EP0073366B2 - Procédé pour décontaminer des surfaces d'acier et éliminer des déchets radioactifs - Google Patents

Procédé pour décontaminer des surfaces d'acier et éliminer des déchets radioactifs Download PDF

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Publication number
EP0073366B2
EP0073366B2 EP82107178A EP82107178A EP0073366B2 EP 0073366 B2 EP0073366 B2 EP 0073366B2 EP 82107178 A EP82107178 A EP 82107178A EP 82107178 A EP82107178 A EP 82107178A EP 0073366 B2 EP0073366 B2 EP 0073366B2
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EP
European Patent Office
Prior art keywords
iron
solution
process according
decontaminating
precipitation
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP82107178A
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German (de)
English (en)
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EP0073366A3 (en
EP0073366A2 (fr
EP0073366B1 (fr
Inventor
Jozef Hanulik
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Der Industrieorientierten Forschung An Den Schweizerischen Hochschulen und Weiteren Institutionen Gesell zur Forderung
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Der Industrieorientierten Forschung An Den Schweizerischen Hochschulen und Weiteren Institutionen Gesell zur Forderung
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Classifications

    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
    • G21F9/002—Decontamination of the surface of objects with chemical or electrochemical processes
    • G21F9/004—Decontamination of the surface of objects with chemical or electrochemical processes of metallic surfaces

Definitions

  • the invention relates to a method for the decontamination of steel surfaces, in particular in reactor cooling circuits, by removing the contaminated surface layer with an acidic aqueous decontamination solution and preparing the decontamination solution containing the detached radioactive substances for disposal.
  • Aqueous solutions of mineral acids have often been used to decontaminate reactor cooling circuits.
  • Mineral acids are aggressive substances for the metal of the cooling circuits, and it is therefore extremely difficult to let the acid concentration alone run the decontamination process in such a way that the contaminated surface layer is effectively removed in an acceptable time, but does not corrode the pure metal of the cooling circuit, because Corroded areas in the cooling system could lead to leaks, U. serious consequences must not arise.
  • Aqueous solutions of alkali metal permanganates, nitric acid, sodium persulfate, sodium bromate and preferably hydrogen peroxide are used here to oxidize the contaminated steel surface layer in the first process step.
  • aqueous solutions of mixtures of mineral acids, such as sulfuric acid and / or nitric acid, and complex-forming substances, such as oxalic acid, citric acid or formic acid are given, to which corrosion inhibitors, e.g. Iron (III) sulfate, iron (III) nitrate, nitric acid, phenylthiourea, or the like can be added.
  • corrosion inhibitors e.g. Iron (III) sulfate, iron (III) nitrate, nitric acid, phenylthiourea, or the like can be added.
  • the use of hydrogen peroxide in the first process stage has the particular advantage that it can easily be broken down into water and oxygen so that the subsequent rinsing with water can
  • the dissolved metallic components together with the radioactive substances are then precipitated from the used decontamination solution of the second process stage.
  • the sulfuric and oxalic acid contained in the decontamination solution can be neutralized with calcium hydroxide, so that calcium sulfates and calcium oxalates are formed, which contain a large proportion of the radioactive substances present and are separated from the liquid by filtration.
  • potassium permanganate can first be added to the used decontamination solution to decompose the oxalic acid and obtain manganese dioxide and manganese sulfates, which can then be obtained by adjusting a pH of about 10 with e.g. Calcium hydroxide can be precipitated.
  • the precipitate precipitates only a small, albeit large, portion of the radioactive substances, so that in both cases the filtrate is still contaminated and must be disposed of in a nuclear waste disposal facility.
  • Such two-stage decontamination processes can be carried out as a continuous process or as a batch process, a so-called batch process.
  • a so-called batch process apart from the large amount of time required, it is unsatisfactory that chemicals and water are required, and above all that liquid radioactive waste is obtained in addition to relatively large amounts of solid radioactive waste, which makes the disposal of used decontamination solutions difficult.
  • the decontamination of reactor cooling circuit runs is complex and comparatively expensive, in particular if corrosion of the pure metal surfaces is excluded for the desired safety.
  • the decontamination solution contains formic acid and / or acetic acid and a reducing agent containing formaldehyde and / or acetaldehyde.
  • these chemicals are not only very cheap but also relatively non-toxic, so that no special precautions are required when handling this decontamination solution.
  • Fe2 + ions dissolve.
  • the decontamination process according to the invention is accordingly a one-step process which ensures a saving in time and effort compared to a two-step process.
  • the reducing agent contained in the decontamination solution keeps the Fe 2+ stable in the solution.
  • the Liquid is then slightly greenish in color, but clearly transparent without clouding, and its composition can be monitored relatively easily during the treatment of the steel surface.
  • the separated solid precipitate then contains practically all radioactive substances from the decontamination solution, while the liquid has at most only an insignificant residual activity, which can be below the tolerance limit, and thus regenerates the liquid for reuse or simple chemical disposal by decomposing the dissolved substances in gaseous products and water, NaOH, possibly Na 2 C0 3 , can be supplied.
  • the chemical composition of the decontamination solution provided according to the invention makes it possible to precipitate the Fe 2+ ions in the form of iron compounds, the density of which corresponds approximately to the density of iron oxide or which can easily be converted into such iron compounds.
  • the radioactive waste obtained in a decontamination process is then approximately equal to the material removed from the contaminated surface and is therefore a minimum.
  • a reactor cooling circuit made of low-alloy or stainless steel can be decontaminated in a continuous process.
  • the size of the inner surface and the capacity of the cooling circuit are known.
  • an aqueous solution of formic acid and / or acetic acid and of at least one reducing agent containing formaldehyde and / or acetaldehyde is to be used as the decontamination solution.
  • radioactive substances are adsorbed in a layer made of a mixture of iron oxides, and the thickness and composition of the surface layer to be removed can be determined through previous sampling (EP-A-36541). Based on the data available or determined and the options available, such as in particular the time available for decontamination, heating or cooling devices, etc., the appropriate composition, the required amount and also the process flow for the decontamination solution the main features.
  • the oxides of the contaminated steel surface are dissolved directly and / or reductively and converted into soluble iron (11) formates and / or iron (11) acetates, which are caused by the decontamination solution, especially by the solution contained reducing agents are stabilized created reducing conditions and in particular an oxidation to noticeable iron (III) compounds does not take place.
  • Used decontamination solution is therefore slightly green in color, but clearly transparent and without clouding and at most contains solid particles of the oxide layer that occur during the solution process, which do not interfere with the decontamination itself or with the treatment of the used decontamination solution for disposal.
  • a decontamination solution according to the invention which generally leads to satisfactory results, needs e.g. contain only formic acid and formaldehyde, the liter of decontamination solution containing, for example, 7-22 ml formic acid and 12-36 ml formaldehyde.
  • decontamination solution according to the invention compared to known decontamination solutions is generally characterized by a low chemical consumption and low costs as well as a high absorption capacity for Iron.
  • the used decontamination solution emerging from the cooling circuit is monitored during the detachment process, the Fe 2 + , acid and aldehyde concentrations being continuously checked.
  • Such a check is analytically simple and permits reliable control of the entire decontamination process, which reliably rules out inadmissible corrosion of the pure metal surface.
  • the iron compounds contained in the decontamination solution emerging from the cooling circuit are precipitated, and the used and thus cleaned decontamination solution is used for reuse, i. H. regenerated for reintroduction into the cooling circuit.
  • the iron compounds are preferably precipitated electrolytically by passing the used decontamination solution through an electrolysis stage which contains an iron cathode and a graphite anode.
  • Another advantage of the decontamination method according to the invention is that the reactions when the contaminated surface layer is detached are irreversible and therefore no carryover of radioactive substances to surface areas that are not or no longer contaminated is to be expected.
  • the decontamination solution After removing the intended layer thickness, the decontamination solution is drained from the cooling circuit. In any case, after draining, any residues will remain in the cooling circuit.
  • the composition of the decontamination solution only those residues are present in the decontamination process according to the invention which, by simple heat treatment at 175-300 ° C., are thermal in iron oxide and in gaseous decomposition products, in particular CO, CO 2 and H 2 0, ie in the cooling circuit Decomposition products, are decomposed and do not have any harmful influence on the operation.
  • This thermal decomposition of the residues can be carried out by introducing hot air or hot water, but is generally not necessary since the cooling circuit warms up to the required temperature in a short time when it is started up again.
  • a cooling circuit which still has residual activities after decontamination can be rinsed in a conventional manner by ion exchange in a nuclear clean manner.
  • a flushing will only be necessary in exceptional cases, since residual activities can be easily excluded by means of a corresponding layer thickness to be removed.
  • the transporter for the removed radioactive substances is the iron itself which has gone into solution and not some other additional substance, so that if the iron precipitates out of the decontamination solution, practically all the activity will be contained in the precipitate and the separated liquid at best will only have permitted radioactivity.
  • the aim is that all radioactive substances contained in the used decontamination solution are adsorbed onto the smallest possible amount of precipitate, that the precipitate is easy to dispose of and that the separated liquid does not cause any environmental pollution.
  • any substances, such as S-compounds can be used for the disposal precipitation, provided that the precipitation results obtained are satisfactory in an economical manner.
  • the iron (III) hydroxide obtained can be separated from the liquid more easily than iron (II) hydroxide, for example by filtration, but more precipitant is required for precipitation than in the case of iron (II) hydroxide.
  • An advantage of this precipitation is that the separated precipitate corresponds in weight to the material removed during decontamination, i.e. practically no weight gain has taken place and that the precipitate can be easily disposed of by mixing with cement without further treatment, expediently producing products similar to ferrocement that ensure a particularly low amount of contaminated material to be disposed of.
  • Another advantage of this iron hydroxide precipitation is the decomposability of the sodium formate obtained.
  • the decontamination solution is expediently divided into several batches. The first batch is then, if necessary after treatment with hydrogen peroxide, the required small amount of precipitant, e.g. NaOH, and after separating the precipitate, the sodium formate obtained is oxidatively, electrolytically or pyrolytically decomposed as indicated above. The liquid product obtained is then used to precipitate the second batch of decontamination solution, etc.
  • the precipitation and liquid can be separated by simple filtration.
  • the used decontamination solution can contain flocculants, e.g. Polyacrylamide can be added, through which the precipitated particles are combined to form larger particles.
  • the precipitate from an earlier precipitation process is used as the preferred flocculant.
  • the separated liquid is either prepared for reuse as a decontamination solution or disposed of “chemically”.
  • formaldehyde in particular is oxidized to formic acid and the formic acid thus obtained is decomposed together with the existing formic acid by an oxidizing agent in H 2 0 and CO 2 and salts of formic acid are also disposed of.
  • the waste materials obtained in this way are the most environmentally friendly and do not cause any problems in disposal.
  • Any oxidizing agent can be used, the selection being based essentially only on economy, i. H. low costs, and care must be taken to ensure that the advantageous chemical disposal is not impaired by the oxidizing agent.
  • the decontamination method according to the invention can be carried out as a continuously running process with circulated decontamination solution as well as a batch process, the advantages achieved being the same.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Food Science & Technology (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Removal Of Specific Substances (AREA)

Claims (16)

1. Procédé pour la décontamination de surfaces d'acier, en particulier, dans des circuits de réfrigération de réacteurs, par enlèvement de la couche superficielle contaminée, avec une solution aqueuse acide de décontamination, de même que pour le traitement de la solution de décontamination usée contenant les matières radioaktives dissoutes, pour l'élimination, caractérisé en ce qu'on traite la surface d'acier contaminée avec une solution aqueuse servant de solution de décontamination et constituée d'acide formique et/ou d'acide acétique en vue de dissoudre les oxydes de fer et le fer, ainsi que d'au moins un agent reducteur contenant du formaldéhyde et/ou de l'acétaldéhyde en vue de stabiliser les ions Fe2+ présents dans la solution dont la composition est contrôlée au cours du traitement, tandis que, de la solution aqueuse usée de décontamination, on sépare, par précipitation, tout le fer dissous sous forme d'un ou plusieurs composées de fer, les matières radioactives étant adsorbées par le ou les composés de fer et le précipité contaminé étant acheminé à une étape d'élimination nucléaire, tandis que la solution exempte d'activité est régénérée pour être réutilisée ou est éliminée chimiquement.
2. Procédé suivant la revendication 1, caractérisé en ce que, pour le traitement de la surface d'acier contaminée, on fait circuler la solution aqueuse de décontamination en circuit, le fer dissous étant précipité hors de la solution usée de décontamination, tandis que la solution de décontamination est amenée à la composition prévue pour un nouveau processus de dissolution.
3. Procédé suivant la revendication 2, caractérisé en ce que, de la solution usée de décontamination, on précipité le fer dissous par électrolyse, les ions Fe2+ étant réduits en métal, de préférence, sur une cathode en fer.
4. Procédé suivant la revendication 1, caractérisé en ce que, après avoir enlevé la couche superficielle contaminée, on soumet la surface d'acier à un traitement thermique à une température de 175 à 300°C à laquelle les résidus sont décomposés thermiquement en oxyde de fer constituant une matière propre à la surface d'acier, ainsi qu'en produits de décomposition gazeux, en particulier, en CO, en CO2 et en H20.
5. Procédé suivant la revendication 1, caractérisé en ce que le fer dissous est précipité sous forme d'un sulfure hors de la solution usée de décontamination.
-6. Procédé suivant la revendication 1, caractérisé en ce que le fer dissous est précipité sous forme d'hydroxide de fer(II) hors de la solution usée de décontamination.
7. Procédé suivant la revendication 1, caractérisé en ce que, avant la précipitation du fer dans la solution usée de décontamination, on oxyde les composés de ferfll) dissous en composés de fer(III) par addition d'un agent oxydant, en particulier, le peroxyde d'hydrogène, tandis qu'on les précipite sous forme de composés de fer(III) insolubles dans l'eau.
8. Procédé suivant la revendication 6 ou 7, caractérisé en ce que, pour précipter l'hydroxyde de fer(II) ou des composés de fer(III) de la solution usée de décontamination, on ajoute un hydroxyde ou un carbonate d'un métal alcalin, en particulier, NaOH et, après séparé le précipité du liquide, on décomposé, par voie oxydante, le sel formiate et/ou le sel acétate d'un métal alcalin qui y est présent en un hydroxyde d'un métal alcalin, en un carbonate d'un métal alcalin, on oxydes de carbone et en eau.
9. Procédé suivant la revendication 8, caractérisé en ce que la précipitation de composés de fer hydrosolubles hors de la solution usée de décontamination est effectuée en charges discontinues tandis que, après précipitation d'une première charge de la solution de décontamination et après traitement par oxydation du liquide séparé, on utilise le liquide ainsi traité pour précipiter des composés de fer hors de la deuxième charge de la solution de décontamination et l'on répète le processus jusqu'à ce que tout le fer soit précipité hors de toute la solution de décontamination.
10. Procédé suivant une des revendications 5 à 9, caractérisé en ce qu'on sépare les composés de fer précipités par filtration du liquide.
11. Procédé suivant la revendication 10, caractérisé en ce que, avant la filtration de la solution usée de décontamination, on ajoute un agent de floculation.
12. Procédé suivant la revendication 11, caractérisé en ce que, comme agent de floculation, on ajoute, à la solution usée de décontamination, un précipité d'un processus de précipitation antérieur.
13. Procédé suivant la revendications 6 à 12, caractérisé en ce que les composés de fer précipités sont décomposés thermiquement et/ou catalytiquement en oxydes de fer contenant des matières radioactives, ainsi qu'en produits de décomposition gazeux exempts d'activité, en particulier, en CO, en C02 et en H20, tandis que les oxydes de fer sont acheminés à une étape d'élimination nucléaire.
14. Procédé suivant une des revendications 5 à 13, caractérisé en ce que les précipités contenant des matières radioactives sont soumis à une élimination nucléaire par mélange avec du ciment.
15. Procédé suivant la revendication 14, caractérisé en ce qu'on prépare un produit analogue au ferro- ciment en mélangement les précipités avec du ciment.
16. Procédé suivant la revendication 1, caractérisé en ce que, pour l'élimination chimique, on oxyde la solution exempte d'activité au moyen d'un agent oxydant et on la décompose en eau et, en particulier, en CO, en C02, en Na2CO3 et éventuellement en NaOH.
EP82107178A 1981-09-01 1982-08-09 Procédé pour décontaminer des surfaces d'acier et éliminer des déchets radioactifs Expired - Lifetime EP0073366B2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH5611/81A CH653466A5 (de) 1981-09-01 1981-09-01 Verfahren zur dekontamination von stahloberflaechen und entsorgung der radioaktiven stoffe.
CH5611/81 1981-09-01

Publications (4)

Publication Number Publication Date
EP0073366A2 EP0073366A2 (fr) 1983-03-09
EP0073366A3 EP0073366A3 (en) 1984-03-28
EP0073366B1 EP0073366B1 (fr) 1986-07-09
EP0073366B2 true EP0073366B2 (fr) 1990-07-11

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EP82107178A Expired - Lifetime EP0073366B2 (fr) 1981-09-01 1982-08-09 Procédé pour décontaminer des surfaces d'acier et éliminer des déchets radioactifs

Country Status (5)

Country Link
US (1) US4508641A (fr)
EP (1) EP0073366B2 (fr)
CA (1) CA1197445A (fr)
CH (1) CH653466A5 (fr)
DE (1) DE3271935D1 (fr)

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DE10238730A1 (de) * 2002-08-23 2004-03-04 Framatome Anp Gmbh Verfahren zur Reinigung des Dampferzeugers eines Druckwasserreaktors
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DE102004024722B4 (de) * 2004-05-19 2011-05-26 Enbw Kraftwerke Ag Kernkraftwerk Philippsburg Binden von radioaktivem Jod in einem Kernreaktor
JP3945780B2 (ja) * 2004-07-22 2007-07-18 株式会社日立製作所 原子力プラント構成部材の放射性核種の付着抑制方法および成膜装置
DE102005020630A1 (de) * 2005-05-03 2006-11-23 Süd-Chemie AG Herstellung von Cu/Zn/Al-Katalysatoren über den Formiatweg
JP4567542B2 (ja) * 2005-07-14 2010-10-20 日立Ｇｅニュークリア・エナジー株式会社 原子力プラント構成部材への放射性核種の付着抑制方法
DE102007038947A1 (de) * 2007-08-17 2009-02-26 Areva Np Gmbh Verfahren zur Dekontamination von mit Alphastrahlern kontaminierten Oberflächen von Nuklearanlagen
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CA1136398A (fr) * 1979-12-10 1982-11-30 William A. Seddon Reactifs de decontamination pour systemes radioactifs

Also Published As

Publication number Publication date
US4508641A (en) 1985-04-02
DE3271935D1 (en) 1986-08-14
EP0073366A3 (en) 1984-03-28
EP0073366A2 (fr) 1983-03-09
EP0073366B1 (fr) 1986-07-09
CA1197445A (fr) 1985-12-03
CH653466A5 (de) 1985-12-31

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