EP0520847B1 - Process for working with a laser in a contaminated zone of a nuclear power plant and device for carrying out the process - Google Patents

Description

The present invention relates to a method and equipment for laser work on a surface contained in a contaminated area of a nuclear installation.

The invention applies in particular to the decontamination by laser beam, in aqueous or gaseous medium, of surfaces which have received a deposit of radioactive materials such as activated metal oxides, in order to reduce the level of radiation and thus allow the access or approach of response personnel.

The primary circuit of pressurized water nuclear power plants is concerned with this invention and more particularly the water box of the steam generators and the primary pipes.

Decontamination may be necessary during a check or repair to be carried out in the contaminated part of the plant, when replacing equipment such as a steam generator, and also when dismantling this plant.

• la projection de particules abrasives pour éliminer par abrasion la pellicule d'oxyde radioactive, ou la dissolution chimique de cette pellicule, qui ont pour inconvénient de produire des quantités importantes d'effluents coûteux à traiter;
• la décontamination par faisceau laser. Dans un procédé connu de ce type, décrit dans le EP-A-91 646, un faisceau laser est émis à l'entrée de la boîte à eau et renvoyé sur la paroi intérieure de celle-ci par des miroirs orientables fixés à la plaque tubulaire. Ce procédé, de par sa conception même, ne permet pas, même avec des impulsions laser à forte densité d'énergie, de traiter de façon uniforme toutes les surfaces à décontaminer. De plus, l'élimination des résidus radioactifs, effectuée par aspiration de l'air contenu dans la boîte à eau, est peu efficace.

Several decontamination processes are known:

• the projection of abrasive particles to remove the radioactive oxide film by abrasion, or the chemical dissolution of this film, which have the disadvantage of producing large quantities of effluents which are expensive to treat;
• laser beam decontamination. In a known method of this type, described in EP-A-91 646, a laser beam is emitted at the entrance to the water box and returned to the inside wall of the latter by orientable mirrors fixed to the plate tubular. This process, by its very design, does not allow, even with high energy density laser pulses, to uniformly treat all surfaces to be decontaminated. In addition, the elimination of radioactive residues, carried out by suction of the air contained in the water box, is not very effective.

The object of the invention is to make it possible to work efficiently by means of a laser in a contaminated area.

To this end, the method according to the invention is characterized in that the working energy is generated, in the form of at least two pulsed laser beams, by means of at least two pulsed laser energy generators synchronized apart the contaminated area; this energy is transported by means of at least two optical fibers associated respectively with said beams, to a location close to said surface; at this location, the laser beams from the optical fibers are combined so as to produce a single resulting combined laser beam; and this resulting combined beam is sent to said surface, possibly via at least one deflection mirror.

• on confine la région de travail et, pendant le travail au laser, on aspire le gaz contenu dans la région confinée;
• on envoie un gaz protecteur ou actif dans la région de travail pendant le travail au laser;
• pour la décontamination de ladite surface, ledit faisceau laser résultant possède des impulsions ayant une énergie de 0,3 à 2 joules, ou plus, et une densité d'énergie de 1 à 4,5 J/cm2;
• lesdites impulsions ont une durée de 10 à 30 ns.

According to other characteristics:

• the working region is confined and, during the laser work, the gas contained in the confined region is sucked;
• a protective or active gas is sent into the working region during laser work;
• for decontamination of said surface, said resulting laser beam has pulses having an energy of 0.3 to 2 joules, or more, and an energy density of 1 to 4.5 J / cm2;
• said pulses have a duration of 10 to 30 ns.

• au moins deux générateurs d'énergie laser pulsée, notamment du type Nd-YAG ou excimère, disposé en dehors de la zone contaminée;
• une fibre optique associée à chaque générateur;
• un dispositif de syncronisation des générateurs;
• un dispositif de combinaison des faisceaux laser, issus des fibres optiques produisant un faisceau laser combiné résultant unique dirigé vers ladite surface, éventuellement par l'intermédiaire d'au moins un miroir de renvoi; et
• des moyens pour déplacer le dispositif de combinaison en regard de ladite surface et au voisinage de celle-ci.

The invention also relates to equipment intended for the implementation of such a method. This equipment is characterized in that it includes:

• at least two pulsed laser energy generators, in particular of the Nd-YAG or excimer type, arranged in outside the contaminated area;
• an optical fiber associated with each generator;
• a generator synchronization device;
• a device for combining the laser beams, coming from the optical fibers producing a single resulting combined laser beam directed towards said surface, optionally by means of at least one deflection mirror; and
• means for moving the combination device facing said surface and in the vicinity thereof.

• l'équipement comprend une enceinte de confinement mobile solidairement avec le dispositif de combinaison ou avec le miroir et munie de moyens d'aspiration;
• l'équipement comprend des moyens d'introduction d'un gaz protecteur ou actif dans l'enceinte de confinement;
• le ou chaque générateur comprend au moins un amplificateur de sortie;
• chaque fibre optique a une longueur d'au moins 10 m environ;
• le miroir de renvoi monté en aval du dispositif de combinaison est mobile par rapport à celui-ci;
• dans le cas du traitement au laser d'une canalisation, le dispositif de combinaison est porté par un support centreur mobile axialement dans la canalisation, et le miroir de renvoi est fixé dans l'enceinte de confinement, laquelle est montée rotative sur ce support, ce dernier portant des moyens d'entraînement en rotation de l'enceinte.

According to other characteristics:

• the equipment comprises a confinement enclosure movable integrally with the combination device or with the mirror and provided with suction means;
• the equipment includes means for introducing a protective or active gas into the containment;
• the or each generator comprises at least one output amplifier;
• each optical fiber has a length of at least about 10 m;
• the deflection mirror mounted downstream of the combination device is movable relative to the latter;
• in the case of laser treatment of a pipeline, the combination device is carried by a centrally movable support axially in the pipeline, and the deflection mirror is fixed in the confinement enclosure, which is rotatably mounted on this support, the latter carrying means for driving the enclosure in rotation.

• la Figure 1 représente schématiquement un équipement de décontamination au laser conforme à l'invention;
• la Figure 2 représente à plus grande échelle un détail de cet équipement;
• la Figure 3 est une vue analogue à la Figure 2 d'une variante; et
• les Figures 4 et 5 sont des vues analogues à la Figure 2 illustrant la décontamination, conformément à l'invention, d'une conduite d'eau primaire.

Examples of implementation of the invention will now be described with reference to the accompanying drawings in which:

• Figure 1 schematically shows a laser decontamination equipment according to the invention;
• Figure 2 shows on a larger scale a detail of this equipment;
• Figure 3 is a view similar to Figure 2 of a variant; and
• Figures 4 and 5 are views similar to Figure 2 illustrating the decontamination, according to the invention, of a primary water pipe.

There is shown in Figure 1, in axial section, one 1 of the two compartments of the water box 2 of a steam generator of a pressurized water nuclear reactor. This compartment 1 is delimited upwards by the tubular plate 3, on one side by the middle vertical partition 4 of the water box, and on the other side and downwards by the hemispherical bottom 5 of the water box , which is crossed by a manhole 6.

FIG. 1 also shows an item of equipment 7 adapted to allow the decontamination by laser beam of the surfaces which delimit the compartment 1. This equipment comprises an external device 8 arranged outside the water box, in a suitable protected room radiation, and an internal apparatus 9 disposed inside the compartment 1 and which can be introduced into the latter through the manhole.

The apparatus 8 comprises a console for control 10, a generator of electrical energy and fluids 11, two identical pulsed laser beam generators 12A, 12B, and a suction pump 13 at the inlet of which a filter 14 is provided.

The apparatus 9 comprises a device or box 15 for combining laser beams and a confinement enclosure 16, carried by a support 17. The box 15 has two inputs respectively connected to the output of the generators 12A and 12B by an optical fiber 18A, 18B multimode type having a length of at least about 15 m. The enclosure 16 is connected on the one hand, via a line 19, to a source of protective (neutral or reducing) or active gas contained in the generator 11, and on the other hand, via a line 20, to the filter 14 and at the pump 13. The support 17 constitutes the end of an articulated robot, shown diagrammatically at 21, remote-controlled from the console 10 and making it possible to arrange the apparatus 9 facing any region of the surfaces 3, 4, 5 to decontaminate and in the vicinity thereof.

The apparatus 9 is shown in more detail in Figure 2. As can be seen in this figure, the housing 15 is fixed to the support 17 and provided with an electrical supply 23 connected via a line 26 (Figure 1) to the generator 11 An inlet face of the housing 15 is pierced by two orifices in which the distal end of the optical fibers 18A, 18B are respectively fixed, and, after their combination in this housing, the two incoming beams form a single parallel pulsed laser beam which comes out through an outlet 29.

At its distal end, the support 17 carries a frame 30 in which several columns 31 parallel to the axis XX of the housing 15, urged by springs 32 in the opposite direction to this housing, are sliding mounted. The enclosure 16, which has a cup shape, has a bottom 33 perpendicular to the axis XX which is fixed to the distal end of the balusters 31, and a side wall 34 whose free edge is provided with rollers 35. The bottom 33 has an orifice 36 of axis XX whose diameter is slightly greater than that of the combined beam 37.

Each laser generator 12A and 12B is of a type allowing the transport of the beam by optical fiber. It can in particular be of the Nd-YAG type (wavelength 1.06 μm) or of the excimer type (wavelength 0.3 μm). It comprises at its output two amplifiers 38, 39 in series (or, as a variant, a single amplifier) and emits pulses having a duration of 10 to 30 ns. A synchronization device or box 40 is associated with the two generators 12A, 12B, and the assembly is adjusted to supply at the output of the combination box 15 a combined beam 37 whose pulses have an energy of 0.3 to 2 joules or plus and an energy density (or fluence) of 1 to 4.5 J / cm2.

In operation, the rollers 35 are applied, with a force determined by the springs 32, to the surface to be decontaminated, which is the partition 4 in the example shown. A protective or active gas scans the enclosure 16, and the pulsed beams emitted by the generators 12A and 12B, transported by the optical fibers 18A, 18B and combined at 15, are sent directly, in the form of the single parallel beam 37, to the surface to be treated, perpendicular to it. All the surfaces to be decontaminated are scanned in this way by moving the support 17 by means of the robot 21.

The above-mentioned energy density is chosen so as to allow thermal penetration corresponding to the thickness, or part of the thickness, of the layer of radioactive oxide to be removed, each pulse creating a shock wave on this layer. The use of a neutral or sweeping gas reduces the oxidation of the etched surface, while the use of an active gas, in particular oxygen, makes it possible to increase the thickness of the oxide layer. interested in laser pulses. The choice of sweep gas will therefore be established according to the specific conditions of each application.

The use of a multimode optical fiber for the transport of each laser beam provides a considerable advantage linked to the distribution of energy in the beam leaving said fiber, and therefore at the spot of impact of the beam on the wall. Indeed, in this case, the energy distribution is substantially constant over the entire surface of the spot; it is in the form of a slot instead of having a distribution comprising a central peak as is the case with transmission of the beam by air. However, the fibers must be long enough for the energy homogenization to be correct, for example of the order of 10 m. With shorter optical fibers, it would be appropriate in certain cases to use in the generators 12A and 12B devices known per se providing a homogeneous distribution, in niche, of the energy.

As will be understood, a distribution of energy by niche makes it possible to work without loss of efficiency with reduced laser powers, which is advantageous.

• les générateurs laser 12A, 12B sont disposés en dehors de la zone contaminée;
• les faisceaux laser peuvent être transportés par fibre optique jusqu'au voisinage de la surface à traiter, avec les avantages précités, ce qui ne serait pas le cas si toute l'énergie du faisceau 37 était fournie par un unique générateur laser, à cause des possibilités limitées de transport de puissance laser des fibres optiques;
• le faisceau 37 étant un faisceau parallèle qui arrive perpendiculairement sur la surface à traiter, la distance entre cette surface et l'orifice de sortie de faisceau 29 du boîtier 15 n'est pas critique, et il n'est pas nécessaire de la maintenir constante.

The use of a combination box 15 near the surface to be decontaminated has many advantages:

• the laser generators 12A, 12B are arranged outside the contaminated area;
• laser beams can be transported by optical fiber to the vicinity of the surface to be treated, with the aforementioned advantages, which would not be the case if all the energy of the beam 37 was supplied by a single laser generator, because of the limited possibilities of power transport fiber optic laser;
• the beam 37 being a parallel beam which arrives perpendicularly on the surface to be treated, the distance between this surface and the beam exit orifice 29 of the housing 15 is not critical, and it is not necessary to keep it constant .

The apparatus 9A shown in Figure 3 differs from that of Figure 2 in that the support 17 is arranged so that the axis X-X of the combination housing 15 is parallel to the surface to be treated. The posts 31 are perpendicular to this axis X-X, and a deflection mirror 38 inclined at 45 ° is fixed opposite the orifice 36 of the enclosure 16. The operation of this variant is the same as that described above. This variant is particularly applicable to laser work in small spaces.

The variant of FIG. 3 can be modified as follows: the 16-column 31-mirror 38 enclosure assembly 38 is connected to the support 17 by means of another support mounted mobile on the latter, in translation and / or in rotation around the axis of the housing 15. It is thus possible, for each position of this housing, to effectively scan a relatively large region to be treated, whatever the shape of this region.

Figures 4 and 5 show such a modification, applied to the decontamination of the wall of a primary pipe, assumed to be straight in the case of Figure 4 and curved in that of Figure 5.

The housing 15 is fixed by spacers 42 in the suction duct 20, as is a motor 43. The conduit 20 is carried by a carriage 44 for centering and guiding in the conduit 45 to be decontaminated. The enclosure 16 constitutes the distal end of an L-shaped tube 46, the other end of which, directly connected to this enclosure by a bypass 20A, is mounted co-axially in rotation in the distal end of the conduit 20 and receives the housing 15. The deflection mirror 38 is fixed in the bend of the tube 46. The proximal end of this tube externally carries a toothed ring 47 which meshes with an output pinion 48 of the motor 43. Appropriate means for advancing the carriage 44, possibly driven by the same motor 43, are generally provided.

FIG. 5 also shows a tip 49 for motorized guidance and advancement of the conduit 20, temporarily mounted at the end of the conduit 45.

In another embodiment of the invention, the two generators 12A, 12B can be replaced by a single laser generator; if the power it emits can be transported by a single optical fiber, the box 15 is a simple device for optical treatment of the laser beam. Otherwise, the beam leaving the generator is divided into two partial beams, each of these is transported by an optical fiber, and they are recombined in the housing 15.

In all cases, it is possible to create several parallel beams 37, entering the enclosure 16 through several orifices 36. A larger surface is then treated at each instant.

Claims (12)

1. Process for working with a laser on a surface (3,4,5) contained in a contaminated zone (2) of a nuclear installation, characterised in that the work energy is generated, in the form of at least two pulsed laser beams, outside the contaminated zone (at 12A,12B), by means of at least two synchronised generators of pulsed laser energy (12A,12B); this energy is transported by means of at least two optical fibres (18A,18B), respectively, associated with said beams, to a location close to said surface; at this location, the laser beams issuing from the optical fibres are combined (at 15) so as to produce a single resultant combined laser beam (37); and this resultant combined beam is directed onto said surface, optionally via at least one reflecting mirror.
2. Process according to claim 1, characterised in that the working region is confined and, during the laser work, the gas contained in the confined region (16) is aspirated.
3. Process according to claim 1 or 2, characterised in that a protective or active gas is emitted into the working region during the laser work.
4. Process according to anyone of claims 1 to 3, for the decontamination of said surface (3 to 5), characterised in that said resulting laser beam (37) has impulses having a density of 0.3 to 2 Joules, or more, and an energy density of 1 to 4.5 J/cm.
5. Process according to claim 4, characterised in that said impulses have a duration of 10 to 30 ns.
6. Equipment for working with a laser on a surface (3,4,5) contained in a contaminated zone (2) of a nuclear installation, characterised in that it comprises:

   at least two generators of pulsed laser energy (12A,12B), notably of the Nd-YAG or excimer type, arranged outside the contaminated zone (2);

   an optical fibre (18A,18B) associated with each generator;

   a device (40) for synchronising the generators;

   a device (15) for combining the laser beams issuing from the optical fibres, which produces a resultant single combined laser beam (37) directed towards said surface, optionally via at least one reflecting mirror; and

   means (21) for moving the combining device (15) opposite said surface and in the vicinity thereof.
7. Equipment according to claim 6, characterised in that it comprises a confining enclosure (16) which is movable along said surface integrally with the combining device (15) or with the mirror (38) and provided with aspirating means (13, 14, 20).
8. Equipment according to claim 7, characterised in that it comprises means (19) for introducing a protective or active gas into the confining enclosure (16)
9. Equipment according to any one of claims 6 to 8, characterised in that the or each generator (12A, 12B) comprises at least one output amplifier (38, 39).
10. Equipment according to any one of claims 6 to 9, characterised in that each optical fibre (18A,18B) is approximately at least 10 m long.
11. Equipment according to any one of claims 6 to 10, characterised in that the reflecting mirror (38) mounted downstream of the combining device (15) is movable relative to the latter.
12. Equipment according to claims 7 and 11 taken together, for laser treatment of pipework, characterised in that the combining device (15) is carried by a centring support (44) which is axially movable in the pipework (45), and in that the reflecting mirror (38) is fixed in the confining enclosure (16), which is rotatably mounted on this support, the latter supporting drive means (43) for rotating the enclosure.

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