FR2674983A1 - METHOD AND EQUIPMENT FOR LASER WORKING IN A CONTAMINATED AREA OF A NUCLEAR FACILITY - Google Patents

Abstract

According to this method, a pulsed laser beam is emitted outside the contaminated zone (at 12), this beam is transported to a location close to said surface, and, at this location, the beam is amplified (at 15) and sends the amplified beam to said surface. Application to the decontamination of the primary circuit of pressurized water nuclear reactors.

Description

The present invention relates to a

  assigned and a laser working installation on a surface contained in a contaminated area of a

nuclear installation.

  The invention is particularly applicable to decontamination by laser beam, in an aqueous or gaseous medium, of surfaces having received a deposit of radioactive materials such as activated metal oxides,

  to reduce the level of radiation and

  Thus, the access or the approach of the intervention personnel The primary circuit of the nuclear power plants with pressurized water is concerned by this invention and more particularly the water box of the generators.

  steam and primary pipes.

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

  Several decontaminating processes are known

  the projection of abrasive particles for

  remove by abrasion the radioactive oxide film

  ve, or the chemical dissolution of this film, which have the disadvantage of producing large quantities of expensive effluents to be treated; Laser beam decontamination In a known method of this type, described in FR-A-2 525 380, a laser beam is emitted at the inlet of the water box and returned to the inner wall thereof by means of adjustable mirrors fixed to the tube plate This process, by its very design, does not allow, even with laser pulses with high energy density, to treat uniformly

  all surfaces to be decontaminated.

  The object of the invention is to enable the efficient working by means of a laser in

a contaminated area.

  For this purpose, the method according to the invention is characterized in that a pulsed laser beam is emitted from the contaminated zone, this beam is transported to a location close to said surface, and at this location, amplification is effected. beam and sends the amplified beam to said surface, possibly via a

mirror of return.

  According to other characteristics, the transport is carried out by means of an optical fiber; a protective or active gas is sent into the working region during laser work; the work area is confined and, during laser work, the gas contained in the confined area is sucked up; the amplified beam is passed through an orifice of an electrode parallel to said surface, and an electric field is created between this electrode and said surface during laser work; for the decontamination of said surface,

  a laser beam is used which, after amplification

  tion, has pulses having an energy of 0.3 to 2 joules, or more, a duration of 10 to 30 ns, and a

  energy density of 1 to 4-5 J / cm 2.

3-

  The invention also relates to a team

  intended for the implementation of such a method.

  This equipment is characterized in that it comprises:

  a pulsed laser beam generator

  placed outside the contaminated area; a laser beam amplifier; means for transporting the pulsed laser beam to the input of this amplifier; and means for moving the amplifier opposite said surface and in the vicinity thereof. According to other characteristics, the generator is of the Nd-YAG or excimetre type, optionally provided with a Gaussian mirror of return, and said means of transport include an optical fiber; the optical fiber has a length of at least about m; the equipment comprises a reflection mirror mounted at the output of the amplifier and possibly

mobile with respect to it.

  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 Figure 4 is a partial view of a

another variant.

  FIG. 1 shows, in axial section, one of the two compartments of the water box 2 of a pressurized water nuclear reactor steam generator. This compartment 1 is delimited upwards by the tube plate 3 on one side by the vertical vertical partition 4 of the water box, and

  on the other side and downwards by the hemisphere background

  5 of the water box, which is crossed by a

manhole 6.

  FIG. 1 also shows a device 7 adapted to allow the decontamination by laser beam of the surfaces which delimit the

  compartment 1 This equipment includes a

  outer layer 8 disposed outside the water box, in a suitable room protected from radiation, and an internal apparatus 9 disposed within the compartment 1 and can be introduced into

  this one through the manhole.

  The apparatus 8 comprises a control panel 10, a generator of electrical energy and fluids 11, a pulsed laser beam generator 12, constituted by an oscillator possibly followed by a preamplifier, and a suction pump 13 to

  the input of which is provided a filter 14.

  The apparatus 9 comprises a laser beam amplifier 15 and a containment enclosure 16

  carried by a support 17 The input of the amplifier

  15 is connected to the output of the generator 12 by an optical fiber 18 of the multimode type having a length of at least approximately 15 m. The enclosure 16 is connected on the one hand, via a pipe 19, to a source of protective gas (Neutral or reducing) or active contained in the generator 11, and secondly, via a line 20, the filter 14 and the pump 13 The support 17 constitutes the end of an articulated robot, shown diagrammatically at 21, remotely controlled from the desk 10 and to have the apparatus 9 facing any region of the surfaces 3, 4, 5 to

  decontaminate and in the vicinity of it.

  Apparatus 9 is shown in more detail.

  Figure 2 As seen in this figure, the amplifier 15 is housed in a housing 22 fixed to the support 17 and provided with conduits 23 of power supply and 24 of arrival and -2 of water discharge The lines F 23 to 25 are connected via a line 26 (FIG. 1) to the generator 11. An inlet face of the housing 12 is pierced with an orifice in which the end is fixed.

  distal to the optical fiber 18, and optical optics

  trea 27 introduces the input of the ampli-

  15 a parallel beam of diameter equal to that of the bar of the amplifier This beam

  amplified spring at the other end of the amplifier

  15, and its diameter is reduced by an output optic 28, then out of the housing 22 as a parallel pulsed beam through an outlet port-29. At its distal end, the support 17 carries a frame 30 in which several columns 31

  parallel to the X-X axis of the amplifier 15,

  mentioned by springs 32 in the opposite direction to this amplifier, are slidably mounted. The chamber 16, which is cup-shaped, has a bottom 33

  perpendicular to the X-X axis which is fixed at the

  distal column 31, and a lateral wall

  34 whose free edge is provided with wheels 35.

  -The bottom 33 has an orifice 36 of axis X-X whose diameter is slightly greater than that of the beam

amplified 37.

  The laser generator 12 is of a type permitting

  both the optical fiber beam transport It can be in particular of the Nd-YAG type (wavelength of 1.06 μm) or of the excimer type (wavelength of 0.3 μm). It emits pulses with a duration of 10 to 30 ns This generator 12 and the amplifier 15 are set to provide an amplified beam 37 whose pulses have an energy of 0.3 to 2 joules or more and a density of energy (or fluence) of 1 to 4, b

J / Cm 2.

  In operation, the wheels 35 are

  applied, with a force determined by the

  spells 32, on the surface to decontaminate, which is the

  partition 4 in the example shown A gas protected

  or asset scans the enclosure 16, and the pulsed beam emitted by the generator 12, transported by the

  optical fiber 18 and amplified in 15 is sent direc-

  in the form of parallel beam 37, on

  the surface to be treated, perpendicular to it.

  All surfaces to be decontaminated are swept in this way by moving the support 17 by means of the robot

21.

  The aforementioned energy density is chosen from

  to allow a corresponding thermal penetration

  thickness, or part of the thickness

  of the radioactive oxide layer to be removed, each pulse creating a shock wave on this layer The use of a neutral gas or sweeping reducer reduces the oxidation of the etched surface, while the use of a active gas, in particular 7- oxygen, makes it possible to increase the thickness of the

  oxide layer interested in the laser pulses.

  The choice of the flushing gas will therefore be established according to the particular conditions of each application. The use of a multimode optical fiber for transporting the unamplified laser beam provides a considerable advantage related to the energy distribution in the beam at the output of said fiber, and therefore at the level of the beam impact spot. On the wall In fact, in this case, the energy distribution is substantially constant over the entire surface of the spot; it is niche-shaped at

  instead of having a distribution with a central peak

  tral as is the case with beam transmission by air, however, it is necessary that the

  fiber is long enough for homogeneity

  The energy consumption is correct, for example at least about 15 m With a shorter optical fiber, it would be appropriate in some cases to use in the generator 12 a so-called "Gaussian" mirror, known per se, providing a homogeneous distribution, in

niche, energy.

  As it is understood, a slot distribution of the energy makes it possible to work without loss of efficiency with reduced laser powers,

which is advantageous.

  The use of an amplifier 15 close to

  of the surface to be decontaminated

many advantages:

  the laser generator 12 is arranged in

  out of the contaminated area; the laser beam 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 the generator 12, because of the possibilities limited laser fiber power transport; the beam 37 being a parallel beam that arrives perpendicular to the surface to be treated, the distance between this surface and the beam output port 29 of the amplifier is not critical, and it is not necessary to maintain it

constant-

  Apparatus 9A shown in Figure 3 differs from that of Figure 2 in that the

  support 17 is arranged so that the X-X axis of the

  plifier 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

  facing the orifice 36 of the enclosure 16 The function

  This variant is the same as that described above. This variant is particularly applicable to laser work in small spaces, for example to decontaminate the pipe wall.

primary.

  The variant of Figure 3 can be modified

  as follows: the 16-column speaker assembly 31-

  mirror 38 is connected to the support 17 by means of another support mounted movably on the latter, in translation and / or in rotation around the axis of

  For example, the amplifier can be

  the amplifier, effectively scan a relatively large area to be processed, regardless of

the shape of this region.

  FIG. 4 illustrates means other than suction means for capturing oxide particles detached from the surface by the impact of the laser beam. In this case, it is an electrode 39 held parallel to the surface to be treated. by spacers not shown and pierced with an orifice allowing the passage of the laser beam 37

  electrode is worn, thanks to an electrical supply

  41, at a high potential with respect to the treated surface, so that the detached oxide particles, ionized by the laser beam, are

attracted to the electrode 39.

Claims (8)

  1 Laser working method on an over-   face (3, 4, 5) contained in a contaminated zone (2) of a nuclear installation, characterized in that a pulsed laser beam is emitted from the contaminated zone (at 12), this beam is transported to a location adjacent to said surface, and at this location, amplifies (at 15) the beam and sends the amplified beam to said surface, possibly via a reflecting mirror. Process according to Claim 1, characterized in that the transport is carried out by means of an optical fiber (18).   Process according to Claim 1 or 2, characterized in that a protective or active gas is supplied to the working region during laser work. 4 Process according to any one of   Claims 1 to 3, characterized in that one   confines the working area and, during laser work, draws the gas contained in the confined area. Process according to any one of   Claims 1 to 4, characterized in that   passing the amplified beam (37) through an orifice (40) of an electrode (39) parallel to said surface, and creating an electric field between this electrode   and said surface during laser work.   6 Process according to any one of   Claims 1 to 5 for the decontamination of   said surface (3 to 5), characterized in that a laser beam is used which, after amplification, has pulses having an energy of 0.3 to 2 joules, or more, a duration of 10 to 30 ns, and a   energy density of 1 to 4.5 J / cm 2.   7 Equipment for laser work on a surface (3, 4, 5) contained in a contaminated zone (2) of a nuclear installation, characterized in that it comprises: a pulsed laser beam generator (12) disposed outside the contaminated area (2); a laser beam amplifier (15); means (18) for transporting the pulsed laser beam to the input of this amplifier; eit   means (21) for moving the amplification   tor (15) facing said surface and in the vicinity of it.   8 Equipment according to claim 7, characterized in that the generator (12) is of the Nd-YAG or excimer type, possibly equipped with a Gaussian mirror of return, and in that said means of   transport (18) comprise an optical fiber.   Equipment according to claim 8, characterized in that the optical fiber (18) has a length of at least approximately 15 m.   Equipment according to any of the   claims 7 to 9, characterized in that   takes a deflection mirror (38) mounted at the output of the amplifier (15) and possibly mobile by report to this one.   11 Equipment according to any of the   claims 7 to 10, characterized in that   takes a mobile confinement enclosure (16)   with the amplifier (15) or with the mirror (38) and provided with suction means (13, 14, 20) and possibly with means (19) for introducing a gas protective or active.   12 Equipment according to any of the   Claims 7 to 11, characterized in that   takes an electrode (39) parallel to said surface, pierced with an orifice (40) for passing the amplified laser beam and movable integrally with the amplifier   (15), and means (41) for creating an electric field   than between this electrode and said surface.