage, dem Absorber 6, in der flüssigen Phase gelöst. Im Absorber 6 wird die erhaltene Lösung mit Flußsäure oder mit Flußsäuredämpfen zur Herstellung von frischer HBF4-Säure versetzt, welche dem Auflöser 1 zugeführt wird. Die Supfprodukte aus dem Verdampfer 3 werden in den Reduktionsteil 7 der Anlage überführt, in welchem sie zu metallischem Eisen, Chrom oder Nickel (u.a.) reduziert werden können. Je nach dem, ob es sich um eine Freidekontamination oder Freimessung handelt, erhalten wir entweder inaktive Produkte aus dem Verdampfer 3, bzw. aus dem Reduktionsanlage-Teil 7, oder aktive, feste Produkte, welche der Entsorgung zugeführt werden. Je nach der vorhandenen Entsorgungs-Infrastruktur kann man mehrere Entsorgungsweisen anwenden:

  • a) Die direkte Entsorgung des Dekontaminationsmittels aus dem Auflöser 1,
  • b) die Entsorgung von Fluorirden in eingedampfter Form,
  • c) die Entsorgung von metallischen Komponenten nach Reduktionen,
  • d) oder deren Kombinationen.
At the beginning of the process is the dissolver 1 (sprinkler system), in which the objects to be decontaminated are placed in a bath for free decontamination or for free measurement or are sprayed by a spraying process. The second part of the process consists of evaporation in an evaporator 3. In the evaporator 3, concentrated solutions with about 200 grams of stainless steel per liter, at elevated temperatures, at atmospheric pressure or under pressure and evaporated down to solid FeF 2 or analogous fluorides of others Metals dried. BF 3 , B 2 O 3 .BF 3 , HBF 4 , H 2 0 and dehydrates of boric acid are evaporated, suctioned off and dissolved in the liquid phase in the next part of the plant, the absorber 6. In the absorber 6, the solution obtained is mixed with hydrofluoric acid or with hydrofluoric acid vapors to produce fresh HBF 4 acid, which is fed to the dissolver 1. The soup products from the evaporator 3 are transferred to the reduction section 7 of the installation, in which they can be reduced to metallic iron, chromium or nickel (among others). Depending on whether it is free decontamination or free measurement, we receive either inactive products from the evaporator 3 or from the reduction system part 7, or active, solid products which are disposed of. Depending on the existing waste disposal infrastructure, several waste disposal methods can be used:
  • a) The direct disposal of the decontamination agent from the dissolver 1,
  • b) the disposal of fluorine earths in evaporated form,
  • c) the disposal of metallic components after reductions,
  • d) or their combinations.

Anstatt die zu dekontaminierenden Gegenstände in ein Dekontaminationsbad einzutauchen und eine mehrstündige oder sogar mehrmalige Dekontamination durchzuführen, genügt es nunmehr, die kontaminierten Gegenstände bei erhöhter Temperatur mit einer duschähnlichen Vorrichtung berieseln zu lassen. Diese Behandlung ist an keine bestimmte Gegenständsgeometrie gebunden. Jeder Gegenstand kann in eine Plastikhülle eingepackt werden, die als Behälter der Anlage dient. Durch das Auffangen der abfliessenden Flüssigkeit im untersten Bereich, kann man das gleiche Dekontaminationsmittel mittels einer Pumpe 2 im Kreislauf wieder verwenden. Die minimale Menge an Dekontaminationsmittein, die zur Aufrechterhaltung des Kreislaufes und für die Benetzung des Systems benötigt wird, bestimmt sich nach den Benetzbarkeitseigenschaften des Dekontaminationsmittels und den Eigenschaften der Materialoberfläche. Aus praktischer Erfahrung haben sich Werte zwischen 0,5 bis 1,5 Liter pro m2 der behandelten Oberfläche ergeben. Die hohe Aufnahmefähigkeit des Dekontaminationsmittels bzw. der Dekontaminationslösung- 1 Liter kann bei 90°C bis zu 220 Gramm rostfreien Stahl auflösen- erlaubt hohe flächenbezogene Dekontaminationsleistungen. Eine so hohe Aufnahmekapazität erlaubt mit nur 1 Liter Dekontaminationslösung bei einem Abtrag von 1 Micrometer ca. 30 m2 der Oberfläche zu dekontaminieren. Im Auflöser 1 kann man eine Konzentration bis zu 220 Gramm rostfreien Stahl pro Liter bei 90°C erreichen. Diese konzentrierte Lösung wird in die elektrolytische Zelle 12 umgepumpt, wo an der Kathode Metall ausgeschieden wierd, während an der Anode BF4―Ionen rekombinieren zu HBF4. Diese Lösung wird dem Dekontaminationsprozess wieder zugeführt.Instead of immersing the objects to be decontaminated in a decontamination bath and carrying out decontamination for several hours or even several times, it is now sufficient to have the contaminated objects sprinkled with a shower-like device at elevated temperature. This treatment is not tied to any particular object geometry. Each item can be wrapped in a plastic sleeve that serves as a container for the system. By collecting the outflowing liquid in the lowest area, the same decontamination agent can be used again in the circuit by means of a pump 2. The minimum amount of decontamination agent required to maintain the circulation and for wetting the system is determined by the wettability properties of the decontamination agent and the properties of the material surface. From practical experience, values between 0.5 and 1.5 liters per m 2 of the treated surface have resulted. The high absorption capacity of the decontamination agent or the decontamination solution - 1 liter can dissolve up to 220 grams of stainless steel at 90 ° C - allows high area-related decontamination performance. Such a high absorption capacity allows to decontaminate approx. 30 m 2 of the surface with only 1 liter of decontamination solution with a removal of 1 micrometer. In the dissolver 1 you can reach a concentration of up to 220 grams of stainless steel per liter at 90 ° C. This concentrated solution is pumped into the electrolytic cell 12, where metal is on the cathode is excreted, while at the anode BF 4 ions recombine to HBF 4 . This solution is returned to the decontamination process.

Entsorgung der sekundären AbfälleDisposal of secondary waste

Als Beispiel wird ein eisenhaltiges Fe (BF4)2-Konzentrat diskutiert. Dieses Konzentrat beinhaltet auch Radioaktivität, was jedoch die chemische Bilanz nicht beeinflusst. Abgelöster rostfreier Stahl, Nickelbasislegierungen und andere kontaminierte Materialien sind analog zu behandeln. Zur direkten Entsorgung von Eisenkonzentraten gilt folgende Gleichung:

Figure imgb0003
An iron-containing Fe (BF 4 ) 2 concentrate is discussed as an example. This concentrate also contains radioactivity, but this does not affect the chemical balance. Detached stainless steel, nickel-based alloys and other contaminated materials are to be treated analogously. The following equation applies to the direct disposal of iron concentrates:
Figure imgb0003

Entsorgung nach elektrochemischer Regeneratiom (minimale Variante):Disposal according to electrochemical regeneration (minimal variant):

Aus dem eisenhaltigen Konzentrat wird Eisen, Chrom, Nickel bzw. Kupfer elektrolytisch entnommen umd anschliessend mit Zement vermischt. Die Elektrolyse läuft folgendermassen ab:

Figure imgb0004
Figure imgb0005
 Iron, chromium, nickel or copper is removed electrolytically from the iron-containing concentrate and then mixed with cement. The electrolysis proceeds as follows:
Figure imgb0004
Figure imgb0005

Die Reaktionen für andere Metalle aus dekontaminierten Legierungen laufen analog ab. Es ist vorteilhaft, als Anode ein korrosionsfestes Material, wie z.B. Grafit, zu verwenden, oder als Opferanode auch das kontaminierte Objekt zu verwenden, was die chemische Auflösung beschleunigt und gleichzeitig die Säure regeneriert.The reactions for other metals made of decontaminated alloys proceed analogously. It is advantageous to use a corrosion-resistant material such as e.g. Graphite, or to use the contaminated object as a sacrificial anode, which accelerates the chemical dissolution and at the same time regenerates the acid.

Entsorgungsvariante nach Abdampfung der HBF4-Säure:

  • Bei normalem Druck, bei Temperaturen bis zu 170°C, oder bei herabgesetzttem Dampfdruck und tieferen Temperaturen, erhält man nach dem Abdampfungsprozeß feste, rötliche Reste von FeF2, Aktivität beinhaltend. Diese ergeben nach der Vermischung mit Wasser und Ca(OH)2 CaF2+Fe(OH)2. Diese festen Produkte sind mit Zement gut verträglich und das Gewicht der Zementmatrix könnte man nach folgende Formel ermitteln:
  • Anzahl Gramm aufgelösten Eisens im Konzentratx12,5=Gewicht der Zementmatrix in Gramm. Das Destillat beinhaltet Dämpfe aus HBF4, BF3, H20, Borsäure und deren Dehydrate. Nach der Kondensation und dem Auffangen der Dämpfe im Wasser, kann man durch Hinzufügen von HF die erwünschte Konzentration von HBF4 einstellen.
Disposal variant after evaporation of HBF 4 acid:
  • At normal pressure, at temperatures up to 170 ° C, or at reduced vapor pressure and lower temperatures, solid, reddish residues of FeF 2 , containing activity, are obtained after the evaporation process. After mixing with water and Ca (OH) 2 these give CaF 2 + Fe (OH) 2 . These solid products are well compatible with cement and the weight of the cement matrix could be determined using the following formula:
  • Number of grams of dissolved iron in the concentrate x 12.5 = weight of the cement matrix in grams. The distillate contains vapors from HBF 4 , BF 3 , H 2 0, boric acid and their dehydrates. After the condensation and the capture of the vapors in the water, the desired concentration of HBF 4 can be set by adding HF.

Reaktionen:Reactions:

Auflöser 1:

  • Fe+2 HBF4→Fe (BF4)2+H2
Resolver 1:
  • Fe + 2 HBF 4 → Fe (BF 4 ) 2 + H 2

Verdampfer 3:

  • a) H20 abdestillieren
  • b) abdestillieren von unreag. HBF4
  • c) Pyrolyse
    Figure imgb0006
    BF3 (g)+B2O3→BF3· B2O3 (g) H3B03 (aus HBF4 Hydrolyse)→B2O3+H2O
Evaporator 3:
  • a) Distill off H 2 0
  • b) distilling off unreag. HBF 4
  • c) pyrolysis
    Figure imgb0006
     BF 3 (g) + B 2 O 3 → BF 3 · B 2 O 3 (g) H 3 B0 3 (from HBF 4 hydrolysis) → B 2 O 3 + H 2 O

Absorber 6:

  • BF3+HF→HBF4
Absorber 6:
  • BF 3 + HF → HBF 4

Reduktion 7:

  • H2+Fe F2→2 HF+Fe.
Reduction 7:
  • H 2 + Fe F 2 → 2 HF + Fe.

Reaktionen HBF4-Metalle:HBF4 metal reactions:

Auflöser: 2 HBF4+Ni=Ni (BF4)2+H2

  • 3 HBF4+Cr=Cr (BF4)3+3/2 H2
  • 2 HBF4+Cu=Cu (BF4)2+H2
  • 2 HBF4+Pb=Pb (BF4)2+H2 in allgem. n HBF4+Me=Me (BF4)n+n/2-H2 Verdampfer: (Pyrolyse) Ni (BF4)2=NiF2+2 BF3
  • Cr (BF4)3=CrF3+3 BF3
  • Cu (BF4)2=CuF2+2 BF3
  • Pb (BF4)2=PbF2+2 BF3
  • Reduktion: Ni F2+H2=Ni+2 HF
  • Cr F3+-3/2 H2=Cr+3 HF
  • Cu F2+H2=Cu+2 HF
  • Pb F2+H2=PbF2+2 HF
Dissolver: 2 HBF 4 + Ni = Ni (BF 4 ) 2 + H 2
  • 3 HBF 4 + Cr = Cr (BF 4 ) 3 +3/2 H 2
  • 2 HBF 4 + Cu = Cu (BF 4 ) 2 + H 2
  • 2 HBF 4 + Pb = Pb (BF 4 ) 2 + H 2 in general. n HBF 4 + Me = Me (BF 4 ) n + n / 2-H 2 evaporator: (pyrolysis) Ni (BF 4 ) 2 = NiF 2 +2 BF 3
  • Cr (BF4) 3 = CrF3 + 3 BF 3
  • Cu (BF 4 ) 2 = CuF 2 +2 BF 3
  • Pb (BF4) 2 = PbF2 +2 BF 3
  • Reduction: Ni F 2 + H 2 = Ni + 2 HF
  • Cr F 3 + -3 / 2 H 2 = Cr + 3 HF
  • Cu F 2 + H 2 = Cu + 2 HF
  • Pb F2 + H2 = PbF2 + 2 HF

Entsorgung mit Ca (OH)2:

  • Ni (BF4)2+4 Ca (OH)2=Ni (OH)2+4 CaF2+2 H3B03
  • Cr (BF4)3+6 Ca (OH)2=Cr (OH)3+6 CaF2+3 H3BO3
  • Cu (BF4)2+4 Ca (OH)2=Cu (OH)2+4 CaF2+2 H3B03
  • Pb (BF4)2+4 Ca (OH)2=Pb (OH)2+4 CaF2+2 H3B03
  • Ni F2+Ca (OH)2=CaF2+Ni (OH)2
  • Cr F3+3/2-Ca (OH)2=Cr (OH)3+3/2-CaF2
  • Cu F2+Ca (OH)2=CaF2+Cu (OH)2
  • Pb F2+Ca (OH)2=Pb (OH)2+CaF2
Disposal with Ca (OH) 2:
  • Ni (BF 4 ) 2 +4 Ca (OH) 2 = Ni (OH) 2 +4 CaF 2 +2 H 3 B0 3
  • C r (BF 4 ) 3 +6 Ca (OH) 2 = C r (OH) 3 +6 CaF 2 +3 H 3 BO 3
  • Cu (BF 4 ) 2 +4 Ca (OH) 2 = Cu (OH) 2 +4 CaF 2 +2 H 3 B0 3
  • Pb (BF 4 ) 2 +4 Ca (OH) 2 = Pb (OH) 2 +4 CaF 2 +2 H 3 B0 3
  • Ni F 2 + Ca (OH) 2 = CaF2 + N i (OH) 2
  • Cr F 3 + 3/2-Ca (OH) 2 = Cr (OH) 3 + 3/2-CaF 2
  • Cu F 2 + Ca (OH) 2 = CaF 2 + Cu (OH) 2
  • Pb F 2 + Ca (OH) 2 = Pb (OH) 2 + CaF 2

Reaktionen H2 Si F6-Metalle:Reactions H 2 Si F 6 metals:

  • Auflöser: Fe+2 H2Si F6=Fe (Si F6)2+2 H2 Dissolver: Fe + 2 H 2 Si F 6 = Fe (Si F 6 ) 2 +2 H 2
  • in allgem. Me+n H2Si F6=Men+ (Si F6)n+n H2 in general Me + n H 2 Si F 6 = Me n + (Si F 6 ) n + n H 2
  • Verdampfer: (Pyrolyse) Fe (Si F6)2=Fe F2+2 Si F4 Evaporator: (pyrolysis) Fe (Si F 6 ) 2 = Fe F 2 +2 Si F 4
  • in allgem. Men+ (Si F6)n=Me Fn+n Si F4 in general Me n + (Si F 6 ) n = Me F n + n Si F 4
  • Absorber: Si F4+2 HF=H2 Si F6 Absorber: Si F 4 +2 HF = H 2 Si F 6
  • Reduktion: Men+ F"+-n/2 H2=Me+n HFReduction: Me n + F " + -n / 2 H 2 = Me + n HF
Entsorgung mit Ca (OH)2:Disposal with Ca (OH) 2:

Figure imgb0007
Figure imgb0007

in allqem.in allqem.

Figure imgb0008
Figure imgb0008

Reaktionen HF-MetalleHF metal reactions

ergeben Fluoride, deren Entsorgung mit Ca (OH)2 bereits skizziert wurde.result in fluorides, the disposal of which has already been outlined with Ca (OH) 2.

Dekontamination von Mauerwerk und zementhaltigen OberflächenDecontamination of masonry and cementitious surfaces

Bei der Dekontamination von porösem Material wird die Aktivität durch die mobile, flüssige Phase ins Material transportiert, was die nasse Dekontamination erschwert bis verunmöglicht. Deshalb wird man oft einen mechanischen Abtrag der kontaminierten Schicht vornehmen müssen. Dieses Verfahren ist teuer, verunstaltet die Oberfläche und verursacht viele sekundäre Abfälle.When porous material is decontaminated, the activity is transported into the material by the mobile, liquid phase, which makes wet decontamination difficult or even impossible. Therefore, you will often have to mechanically remove the contaminated layer. This process is expensive, blemishes the surface and creates a lot of secondary waste.

Die Aufgabe der vorliegenden Erfindung ist, die genannten aber auch noch weitere Nachteile des Standes der Technik auf dem Gebiet der Dekontamination zu beseitigen. Diese Aufgabe wird beim Verfahren der eingangs genannten Art erfindungsgemäß so gelöst, wie dies im kennzeichnenden Teil des Anspruchs 1 definiert ist.The object of the present invention is to eliminate the mentioned but also further disadvantages of the prior art in the field of decontamination. This object is achieved according to the invention in the method of the type mentioned at the outset, as defined in the characterizing part of claim 1.

Anwendungsbeispiel und Mechanismus.Application example and mechanism.

Die Mauerwerkoberfläche wird mit HBF4―und/oder H2SiF6―Säure benebelt/befeuchtet. Durch die chemische Reaktion zwischen den Carbonaten im Mauerwerk und den Säuren entsteht gasförmiges C02. Die Gasbläschen bilden mit der Säure einen Schaum, welcher ein hervorragendes Flotationsmittel für die Kontaminanten ist. Anschliessend wird der Schaum mit der Aktivität abgesaugt. Fluor- Ionen aus den Fluorokomplexen der Säuren reagieren mit dem anwesenden Calcium und bilden einen unlöslichen, voluminösen Niederschlag von CaF2, welcher die an der Oberfläche vorhandenen Poren verstopft. Durch die beschriebene Imprägnierung des Mauerwerkes wird der Aktivitätstransport ins Materialinnere massiv behindert. Bei Radium-kontaminiertem Beton wurden bei der Dekontamination Dekofaktoren zwischen 10 und 15 erreicht.The masonry surface is misted / moistened with HBF 4 ― and / or H 2 SiF 6 ― acid. The chemical reaction between the carbonates in the masonry and the acids produces gaseous C0 2 . The gas bubbles form a foam with the acid, which is an excellent flotation agent for the contaminants. The foam is then suctioned off with the activity. Fluorine ions from the fluorocomplexes of the acids react with the calcium present and form an insoluble, voluminous precipitate of CaF 2 , which clogs the pores on the surface. The impregnation of the masonry described massively impedes the transport of activity into the interior of the material. With radium-contaminated concrete, decofactors between 10 and 15 were achieved during decontamination.

Neuer Eis-abrasive-Dekontaminationsnachbehandlung-Prozeß.New ice-abrasive decontamination after-treatment process.

In der Dekontaminationslösung entstehen an der Gegenstandoberfläche unerwünschte, feste Reaktionsnebenprodukte, welche auf den Gegenstandoberfläche haften bleiben und welche unter Umständen die Dekontaminationsergebnisse deutlich verschlectern. Diese Schicht ist relativ leicht abwischbar, solange sie nicht eingetrocknet und mit der Oberfläche verkrustet ist. Nach Abschluß der vorausberechneten (bzw. abgeschätzten) Dekobehandlung wird das gesamte System mit Feststoff-Eispartikeln abrasiv behandelt. Die abwischbaren und kontaminierten Teile der Ablagerungsschicht werden entfernt und mobilisiert.In the decontamination solution, undesired, solid reaction by-products are formed on the surface of the object, which stick to the surface of the object and which, under certain circumstances, significantly deteriorate the decontamination results. This layer is relatively easy to wipe off as long as it has not dried out and is encrusted with the surface. After completing the pre-calculated (or estimated) deco treatment, the entire system is treated with solid ice particles. The wipeable and contaminated parts of the deposit layer are removed and mobilized.

Die Einrichtung zur Durchführung des vorliegenden Verfahrens enthält einen Reaktionsbehälter 1, in dem kontaminierte Borsäure in eine leicht verdampfbare Borverbindung umgewandelt wird (Bild 2). Durch eine erste Leitung 2 wird kontaminierte Borsäure in den Reaktionsbehälter 1 eingeführt. Es handelt sich in der Regel um eine Flüssigkeit, die neben Borsäure auch Wasser, Kontaminanden, wie z.B. Kobaltverbindungen, sowie Verunreinigungen, wie z.B. Rostreste, Stofffasern, Staub usw. enthält. Durch eine weitere Leitung 3 wird dem Reaktionsgefäss 1 ein chemischer Stoff zugeführt, der die genannte Umwandlung verursacht. Es kann sich um gasförmiges Fluor oder um Flußsäure handeln. Flußsäure kann entweder in Form von Flüssigkeit oder in Form von Gas angewendet werden.The device for carrying out the present method contains a reaction container 1, in which contaminated boric acid is converted into an easily evaporable boron compound (Figure 2). Contaminated boric acid is introduced into the reaction vessel 1 through a first line 2. It is usually a liquid that, in addition to boric acid, also water, contaminants such as Cobalt compounds, as well as impurities, e.g. Contains rust, fabric fibers, dust, etc. Through a further line 3, a chemical substance is supplied to the reaction vessel 1, which causes the conversion mentioned. It can be gaseous fluorine or hydrofluoric acid. Hydrofluoric acid can be used either in the form of liquid or in the form of gas.

An den Reaktionsbehälter 2 ist eine Pumpe 4 angeschlossen, welche des Reaktionsprodukt aus dem Reaktionsgefäss 1 in eine Destillationsvorrichtung 5 einer an sich bekannten Art fördert. Die Geschwindigkeit der Einführung der zwei genannten Komponenten durch die Leitungen 2 und 3 in den Reaktionsbehälter 1 und die Geschwindigkeit des Abzuges des Reaktionsproduktes aus dem Reaktionsbehälter 1 wird so gewählt, dass dem zugeführten Material genügend Zeit für den vollständigen Verlauf der genannten Reaktion gewährt wird. Der Sumpf, der in der Destillationsvorrichtung 5 zurückbleibt, wird dieser entnommen und zur Entsorgung konditioniert. Zu diesem Zweck wird der Sumpf zunächst in einem weiteren Gefäss 6 beispielsweise mit Kalziumhydroxid neutralisiert. Das neutralisierte Sumpfmaterial kann nur noch bloss getrocknet und danach gleich abgelagert werden. Es kann jedoch auch mit Zement oder Bitumen verfestigt und erst dann abgelagert werden. Die für die Destillation in der Vorrichtung 5 erforderliche Wärmeenergie wird vorteilhaft flüssigen oder gasförmigen Medien entnommen. Vorteilhaft wird die Destillation bei Unterdruck durchgeführt, weil die Temperaturen in der Vorrichtung 5 dann verhältnismässig niedrig sind und bei solchen Temperaturen kann praktisch keine Pyrolyse stattfinden.A pump 4 is connected to the reaction container 2 and conveys the reaction product from the reaction vessel 1 into a distillation device 5 of a type known per se. The speed of the introduction of the two components mentioned through lines 2 and 3 in the Reaction container 1 and the rate at which the reaction product is withdrawn from the reaction container 1 are selected such that the material supplied is given sufficient time for the reaction to proceed to completion. The sump that remains in the distillation device 5 is removed from it and conditioned for disposal. For this purpose, the sump is first neutralized in a further vessel 6, for example with calcium hydroxide. The neutralized sump material can only be dried and then immediately deposited. However, it can also be solidified with cement or bitumen and only then deposited. The thermal energy required for the distillation in the device 5 is advantageously taken from liquid or gaseous media. The distillation is advantageously carried out under reduced pressure because the temperatures in the device 5 are then relatively low and at such temperatures virtually no pyrolysis can take place.

Die bei der Destillation anfallende HBF4-Säure wird aus der Destillationvorrichtung 5 durch eine Leitung 6 herausgeführt. Diese Säure kann als völlig regeneierbares Dekontaminationsmittel verwendet werden, wie dies in einer schweizerischen Patentanmeldung Nr. 2238/85 desselben Anmelders beschrieben ist, oder die Säure kann der chemischen Industrie verkauft werden, wo sie beispielsweise in der Galvanotechnik verwendet werden kann.The HBF 4 acid obtained during the distillation is led out of the distillation device 5 through a line 6. This acid can be used as a fully regenerable decontamination agent as described in a Swiss patent application no. 2238/85 by the same applicant, or the acid can be sold to the chemical industry, where it can be used, for example, in electroplating.

Die wesentlichen Vorteile des vorliegenden Verfahrens sind darin zu sehen, dass die Borfluorosäure, die bei der Destillation anfällt, nicht in das Endlager für radioaktives Material gelangt, sondern beispielsweise an die chemische Industrie verkauft und somit weiter verwendet werden kann. Der Sumpf, weil er nunmehr ein kleineres Volumen aufweist, kann entsorgt werden, ohne grosse Kosten zu verursachen. Dem vorliegenden Verfahren liegt die Erkenntnis zugrunde, daß Borfluorosäure HBF4, im Unterschied zu H3B03, destillierbar und somit von den Kontaminanden, wie z.B. von Co-60 Cs-Nukliden, trennbar ist. Zudem lässt sich die Borfluorosäure bei der Destillation in Fraktionen verschiedener Dichte trennen. Die Prinzipreaktionen, die dem vorliegenden Verfahren zugrunde liegen sind wie folgt:

Figure imgb0009
The main advantages of the present process can be seen in the fact that the borofluoric acid, which is obtained during the distillation, does not end up in the repository for radioactive material, but can be sold to the chemical industry, for example, and thus can be used further. The swamp, because it now has a smaller volume, can be disposed of without incurring great costs. The present process is based on the knowledge that, in contrast to H 3 B0 3 , borofluoric acid HBF 4 can be distilled and can thus be separated from the contaminants, such as, for example, from Co-60 Cs nuclides. In addition, the borofluoric acid can be separated into fractions of different densities during distillation. The principle reactions on which the present method is based are as follows:
Figure imgb0009

In einem praktischen Fall wurden 15,46 g H3B03 binnen etwa 20 Min. zu 20 g HF zugegeben.In a practical case, 15.46 g H 3 B0 3 were added to 20 g HF within about 20 minutes.

ZahlenbeispielNumerical example

10 m3 borhaltiges Konzentrat (16% H3B03) beinhaltet 1600 kg Borsäure (ca. 26'000 Mol). Nach dem Eindampfen wird zur Borsäure der vierfache Mol-überschuss von HF beigemischt (104'000 Mol HF) d.h., z.B. 2457 Liter 70% HF, 1 Liter zu Sfr. 12.- (=Sfr. 29'500.-). Das Destillat ergibt ca. 26'00 Mol HBF4, was Sfr. 24.700.- entspricht (1 Liter=8 Mol-50%)=Sfr. 7,6). Wir erhalten je nach der Prozessführung 4500 kg von ca. 57%-HBF4-Säure oder die entsprechende Verdünnung je nach der Anfangskonzentration der Borsäure. Die erhaltene HBF4-Säure darf auch Spuren von Aktivität beinhalten (bei der Einstufen-Destillation), weil sie als völlig regenerierbares Dekontaminationsmittel für Komponenten aus DWR und SWR verwendet werden kann. Die Option für eine inaktive Verwendung (z.B. in der Galvanotechnik) besteht bei der Durchführung einer mehrstufigen Destillation.10 m 3 boron-containing concentrate (16% H 3 B0 3 ) contains 1600 kg boric acid (approx. 26'000 mol). After evaporation, four times the molar excess of HF is added to the boric acid (104,000 mol HF), ie, 2457 liters of 70% HF, 1 liter to Sfr. 12.- (= Sfr. 29'500.-). The distillate gives about 26'00 mol HBF 4 , which Sfr. 24,700.- corresponds to (1 liter = 8 mol-50%) = Sfr. 7.6). Depending on the process control, we receive 4500 kg of approx. 57% HBF 4 acid or the corresponding dilution depending on the initial concentration of boric acid. The HBF 4 acid obtained may also contain traces of activity (in single-stage distillation) because it can be used as a completely regenerable decontamination agent for components made from DWR and SWR. The option for an inactive use (e.g. in electroplating) is when carrying out a multi-stage distillation.

ZusammenfassungSummary

Kontaminierte Oberflächenschichten werden durch Behandlung mit einer wässrigen fluorobasishaltigen Dekontaminationslösung dekontaminiert. Die wässrige Lösung enthält 0,05 bis 50 Mol Dekontaminationsmittel je Liter, wobei das Dekontaminationsmittel vorzugsweise wenigstens ein Stoff der Stoffgruppe Hexafluorosilikatsäure, Fluoroborsäure und deren beider Salze ist. Die Dekontaminationslösung erbringt insbesondere auch an DWR, SWR, Hochtemperaturlegierungen und Mauerwerke notwendighohe Dekontaminationsfaktoren. Die gebrauchte Dekontaminationslösung kann nach der Regeneration in den Dekontaminationsprozess rezykliert werden.Contaminated surface layers are decontaminated by treatment with an aqueous fluorobase-containing decontamination solution. The aqueous solution contains 0.05 to 50 moles of decontamination agent per liter, the decontamination agent preferably being at least one substance from the group of hexafluorosilicate acids, fluoroboric acid and their salts. The decontamination solution provides the necessary decontamination factors, particularly on DWR, SWR, high-temperature alloys and masonry. The used decontamination solution can be recycled into the decontamination process after regeneration.

Durch die Auflösung der dekontaminierten Gegenstände mit komplizierter und schwer messbarer Geometrie erhält man eine homogene, messbare Geometrie, wodurch die Freigabe ermöglicht wird.By dissolving the decontaminated objects with complicated and difficult to measure geometry, a homogeneous, measurable geometry is obtained, which enables the release.

Das Dekontaminationsmittel (HBF4-Säure) wird vorteilhaft aus kontaminierter Borsäure aus DWR-Abfällen mit Hilfe von Fluor- oder Flusssäure hergestellt. Die so hergestellte HBF4-Säure wird durch die Destillation von den Kontaminanten und Verunreinigungen getrennt.The decontamination agent (HBF 4 acid) is advantageously produced from contaminated boric acid from DWR waste with the help of fluoric or hydrofluoric acid. The HBF 4 acid thus produced is separated from the contaminants and impurities by the distillation.

Claims (13)

1. Process for the decontamination of radioactively contaminated objects made from metal or cement- containing material, characterized in that the objects to be decontaminated are brought into contact with a decontamination agent containing fluoroboric acid in aqueous solution with a concentration of 0.05 to approximately 50 mole/litre, that the contaminated objects or at least the surfaces thereof are dissolved by the decontamination agent and the contaminated materials converted into a measurable geometry are measured with regards to their radioactivity and the radioactive contaminants and impurities forming a sump or bottoms are separated by distillation from the decontamination agent and the latter is reused.
2. Process according to claim 1, characterized in that the surface layer of the radioactively contaminated objects are dissolved by immersion or spraying in or with the decontamination agent and the sump left behind after distillation is conditioned for disposal.
3. Process according to claim 2, characterized in that the sump is neutralized with calcium hydroxide, dried and dumped.
4. Process according to claim 2, characterized in that the sump is neutralized with calcium hydroxide and that said mixture is subsequently consolidated with cement or bitumen.
5. Process according to claim 2, characterized in that the dissolved material during and/or after the removal of the surface coating is separated from the decontamination solution, that the decontamination solution is reintroduced into the decontamination process and that water is added for reusing the decontamination agent.
6. Process according to claim 2, characterized in that material dissolved in the spent decontamination solution is precipitated chemically, particularly in the form of hydroxides, or is separated by electrolysis.
7. Process according to claim 2, characterized in that activity, oxide, graphite, carbide, dye or mixed oxide islands, left behind on the object surface after remcving the contaminated material are removed mechanically, particularly by blasting with ice crystals and/or brushing from the object.
8. Process according to claim 2, characterized in that the pH and/or colorimetry and/or density and/or radioactivity measurements are performed on the spent decontamination solution during the removal of the surface layer, in order to establish the composition of the decontamination solution and in particular the metals dissolved therein and/or the radioactivity thereof.
9. Process according to claim 6, characterized in that the dissolved metals are separated from the spent decontamination solution by electrolysis, that the decontamination agent is chemically precipitated and that the metal removed and the precipitate separated from the liquid undergo nuclear disposal, if the radioactivity thereof exceeds the maximum value authorized for these materials. I Ivi
10. Process according to claim 9, characterized in that cations, particularly Ca2+ ions in the form of Ca(OH)2 are added to the residual liquid, in order to precipitate the decontamination agent and that the separated precipitate is conditioned by mixing the cement for nuclear disposal.
11. Process according to claim 9, characterized in that the decontamination agent and the dissolved material particles are chemically separated from the spent decontamination solution, the precipitates of all or virtually all the radioactive substances being taken from the removed material and that the precipitates separated from the liquid can undergo nuclear disposal.
12. Process according to claim 9, characterized in that the dissolved material parts are precipitated as hydroxides from the spent decontamination solution and that to the latter are added cations, particularly Ca2+-ions, in order to transfer the decontamination agent contained therein into a compound which is difficult to dissolve or insoluble in water.
13. Process according to claim 2, characterized in that the spent decontamination solution is distilled until dry and the sump or bottoms product is pyrolysed.
EP86903176A 1985-05-28 1986-05-27 Process for decontaminating radioactively contaminated metalic or cement-containing materials Expired - Lifetime EP0224510B1 (en)

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