EP0418722B1 - Verfahren zur vollständigen Dekontaminierung radioaktiver metallischer Werkstoffe - Google Patents

Verfahren zur vollständigen Dekontaminierung radioaktiver metallischer Werkstoffe Download PDF

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Publication number
EP0418722B1
EP0418722B1 EP90117571A EP90117571A EP0418722B1 EP 0418722 B1 EP0418722 B1 EP 0418722B1 EP 90117571 A EP90117571 A EP 90117571A EP 90117571 A EP90117571 A EP 90117571A EP 0418722 B1 EP0418722 B1 EP 0418722B1
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EP
European Patent Office
Prior art keywords
tank
bath
water
washing
solution
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
Application number
EP90117571A
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English (en)
French (fr)
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EP0418722A1 (de
Inventor
Fiorenzo Bregani
Antonio Garofalo
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Enel SpA
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Enel SpA
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Publication date
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Publication of EP0418722A1 publication Critical patent/EP0418722A1/de
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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

Definitions

  • the prevent invention relates to a total decontamination process for radioactive metal material, in particular to radioactive metal material presenting big surfaces and recesses, like the tubes for the tube nests in the heat exchangers of a nuclear power station.
  • radioactive metal surfaces are decontaminated by means of chemical solutions, electrolytic processes, mechanical means, pressurized water jets and application of ultrasounds.
  • EP-A-0 106 595 that discloses a decontamination process comprising a step in which a radioactive metal material to be decontaminated is immersed into a water bath under continuous application of ultrasounds;
  • FR-A-2 590 716 that discloses a decontamination process comprising the further immersion of said contaminated material into a water solution of strong mineral acids, the control of the temperature of the bath and the application to said bath of ultrasounds at a defined frequency and power and
  • JP-A-1 233 398 a summary issued from the Patent Office of Japan, that discloses a three step process involving a first immersion in a decontamination liquid bath, a further pre-cleaning liquid bath and a final cleaning step with simultaneous application of ultrasounds.
  • the main drawback common to the prior art processes resides in an unsatisfactory effectiveness when said processes are applied to material presenting big surfaces and recesses, as it happens in said tubes particularly, so that there is always some residual radioactivity preventing from completing the decontamination, i.e. from achieving what is called in this technical field a "total decontamination" and, consequently, from reducing the waste amount to be delivered to said storages.
  • the length of above third step varies according to the strength of the acid bath and decreases as the material dissolves; preferably, a sequence of lifts and immersions is carried out; at the end of each immersion, the material is lifted from the bath in order to carry out a preliminary visual examination and the material presenting metallic gloss on its inner and outer surfaces is removed from the bath and delivered to radiometric checking.
  • the solution is considered exhaust as the iron concentration is higher than 30 g/l (the iron concentration may be determined, for instance, by a spectrophotometer).
  • this invented process is particularly suitable to decontaminate tubes of the tube nests of the heat exchangers in the nuclear power stations and more particularly tube nests of the feeding regenerators in boiling water power stations.
  • the paramount advantage of this invented process resides in that the radioactive material is decontaminated over those standards that are usually accepted for releasing non-inspected or non-conditioned material and in that the waste to be delivered to said storages, consisting in the residuals from the decontaminating solutions, are much reduced in amount.
  • a monorail 1 moves in the direction of arrow 2 a plurality of hung and conveniently spaced cages 3, each containing a set 4 of one hundred tubes each being one meter long and set in the cage vertically; each set of tubes 4 in its cage is dipped sequentially in the tanks 5, 6, 7 and 8 by hoists 9, as detailed below.
  • First tank 5 comprises an inner tank 5A and an outer tank 5B, both covered by a common cover 5C; inner tank 5A contains washing water for the tubes and in outer tank 5B is circulated a diathermic solution to keep at 55° C the temperature of the washing water in tank 5A.
  • Said solution is supplied from a suitable conventional first boiler, not shown in the figure, that gives it the required temperature; a pump, not shown in the figure, supplies the solution to the tank through inlet duct 10 and the solution comes back to said boiler through outlet duct 11.
  • Bottom exhaust means 12 allows to completely empty tank 5B, if necessary.
  • An assembly of ultrasound emitting piezoelectric transducers 13, of 20 kHz frequency, is applied to the outer of side and bottom walls of tank 5B, said transducers being of such specification and number as to maintain in the inner tank 5A an homogeneous power density of 25 Watt per liter (W/1).
  • the tank 5A inner sizes are 50 x 50 x 150 cm (150 cm height).
  • the tube set 4 is left in the washing water during a time period of 2 hours.
  • Second tank 6 recycles a steam of fresh water from an outer source through inlet and outlet ducts, not shown in the figure, to energetically wash the tubes of a set of tubes 4 dipped in said tank together with its cage 3, after removal from tank 5.
  • Tank 6 too comprises bottom exhaust means 14.
  • Third tank 7 comprises an inner tank 7A and an outer tank 7B; the inner tank contains a solution from 3,0% to 4,0% of HF (hydrofluoric acid) and from 5,0% to 6,0% of HNO3 (nitric acid) (% in volume), in water maintained at the temperature of 70° C by a diathermic solution which is supplied to tank 7B through inlet duct 15 and removed through outlet 16, similarly to the explanation referred to tank 5.
  • Tank 7A is covered by cover 17 provided with an opening connected with an intake tube 18 to remove acid vapours emitted from the solution in the tank.
  • Tank 7B is provided with a bottom exhaust means 21.
  • An assembly of ultrasound emitting piezoelectric transducers 20 is applied to the outer side and bottom walls of tank 7B, similarly to the description referred to tank 5.
  • the ratio between the total inner and outer surface of said tubes and the volume of said hydrofluoric acid and nitric acid solution in this second bath is 3 dm2/l as a maximum.
  • Fourth tank 8 is similar to tank 6 described above.
  • the decontaminated tubes are washed in running water energetically in said fourth tank 8 to release in the water the residual radioactive material particles detached from the tube outer and, in particular, inner surface.
  • This tank too is provided with a bottom exhaust means 22.
  • a cable 23 is associated with a hoist 9 supporting a cage 3 and a clamp 24 at the bottom of said cable holds said cage.
  • tanks and other parts which may be in contact with radioactive materials and with acid are made of suitable material.

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  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Food Science & Technology (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Cleaning By Liquid Or Steam (AREA)

Claims (4)

  1. Verfahren zur Totaldekontamination von radioaktivem metallischem Material, mit den Schritten:
    a) als erster Schritt das Waschen des Materials in einem ersten Wasserbad unter kontinuierlicher erster Ultraschallbestrahlung,
    b) als zweiter Schritt das Entfernen des Materials aus dem ersten Wasserbad und Waschen des Materials in frischem Wasser,
    c) als dritter Schritt das Waschen des Materials in einem zweiten Wasserbad, bestehend aus einer wässrigen Lösung von 3,0 % bis 4,0 % Fluorwasserstoffsäure und 5,0 % bis 6,0 % Salpetersäure bei einer kontrollierten Temperatur im Bereich vom 60°C bis 70°C und gleichzeitiges Aussetzen des Materials in der Lösung der Einwirkung einer kontinuierlichen zweiten Ultraschallbestrahlung mit kontrollierter Frequenz und Leistung und
    d) als vierter Schritt das Entfernen des Materials aus dem zweiten Bad und Waschen des Materials in Frischwasser.
  2. Verfahren nach Anspruch 1,
    dadurch gekennzeichnet, daß der Schritt a) während einer Zeitdauer von 50 - 70 Minuten angewendet wird, daß das erste Wasserbad bei einer Temperatur im Bereich von 50°C - 60°C gehalten wird und daß die erste und zweite Ultraschallbestrahlung eine Frequenz von 20 KHz bis 22 KHz und eine Leistungsdichte von mindestens 15 W/l haben.
  3. Verfahren nach Anspruch 1,
    dadurch gekennzeichnet, daß der Schritt c) während einer Zeitdauer von 75 - 120 Minuten angewendet wird.
  4. Verfahren nach Anspruch 1,
    dadurch gekennzeichnet, daß das Verhältnis zwischen der Gesamtoberfläche des Materials und dem Volumen der Lösung von Fluorwasserstoffsäure und Salpetersäure in dem zweiten Bad maximal 3 dm²/l beträgt.
EP90117571A 1989-09-21 1990-09-12 Verfahren zur vollständigen Dekontaminierung radioaktiver metallischer Werkstoffe Expired - Lifetime EP0418722B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT8921777A IT1232632B (it) 1989-09-21 1989-09-21 Processo di decontaminazione totale di materiali metallici radioattivi.
IT2177789 1989-09-21

Publications (2)

Publication Number Publication Date
EP0418722A1 EP0418722A1 (de) 1991-03-27
EP0418722B1 true EP0418722B1 (de) 1994-12-28

Family

ID=11186713

Family Applications (1)

Application Number Title Priority Date Filing Date
EP90117571A Expired - Lifetime EP0418722B1 (de) 1989-09-21 1990-09-12 Verfahren zur vollständigen Dekontaminierung radioaktiver metallischer Werkstoffe

Country Status (3)

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EP (1) EP0418722B1 (de)
DE (1) DE69015529D1 (de)
IT (1) IT1232632B (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102016208202A1 (de) * 2016-05-12 2017-11-16 Rwe Power Aktiengesellschaft Chemische Dekontamination von radioaktiven Metalloberflächen

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106158060A (zh) * 2016-08-23 2016-11-23 中国工程物理研究院核物理与化学研究所 一种去除放射性表面污染的超声电解自动去污系统

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3238886A1 (de) * 1982-10-21 1984-04-26 Brown Boveri Reaktor GmbH, 6800 Mannheim Verfahren und einrichtung zum entfernen von ablagerungen auf den oberflaechen der bauteile einer wassergekuehlten kernreaktoranlage
FR2586322B1 (fr) * 1985-08-14 1990-05-18 Framatome Sa Procede de nettoyage et de decontamination par ultrasons d'enceintes et dispositif correspondant
FR2590716B1 (fr) * 1985-11-26 1992-05-15 Electricite De France Procede de decontamination de parois de reacteurs nucleaires, en particulier des parois du circuit primaire des reacteurs nucleaires a circuit d'eau pressurisee

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102016208202A1 (de) * 2016-05-12 2017-11-16 Rwe Power Aktiengesellschaft Chemische Dekontamination von radioaktiven Metalloberflächen

Also Published As

Publication number Publication date
DE69015529D1 (de) 1995-02-09
EP0418722A1 (de) 1991-03-27
IT1232632B (it) 1992-02-28
IT8921777A0 (it) 1989-09-21

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