EP0681735B1 - Methods and equipments for decontaminating a radioactive surface with a coherentlight beam - Google Patents

Methods and equipments for decontaminating a radioactive surface with a coherentlight beam Download PDF

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Publication number
EP0681735B1
EP0681735B1 EP94905154A EP94905154A EP0681735B1 EP 0681735 B1 EP0681735 B1 EP 0681735B1 EP 94905154 A EP94905154 A EP 94905154A EP 94905154 A EP94905154 A EP 94905154A EP 0681735 B1 EP0681735 B1 EP 0681735B1
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EP
European Patent Office
Prior art keywords
liquid
decontaminated
coherent light
swept
radioactive
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EP94905154A
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German (de)
French (fr)
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EP0681735A1 (en
Inventor
Jean-Paul Gauchon
Philippe Bournot
Philippe Cité Burel - Bat. 13 à 24 CAMINAT
Arnaud Dupont
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique CEA
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/28—Treating solids
    • G21F9/30—Processing

Definitions

  • the invention relates mainly to a method for decontaminating a radioactive surface by scanning this surface by means of a focused coherent light beam.
  • the invention also relates to installations implementing this method.
  • the surface contamination of metal parts by radioactive elements is manifested by the presence of radioactive elements in the layer of metal oxide that forms on the surface of these parts.
  • the thickness of this contaminated surface layer is generally between 1 ⁇ m and 10 ⁇ m. The purpose of decontaminating these surfaces is therefore to eliminate the thin surface layer which covers the surface of the parts.
  • a first family of known methods consists in decontaminating the surface by attacking the surface layer deposited thereon by means of a chemical agent which can in particular be in the form of acids, bases, oxidizing gels, etc.
  • a chemical agent which can in particular be in the form of acids, bases, oxidizing gels, etc.
  • document FR-A-2 656 949 illustrates the use of an oxidizing gel.
  • Patent Abstract of Japan vol. 009, No. 176 (M-398), which corresponds to the document JP-A-60 046893, also relates to the treatment of a semiconductor substrate by a laser beam. So that the parts of the substrate detached by fusion do not come to glue on this substrate, the latter is placed in a liquid such as water, capable of rapidly cooling the molten parts of the substrate.
  • the subject of the invention is precisely a new method for decontaminating a radioactive surface by means of a focused coherent light beam, the original design of which enables it to practically eliminate the redeposition of radioactive aerosols which are formed when the beam of coherent light strikes the surface to be decontaminated, so as to considerably reduce the residual contamination of this surface.
  • this result is obtained by means of a method of decontamination of a radioactive surface, by scanning this surface by means of a beam of focused coherent light, in which the surface is scanned by the beam in the presence of a liquid over the entire surface to be decontaminated.
  • the liquid can be present on this surface, either in the form of a film which one makes trickle on the surface while carrying out the scanning of this surface by the bundle, or in the form of a volume of liquid filling a container whose inner surface constitutes the surface to be decontaminated. In the latter case, the container is filled before scanning the surface by the beam.
  • the liquid is recycled and filtered during the scanning of the surface to be decontaminated.
  • the liquid used can simply consist of water.
  • an aqueous solution loaded with chemical reagent will advantageously be used. Indeed, the effectiveness of the decontamination can be further improved by a judicious choice of this chemical reagent according to the nature of the metal in which the part is made of which it is desired to decontaminate the surface and the nature of the radioactive elements deposited on this area.
  • This chemical reagent can in particular be nitric acid, at a concentration of approximately 5 moles / l.
  • the wavelength of the coherent light beam used is preferably 248 nm, 308 nm, 532 nm or 1064 nm.
  • the invention also relates to different types of installations making it possible to implement the method defined above.
  • a decontamination installation comprising a coherent light source, as well as means for directing and focusing a beam of light coherent emitted by this source on the surface to be decontaminated, so as to allow scanning of this surface by the beam, characterized in that it further comprises means for causing a film of liquid to flow over the entire surface to be decontaminated when sweeping this surface.
  • the means for trickling a film of liquid onto the surface to be decontaminated advantageously comprise a spraying ramp running along the entire length of the upper edge of the surface, a retention tank placed below the lower edge of the surface. , and a recycling circuit connecting the retention tank to the spraying boom, this recycling circuit including pumping means and liquid filtering means.
  • a decontamination installation comprising a coherent light source, as well as means for directing and focusing a beam of coherent light emitted by this source on the surface to be decontaminated. , so as to allow this surface to be scanned by the beam, characterized in that it further comprises a circuit for recycling a liquid contained in the container during the scanning of the surface to be decontaminated, this recycling circuit including pumping means and liquid filtering means.
  • the means for directing and focusing the beam on the surface to be decontaminated advantageously carry at their end a box open towards this surface and the recycling circuit takes the liquid in this box and discharges it into the container.
  • the reference 10 designates the surface to be decontaminated.
  • this surface is a flat surface which is inclined relative to the horizontal, so as to have an upper edge 10a and a lower edge 10b.
  • This example should not be considered as limiting and it will be readily understood that an installation comparable to that which will be described could be used to decontaminate a surface of different shape and / or orientation.
  • the surface to be decontaminated can be oriented either in a direction inclined relative to the horizontal as illustrated in FIG. 1, or in a vertical direction.
  • the surface to be decontaminated can be flat, cylindrical or the like.
  • an installation comparable to that illustrated in FIG. 1 could be used to decontaminate the interior surface of piping with a vertical axis.
  • the decontamination installation illustrated diagrammatically in FIG. 1 firstly comprises a source 12 of coherent light, constituted for example by a YAG type pulsed laser, possibly equipped with a doubler.
  • the coherent light source 12 When activated, the coherent light source 12 emits a coherent light beam whose wavelength is preferably 248 nm, 308 nm, 532 nm or 1064 nm.
  • the coherent light source 12 is oriented so that the beam emitted by this source is directed vertically downward in a sealed telescopic tube 14 forming a waveguide.
  • the lower end of this tube 14 is extended by a 90 ° bend 16, in which the beam of coherent light is deflected by a mirror 18.
  • the horizontal branch of the bend 16 is closed at its end by a waterproof lens 20, at through which a focused coherent light beam 21 is directed towards the surface 10.
  • the sealed telescopic tube 14 can rotate around its axis as schematically illustrated by arrow F1 in FIG. 1.
  • the variation in its length, illustrated by arrow F2 makes it possible to vary the level of the beam of focused light coming out of the lens 20.
  • the two movements illustrated by the arrows F1 and F2 allow the coherent light beam coming out of the lens 20 to scan the entire surface 10 to be decontaminated.
  • these movements are controlled by motors slaved to a programmable control unit, so that the scanning of the surface can be carried out in an automated manner.
  • the decontamination installation illustrated in FIG. 1 further comprises means for making a film of liquid trickle over the surface 10 to be decontaminated, during the scanning of this surface by the beam of coherent light.
  • these means are generally designated by the reference 22. They comprise a spraying ramp 24 placed above the upper edge 10a of the surface 10 to be decontaminated and extending over the entire length of this edge .
  • This spray bar 24 is supplied with liquid by a recycling circuit 26.
  • the recycling circuit 26 communicates the spray bar 24 with the bottom of a retention tank 28 placed below the lower edge 10b of the surface 10 to be decontaminated.
  • a pump 30 placed in the circuit 26 allows the liquid 29 present in the retention tank 28 to be conveyed to the spraying boom 24.
  • the recycling circuit 26 also includes a filter 32 which retains the radioactive elements removed from the surface by the beam of coherent light, so that the liquid flowing on the surface 10 to be decontaminated from the spray boom 24 is free of radioactive elements.
  • the retention tank 28 contains a sufficient quantity of liquid 29 so that the surface 10 to be decontaminated is completely covered with a film of liquid when the pump is actuated.
  • the liquid used can be either pure water or an aqueous solution loaded with a chemical reagent such as nitric acid or a mixture of citric and oxalic acid.
  • the pump 30 is actuated so that a film of liquid 29 trickles over the entire surface 10. Consequently, the surface radioactive layer torn from the surface 10 by the action of the coherent light beam does not redeposit on this surface, but is entrained by the liquid 29 in the retention tank 28.
  • this liquid is taken up in the tank by the pump 30 to be returned to the spray boom 24, it is cleared by the filter 32 of the radioactive elements torn from the surface.
  • the film of liquid which continuously flows over the latter therefore has, throughout the duration of the scanning, a substantially uniform composition.
  • the installation shown is designed to decontaminate the interior surfaces 10 of a swimming pool 11 for discharging or storing nuclear fuel, that is to say, both the bottom and the vertical walls of this pool.
  • an installation comparable to that illustrated in this figure can be used to decontaminate the interior surfaces of a container. different shape and function, insofar as this container can be filled with a liquid making it possible to completely cover the interior surface to be decontaminated.
  • an installation comparable to the installation shown in FIG. 2 can be used to decontaminate the interior surfaces of a water box of a steam generator used to ensure heat transfer between water from the primary circuit and water from the secondary circuit in a pressurized water reactor.
  • the installation illustrated in FIG. 2 comprises a source 12 of coherent light constituted by a pulsed laser such as a YAG laser.
  • This source 12 sends downwards and in a vertical direction a beam of coherent light into a sealed telescopic tube 14 forming a waveguide.
  • a bend 16 at right angles is placed at the bottom of the telescopic tube 14, so as to return the beam in a horizontal direction towards the side walls of the pool, under the action of a mirror 18 placed in the bend 16.
  • L 'open end of the horizontal branch of the elbow 16 is provided with a sealed lens 20 which directs a beam of coherent light focused 21 towards the side wall of the pool.
  • the telescopic nature of the tube 14 (arrow F2), associated with a degree of freedom of rotation (arrow F1) of this tube around its axis, make it possible to scan the side walls of the pool.
  • this scanning is programmed and carried out automatically by motorization systems not illustrated in FIG. 2.
  • the two above-mentioned degrees of freedom can possibly be supplemented by one or more additional degrees of freedom, for example by placing the source 12 on a trolley capable of moving in a horizontal plane in two orthogonal directions parallel to the side walls of the pool.
  • the techniques for scanning the surfaces to be decontaminated are well known, so that no detailed description is made of them.
  • the coherent light beam delivered by the source 12 can also carry out the decontamination of the substantially horizontal bottom of the swimming pool, it is in particular possible to disassemble the elbow 16 and mount the waterproof lens 20 directly at the lower end of the vertical telescopic tube 14.
  • a sealed housing 36 is fixed at the end of the horizontal branch of the elbow 16, but the side facing the surface 10 during treatment is open.
  • the installation comprises a recycling circuit 26, one end of which is connected to the housing 36, so as to draw the liquid inside the latter.
  • This recycling circuit includes a pump 30 which recycles the liquid 29 in a filter 32, before discharging it directly into the pool 11.
  • Table A gives an estimate of the average ablation depths (in ⁇ m) per pulse, when laser beams with different wavelengths are made to act on AISI 304 steel in air and under water, respectively.
  • the pulse ablation depth is significantly greater under water runoff than in air, the gain provided by the process according to the invention being variable depending on the length d wave of the laser beam.
  • the ablation depth is only multiplied by a factor of about 3.5 in the ultraviolet, while it is multiplied by a factor of 16 in the near infrared.
  • Table B presents an estimate of the average pulse ablation depths when a laser beam of wavelength 308 nm and a laser beam of wavelength 1064 nm are made to act on the contaminated surface. , respectively in air and under water, of silica or alumina parts, representative of construction materials such as concrete, and / or ceramics.
  • each pulse is 30 ns at the wavelength 308 nm and 7 ns at the wavelength of 1064 nm, the firing frequency being in all cases 1 Hz.
  • Table C shows the results of comparative decontamination tests carried out on samples of oxidized Inconel 600, contaminated with Co 60 by causing a laser beam to act on samples having similar initial activities, respectively in the presence of ambient air with suction at a flow rate of 86 m 3 / h, in the presence of a film of water on the surface of the sample at a flow rate of 50 l / h and in the presence of a film of water added 5 moles / l of nitric acid at a flow rate of 50 l / h.
  • This table C notably shows very clearly the essential gain brought by the presence of a liquid film on the surface of the decontaminated part.
  • a comparable decontamination factor (21 or 22) can be obtained for an energy density deposited five times lower (100 J / cm 2 instead 500 J / cm 2 ), replacing the film of water with a film of water with added nitric acid.
  • Table D is a table comparable to Table C, in which the samples tested were samples of AISI 304 steel coated with oxide contaminated with Co 60. The characteristics of the laser beam were also identical to those of Table C.
  • Table D shows even more clearly than Table C the influence of the nature of the liquid which covers the surface decontaminated by the laser beam. Indeed, five different samples presenting similar initial activities were treated by a laser beam respectively in the presence of ambient air with a suction at a flow rate of 86m 3 / h, in the presence of a film of water at a flow rate of 50 l / h, in the presence of a film of water to which 1.5% of citric and oxalic acids ("CITROX”) were added at a flow rate of 50 l / h, in the presence of a film of water added with 0.5 mole / l of nitric acid at a flow rate of 50 l / h and in the presence of a film of water added with 5 moles / l of nitric acid at a flow rate of 50 l / h.
  • CITROX citric and oxalic acids
  • Table E illustrates test results comparable to those given in Tables C and D, in the case where surface decontamination of samples of AISI 304 steel contaminated with Cs137 is carried out.
  • the characteristics of the laser beam used are identical to those indicated in the context of the tests illustrated in Tables C and D.
  • Table E illustrates in particular that a comparable decontamination factor (approximately 50) can be obtained with an energy density deposited approximately seven times lower (15 J / cm 2 instead of 100 J / cm 2 ) by carrying out the abrasion in the presence of a film of water added with 5 moles / l of nitric acid, rather than in carrying out the abrasion in the presence of a simple film of water.

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  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
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Abstract

A radioactive surface (10) may be decontaminated by scanning it with a focused laser beam (21) in the presence of a liquid (29) such as water or preferably a nitric acid solution over the whole surface. The liquid (29) may particularly form a film trickling down the surface and is advantageously recirculated. Highly efficient decontamination is thus achieved.

Description

L'invention concerne principalement un procédé permettant de décontaminer une surface radioactive en effectuant un balayage de cette surface au moyen d'un faisceau de lumière cohérente focalisé. L'invention concerne également des installations mettant en oeuvre ce procédé.The invention relates mainly to a method for decontaminating a radioactive surface by scanning this surface by means of a focused coherent light beam. The invention also relates to installations implementing this method.

Dans l'industrie nucléaire, la contamination de la surface des pièces par des éléments radioactifs pose un problème constant. En effet, les rayonnements nocifs de ces éléments radioactifs compliquent l'intervention humaine sur ces pièces elles-mêmes et dans leur voisinage. Pour faciliter cette intervention, on procède donc le plus souvent à une décontamination préalable des surfaces des pièces métalliques contaminées.In the nuclear industry, contamination of the surface of parts with radioactive elements poses a constant problem. In fact, the harmful radiation from these radioactive elements complicates human intervention on these parts themselves and in their vicinity. To facilitate this intervention, we therefore most often proceed to a preliminary decontamination of the surfaces of the contaminated metal parts.

La contamination superficielle des pièces métalliques par des éléments radioactifs se manifeste par la présence d'éléments radioactifs dans la couche d'oxyde métallique qui se forme à la surface de ces pièces. L'épaisseur de cette couche superficielle contaminée est généralement comprise entre 1µm et 10µm. La décontamination de ces surfaces a donc pour objectif l'élimination de la fine couche superficielle qui recouvre la surface des pièces.The surface contamination of metal parts by radioactive elements is manifested by the presence of radioactive elements in the layer of metal oxide that forms on the surface of these parts. The thickness of this contaminated surface layer is generally between 1 μm and 10 μm. The purpose of decontaminating these surfaces is therefore to eliminate the thin surface layer which covers the surface of the parts.

Il existe déjà de nombreux procédés pour décontaminer des surfaces radioactives.There are already many methods for decontaminating radioactive surfaces.

Une première famille de procédés connue consiste à décontaminer la surface en attaquant la couche superficielle déposée sur celle-ci au moyen d'un agent chimique qui peut notamment se présenter sous la forme d'acides, de bases, de gels oxydants, etc. A titre d'exemple, le document FR-A-2 656 949 illustre l'utilisation d'un gel oxydant.A first family of known methods consists in decontaminating the surface by attacking the surface layer deposited thereon by means of a chemical agent which can in particular be in the form of acids, bases, oxidizing gels, etc. By way of example, document FR-A-2 656 949 illustrates the use of an oxidizing gel.

Il est également connu de décontaminer des surfaces radioactives par des techniques hydromécaniques. Parmi ces techniques, on citera à titre d'exemple, l'utilisation de jets d'eau ou de glaçons à haute pression, ainsi que l'utilisation des ultrasons qui se propagent jusqu'à la surface à décontaminer au travers d'un liquide.It is also known to decontaminate radioactive surfaces by hydromechanical techniques. Among these techniques, there may be mentioned by way of example, the use of water jets or high pressure ice cubes, as well as the use of ultrasound which propagates to the surface to be decontaminated through a liquid. .

Cependant, ces techniques chimiques et hydromécaniques nécessitent le plus souvent une manipulation préliminaire des pièces à traiter telle que leur démontage, leur mise au gabarit, etc. Comme l'illustre notamment le document EP-A-091 646, il a aussi été proposé de décontaminer une surface radioactive au moyen d'un faisceau de lumière cohérente que l'on focalise sur la surface. Cependant, l'interaction du faisceau de lumière cohérente avec une surface métallique conduit à des effets (photothermiques, photoablatifs, etc.) qui ne permettent qu'une décontamination partielle. En outre, les effets thermiques du faisceau de lumière cohérente créent une zone fondue sur la surface métallique ainsi que des aérosols radioactifs dont une partie se redépose et diffuse au sein de la zone fondue. Pour limiter la redéposition des aérosols radioactifs, on a coutume d'utiliser des moyens de soufflage et/ou d'aspiration d'air. Toutefois, la contamination résiduelle reste élevée.However, these chemical and hydromechanical techniques most often require a preliminary manipulation of the parts to be treated such as their disassembly, their layout, etc. As illustrated in particular in document EP-A-091 646, it has also been proposed to decontaminate a radioactive surface by means of a beam of coherent light which is focused on the surface. However, the interaction of the coherent light beam with a metallic surface leads to effects (photothermal, photoablatives, etc.) which only allow partial decontamination. In addition, the thermal effects of the coherent light beam create a molten zone on the metal surface as well as radioactive aerosols, part of which is redeposited and diffuses within the molten zone. To limit the redeposition of radioactive aerosols, it is customary to use blowing and / or air suction means. However, residual contamination remains high.

Dans l'industrie électronique, le document "Patent Abstract of Japan", vol 004, n° 129 (C-024), qui correspond au document JP-A-55 082 780, propose de placer un objet tel qu'un semi-conducteur dans une enceinte fermée, de faire circuler dans cette enceinte un gaz ou un liquide halogène apte à transmettre la lumière et à provoquer une décomposition thermique au-delà d'un certain seuil de température, et à procéder au nettoyage, puis à la décomposition thermique de la surface de l'objet en la bombardant à l'aide d'un faisceau laser.In the electronics industry, the document "Patent Abstract of Japan", vol 004, n ° 129 (C-024), which corresponds to the document JP-A-55 082 780, proposes to place an object such as a semi conductor in a closed enclosure, to circulate in this enclosure a halogen gas or liquid capable of transmitting light and causing thermal decomposition beyond a certain temperature threshold, and to carry out cleaning, then decomposition the surface of the object by bombarding it with a laser beam.

Le document "Patent Abstract of Japan", vol. 009, n° 176 (M-398), qui correspond au document JP-A-60 046893, concerne également le traitement d'un substrat semi-conducteur par un faisceau laser. Afin que les parties du substrat détachées par fusion ne viennent pas se recoller sur ce substrat, celui-ci est placé dans un liquide tel que de l'eau, apte à refroidir rapidement les parties fondues du substrat.The document "Patent Abstract of Japan", vol. 009, No. 176 (M-398), which corresponds to the document JP-A-60 046893, also relates to the treatment of a semiconductor substrate by a laser beam. So that the parts of the substrate detached by fusion do not come to glue on this substrate, the latter is placed in a liquid such as water, capable of rapidly cooling the molten parts of the substrate.

L'article "Liquid Film Enhanced Laser Cleaning" de W. Zapka et al., dans la revue "Microelectronic Engineering" vol. 17, 1992, pages 473-477, décrit également une technique de nettoyage d'un substrat semiconducteur, à l'aide d'un laser pulsé. L'installation comprend une buse permettant d'envoyer de l'eau sur la zone d'impact du faisceau laser.The article "Liquid Film Enhanced Laser Cleaning" by W. Zapka et al., In the journal "Microelectronic Engineering" vol. 17, 1992, pages 473-477, also describes a technique for cleaning a semiconductor substrate, using a pulsed laser. The installation includes a nozzle for sending water to the impact area of the laser beam.

L'invention a précisément pour objet un nouveau procédé de décontamination d'une surface radioactive au moyen d'un faisceau de lumière cohérente focalisé, dont la conception originale lui permet de faire pratiquement disparaître la redéposition des aérosols radioactifs qui se forment lorsque le faisceau de lumière cohérente frappe la surface à décontaminer, de façon à réduire considérablement la contamination résiduelle de cette surface.The subject of the invention is precisely a new method for decontaminating a radioactive surface by means of a focused coherent light beam, the original design of which enables it to practically eliminate the redeposition of radioactive aerosols which are formed when the beam of coherent light strikes the surface to be decontaminated, so as to considerably reduce the residual contamination of this surface.

Selon l'invention, ce résultat est obtenu au moyen d'un procédé de décontamination d'une surface radioactive, par balayage de cette surface au moyen d'un faisceau de lumière cohérente focalisée, dans lequel on procède au balayage de la surface par le faisceau en présence d'un liquide sur toute la surface à décontaminer.According to the invention, this result is obtained by means of a method of decontamination of a radioactive surface, by scanning this surface by means of a beam of focused coherent light, in which the surface is scanned by the beam in the presence of a liquid over the entire surface to be decontaminated.

En effet, on a découvert que la présence d'un liquide sur la surface soumise à l'action du faisceau de lumière cohérente atténue l'effet thermique et fait pratiquement disparaître le phénomène de redéposition des aérosols radioactifs produits par l'action du faisceau sur la surface. La contamination résiduelle est donc extrêmement réduite, ce qui n'était pas le cas lorsqu'on utilisait simplement un faisceau de lumière cohérente associé à des moyens de soufflage et/ou d'aspiration d'air.Indeed, it has been discovered that the presence of a liquid on the surface subjected to the action of the coherent light beam attenuates the thermal effect and virtually eliminates the phenomenon of redeposition of radioactive aerosols produced by the action of the beam on the surface. Residual contamination is therefore extremely reduced, which was not the case when simply using a coherent light beam associated with blowing and / or air suction means.

Selon les caractéristiques propres à la surface que l'on désire décontaminer, le liquide peut être présent sur cette surface, soit sous la forme d'un film que l'on fait ruisseler sur la surface tout en procédant au balayage de cette surface par le faisceau, soit sous la forme d'un volume de liquide remplissant un récipient dont la surface intérieure constitue la surface à décontaminer. Dans ce dernier cas, le remplissage du récipient est effectué avant que l'on procède au balayage de la surface par le faisceau.According to the characteristics specific to the surface which one wishes to decontaminate, the liquid can be present on this surface, either in the form of a film which one makes trickle on the surface while carrying out the scanning of this surface by the bundle, or in the form of a volume of liquid filling a container whose inner surface constitutes the surface to be decontaminated. In the latter case, the the container is filled before scanning the surface by the beam.

Dans une mise en oeuvre préférentielle du procédé conforme à l'invention, on procède au recyclage et au filtrage du liquide lors du balayage de la surface à décontaminer.In a preferred implementation of the method according to the invention, the liquid is recycled and filtered during the scanning of the surface to be decontaminated.

Le liquide utilisé peut être simplement constitué par de l'eau. Cependant, on utilisera avantageusement une solution aqueuse chargée en réactif chimique. En effet, l'efficacité de la décontamination peut encore être améliorée par un choix judicieux de ce réactif chimique en fonction de la nature du métal dans lequel est réalisée la pièce dont on désire décontaminer la surface et de la nature des éléments radioactifs déposés sur cette surface. Ce réactif chimique peut notamment être de l'acide nitrique, à une concentration d'environ 5 moles/l.The liquid used can simply consist of water. However, an aqueous solution loaded with chemical reagent will advantageously be used. Indeed, the effectiveness of the decontamination can be further improved by a judicious choice of this chemical reagent according to the nature of the metal in which the part is made of which it is desired to decontaminate the surface and the nature of the radioactive elements deposited on this area. This chemical reagent can in particular be nitric acid, at a concentration of approximately 5 moles / l.

Par ailleurs, la longueur d'onde du faisceau de lumière cohérente utilisée est de préférence de 248 nm, 308 nm, 532 nm ou 1064 nm.Furthermore, the wavelength of the coherent light beam used is preferably 248 nm, 308 nm, 532 nm or 1064 nm.

L'invention a aussi pour objet différents types d'installations permettant de mettre en oeuvre le procédé défini précédemment.The invention also relates to different types of installations making it possible to implement the method defined above.

Ainsi, lorsque la surface à décontaminer n'est pas une surface horizontale et comporte un bord supérieur et un bord inférieur, il est proposé une installation de décontamination comprenant une source de lumière cohérente, ainsi que des moyens pour diriger et focaliser un faisceau de lumière cohérente émis par cette source sur la surface à décontaminer, de façon à permettre un balayage de cette surface par le faisceau, caractérisée par le fait qu'elle comprend de plus des moyens pour faire ruisseler un film de liquide sur toute la surface à décontaminer, lors du balayage de cette surface.Thus, when the surface to be decontaminated is not a horizontal surface and has an upper edge and a lower edge, a decontamination installation is proposed comprising a coherent light source, as well as means for directing and focusing a beam of light coherent emitted by this source on the surface to be decontaminated, so as to allow scanning of this surface by the beam, characterized in that it further comprises means for causing a film of liquid to flow over the entire surface to be decontaminated when sweeping this surface.

Dans ce cas, les moyens pour faire ruisseler un film de liquide sur la surface à décontaminer comprennent avantageusement une rampe d'aspersion cheminant sur toute la longueur du bord supérieur de la surface, un bac de rétention placé en dessous du bord inférieur de la surface, et un circuit de recyclage reliant le bac de rétention à la rampe d'aspersion, ce circuit de recyclage incluant des moyens de pompage et des moyens de filtrage du liquide.In this case, the means for trickling a film of liquid onto the surface to be decontaminated advantageously comprise a spraying ramp running along the entire length of the upper edge of the surface, a retention tank placed below the lower edge of the surface. , and a recycling circuit connecting the retention tank to the spraying boom, this recycling circuit including pumping means and liquid filtering means.

Lorsque la surface à décontaminer forme une surface intérieure d'un récipient, il est proposé une installation de décontamination comprenant une source de lumière cohérente, ainsi que des moyens pour diriger et focaliser un faisceau de lumière cohérente émis par cette source sur la surface à décontaminer, de façon à permettre un balayage de cette surface par le faisceau, caractérisé par le fait qu'elle comprend de plus un circuit de recyclage d'un liquide contenu dans le récipient lors du balayage de la surface à décontaminer, ce circuit de recyclage incluant des moyens de pompage et des moyens de filtrage du liquide.When the surface to be decontaminated forms an interior surface of a container, a decontamination installation is proposed comprising a coherent light source, as well as means for directing and focusing a beam of coherent light emitted by this source on the surface to be decontaminated. , so as to allow this surface to be scanned by the beam, characterized in that it further comprises a circuit for recycling a liquid contained in the container during the scanning of the surface to be decontaminated, this recycling circuit including pumping means and liquid filtering means.

Dans ce cas, les moyens pour diriger et focaliser le faisceau sur la surface à décontaminer portent avantageusement à leur extrémité un boîtier ouvert vers cette surface et le circuit de recyclage prélève le liquide dans ce boîtier et le rejette dans le récipient.In this case, the means for directing and focusing the beam on the surface to be decontaminated advantageously carry at their end a box open towards this surface and the recycling circuit takes the liquid in this box and discharges it into the container.

On décrira à présent, à titre d'exemples non limitatifs, deux installations de décontamination mettant en oeuvre le procédé conforme à l'invention, en se référant aux dessins annexés, dans lesquels :

  • la figure 1 représente schématiquement une installation permettant de décontaminer une surface plane inclinée au moyen d'un faisceau de lumière cohérente focalisé sur cette surface, tout en faisant ruisseler un film de liquide sur la totalité de la surface à décontaminer ; et
  • la figure 2 représente schématiquement une installation permettant de décontaminer la surface intérieure d'une piscine remplie de liquide, au moyen d'un faisceau de lumière cohérente.
There will now be described, by way of nonlimiting examples, two decontamination installations implementing the method according to the invention, with reference to the accompanying drawings, in which:
  • FIG. 1 schematically represents an installation making it possible to decontaminate a flat inclined surface by means of a beam of coherent light focused on this surface, while causing a film of liquid to trickle over the entire surface to be decontaminated; and
  • FIG. 2 schematically represents an installation making it possible to decontaminate the interior surface of a swimming pool filled with liquid, by means of a beam of coherent light.

Sur la figure 1, la référence 10 désigne la surface à décontaminer. Dans l'exemple représenté, cette surface est une surface plane qui est inclinée par rapport à l'horizontale, de façon à présenter un bord supérieur 10a et un bord inférieur 10b. Cet exemple ne doit pas être considéré comme limitatif et on comprendra aisément qu'une installation comparable à celle qui va être décrite pourrait être utilisée pour décontaminer une surface de forme et/ou d'orientation différentes. En effet, la surface à décontaminer peut être orientée soit selon une direction inclinée par rapport à l'horizontale comme cela est illustré sur la figure 1, soit selon une direction verticale. De même, la surface à décontaminer peut être plane, cylindrique ou autre. Ainsi, une installation comparable à celle qui est illustrée sur la figure 1 pourrait être utilisée pour décontaminer la surface intérieure d'une tuyauterie d'axe vertical.In FIG. 1, the reference 10 designates the surface to be decontaminated. In the example shown, this surface is a flat surface which is inclined relative to the horizontal, so as to have an upper edge 10a and a lower edge 10b. This example should not be considered as limiting and it will be readily understood that an installation comparable to that which will be described could be used to decontaminate a surface of different shape and / or orientation. Indeed, the surface to be decontaminated can be oriented either in a direction inclined relative to the horizontal as illustrated in FIG. 1, or in a vertical direction. Likewise, the surface to be decontaminated can be flat, cylindrical or the like. Thus, an installation comparable to that illustrated in FIG. 1 could be used to decontaminate the interior surface of piping with a vertical axis.

L'installation de décontamination illustrée schématiquement sur la figure 1 comprend tout d'abord une source 12 de lumière cohérente, constituée par exemple par un laser impulsionnel de type YAG, éventuellement équipé d'un doubleur. Lorsqu'elle est actionnée, la source 12 de lumière cohérente émet un faisceau de lumière cohérente dont la longueur d'onde est, de préférence, de 248 nm, 308 nm, 532 nm ou 1064 nm.The decontamination installation illustrated diagrammatically in FIG. 1 firstly comprises a source 12 of coherent light, constituted for example by a YAG type pulsed laser, possibly equipped with a doubler. When activated, the coherent light source 12 emits a coherent light beam whose wavelength is preferably 248 nm, 308 nm, 532 nm or 1064 nm.

La source 12 de lumière cohérente est orientée de telle sorte que le faisceau émis par cette source soit dirigé verticalement vers le bas dans un tube télescopique étanche 14 formant guide d'onde. L'extrémité inférieure de ce tube 14 est prolongée par un coude 16 à 90°, dans lequel le faisceau de lumière cohérente est dévié par un miroir 18. La branche horizontale du coude 16 est fermée à son extrémité par une lentille étanche 20, au travers de laquelle un faisceau de lumière cohérente focalisé 21 est dirigé vers la surface 10.The coherent light source 12 is oriented so that the beam emitted by this source is directed vertically downward in a sealed telescopic tube 14 forming a waveguide. The lower end of this tube 14 is extended by a 90 ° bend 16, in which the beam of coherent light is deflected by a mirror 18. The horizontal branch of the bend 16 is closed at its end by a waterproof lens 20, at through which a focused coherent light beam 21 is directed towards the surface 10.

Le tube télescopique étanche 14 peut tourner autour de son axe comme l'illustre schématiquement la flèche F1 sur la figure 1. La variation de sa longueur, illustrée par la flèche F2, permet, quant à elle, de faire varier le niveau du faisceau de lumière focalisé sortant de la lentille 20. Les deux mouvements illustrés par les flèches F1 et F2 permettent au faisceau de lumière cohérente sortant de la lentille 20 de balayer la totalité de la surface 10 à décontaminer. Avantageusement, ces mouvements sont commandés par des moteurs asservis à une unité de commande programmable, de telle sorte que le balayage de la surface puisse être effectué d'une manière automatisée.The sealed telescopic tube 14 can rotate around its axis as schematically illustrated by arrow F1 in FIG. 1. The variation in its length, illustrated by arrow F2, makes it possible to vary the level of the beam of focused light coming out of the lens 20. The two movements illustrated by the arrows F1 and F2 allow the coherent light beam coming out of the lens 20 to scan the entire surface 10 to be decontaminated. Advantageously, these movements are controlled by motors slaved to a programmable control unit, so that the scanning of the surface can be carried out in an automated manner.

Les différents moyens pour réaliser le balayage de la surface à décontaminer à l'aide d'un faisceau de lumière cohérente dépendent de la forme et de l'orientation de cette surface et pourraient être différents de ceux qui viennent d'être décrits brièvement. Dans tous les cas, ces moyens appartiennent à une technologie bien connue qui ne sera pas décrite en détail.The various means for carrying out the scanning of the surface to be decontaminated using a coherent light beam depend on the shape and the orientation of this surface and could be different from those which have just been described briefly. In all cases, these means belong to a well-known technology which will not be described in detail.

L'installation de décontamination illustrée sur la figure 1 comprend de plus des moyens pour faire ruisseler un film de liquide sur la surface 10 à décontaminer, lors du balayage de cette surface par le faisceau de lumière cohérente.The decontamination installation illustrated in FIG. 1 further comprises means for making a film of liquid trickle over the surface 10 to be decontaminated, during the scanning of this surface by the beam of coherent light.

Sur la figure 1, ces moyens sont désignés de façon générale par la référence 22. Ils comprennent une rampe d'aspersion 24 placée au-dessus du bord supérieur 10a de la surface 10 à décontaminer et s'étendant sur toute la longueur de ce bord. Cette rampe d'aspersion 24 est alimentée en liquide par un circuit de recyclage 26.In FIG. 1, these means are generally designated by the reference 22. They comprise a spraying ramp 24 placed above the upper edge 10a of the surface 10 to be decontaminated and extending over the entire length of this edge . This spray bar 24 is supplied with liquid by a recycling circuit 26.

De façon plus précise, le circuit de recyclage 26 fait communiquer la rampe d'aspersion 24 avec le fond d'un bac de rétention 28 placé en dessous du bord inférieur 10b de la surface 10 à décontaminer. Une pompe 30 placée dans le circuit 26 permet d'acheminer le liquide 29 présent dans le bac de rétention 28 jusqu'à la rampe d'aspersion 24. Le circuit de recyclage 26 comporte également un filtre 32 qui retient les éléments radioactifs décollés de la surface par le faisceau de lumière cohérente, de telle sorte que le liquide qui ruisselle sur la surface 10 à décontaminer depuis la rampe d'aspersion 24 soit dépourvu d'éléments radioactifs.More specifically, the recycling circuit 26 communicates the spray bar 24 with the bottom of a retention tank 28 placed below the lower edge 10b of the surface 10 to be decontaminated. A pump 30 placed in the circuit 26 allows the liquid 29 present in the retention tank 28 to be conveyed to the spraying boom 24. The recycling circuit 26 also includes a filter 32 which retains the radioactive elements removed from the surface by the beam of coherent light, so that the liquid flowing on the surface 10 to be decontaminated from the spray boom 24 is free of radioactive elements.

Il est à noter qu'avant la mise en route de la pompe 30, le bac de rétention 28 contient une quantité de liquide 29 suffisante pour que la surface 10 à décontaminer soit recouverte en totalité d'un film de liquide lorsque la pompe est actionnée. Comme on le verra plus en détail par la suite, le liquide utilisé peut être soit de l'eau pure, soit une solution aqueuse chargée d'un réactif chimique tel que de l'acide nitrique ou un mélange d'acide citrique et oxalique.It should be noted that before the pump 30 is started, the retention tank 28 contains a sufficient quantity of liquid 29 so that the surface 10 to be decontaminated is completely covered with a film of liquid when the pump is actuated. . As will be seen in more detail below, the liquid used can be either pure water or an aqueous solution loaded with a chemical reagent such as nitric acid or a mixture of citric and oxalic acid.

Pendant toute la durée du balayage de la surface 10 à décontaminer par le faisceau de lumière cohérente en provenance de la source 12, la pompe 30 est actionnée de telle sorte qu'un film de liquide 29 ruisselle sur toute la surface 10. Par conséquent, la couche radioactive superficielle arrachée de la surface 10 par l'action du faisceau de lumière cohérente ne se redépose pas sur cette surface, mais se trouve entraînée par le liquide 29 dans le bac de rétention 28. Lorsque ce liquide est repris dans le bac par la pompe 30 pour être renvoyé vers la rampe d'aspersion 24, il est débarrassé par le filtre 32 des éléments radioactifs arrachés à la surface. Le film de liquide qui ruisselle en permanence sur cette dernière présente donc pendant toute la durée du balayage une composition sensiblement uniforme.Throughout the duration of the scanning of the surface 10 to be decontaminated by the beam of coherent light coming from the source 12, the pump 30 is actuated so that a film of liquid 29 trickles over the entire surface 10. Consequently, the surface radioactive layer torn from the surface 10 by the action of the coherent light beam does not redeposit on this surface, but is entrained by the liquid 29 in the retention tank 28. When this liquid is taken up in the tank by the pump 30 to be returned to the spray boom 24, it is cleared by the filter 32 of the radioactive elements torn from the surface. The film of liquid which continuously flows over the latter therefore has, throughout the duration of the scanning, a substantially uniform composition.

On décrira à présent en se référant à la figure 2 une autre installation de décontamination mettant en oeuvre le procédé conforme à l'invention.Another decontamination installation implementing the method according to the invention will now be described with reference to FIG. 2.

Pour faciliter la compréhension, les éléments de l'installation de la figure 2, comparables aux éléments de l'installation de la figure 1 sont désignés par les mêmes chiffres de référence.To facilitate understanding, the elements of the installation of FIG. 2, comparable to the elements of the installation of FIG. 1, are designated by the same reference numbers.

Dans l'exemple de réalisation de la figure 2, l'installation représentée est conçue pour décontaminer les surfaces intérieures 10 d'une piscine 11 de déchargement ou de stockage de combustible nucléaire, c'est-à-dire, aussi bien le fond que les parois verticales de cette piscine. Il est à noter cependant qu'une installation comparable à celle qui est illustrée sur cette figure peut être utilisée pour décontaminer les surfaces intérieures d'un récipient de forme et de fonction différentes, dans la mesure où ce récipient peut être rempli d'un liquide permettant de recouvrir en totalité la surface intérieure à décontaminer. Ainsi, et uniquement à titre d'exemple, une installation comparable à l'installation représentée sur la figure 2, peut être utilisée pour décontaminer les surfaces intérieures d'une boîte à eau d'un générateur de vapeur servant à assurer le transfert thermique entre l'eau du circuit primaire et l'eau du circuit secondaire dans un réacteur à eau pressurisée.In the embodiment of FIG. 2, the installation shown is designed to decontaminate the interior surfaces 10 of a swimming pool 11 for discharging or storing nuclear fuel, that is to say, both the bottom and the vertical walls of this pool. It should be noted, however, that an installation comparable to that illustrated in this figure can be used to decontaminate the interior surfaces of a container. different shape and function, insofar as this container can be filled with a liquid making it possible to completely cover the interior surface to be decontaminated. Thus, and only by way of example, an installation comparable to the installation shown in FIG. 2, can be used to decontaminate the interior surfaces of a water box of a steam generator used to ensure heat transfer between water from the primary circuit and water from the secondary circuit in a pressurized water reactor.

Comme dans l'installation de la figure 1, l'installation illustrée sur la figure 2 comprend une source 12 de lumière cohérente constituée par un laser impulsionnel tel qu'un laser YAG. Cette source 12 envoie vers le bas et selon une direction verticale un faisceau de lumière cohérente dans un tube télescopique étanche 14 formant guide d'onde. Un coude 16 à angle droit est placé dans le bas du tube télescopique 14, de façon à renvoyer le faisceau selon une direction horizontale vers les parois latérales de la piscine, sous l'action d'un miroir 18 placé dans le coude 16. L'extrémité ouverte de la branche horizontale du coude 16 est munie d'une lentille étanche 20 qui dirige un faisceau de lumière cohérente focalisé 21 vers la paroi latérale de la piscine.As in the installation of FIG. 1, the installation illustrated in FIG. 2 comprises a source 12 of coherent light constituted by a pulsed laser such as a YAG laser. This source 12 sends downwards and in a vertical direction a beam of coherent light into a sealed telescopic tube 14 forming a waveguide. A bend 16 at right angles is placed at the bottom of the telescopic tube 14, so as to return the beam in a horizontal direction towards the side walls of the pool, under the action of a mirror 18 placed in the bend 16. L 'open end of the horizontal branch of the elbow 16 is provided with a sealed lens 20 which directs a beam of coherent light focused 21 towards the side wall of the pool.

Le caractère télescopique du tube 14 (flèche F2), associé à un degré de liberté de rotation (flèche F1) de ce tube autour de son axe, permettent d'effectuer un balayage des parois latérales de la piscine. De préférence, ce balayage est programmé et réalisé de manière automatique par des systèmes de motorisation non illustrés sur la figure 2. Les deux degrés de liberté précités peuvent éventuellement être complétés par un ou plusieurs degrés de liberté supplémentaires, par exemple en plaçant la source 12 sur un chariot apte à se déplacer dans un plan horizontal selon deux directions orthogonales parallèles aux parois latérales de la piscine. Comme on l'a déjà indiqué à propos de l'installation illustrée sur la figure 1, les techniques permettant d'effectuer le balayage des surfaces à décontaminer sont bien connues, de telle sorte qu'il n'en est fait aucune description détaillée.The telescopic nature of the tube 14 (arrow F2), associated with a degree of freedom of rotation (arrow F1) of this tube around its axis, make it possible to scan the side walls of the pool. Preferably, this scanning is programmed and carried out automatically by motorization systems not illustrated in FIG. 2. The two above-mentioned degrees of freedom can possibly be supplemented by one or more additional degrees of freedom, for example by placing the source 12 on a trolley capable of moving in a horizontal plane in two orthogonal directions parallel to the side walls of the pool. As already indicated with regard to the installation illustrated in FIG. 1, the techniques for scanning the surfaces to be decontaminated are well known, so that no detailed description is made of them.

Afin que le faisceau de lumière cohérente délivré par la source 12 puisse également effectuer la décontamination du fond sensiblement horizontal de la piscine, on peut notamment démonter le coude 16 et monter la lentille étanche 20 directement à l'extrémité inférieure du tube télescopique vertical 14. On peut aussi envisager d'utiliser un coude 16 articulé, équipé d'un miroir 18 escamotable, permettant d'amener la branche horizontale du coude 16 dans une position verticale, pour décontaminer directement le fond de la piscine.So that the coherent light beam delivered by the source 12 can also carry out the decontamination of the substantially horizontal bottom of the swimming pool, it is in particular possible to disassemble the elbow 16 and mount the waterproof lens 20 directly at the lower end of the vertical telescopic tube 14. One can also consider using an articulated elbow 16, equipped with a retractable mirror 18, making it possible to bring the horizontal branch of the elbow 16 into a vertical position, to directly decontaminate the bottom of the pool.

Dans l'installation illustrée sur la figure 2, la présence de liquide sur les surfaces intérieures 10 de la piscine est obtenue directement en remplissant cette piscine de liquide 29 dont la nature peut être la même que dans l'installation de la figure 1.In the installation illustrated in FIG. 2, the presence of liquid on the interior surfaces 10 of the swimming pool is obtained directly by filling this swimming pool with liquid 29 the nature of which can be the same as in the installation in FIG. 1.

Compte tenu du volume important de la piscine, il est intéressant de confiner le volume de liquide qui se trouve à proximité immédiate de la surface 10 en cours de traitement par le faisceau de lumière cohérente. A cet effet, on fixe à l'extrémité de la branche horizontale du coude 16 un boîtier 36 étanche, mais dont la face tournée vers la surface 10 en cours de traitement est ouverte.Given the large volume of the swimming pool, it is advantageous to confine the volume of liquid which is in the immediate vicinity of the surface 10 during treatment with the beam of coherent light. To this end, a sealed housing 36 is fixed at the end of the horizontal branch of the elbow 16, but the side facing the surface 10 during treatment is open.

La présence du boîtier 36 permet d'effectuer un recyclage du liquide qui se trouve à proximité immédiate de la partie de la surface 10 en cours de décontamination. A cet effet, l'installation comprend un circuit de recyclage 26 dont une extrémité est raccordée sur le boîtier 36, de façon à prélever le liquide à l'intérieur de ce dernier. Ce circuit de recyclage comporte une pompe 30 qui recycle le liquide 29 dans un filtre 32, avant de le rejeter directement dans la piscine 11.The presence of the housing 36 makes it possible to recycle the liquid which is in the immediate vicinity of the part of the surface 10 during decontamination. To this end, the installation comprises a recycling circuit 26, one end of which is connected to the housing 36, so as to draw the liquid inside the latter. This recycling circuit includes a pump 30 which recycles the liquid 29 in a filter 32, before discharging it directly into the pool 11.

On réalise ainsi le maintien d'un volume de liquide sensiblement constant dans la piscine, tout en extrayant de ce liquide les éléments radioactifs qui sont arrachés de la surface 10 par le faisceau de lumière cohérente.This achieves the maintenance of a substantially constant volume of liquid in the pool, while extracting from this liquid the radioactive elements which are torn from the surface 10 by the beam of coherent light.

Lorsqu'une installation comparable à celle de la figure 2 est utilisée pour décontaminer les surfaces intérieures d'un récipient de dimensions et de formes différentes, certaines des caractéristiques qui viennent d'être décrites peuvent être modifiées ou supprimées. Ainsi, lorsqu'une installation de ce type est utilisée pour décontaminer les surfaces intérieures d'une boîte à eau de générateur de vapeur, le volume intérieur de cette boîte à eau est suffisamment faible pour que le boîtier 36 puisse être supprimé. Les deux extrémités du circuit de recyclage 26 débouchent alors directement dans la boîte à eau. Par ailleurs, les trous d'homme permettant d'accéder à la boîte à eau étant située sur la paroi hémisphérique inférieure de cette dernière, le circuit de recyclage 26, comme le tube télescopique 14 doivent traverser ce trou d'homme, ce qui signifie que le faisceau de lumière cohérente est alors orienté vers le haut.When an installation comparable to that of FIG. 2 is used to decontaminate the interior surfaces of a container of different dimensions and shapes, some of the characteristics which have just been described can be modified or eliminated. Thus, when an installation of this type is used to decontaminate the interior surfaces of a steam generator water box, the interior volume of this water box is small enough that the box 36 can be eliminated. The two ends of the recycling circuit 26 then open directly into the water box. Furthermore, the manholes allowing access to the water box being located on the lower hemispherical wall of the latter, the recycling circuit 26, like the telescopic tube 14 must pass through this manhole, which means that the coherent light beam is then directed upwards.

Différentes expérimentations ont été effectuées afin de contrôler l'efficacité du procédé de décontamination selon l'invention dans des conditions permettant notamment de mettre en évidence les influences respectives de la longueur d'onde du rayon laser utilisé, du matériau dont on désire décontaminer la surface et de la nature des éléments radioactifs déposés sur cette surface. Etant donné que ces expériences ont toutes été effectuées à la fois avec un faisceau de lumière cohérente associé à un système d'aspiration d'air et avec un faisceau de lumière cohérente associé à un film liquide ruisselant sur la surface, pour différentes compositions de liquide, elles permettent également de mettre en évidence les avantages essentiels procurés par l'invention ainsi que l'influence de la nature du liquide utilisé sur la qualité de la décontamination. Les résultats de ces différents essais sont illustrés par des tableaux qui vont à présent être explicités et commentés.Various experiments were carried out in order to control the effectiveness of the decontamination process according to the invention under conditions making it possible in particular to highlight the respective influences of the wavelength of the laser beam used, of the material whose surface is to be decontaminated. and the nature of the radioactive elements deposited on this surface. Since these experiments were all carried out both with a coherent light beam associated with an air suction system and with a coherent light beam associated with a liquid film trickling on the surface, for different liquid compositions , they also make it possible to highlight the essential advantages provided by the invention as well as the influence of the nature of the liquid used on the quality of the decontamination. The results of these various tests are illustrated by tables which will now be explained and commented on.

Le tableau A donne une estimation des profondeurs moyennes d'ablation (en µm) par impulsion, lorsqu'on fait agir des faisceaux laser présentant différentes longueurs d'onde sur de l'acier AISI 304 respectivement sous air et sous eau. TABLEAU A longueur d'onde du rayon laser (nm) Densité d'énergie par impulsion (J/cm2) Profondeur d'ablation par impulsion (µm) AIR Moy.s/50 impulsions EAU Moy.s/10 impulsions EAU Moy.s/50 impulsions 248 20 0,24 1,3 0,8 308 5 0,3 2,5 1,4 532 28 0,1 1,5 0,9 1064 8,5 0,1 2,5 1,6 Table A gives an estimate of the average ablation depths (in µm) per pulse, when laser beams with different wavelengths are made to act on AISI 304 steel in air and under water, respectively. TABLE A wavelength of the laser beam (nm) Energy density per pulse (J / cm2) Pulse ablation depth (µm) AIR Average s / 50 pulses WATER Avg. / 10 pulses WATER Avg. / 50 pulses 248 20 0.24 1.3 0.8 308 5 0.3 2.5 1.4 532 28 0.1 1.5 0.9 1064 8.5 0.1 2.5 1.6

On observe tout d'abord sur le Tableau A que la profondeur d'ablation par impulsion est sensiblement plus importante sous ruissellement d'eau que dans l'air, le gain apporté par le procédé conforme à l'invention étant variable selon la longueur d'onde du faisceau laser. Ainsi, la profondeur d'ablation est seulement multipliée d'un facteur d'environ 3,5 dans l'ultraviolet, alors qu'elle est multipliée par un facteur 16 dans le proche infrarouge.First of all, it can be seen in Table A that the pulse ablation depth is significantly greater under water runoff than in air, the gain provided by the process according to the invention being variable depending on the length d wave of the laser beam. Thus, the ablation depth is only multiplied by a factor of about 3.5 in the ultraviolet, while it is multiplied by a factor of 16 in the near infrared.

On observe également sur ce Tableau A que, sous film d'eau, la profondeur d'ablation par impulsion est plus importante pour les premières impulsions qui agissent d'abord sur la couche d'oxydes superficielle déposée sur le matériau de base.It is also observed in this Table A that, under a film of water, the depth of ablation per pulse is greater for the first pulses which act first on the surface oxide layer deposited on the base material.

On observe enfin sur le Tableau A que ce sont les longueurs d'onde de 308 nm et 1064 nm qui autorisent l'ablation aux seuils d'énergie les plus bas (respectivement 5 et 8,5 J/cm2 par impulsion), tout en ayant les rendements relatifs les plus élevés (2,5 µm par impulsion).Finally, it can be seen in Table A that it is the wavelengths of 308 nm and 1064 nm which allow ablation at the lowest energy thresholds (5 and 8.5 J / cm 2 per pulse respectively), all by having the highest relative yields (2.5 µm per pulse).

Le Tableau B présente, quant à lui, une estimation des profondeurs moyennes d'ablation par impulsion, lorsqu'on fait agir un faisceau laser de longueur d'onde 308 nm et un faisceau laser de longueur d'onde 1064 nm sur la surface contaminée, respectivement sous air et sous eau, de pièces en silice ou en alumine, représentatives des matériaux de construction tels que les bétons, et/ou des céramiques.Table B presents an estimate of the average pulse ablation depths when a laser beam of wavelength 308 nm and a laser beam of wavelength 1064 nm are made to act on the contaminated surface. , respectively in air and under water, of silica or alumina parts, representative of construction materials such as concrete, and / or ceramics.

La durée de chaque impulsion est de 30 ns à la longueur d'onde 308 nm et de 7 ns à la longueur d'onde de 1064 nm, la fréquence de tir étant dans tous les cas de 1 Hz. TABLEAU B longueur d'onde (nm) nature des matériaux densité d'énergie par impulsion (J/cm2) profondeur moyenne d'ablation par impulsion (µm) profondeur moyenne d'ablation par impulsion (µm) AIR EAU 308 Silice oxydée 20 0,06 (1) 0,4 (1) 308 Alumine 20 0,24 (1) 2,5 (1) 1064 Alumine 15 0,6 (1) Plaque perforée (1) e # 0,5 mm 1064 Alumine 15 0 (2) 12 (2;3) (1) Nombre d'impulsions successives : 50(1), 52(2), 10(3). The duration of each pulse is 30 ns at the wavelength 308 nm and 7 ns at the wavelength of 1064 nm, the firing frequency being in all cases 1 Hz. TABLE B wavelength (nm) nature of materials energy density per pulse (J / cm 2 ) average pulse ablation depth (µm) average pulse ablation depth (µm) AIR WATER 308 Oxidized silica 20 0.06 (1) 0.4 (1) 308 Alumina 20 0.24 (1) 2.5 (1) 1064 Alumina 15 0.6 (1) Perforated plate (1) e # 0.5 mm 1064 Alumina 15 0 (2) 12 (2; 3) (1) Number of successive pulses: 50 (1), 52 (2), 10 (3).

Sur le Tableau C, on a porté les résultats d'essais comparatifs de décontamination effectués sur des échantillons en Inconel 600 oxydé, contaminé au Co 60 en faisant agir un faisceau laser sur des échantillons présentant des activités initiales voisines, respectivement en présence de l'air ambiant avec une aspiration à un débit de 86 m3/h, en présence d'un film d'eau sur la surface de l'échantillon à un débit de 50 l/h et en présence d'un film d'eau additionné de 5 moles/l d'acide nitrique à un débit de 50 l/h.Table C shows the results of comparative decontamination tests carried out on samples of oxidized Inconel 600, contaminated with Co 60 by causing a laser beam to act on samples having similar initial activities, respectively in the presence of ambient air with suction at a flow rate of 86 m 3 / h, in the presence of a film of water on the surface of the sample at a flow rate of 50 l / h and in the presence of a film of water added 5 moles / l of nitric acid at a flow rate of 50 l / h.

Pour effectuer ces essais, on a utilisé un faisceau laser de longueur d'onde 532 nm, la largeur temporelle des impulsions étant de 7 ns, le taux de répétition de 30 Hz et la densité d'énergie par impulsion de 7 J/cm2. TABLEAU C Activité initiale (Bq/cm2) 20 400 19 700 21 500 Densité d'énergie déposée (J/cm2) Facteur de décontamination (air + aspiration) Facteur de décontamination (Film d'eau) Facteur de décontamination (Film d'eau + HNO3 5 moles/l) 100 3 22 200 1,4 7 94 300 1,5 11 170 400 1,5 16.5 250 450 1,6 19 280 500 21 550 24 Activité résiduelle (Bq/cm2) 12 750 830 15 To perform these tests, a laser beam of wavelength 532 nm was used, the temporal width of the pulses being 7 ns, the repetition rate of 30 Hz and the energy density per pulse of 7 J / cm 2 . TABLE C Initial activity (Bq / cm 2 ) 20,400 19,700 21,500 Deposited energy density (J / cm 2 ) Decontamination factor (air + suction) Decontamination factor (Water film) Decontamination factor (Water film + HNO 3 5 moles / l) 100 3 22 200 1.4 7 94 300 1.5 11 170 400 1.5 16.5 250 450 1.6 19 280 500 21 550 24 Residual activity (Bq / cm 2 ) 12,750 830 15

Ce tableau C fait notamment apparaître de façon très nette le gain essentiel apporté par la présence d'un film liquide à la surface de la pièce décontaminée. En outre, il montre, dans le cadre du procédé conforme à l'invention, qu'un facteur de décontamination comparable (21 ou 22) peut être obtenu pour une densité d'énergie déposée cinq fois moindre (100 J/cm2 au lieu de 500 J/cm2), en remplaçant le film d'eau par un film d'eau additionné d'acide nitrique.This table C notably shows very clearly the essential gain brought by the presence of a liquid film on the surface of the decontaminated part. In addition, it shows, within the framework of the process according to the invention, that a comparable decontamination factor (21 or 22) can be obtained for an energy density deposited five times lower (100 J / cm 2 instead 500 J / cm 2 ), replacing the film of water with a film of water with added nitric acid.

Le Tableau D est un tableau comparable au Tableau C, dans lequel les échantillons testés étaient des échantillons d'acier AISI 304 recouvert d'oxyde contaminé au Co 60. Les caractéristiques du faisceau laser étaient par ailleurs identiques à celles du Tableau C.

Figure imgb0001
Table D is a table comparable to Table C, in which the samples tested were samples of AISI 304 steel coated with oxide contaminated with Co 60. The characteristics of the laser beam were also identical to those of Table C.
Figure imgb0001

Le Tableau D fait apparaître encore plus clairement que le Tableau C l'influence de la nature du liquide qui recouvre la surface décontaminée par le faisceau laser. En effet, cinq échantillons différents présentant des activités initiales voisines ont été traités par un faisceau laser respectivement en présence de l'air ambiant avec une aspiration à un débit de 86m3/h, en présence d'un film d'eau à un débit de 50 l/h, en présence d'un film d'eau auquel étaient ajoutés 1,5 % d'acides citrique et oxalique ("CITROX") à un débit de 50 l/h, en présence d'un film d'eau additionné de 0,5 mole/l d'acide nitrique à un débit de 50 l/h et en présence d'un film d'eau additionné de 5 moles/l d'acide nitrique à un débit de 50 l/h.Table D shows even more clearly than Table C the influence of the nature of the liquid which covers the surface decontaminated by the laser beam. Indeed, five different samples presenting similar initial activities were treated by a laser beam respectively in the presence of ambient air with a suction at a flow rate of 86m 3 / h, in the presence of a film of water at a flow rate of 50 l / h, in the presence of a film of water to which 1.5% of citric and oxalic acids ("CITROX") were added at a flow rate of 50 l / h, in the presence of a film of water added with 0.5 mole / l of nitric acid at a flow rate of 50 l / h and in the presence of a film of water added with 5 moles / l of nitric acid at a flow rate of 50 l / h.

L'observation des résultats donnés par le Tableau D fait apparaître qu'un facteur de décontamination comparable (130) est obtenu pour une densité d'énergie près de trois fois moindre (200 J/cm2 au lieu de 550 J/cm2), lorsqu'on travaille en présence d'un film d'eau additionné de 5 moles/l d'acide nitrique, par rapport à une décontamination effectuée simplement en présence d'un film d'eau.The observation of the results given in Table D shows that a comparable decontamination factor (130) is obtained for an energy density almost three times lower (200 J / cm 2 instead of 550 J / cm 2 ) , when working in the presence of a film of water added with 5 moles / l of nitric acid, compared to a decontamination carried out simply in the presence of a film of water.

Enfin, le tableau E illustre des résultats d'essais comparables à ceux qui sont donnés sur les Tableaux C et D, dans le cas où l'on effectue la décontamination de surface d'échantillons en acier AISI 304 contaminé au Cs137. Les caractéristiques du faisceau laser utilisé sont identiques à celles qui ont été indiquées dans le cadre des essais illustrés sur les Tableaux C et D.

Figure imgb0002
Finally, Table E illustrates test results comparable to those given in Tables C and D, in the case where surface decontamination of samples of AISI 304 steel contaminated with Cs137 is carried out. The characteristics of the laser beam used are identical to those indicated in the context of the tests illustrated in Tables C and D.
Figure imgb0002

Les essais dont les résultats sont portés sur le Tableau E ont été effectués respectivement en présence d'air avec un système d'aspiration à un débit de 86 m3/h, en présence d'un film d'eau à un débit de 50 l/h, en présence d'un film d'eau additionné de 1,5 % d'acides citrique et oxalique ("CITROX") à un débit de 50 l/h et en présence d'un film d'eau additionné de 5 moles/l d'acide nitrique à un débit de 50 l/h.The tests, the results of which are given in Table E, were carried out respectively in the presence of air with a suction system at a flow rate of 86 m 3 / h, in the presence of a film of water at a flow rate of 50 l / h, in the presence of a film of water supplemented with 1.5% citric and oxalic acids ("CITROX") at a flow rate of 50 l / h and in the presence of a film of water supplemented with 5 moles / l of nitric acid at a flow rate of 50 l / h.

Le Tableau E illustre notamment qu'un facteur de décontamination comparable (environ 50) peut être obtenu avec une densité d'énergie déposée environ sept fois moindre (15 J/cm2 au lieu de 100 J/cm2) en effectuant l'abrasion en présence d'un film d'eau additionné de 5 moles/l d'acide nitrique, plutôt qu'en effectuant l'abrasion en présence d'un simple film d'eau.Table E illustrates in particular that a comparable decontamination factor (approximately 50) can be obtained with an energy density deposited approximately seven times lower (15 J / cm 2 instead of 100 J / cm 2 ) by carrying out the abrasion in the presence of a film of water added with 5 moles / l of nitric acid, rather than in carrying out the abrasion in the presence of a simple film of water.

Inversement, les résultats indiqués sur les Tableaux C, D et E montrent qu'un même facteur de décontamination peut être obtenu en réalisant le balayage de la surface à décontaminer par le faisceau laser en présence d'une solution d'acide nitrique, pour une quantité d'énergie déposée plus faible.Conversely, the results indicated in Tables C, D and E show that the same decontamination factor can be obtained by scanning the surface to be decontaminated by the laser beam in the presence of a nitric acid solution, for a lower amount of energy deposited.

Claims (11)

  1. Method for decontaminating a radioactive surface (10) by sweeping this surface using a focused beam of coherent light (21), characterized in that the entire surface (10) to be decontaminated is irrigated with a liquid film (29) while this surface is swept with the beam.
  2. Method for decontaminating a radioactive surface (10) by sweeping this surface using a focused beam of coherent light (21), characterized in that, the surface (10) to be decontaminated being an internal surface of a container, this container is filled with liquid (29) before this surface is swept with the beam.
  3. Method according to either one of the preceding claims, characterized in that, when the surface (10) to be decontaminated is swept, the liquid (29) is recycled and filtered.
  4. Method according to any one of the preceding claims, characterized in that the liquid (29) used is water.
  5. Method according to any one of Claims 1 to 3, characterized in that the liquid (29) used is an aqueous solution containing chemical reagent.
  6. Method according to Claim 5, characterized in that the chemical reagent is nitric acid.
  7. Method according to any one of the preceding claims, characterized in that the beam (21) of coherent light has a wavelength of 248 nm, 308 nm, 532 nm or 1064 nm.
  8. Installation for decontaminating a radioactive surface (10), comprising a coherent light source (12) and means (14, 16, 18, 20) for directing and focusing a beam of coherent light emitted by this source onto the surface (10) to be decontaminated, so as to allow this surface to be swept by the beam, characterized in that it furthermore comprises means (22) for irrigating the entire surface to be decontaminated with a liquid film (29) when the surface is swept.
  9. Installation according to Claim 8, characterized in that the means (22) for irrigating the surface to be decontaminated with a liquid film (29) comprise a spray pipe (24) running along the entire length of an upper edge (10a) of the surface, a collection tank (28) placed below a lower edge (10b) of the surface, and a recycling circuit (26) which joins the collection tank to the spray pipe, this recycling circuit including means (30) for pumping and means (32) for filtering the liquid.
  10. Installation for decontaminating a radioactive surface (10) forming an internal surface of a container, comprising a coherent light source (12) and means (14, 16, 18, 20) for directing and focusing a beam of coherent light emitted by this source onto the surface (10) to be decontaminated, so as to allow this surface to be swept by the beam, characterized in that it furthermore comprises a circuit (26) for recycling a liquid (29) contained in the container when the surface to be decontaminated is swept, this recycling circuit including means (30) for pumping and means (32) for filtering the liquid.
  11. Installation according to Claim 10, characterized in that, at their end the means (14, 16, 18, 20) for directing and focusing the beam onto the surface to be decontaminated have a casing (36) which is open towards the said surface, and in that the recycling circuit (26) draws off the liquid (29) from this casing and discharges it into the container.
EP94905154A 1993-01-26 1994-01-25 Methods and equipments for decontaminating a radioactive surface with a coherentlight beam Expired - Lifetime EP0681735B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR9300723 1993-01-26
FR9300723A FR2700882B1 (en) 1993-01-26 1993-01-26 Method and installation for decontamination of a radioactive surface by means of a beam of coherent light.
PCT/FR1994/000089 WO1994017529A1 (en) 1993-01-26 1994-01-25 Method and equipment for decontaminating a radioactive surface with a coherent light beam

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TWI803118B (en) * 2020-12-28 2023-05-21 美商西屋電器公司 Autonomous path planning and path execution for decontamination of nuclear power plant objects

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FR2777822B1 (en) * 1998-04-23 2000-07-07 Calhene WATERTIGHT TRANSFER DEVICE WITH INTEGRATED DECONTAMINATION BY ULTRAVIOLET RADIATION
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FR3031116B1 (en) * 2014-12-30 2019-07-12 Commissariat A L'energie Atomique Et Aux Energies Alternatives IMPROVED METHOD OF DECONTAMINATING THE SURFACE OF A STAINLESS STEEL WORKPIECE
FR3101558B1 (en) * 2019-10-03 2021-10-22 Onet Tech Cn Process for decontaminating a metal part containing a gas by laser irradiation in a liquid medium

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CA1198482A (en) * 1982-04-14 1985-12-24 Thaddeus A. Wojcik Laser decontamination method
JPS6046893A (en) * 1983-08-25 1985-03-13 Seiko Epson Corp Laser working device

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TWI803118B (en) * 2020-12-28 2023-05-21 美商西屋電器公司 Autonomous path planning and path execution for decontamination of nuclear power plant objects
US11685054B2 (en) 2020-12-28 2023-06-27 Westinghouse Electric Company Llc Autonomous path planning and path execution for decontamination of nuclear power plant objects

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ES2102825T3 (en) 1997-08-01
WO1994017529A1 (en) 1994-08-04

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