EP0180826B1 - Process for chemically decontaminating the metallic main components and systems of nuclear reactors - Google Patents

Process for chemically decontaminating the metallic main components and systems of nuclear reactors Download PDF

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Publication number
EP0180826B1
EP0180826B1 EP85113144A EP85113144A EP0180826B1 EP 0180826 B1 EP0180826 B1 EP 0180826B1 EP 85113144 A EP85113144 A EP 85113144A EP 85113144 A EP85113144 A EP 85113144A EP 0180826 B1 EP0180826 B1 EP 0180826B1
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Prior art keywords
ozone
process according
primary coolant
decontamination
systems
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EP85113144A
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German (de)
French (fr)
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EP0180826A1 (en
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Horst-Otto Bertholdt
Bernhard Dipl.-Ing. Kress (Fh)
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Siemens AG
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Siemens AG
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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
    • 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 chemical decontamination of large components and systems made of metallic materials of nuclear reactors with a liquid primary coolant.
  • a decontamination process known from DE-OS-26 13 351 is a multi-stage process in which oxidative treatments and acid treatments are carried out alternately at temperatures above 90 ° C.
  • the ongoing change of chemicals requires a relatively large amount of time, chemicals and energy.
  • a multi-stage process is also known from the older European patent application 84304726.7 with the publication number 0134 664, a process step of the multi-stage process being described in more detail.
  • the oxidation step explained in more detail is preceded by a decontamination step with organic acids.
  • a cerium IV compound is used only in the second process step.
  • WO-A-84/03 170 describes a multi-stage process which provides at least two process steps. First, an oxidation step makes corrosion products acid-soluble. This is followed by the addition of an acidic decontamination solution in an acid treatment step. Among other things, permanganate and chromic acid and ozone are used to carry out the process.
  • Multi-stage decontamination processes require that all the chemicals required for this have to be removed from the container to be decontaminated after each stage or after each process step. Only then can the second process step be initiated. A rinsing step is often necessary as an intermediate step to remove chemical residues.
  • Multi-stage processes require a lot of time and leave a lot of secondary waste.
  • the invention was based on the object of proposing a method for chemical decontamination with which decontamination can be carried out quickly, the decontamination effect is increased compared to the known method and, at the same time, the amount of secondary waste is reduced.
  • the treatment temperature should be less than or equal to 50 ° C.
  • the object is achieved according to the invention by a process for the chemical decontamination of large components and systems made of metallic materials of nuclear reactors with a liquid primary coolant, the treatment being carried out as a one-step treatment without an acid treatment step using an aqueous solution of oxidizing chemicals which are contaminated by the large components and Systems is moved, with nitrates, chromates or cerium IV salts and additionally ozone being added to the primary coolant, which contains borate in particular, as oxidizing chemicals.
  • the decontamination is carried out as a one-step treatment using an aqueous solution of oxidizing chemicals with the additional addition of ozone.
  • the oxidizing chemicals for example nitrates, chromates, cerium salts are inexpensive and lead to ions that can be easily removed with ion exchange resins.
  • the pH value is lowered during the decontamination by withdrawing the cations using an ion exchanger.
  • the concentration range of the oxidizing chemicals is preferably 100-1000 mg kg- 1 , of ozone 10-40 mg kg- '.
  • the effectiveness of the solution is monitored by measuring the red-ox potential.
  • the ozone content is maintained according to the further invention by means of an external ozone enrichment path.
  • continuous degassing advantageously prevents gas cushions from forming in the system to be decontaminated.
  • the ozone fed in comes from an ozone generator 8, which is supplied with oxygen from the tank 9. This is partly converted into ozone by means of silent electrical discharge.
  • the gas containing ozone is sucked into the enrichment section 5 by the injector 6. The mass transfer between gas and liquid takes place in the injector 6 and in the subsequent liquid column.
  • Excess oxygen present in the decontamination circuit and the non-absorbed ozone from the enrichment section 5 are released from their upper end via an aerosol separator 10 and, after heating in a heating device 11, via a catalytic ozone destruction system 12.
  • the cations formed during the decontamination and the dissolved activity are withdrawn via ion exchangers 13 in a second bypass with a pump 14.
  • the ion exchangers 13 are then disposed of using known measures, for example dried and solidified with bitumen.

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  • Engineering & Computer Science (AREA)
  • Food Science & Technology (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Treatment Of Water By Oxidation Or Reduction (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)
  • Apparatus For Disinfection Or Sterilisation (AREA)

Abstract

1. Process for the chemical decontamination of large components and systems of metallic materials of nuclear reactors with a liquid primary coolant, wherein the treatment is carried out as a one-step treatment without an acid treatment step by means of an aqueous solution of oxidising chemicals which is moved through the large components and systems to be contaminated, with nitrates, chromates or Cer-IV-salts and additionally ozone being introduced as oxidising chemicals into the primary coolant which contains in particular borate.

Description

Die Erfindung betrifft ein Verfahren zur chemischen Dekontamination von Großkomponenten und Systemen aus metallischen Werkstoffen von Kernreaktoren mit einem flüssigen Primärkühlmittel.The invention relates to a method for the chemical decontamination of large components and systems made of metallic materials of nuclear reactors with a liquid primary coolant.

Ein aus der DE-OS-26 13 351 bekanntes Dekontaminationsverfahren ist ein Mehrstufenverfahren, bei dem im Wechsel oxidative Behandlungen und Säurebehandlungen bei Temperaturen von über 90°C durchgeführt werden. Der laufende Chemikalienwechsel erfordert einen relativ hohen Aufwand an Zeit und Chemikalien sowie an Energie.A decontamination process known from DE-OS-26 13 351 is a multi-stage process in which oxidative treatments and acid treatments are carried out alternately at temperatures above 90 ° C. The ongoing change of chemicals requires a relatively large amount of time, chemicals and energy.

Aus der älteren europäischen Patentanmeldung 84304726.7 mit der Veröffentlichungsnummer 0134 664 ist auch ein Mehrstufenverfahren bekannt, wobei ein Verfahrensschritt des Mehrstufenverfahrens näher beschrieben wird. Dem näher erläuterten Oxidationsschritt geht ein Dekontaminationsschritt mit organischen Säuren voraus. Nur im zweiten Verfahrensschritt wird eine Cer-IV-Verbindung eingesetzt.A multi-stage process is also known from the older European patent application 84304726.7 with the publication number 0134 664, a process step of the multi-stage process being described in more detail. The oxidation step explained in more detail is preceded by a decontamination step with organic acids. A cerium IV compound is used only in the second process step.

Die WO-A-84/03 170 beschreibt ein Mehrstufenverfahren, das zumindest zwei Verfahrensschritte vorsieht. Zunächst werden durch einen Oxidationsschritt Korrosionsprodukte säurelöslich gemacht. Darauf folgt die Zugabe einer sauren Dekontaminationslösung in einem Säurebehandlungsschritt. Zur Durchführung des Verfahrens werden unter anderem Permanganat und Chromsäure sowie Ozon eingesetzt.WO-A-84/03 170 describes a multi-stage process which provides at least two process steps. First, an oxidation step makes corrosion products acid-soluble. This is followed by the addition of an acidic decontamination solution in an acid treatment step. Among other things, permanganate and chromic acid and ozone are used to carry out the process.

Mehrstufenverfahren zur Dekontamination erfordern, daß nach jeder Stufe oder nach jedem Verfahrensschritt alle dafür benötigten Chemikalien aus dem zu dekontaminierenden Behälter entfernt werden müssen. Erst danach kann der zweite Verfahrensschritt eingeleitet werden. Oft ist zum Entfernen von Chemikalienresten sogar als Zwischenschritt ein Spülschritt notwendig.Multi-stage decontamination processes require that all the chemicals required for this have to be removed from the container to be decontaminated after each stage or after each process step. Only then can the second process step be initiated. A rinsing step is often necessary as an intermediate step to remove chemical residues.

Mehrstufenverfahren erfordern einen hohen Zeitaufwand und hinterlassen sehr viel Sekundärabfall.Multi-stage processes require a lot of time and leave a lot of secondary waste.

Der Erfindung lag die Aufgabe zugrunde, ein Verfahren zur chemischen Dekontamination vorzuschlagen, mit dem eine Dekontamination schnell durchzuführen ist, die Dekontaminationswirkung gegenüber dem Bekannten erhöht ist und gleichzeitig der Anfall von Sekundärabfall vermindert ist. Die Behandlungstemperatur soll kleiner oder gleich 50°C sein.The invention was based on the object of proposing a method for chemical decontamination with which decontamination can be carried out quickly, the decontamination effect is increased compared to the known method and, at the same time, the amount of secondary waste is reduced. The treatment temperature should be less than or equal to 50 ° C.

Die Aufgabe wird gemäß der Erfindung durch ein Verfahren zur chemischen Dekontamination von Großkomponenten und Systemen aus metallischen Werkstoffen von Kernreaktoren mit einem flüssigen Primärkühlmittel gelöst, wobei die Behandlung als Einstufenbehandlung ohne Säurebehandlungsschritt mittels einer wäßrigen Lösung oxidierender Chemikalien durchgeführt wird, die durch die zu kontaminierenden Großkomponenten und Systeme bewegt wird, wobei als oxidierende Chemikalien Nitrate, Chromate oder Cer-IV-Salze und zusätzlich Ozon in das insbesondere borathaltige Primärkühlmittel eingegeben werden.The object is achieved according to the invention by a process for the chemical decontamination of large components and systems made of metallic materials of nuclear reactors with a liquid primary coolant, the treatment being carried out as a one-step treatment without an acid treatment step using an aqueous solution of oxidizing chemicals which are contaminated by the large components and Systems is moved, with nitrates, chromates or cerium IV salts and additionally ozone being added to the primary coolant, which contains borate in particular, as oxidizing chemicals.

Damit wird die Dekontamination als Einstufenbehandlung mittels einer wäßrigen Lösung oxidierender Chemikalien unter zusätzlicher Zugabe von Ozon durchgeführt. Die oxidierend wirkenden Chemikalien, zum Beispiel Nitrate, Chromate, Cer-Salze sind preiswert und führen zu lonen, die mit lonentauscherharzen gut entfernbar sind. Dabei wird während der Dekontamination durch Entzug der Kationen mittels Ionentauscher der pH-Wert abgesenkt. Der Konzentrationsbereich der oxidierenden Chemikalien liegt vorzugsweise bei 100-1000 mg kg-1, von Ozon bei 10-40 mg kg-'. Die Wirksamkeit der Lösung wird hierbei über die Messung des Red-Ox-Potentials verfolgt.The decontamination is carried out as a one-step treatment using an aqueous solution of oxidizing chemicals with the additional addition of ozone. The oxidizing chemicals, for example nitrates, chromates, cerium salts are inexpensive and lead to ions that can be easily removed with ion exchange resins. The pH value is lowered during the decontamination by withdrawing the cations using an ion exchanger. The concentration range of the oxidizing chemicals is preferably 100-1000 mg kg- 1 , of ozone 10-40 mg kg- '. The effectiveness of the solution is monitored by measuring the red-ox potential.

Tabelle 1 zeigt Ergebnisse der erfindungsgemäßen Einstufenbehandlung am Beispiel von original kontaminierten Proben aus einem Druckwasser-Kernkraftwerk.

Figure imgb0001

  • Werkstoff: 1.4024
Table 1 shows results of the one-step treatment according to the invention using the example of original contaminated samples from a pressurized water nuclear power plant.
Figure imgb0001
  • Material: 1.4024

Mit zunehmender Betriebsdauer nimmt die Säurelöslichkeit bei aktiven Oxid-Schutzschichten des Primärkreislaufs eines Druckwasserreaktors ab. Durch Variieren der Kombination von oxidativen Chemikalien und Ozon und durch selektiven Entzug von Kationen kann das Verfahren auf die jeweils vorliegende Oxidschutzschicht eingestellt werden. Das in der beiliegenden Zeichnung als Fig. 1 dargestellte Diagramm zeigt an Hand der NO-3-Parameter-Studie den Metallabtrag M.With increasing operating time, the acid solubility decreases with active oxide protective layers of the primary circuit of a pressurized water reactor. By varying the combination of oxidative chemicals and ozone and by selectively removing cations, the process can be adjusted to the respective oxide protective layer. The diagram shown in FIG. 1 in the accompanying drawing shows the metal removal M using the NO 3 parameter study.

Da in Wasser gelöstes Ozon in Kontakt mit oxidischen Oberflächenschichten nur eine begrenzte Halbwertszeit hat, wird gemäß der weiteren Erfindung mittels einer externen Ozonanreicherungsstrecke der Ozon-Gehalt aufrechterhalten. Gleichzeitig wird durch eine laufende Entgasung vorteilhafterweise verhindert, daß sich im zu dekontaminierenden System Gaspolster ausbilden.Since ozone dissolved in water has only a limited half-life in contact with oxidic surface layers, the ozone content is maintained according to the further invention by means of an external ozone enrichment path. At the same time, continuous degassing advantageously prevents gas cushions from forming in the system to be decontaminated.

Die Fig. 2 der beiliegenden Zeichnung zeigt in vereinfachter Form ein kontaminiertes System mit den dazugehörigen Hilfseinrichtungen zur Dekontamination nach dem erfindungsgemäßen Verfahren. Anhand dieses Ausführungsbeispiels wird das Verfahren näher erläutert:

  • Die Dekontaminationschemikalien werden aus dem Ansetzbehälter 1 mit einer Dosierpumpe 2 dem zu dekontaminierenden System 3, nämlich dem mit borathaltigem Primärkühlwasser gefüllten Primärkreis eines Druckwasserreaktors, auf der Saugseite einer Pumpe 4 zugeführt. Mit der Pumpe 4 wird ein aus dem zu dekontaminierendem System 3 abgezweigter Teilstrom über eine Ozon-Anreicherungsstrecke 5 mit einem Injektor 6 gefördert. Dieser Teilstrom über die Anreicherungsstrecke 5 beträgt 2:10% des während der Dekontamination umgewälzten Kühlwasser-Volumens. Zur Verbesserung der Stoffaustauschleistung in der Anreicherungsstrecke wird der Injektor 6 mit einer Druckerhöhungspumpe 7 betrieben.
2 of the accompanying drawing shows in simplified form a contaminated system with the associated auxiliary devices for decontamination using the method according to the invention. The method is explained in more detail using this exemplary embodiment:
  • The decontamination chemicals are fed from the preparation tank 1 with a metering pump 2 to the system 3 to be decontaminated, namely the primary circuit of a pressurized water reactor filled with borate-containing primary cooling water, on the suction side of a pump 4. With the pump 4, a partial flow branched off from the system 3 to be decontaminated is conveyed via an ozone enrichment path 5 with an injector 6. This partial flow over the enrichment section 5 is 2: 10% of the cooling water volume circulated during the decontamination. To improve the mass transfer performance in the enrichment section, the injector 6 is operated with a booster pump 7.

Das eingespeiste Ozon stammt aus einem Ozongenerator 8, der aus dem Tank 9 mit Sauerstoff versorgt wird. Dieser wird mittels stiller elektrischer Entladung zum Teil in Ozon umgewandelt. Das ozonhaltige Gas wird vom Injektor 6 in die Anreicherungsstrecke 5 gesaugt. Im Injektor 6 und in der anschließenden Flüssigkeitssäule erfolgt der Stoffaustausch zwischen Gas und Flüssigkeit.The ozone fed in comes from an ozone generator 8, which is supplied with oxygen from the tank 9. This is partly converted into ozone by means of silent electrical discharge. The gas containing ozone is sucked into the enrichment section 5 by the injector 6. The mass transfer between gas and liquid takes place in the injector 6 and in the subsequent liquid column.

In dem Dekontaminationskreislauf vorhandener überschüssiger Sauerstoff und das nicht absorbierte Ozon aus der Anreicherungsstrecke 5 gelangt aus deren oberem Ende über einen Aerosolabscheider 10 und nach Erwärmung in einer Heizeinrichtung 11 über eine katalytische Ozonvernichtungsanlage 12 ins Freie.Excess oxygen present in the decontamination circuit and the non-absorbed ozone from the enrichment section 5 are released from their upper end via an aerosol separator 10 and, after heating in a heating device 11, via a catalytic ozone destruction system 12.

Der Entzug der bei der Dekontamination gebildeten Kationen und der gelösten Aktivität erfolgt über Ionentauscher 13 in einem zweiten Bypass mit einer Pumpe 14. Die lonentauscher 13 werden dann mit bekannten Maßnahmen entsorgt, zum Beispiel getrocknet und mit Bitumen verfestigt.The cations formed during the decontamination and the dissolved activity are withdrawn via ion exchangers 13 in a second bypass with a pump 14. The ion exchangers 13 are then disposed of using known measures, for example dried and solidified with bitumen.

Claims (13)

1. Process for the chemical decontamination of large components and systems of metallic materials of nuclear reactors with a liquid primary coolant, wherein the treatment is carried out as a one-step treatment without an acid treatment step by means of an aqueous solution of oxidising chemicals which is moved through the large components and systems to be contaminated, with nitrates, chromates or Cer-IV-salts and additionally ozone being introduced as oxidising chemicals into the primary coolant which contains in particular borate.
2. Process according to claim 1, characterised in that ozone is used in a concentration range of from 10-40 mg kg-1.
3. Process according to claim 1 or 2, characterized in that ozone is continuously replenished into the primary coolant via an ozone enrichment section.
4. Process according to claim 3, characterised in that the ozone enrichment is effected by means of an injection, a bubble column or a bubble column-downstream reactor.
5. Process according to claim 4, characterised in that oxygen and ozone gas removal with subsequent ozone annihilation takes place in the flow direction upstream of the ozone enrichment area.
6. Method according to claim 5, characterised in that the ozone annihilation takes place catalytically.
7. Process according to one of claims 1 to 6, characterised in that the effectiveness of the decontamination solution is controlled by determining the redox potential.
8. Process according to one of claims 1 to 7, characterised in that the concentration of the dissolved ozone is continuously analytically monitored.
9. Process according to claim 8, characterised in that the continuous monitoring of a partial stream stripped out with air takes place photometrically.
10. Process according to one of claims 1 to 9, characterised in that the dissolved activity is removed continuously from the primary coolant by means of ion exchange.
11. Process according to claim 10, characterised in that the cations are removed from the oxidising chemicals during the decontamination.
12. Process according to one of claims 1 to 11, characterised in that the oxidising chemicals are used in a concentration range of from 100-1000 mg kg-'.
13. Process according to one of claims 1 to 12, characterised in that the primary coolant is kept at temperatures of 20 to 60°C during the treatment.
EP85113144A 1984-10-31 1985-10-16 Process for chemically decontaminating the metallic main components and systems of nuclear reactors Expired - Lifetime EP0180826B1 (en)

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DE3439857 1984-10-31

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ES (1) ES8700486A1 (en)

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EP0278256A1 (en) * 1987-01-28 1988-08-17 Siemens Aktiengesellschaft Method and apparatus for removing oxide layers
EP0355628B1 (en) * 1988-08-24 1993-11-10 Siemens Aktiengesellschaft Process for chemically decontaminating the surface of a metallic construction element of a nuclear power plant
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US5244000A (en) * 1991-11-13 1993-09-14 Hughes Aircraft Company Method and system for removing contaminants
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FR2701155B1 (en) * 1993-02-02 1995-04-21 Framatome Sa Method and installation for decontamination of used lids of light water nuclear reactor vessels.
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DE19818772C2 (en) * 1998-04-27 2000-05-31 Siemens Ag Process for reducing the radioactivity of a metal part
US6635232B1 (en) 1999-05-13 2003-10-21 Kabushiki Kaisha Toshiba Method of chemically decontaminating components of radioactive material handling facility and system for carrying out the same
JP3977963B2 (en) * 1999-09-09 2007-09-19 株式会社日立製作所 Chemical decontamination method
US6466636B1 (en) * 2000-07-26 2002-10-15 Westinghouse Electric Company Llc Decontamination method
JP3849925B2 (en) * 2000-12-21 2006-11-22 株式会社東芝 Chemical decontamination method
TW529041B (en) * 2000-12-21 2003-04-21 Toshiba Corp Chemical decontamination method and treatment method and apparatus of chemical decontamination solution
KR100724710B1 (en) * 2002-11-21 2007-06-04 가부시끼가이샤 도시바 System and method for chemical decontamination of radioactive material
JP2004191259A (en) * 2002-12-12 2004-07-08 Toshiba Corp Chemical decontamination method
JP3945780B2 (en) * 2004-07-22 2007-07-18 株式会社日立製作所 Radionuclide adhesion suppression method and film forming apparatus for nuclear plant components
JP6901947B2 (en) * 2017-09-29 2021-07-14 三菱重工業株式会社 Chemical decontamination method

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JPS61110100A (en) 1986-05-28
US4942594A (en) 1990-07-17
ES548371A0 (en) 1986-10-16
EP0180826A1 (en) 1986-05-14
DE3578635D1 (en) 1990-08-16

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