CA1198482A - Laser decontamination method - Google Patents
Laser decontamination methodInfo
- Publication number
- CA1198482A CA1198482A CA000424947A CA424947A CA1198482A CA 1198482 A CA1198482 A CA 1198482A CA 000424947 A CA000424947 A CA 000424947A CA 424947 A CA424947 A CA 424947A CA 1198482 A CA1198482 A CA 1198482A
- Authority
- CA
- Canada
- Prior art keywords
- laser
- approximately
- steam generator
- component
- radiation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- 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
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
- F22B37/00—Component parts or details of steam boilers
- F22B37/002—Component parts or details of steam boilers specially adapted for nuclear steam generators, e.g. maintenance, repairing or inspecting equipment not otherwise provided for
- F22B37/003—Maintenance, repairing or inspecting equipment positioned in or via the headers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B08—CLEANING
- B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- B08B7/00—Cleaning by methods not provided for in a single other subclass or a single group in this subclass
- B08B7/0035—Cleaning by methods not provided for in a single other subclass or a single group in this subclass by radiant energy, e.g. UV, laser, light beam or the like
- B08B7/0042—Cleaning by methods not provided for in a single other subclass or a single group in this subclass by radiant energy, e.g. UV, laser, light beam or the like by laser
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
- G21F9/005—Decontamination of the surface of objects by ablation
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- High Energy & Nuclear Physics (AREA)
- Optics & Photonics (AREA)
- Thermal Sciences (AREA)
- Mechanical Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Food Science & Technology (AREA)
- Cleaning In General (AREA)
- Laser Beam Processing (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
- Apparatus For Disinfection Or Sterilisation (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The laser decontamination method comprises directing a laser beam at the surface of the radioactive component to be decontaminated for removing the radioactive oxide layer from the component without damaging the compo-nent. The method further comprises reflecting the laser beam from a reflective surface for directing the reflected laser beam to inaccessible areas of the component to be decontaminated. In addition, the method may comprise isolating the area to be decontaminated so that the oxide film that is removed from the component may be collected so as to prevent recontamination or contamination of other components.
The laser decontamination method comprises directing a laser beam at the surface of the radioactive component to be decontaminated for removing the radioactive oxide layer from the component without damaging the compo-nent. The method further comprises reflecting the laser beam from a reflective surface for directing the reflected laser beam to inaccessible areas of the component to be decontaminated. In addition, the method may comprise isolating the area to be decontaminated so that the oxide film that is removed from the component may be collected so as to prevent recontamination or contamination of other components.
Description
il9~ 2 1 49,~98 LASER DECONTAMINATION METHOD
BACKGROUND OF THE ~NVENTION
This invention relates to decontamination methods and more particularly to methods for laser decontaminating components of nuclear power plants.
During the operation of nuclear power plants and similar apparatus, certain components become exposed to radiation and may develop a thin radioactive film on the surface of the component. From time to time, it is neces-sary to either inspect or repair these components of the nuclear reactor power plant. During the inspection or repair of the components, it is necessary for working personnel to enter the component or to be stationed in close proximity to the component whereby working personnel may be exposed to radiation emitted from the contaminated component. In some circumstances, the radiation ield emitted from these components is such that a worker would receive the maximum permissible radiation dose in less than five minutes of working time. Such a situation means that a given worker may spend only a relatively short amount of time working on the inspection or the repair operation o~ the nuclear component. ~aving each worker spend a relatively short amount of time in the repair or inspection procedura, necessitates the use of many workers with each worker working a short time, in order to accom-plish the desired procedure. While this may ~e an accept-able practice for minor inspections or repair procedures, ,. ~
1~9~
BACKGROUND OF THE ~NVENTION
This invention relates to decontamination methods and more particularly to methods for laser decontaminating components of nuclear power plants.
During the operation of nuclear power plants and similar apparatus, certain components become exposed to radiation and may develop a thin radioactive film on the surface of the component. From time to time, it is neces-sary to either inspect or repair these components of the nuclear reactor power plant. During the inspection or repair of the components, it is necessary for working personnel to enter the component or to be stationed in close proximity to the component whereby working personnel may be exposed to radiation emitted from the contaminated component. In some circumstances, the radiation ield emitted from these components is such that a worker would receive the maximum permissible radiation dose in less than five minutes of working time. Such a situation means that a given worker may spend only a relatively short amount of time working on the inspection or the repair operation o~ the nuclear component. ~aving each worker spend a relatively short amount of time in the repair or inspection procedura, necessitates the use of many workers with each worker working a short time, in order to accom-plish the desired procedure. While this may ~e an accept-able practice for minor inspections or repair procedures, ,. ~
1~9~
2 49,298 this is not an acceptable practice where there is an extensive inspection or an extensive repair job to be performed. Where the procedure to be performed is a time-consuming procedure, it is likely that an unusally large number of highly trained personnel would be necessary to carry out the task. Such a situation may not only be unacceptable from a financial aspect, but may also be unacceptable from a manpower level aspect. A solution of this problem may be to reduce the radiation field associ-ated with the component to allow the workin~ personnel alonger working time. One approach for reducing the radia-tion field associated with the nuclear component on which the repair operation is to be performed, is to remove the deposited film of radioactive metal oxides from the exposed surfaces of the nuclear component.
There are several methods known in the art for removing the radioactive oxide layer from the nuclear component so as to reduce the radiation field associated with that component. For example, an abrasive grit may be sprayed against the component to abrade the oxide film from the component thereby lowering the radiation field associated with the component. In addition, chemical processes have been attempted to dissolve the oxide film from the component to thereby remove the oxide ilm and associated radiation field from the component.
In addition to the methods that have been previ-ously attempted for reducing radiation fields associated with nuclear components, it is known in the prior art to use laser radiation and radiation rom pulsed flash lamps to remove various kinds of surface films from objects such as artworks and structures. This type of laser radiation may employ intensities which have the ability to kill mildew on rare old books, to remove paint from metal surfaces, to chip away limestone deposits from Indian cliff paintings or to convert rust to magnetite on stael structures. However, none of these procedures have been developed for use in removing radioactive oxide ilms rom il9~ 2
There are several methods known in the art for removing the radioactive oxide layer from the nuclear component so as to reduce the radiation field associated with that component. For example, an abrasive grit may be sprayed against the component to abrade the oxide film from the component thereby lowering the radiation field associated with the component. In addition, chemical processes have been attempted to dissolve the oxide film from the component to thereby remove the oxide ilm and associated radiation field from the component.
In addition to the methods that have been previ-ously attempted for reducing radiation fields associated with nuclear components, it is known in the prior art to use laser radiation and radiation rom pulsed flash lamps to remove various kinds of surface films from objects such as artworks and structures. This type of laser radiation may employ intensities which have the ability to kill mildew on rare old books, to remove paint from metal surfaces, to chip away limestone deposits from Indian cliff paintings or to convert rust to magnetite on stael structures. However, none of these procedures have been developed for use in removing radioactive oxide ilms rom il9~ 2
3 49,298 nuclear components in a manner to prevent damage to the nuclear component and in a manner to prevent redeposition of higher levels of radioactive oxides on the nuclear component.
5Therefore, what is needed is a decontamination method that reduces the radiation field in components of nuclear reactor power plants without damagin~ the component or cre~ting a situation in which the rate of deposition of radioactive oxide on the component is accelerated when the component is placed into service.
SUMMARY OF THE INVENTION
The laser decontamination method comprises directing a laser beam at the surface of the radioactive component to be decontaminated for removing the radioactive oxide layer from the component without damaging the compo-nent. The method further comprises reflecting the laser beam from a reflective surface for directing the reflected laser beam to inaccessible areas of the component to be decontaminated. In addition, the method may comprise isolating the area to be decontaminated so that the oxide film that is removed from the component ma~ be collected so as to prevent recontamination or contamination of other components.
BRIEF DESCRIPTION OF THE DRAWINGS
25While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the invention, it is believed the inven-tion will be better understood from the following descrip-tion, taken in conjunction with the accompanied drawing, 30 ~ wherein the single figure of the drawing is a schematic diagram of the laser apparatus to be employed in the method.
DESCRIPTION OF THF. ~REFERRED EMBODIMENT
During operation o a typical nuclear power plant, certain components of the nuclear power plant such as the nuclear steam ~generators, become radioactively contaminated. Since certain repair or inspection opera-~9~3~fl2
5Therefore, what is needed is a decontamination method that reduces the radiation field in components of nuclear reactor power plants without damagin~ the component or cre~ting a situation in which the rate of deposition of radioactive oxide on the component is accelerated when the component is placed into service.
SUMMARY OF THE INVENTION
The laser decontamination method comprises directing a laser beam at the surface of the radioactive component to be decontaminated for removing the radioactive oxide layer from the component without damaging the compo-nent. The method further comprises reflecting the laser beam from a reflective surface for directing the reflected laser beam to inaccessible areas of the component to be decontaminated. In addition, the method may comprise isolating the area to be decontaminated so that the oxide film that is removed from the component ma~ be collected so as to prevent recontamination or contamination of other components.
BRIEF DESCRIPTION OF THE DRAWINGS
25While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the invention, it is believed the inven-tion will be better understood from the following descrip-tion, taken in conjunction with the accompanied drawing, 30 ~ wherein the single figure of the drawing is a schematic diagram of the laser apparatus to be employed in the method.
DESCRIPTION OF THF. ~REFERRED EMBODIMENT
During operation o a typical nuclear power plant, certain components of the nuclear power plant such as the nuclear steam ~generators, become radioactively contaminated. Since certain repair or inspection opera-~9~3~fl2
4 49,298 tions that must be performed periodically on the nuclearpower plant components require working personnel to be present in or near the components, it is important that the radiation field associated with the component be at a level that is compatible with the presence of working personnel for an extended period of time. The invention, described herein, is a method for laser decontaminating nuclear componentR so that working personnel may perform operations thereon.
A one-dimensional surface heating model of a laser beam interacting with a surface is generally known in the art. This model assumes that the laser beam is uniform with no transverse variations and that the surface film is approximately uniform. The model also assumes that the surface is planer and normal to the incident direction of the laser beam. These conditions are approx-imately true if: ~
1. The transverse dimensions of the actual laser beam are much greater than the surface film thickness;
2. The transverse dimensions of the actual laser beam are much greater than the thermal diffusion distance in the material; and 3. The lateral scale size for changes in the surface contour and film thickness is much greater than the average film thickness.
The first condition is satisfied in most situa-tions where the laser beams are 0.1 to 1 cm in diameter and the oxide films of interest are typically less than 10 4 cm (approximately 40 microinches). In the case of typical nuclear components, the transverse dimensions of the actual laser beam are much greater than the oxide film thicknesses o the nuclear reactor component which satis-fied the first condition. The second condition requires consideration of the thermal difusivity for the material and the laser pulse length. For typical metals and metal oxides of nuclear reactor components, the thermal di-fl2 49,298 fusivity is approximately 0.2 cm sq. per second. The distance that a thermal wave will advance into such a material during a typical laser pulse length of approxi-mately 1 microsecond is approximately 4.0 x 10 4 cm (1.7 x 10 4 inches) which easily satisfies the second condition that the transverse dimensions of the actual laser beam be much greater than the thermal diffusion distance into the material. The third condition should be satisfied over most of the area of the nuclear component, because the lateral scale size for changes in the surface contour and oxide thickness is much greater than the average oxide thickness itself. Therefore, it appears that a one-dimensional surface heating model of a laser beam inter-acting with an oxide covered surface will ade~uately predict the interaction of a suitable laser on the oxide layer of a nuclear component.
As noted earlier, the oxide films encount~red on nuclear components are typically less than approximately 40 microinches thick. It has been found that to achieve thermal penetration depths comparable to the film thick-nesses on these components thereby avoiding extensive thermal damage to the base metal, the laser pulse length should be approximately one microsecond in duration. Both the pulsed TE C02 laser and Q-switched YAG laser can be used to satisfy this pulse length criteria.
In addition to determining the penetration depth of a pulse of the laser, it is also important to be able to determine the oxide surface temperatures as a unction of the incident laser pulse length so as to be able to ascertain the laser energy densities required. In order to remove oxide films of this nature, high surface temper-atures of approximately 2,000-3,000K are generally required. Since short laser pulses of approximately 1 microsecond are required to limit the thermal penetration depth to avoid base metal damage and in order to achieve surface temperatures of approximately 2,000-3,00QK with a laser pulse length of approximately 1 mircosecond, it is ~19~ 2 6 49,298 generally desirable to have laser energy densities of approximately 10 to 20 joules per square inch. Laser energy densities of approximately 10 to 20 joules per square inch are easily produced by pulsed C02 and YAG
A one-dimensional surface heating model of a laser beam interacting with a surface is generally known in the art. This model assumes that the laser beam is uniform with no transverse variations and that the surface film is approximately uniform. The model also assumes that the surface is planer and normal to the incident direction of the laser beam. These conditions are approx-imately true if: ~
1. The transverse dimensions of the actual laser beam are much greater than the surface film thickness;
2. The transverse dimensions of the actual laser beam are much greater than the thermal diffusion distance in the material; and 3. The lateral scale size for changes in the surface contour and film thickness is much greater than the average film thickness.
The first condition is satisfied in most situa-tions where the laser beams are 0.1 to 1 cm in diameter and the oxide films of interest are typically less than 10 4 cm (approximately 40 microinches). In the case of typical nuclear components, the transverse dimensions of the actual laser beam are much greater than the oxide film thicknesses o the nuclear reactor component which satis-fied the first condition. The second condition requires consideration of the thermal difusivity for the material and the laser pulse length. For typical metals and metal oxides of nuclear reactor components, the thermal di-fl2 49,298 fusivity is approximately 0.2 cm sq. per second. The distance that a thermal wave will advance into such a material during a typical laser pulse length of approxi-mately 1 microsecond is approximately 4.0 x 10 4 cm (1.7 x 10 4 inches) which easily satisfies the second condition that the transverse dimensions of the actual laser beam be much greater than the thermal diffusion distance into the material. The third condition should be satisfied over most of the area of the nuclear component, because the lateral scale size for changes in the surface contour and oxide thickness is much greater than the average oxide thickness itself. Therefore, it appears that a one-dimensional surface heating model of a laser beam inter-acting with an oxide covered surface will ade~uately predict the interaction of a suitable laser on the oxide layer of a nuclear component.
As noted earlier, the oxide films encount~red on nuclear components are typically less than approximately 40 microinches thick. It has been found that to achieve thermal penetration depths comparable to the film thick-nesses on these components thereby avoiding extensive thermal damage to the base metal, the laser pulse length should be approximately one microsecond in duration. Both the pulsed TE C02 laser and Q-switched YAG laser can be used to satisfy this pulse length criteria.
In addition to determining the penetration depth of a pulse of the laser, it is also important to be able to determine the oxide surface temperatures as a unction of the incident laser pulse length so as to be able to ascertain the laser energy densities required. In order to remove oxide films of this nature, high surface temper-atures of approximately 2,000-3,000K are generally required. Since short laser pulses of approximately 1 microsecond are required to limit the thermal penetration depth to avoid base metal damage and in order to achieve surface temperatures of approximately 2,000-3,00QK with a laser pulse length of approximately 1 mircosecond, it is ~19~ 2 6 49,298 generally desirable to have laser energy densities of approximately 10 to 20 joules per square inch. Laser energy densities of approximately 10 to 20 joules per square inch are easily produced by pulsed C02 and YAG
5 lasers.
From this analysis, it can be seen tha~ lasers are available having the required chara~teristics to remove radioactive oxide films from nuclear components without damaging the base metal of the component.
Referring to the drawing, a typical nuclear component that may be suitable for radioactive decontami-nation may be a nuclear steam generator and is referred to generally as 20. Steam generator 20 comprises an outer shell 22 with a divider plate 24 and tubesheet 26 disposed 15 therein as is well known in the art. Outer shell 22, divider plate 24, and tubesheet 26 define a plenum 28 through which the reactor coolant passes. In addition, a manw~y 30 is provided in outer shell 22 for allowing access to plenum 28 by working personnel. Durin~ operation 20 of steam generator 20, a reactor coolant flows through plenum 28 and through tubes 32 which are disposed through tube sheet 26. Since the reactor coolant flowing through steam generator 20 is radioactive, various surfaces of steam ~enerator 20 become deposited with an oxide film 25 that is radioactive. For example, the inner surface of shell 22, divider plate 24 and the lower surface of tube sheet 26 develop an oxide coating thereon that is radio-active. When it is desired to perform maintenance on heat exchanger tubes 32, working personnel may enter plenum 28 30 through manway 30 to perform maintenance on tubes 32. In order to increase the time in which working personnel may remain in plenum 28 to perform the maintenance, it is desirable to reduce the radiation field in plenum 28.
This may be accomplished by removing the oxide film that 35 is deposited on the surfaces o the components o steam generator 22 such as divider plate 24, tubesheet 2~ and the inner surface of shell 22 thereby reducing the radia-l~B~.ta~Z
7 49,298 tion field emitted therefrom. The invention describedherein provides a laser decontamination means for removing the oxide film on the surfaces of steam generator 20 to thereby reduce the radiation field associated with those surfaces.
Still referring to the figure, when steam gener-ator 20 has been deactivated an optical mechanism 34 may be placed in plenum ~8 and suspended from tubesheet 26 by attachment to the open ends of tubes 32. Optical mechanism 34 may comprise an electrically controlled movable reflec-tive mechanism 36 for reflecting radiation, such as light, to various surfaces of the steam generator. For example, reflective mechanism 36 may comprise a plurality of mirrors or prisms attached to the bottom of optical mechanism 34 for reflecting radiation that is directed to those reflec-tive surfaces. Optical mechanism 34 is connected electri-cally by electrical line 38 to an optical mechanism power supply 40 which may be located remote from steam generator 20 and separated from steam generator ~0 by a biological shield 42. In this manner, optical mechanism 34 may be remotely controlled and manipulated so that the operator is not exposed to the radiation field associated with steam generator 20. Optical mechanism power supply 40 provides a means by which optical mechanism 34 may be adjusted so as to change the reflective angles of the mirrors or prisms of reflective mechanism 36 which thereby redirects the radiation that is reflected from the mirrors or prisms to the desired surface to be decontaminated.
A power laser 46 as previously described herein may be arranged near the opening of manway 30 so that the radiation emitted from power laser 46 may be directed toward optical mechanism 34 as shown in the drawing.
Power laser 46 may be mounted on a support fixture 48 that i5 capable of moving power laser 46 relative to manway 30 and relative to optic.al mechanism 34 for properly aligning the radiation beam emitted from power laser 46. Support fixture 48 may be mounted on a generator platform 50 ~9S~Z
8 49,298 arranged near the opening of manway 30. Power laser 46 is connected electrically by electrical line 52 to laser power supply 54 located remote from steam generator 20 and behind a biological shield 42.
Power laser 46 may be a laser capable of emitting pulses of radiation with pulse lengths of less than 100 microseconds and preferably less than approximately 1 microseconds in duration. Power laser 46 may also be capable of emitting pulses having a wavelength of less than approximately 12 micrometers and preferably between approximately 0.30 to 1.5 micrometers for typical decon-tamination applications. In addition, power laser 46 may be capable of producing pulses with energy densities of between 1 to 104 joules/in2 and preferably of approximately 30-150 joules/in2 at the surface to be decontaminated. Of course, typical optical instruments such as lenses and mirrors may be employed in conjunctio~ with power laser 46 to achieve the desired energy densities at the surface.
More specifically, power laser 46 may be a Neodymium YAG
pulsed laser capable of emitting pulses of radiation with a wavelength of approximately 1.06 micrometers, an energy output of approximately 0.3 joules/pulse, a pulse length of approximately 30-40 nanoseconds and an energy density of approximately 50-60 joules/in2.
A shield plate 56 having an aperture 58 may be bolted to the outside of manway 30 for isolating plenum 28 from the outside of steam generator 20 for containing the radiation removed from the surfaces of plenum 28. Aperture 58 is provided for allowing the radiation beam from power laser 46 to pass therethrouqh and at optical mechanism 34.
A suction mechanism 60 may also be attached to shield plate 56 and extend therethrough into plenum 28 and may extend at the other end to a radioactive waste filtering system 62. Suction mechanism 60 provides a means by which the contamination removed from plenum 28 may be suctioned out of plenum 28 and into a radioactive waste filterin~
system 62 for disposal of the wa~te.
~19~ 2 9 4g,298 In operation, steam ~enerator 20 is deactivated and the reactor coolant is drained therefrom. The manway cover is removed from manway 30 and optical mechanism 34 is suspended from tube sheet 26 either manually or remote-ly. Shield plate 56 is then attached to manway 30 andpower laser 46 is arranged near aperture ~8 as shown in the drawing. Next, power laser 46 is activated by laser power supply 54 so that a beam of radiation is emitted from power laser 46 and directed toward the reflective surfaces of optical mechanism 34. From the reflective mechanism 36 of optical mechanism 34, the radiation emitted from power laser 46 is reflected toward the selected surface of the interior of steam generator 20. Power laser 46 may be pulsed with a pulse length of approximately 30-40 nanoseconds and at an energy level of approximately 0~3 joules/pulse so as to impinge the surface to be decon-taminated with an energy density of approximately 50~60 joules/in2. As described previously, the laser radiation is such that it removes an oxide layer of approximately 0.00002 inches from the surfaces of plenum 28 and thereby reduces the radiation field associated with the oxide film without damaging the base metal. The oxide layer removed is exhausted from plenum 28 by means of suction mechanism 60. As this process continues, optical mechanism 34 is controlled so as to allow the laser beam from power laser 46 to scan all of the surfaces of the interior of plenum 28. In this manner, the entire interior of plenum 28 may be decontaminated. Of course, power laser 46 need not be directed toward optical mechanism 34, but rather it can be aimed directly at the surface to be decontaminated.
Therefore t the in~ention provides a decontamina-- tion method that reduces the radiation field in components of nuclear reactor power plants without damagin~ the component.
From this analysis, it can be seen tha~ lasers are available having the required chara~teristics to remove radioactive oxide films from nuclear components without damaging the base metal of the component.
Referring to the drawing, a typical nuclear component that may be suitable for radioactive decontami-nation may be a nuclear steam generator and is referred to generally as 20. Steam generator 20 comprises an outer shell 22 with a divider plate 24 and tubesheet 26 disposed 15 therein as is well known in the art. Outer shell 22, divider plate 24, and tubesheet 26 define a plenum 28 through which the reactor coolant passes. In addition, a manw~y 30 is provided in outer shell 22 for allowing access to plenum 28 by working personnel. Durin~ operation 20 of steam generator 20, a reactor coolant flows through plenum 28 and through tubes 32 which are disposed through tube sheet 26. Since the reactor coolant flowing through steam generator 20 is radioactive, various surfaces of steam ~enerator 20 become deposited with an oxide film 25 that is radioactive. For example, the inner surface of shell 22, divider plate 24 and the lower surface of tube sheet 26 develop an oxide coating thereon that is radio-active. When it is desired to perform maintenance on heat exchanger tubes 32, working personnel may enter plenum 28 30 through manway 30 to perform maintenance on tubes 32. In order to increase the time in which working personnel may remain in plenum 28 to perform the maintenance, it is desirable to reduce the radiation field in plenum 28.
This may be accomplished by removing the oxide film that 35 is deposited on the surfaces o the components o steam generator 22 such as divider plate 24, tubesheet 2~ and the inner surface of shell 22 thereby reducing the radia-l~B~.ta~Z
7 49,298 tion field emitted therefrom. The invention describedherein provides a laser decontamination means for removing the oxide film on the surfaces of steam generator 20 to thereby reduce the radiation field associated with those surfaces.
Still referring to the figure, when steam gener-ator 20 has been deactivated an optical mechanism 34 may be placed in plenum ~8 and suspended from tubesheet 26 by attachment to the open ends of tubes 32. Optical mechanism 34 may comprise an electrically controlled movable reflec-tive mechanism 36 for reflecting radiation, such as light, to various surfaces of the steam generator. For example, reflective mechanism 36 may comprise a plurality of mirrors or prisms attached to the bottom of optical mechanism 34 for reflecting radiation that is directed to those reflec-tive surfaces. Optical mechanism 34 is connected electri-cally by electrical line 38 to an optical mechanism power supply 40 which may be located remote from steam generator 20 and separated from steam generator ~0 by a biological shield 42. In this manner, optical mechanism 34 may be remotely controlled and manipulated so that the operator is not exposed to the radiation field associated with steam generator 20. Optical mechanism power supply 40 provides a means by which optical mechanism 34 may be adjusted so as to change the reflective angles of the mirrors or prisms of reflective mechanism 36 which thereby redirects the radiation that is reflected from the mirrors or prisms to the desired surface to be decontaminated.
A power laser 46 as previously described herein may be arranged near the opening of manway 30 so that the radiation emitted from power laser 46 may be directed toward optical mechanism 34 as shown in the drawing.
Power laser 46 may be mounted on a support fixture 48 that i5 capable of moving power laser 46 relative to manway 30 and relative to optic.al mechanism 34 for properly aligning the radiation beam emitted from power laser 46. Support fixture 48 may be mounted on a generator platform 50 ~9S~Z
8 49,298 arranged near the opening of manway 30. Power laser 46 is connected electrically by electrical line 52 to laser power supply 54 located remote from steam generator 20 and behind a biological shield 42.
Power laser 46 may be a laser capable of emitting pulses of radiation with pulse lengths of less than 100 microseconds and preferably less than approximately 1 microseconds in duration. Power laser 46 may also be capable of emitting pulses having a wavelength of less than approximately 12 micrometers and preferably between approximately 0.30 to 1.5 micrometers for typical decon-tamination applications. In addition, power laser 46 may be capable of producing pulses with energy densities of between 1 to 104 joules/in2 and preferably of approximately 30-150 joules/in2 at the surface to be decontaminated. Of course, typical optical instruments such as lenses and mirrors may be employed in conjunctio~ with power laser 46 to achieve the desired energy densities at the surface.
More specifically, power laser 46 may be a Neodymium YAG
pulsed laser capable of emitting pulses of radiation with a wavelength of approximately 1.06 micrometers, an energy output of approximately 0.3 joules/pulse, a pulse length of approximately 30-40 nanoseconds and an energy density of approximately 50-60 joules/in2.
A shield plate 56 having an aperture 58 may be bolted to the outside of manway 30 for isolating plenum 28 from the outside of steam generator 20 for containing the radiation removed from the surfaces of plenum 28. Aperture 58 is provided for allowing the radiation beam from power laser 46 to pass therethrouqh and at optical mechanism 34.
A suction mechanism 60 may also be attached to shield plate 56 and extend therethrough into plenum 28 and may extend at the other end to a radioactive waste filtering system 62. Suction mechanism 60 provides a means by which the contamination removed from plenum 28 may be suctioned out of plenum 28 and into a radioactive waste filterin~
system 62 for disposal of the wa~te.
~19~ 2 9 4g,298 In operation, steam ~enerator 20 is deactivated and the reactor coolant is drained therefrom. The manway cover is removed from manway 30 and optical mechanism 34 is suspended from tube sheet 26 either manually or remote-ly. Shield plate 56 is then attached to manway 30 andpower laser 46 is arranged near aperture ~8 as shown in the drawing. Next, power laser 46 is activated by laser power supply 54 so that a beam of radiation is emitted from power laser 46 and directed toward the reflective surfaces of optical mechanism 34. From the reflective mechanism 36 of optical mechanism 34, the radiation emitted from power laser 46 is reflected toward the selected surface of the interior of steam generator 20. Power laser 46 may be pulsed with a pulse length of approximately 30-40 nanoseconds and at an energy level of approximately 0~3 joules/pulse so as to impinge the surface to be decon-taminated with an energy density of approximately 50~60 joules/in2. As described previously, the laser radiation is such that it removes an oxide layer of approximately 0.00002 inches from the surfaces of plenum 28 and thereby reduces the radiation field associated with the oxide film without damaging the base metal. The oxide layer removed is exhausted from plenum 28 by means of suction mechanism 60. As this process continues, optical mechanism 34 is controlled so as to allow the laser beam from power laser 46 to scan all of the surfaces of the interior of plenum 28. In this manner, the entire interior of plenum 28 may be decontaminated. Of course, power laser 46 need not be directed toward optical mechanism 34, but rather it can be aimed directly at the surface to be decontaminated.
Therefore t the in~ention provides a decontamina-- tion method that reduces the radiation field in components of nuclear reactor power plants without damagin~ the component.
Claims (6)
We claim as our invention:
1. A method for decontaminating a radioactive nuclear steam generator comprising:
mounting a neodymium YAG pulsed laser near the manway of said steam generator;
mounting a remotely movable reflective mechanism to the tube sheet of said steam generator;
mounting on said manway a shield plate having an aperture therein;
directing a laser beam through said aperture of said shield plate to said reflective mechanism; and activating said laser and causing said laser to emit pulses of radiation toward said reflective mechanism with said reflective mechanism redirecting said pulses of radiation toward the surfaces of said steam generator and producing energy densities at said surfaces of approximately 30-150 joules/in2 for removing a thin layer of radioactively contaminated metal from said surface thus lowering the radiation level associated with said surface.
mounting a neodymium YAG pulsed laser near the manway of said steam generator;
mounting a remotely movable reflective mechanism to the tube sheet of said steam generator;
mounting on said manway a shield plate having an aperture therein;
directing a laser beam through said aperture of said shield plate to said reflective mechanism; and activating said laser and causing said laser to emit pulses of radiation toward said reflective mechanism with said reflective mechanism redirecting said pulses of radiation toward the surfaces of said steam generator and producing energy densities at said surfaces of approximately 30-150 joules/in2 for removing a thin layer of radioactively contaminated metal from said surface thus lowering the radiation level associated with said surface.
2. The method according to claim 1 wherein said method further comprises remotely manipulating said reflective mechanism for causing said pulses of radiation to scan said surface.
3. The method according to claim 2 wherein said method further comprises suctioning said contaminants removed from said surface for transporting said contaminants away from said steam generator.
4. The method according to claim 3 wherein said method further comprises filtering said contaminants for collecting said contaminants for disposal.
5. The method according to claim 3 wherein said laser produces an energy density at said surface of approxi-mately 50-60 joules/in2.
6. The method according to claim 5 wherein said laser emits pulses of approximately 0.3 joules/pulse with a pulse length of approximately 30-40 nanoseconds and at a wave-length of approximately 1.06 micrometers.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US368,075 | 1982-04-11 | ||
| US36807582A | 1982-04-14 | 1982-04-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1198482A true CA1198482A (en) | 1985-12-24 |
Family
ID=23449771
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000424947A Expired CA1198482A (en) | 1982-04-14 | 1983-03-30 | Laser decontamination method |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0091646B1 (en) |
| JP (1) | JPS58187898A (en) |
| KR (1) | KR840004610A (en) |
| CA (1) | CA1198482A (en) |
| DE (1) | DE3368800D1 (en) |
| ES (1) | ES8703050A1 (en) |
| FR (1) | FR2525380A1 (en) |
Families Citing this family (29)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2169496B (en) * | 1985-01-16 | 1987-12-23 | Stc Plc | Cleaning metal surfaces |
| US5821175A (en) * | 1988-07-08 | 1998-10-13 | Cauldron Limited Partnership | Removal of surface contaminants by irradiation using various methods to achieve desired inert gas flow over treated surface |
| US5531857A (en) * | 1988-07-08 | 1996-07-02 | Cauldron Limited Partnership | Removal of surface contaminants by irradiation from a high energy source |
| US5643472A (en) * | 1988-07-08 | 1997-07-01 | Cauldron Limited Partnership | Selective removal of material by irradiation |
| US6048588A (en) * | 1988-07-08 | 2000-04-11 | Cauldron Limited Partnership | Method for enhancing chemisorption of material |
| FR2674983B1 (en) * | 1991-04-05 | 1994-08-05 | Framatome Sa | LASER WORKING PROCESS AND EQUIPMENT IN A CONTAMINATED AREA OF A NUCLEAR FACILITY. |
| FR2678418B1 (en) * | 1991-06-26 | 1994-08-05 | Framatome Sa | LASER WORKING PROCESS IN A CONTAMINATED AREA OF A NUCLEAR FACILITY, AND EQUIPMENT FOR ITS IMPLEMENTATION. |
| US5425072A (en) * | 1992-01-04 | 1995-06-13 | British Nuclear Fuels Plc | Method of heat treating a radioactive surface |
| FR2700882B1 (en) * | 1993-01-26 | 1995-03-03 | Commissariat Energie Atomique | Method and installation for decontamination of a radioactive surface by means of a beam of coherent light. |
| GB9322845D0 (en) * | 1993-11-05 | 1993-12-22 | British Nuclear Fuels Plc | A method of treating a surface |
| GB9323052D0 (en) * | 1993-11-09 | 1994-01-05 | British Nuclear Fuels Plc | Radioactive decontamination |
| JP2615362B2 (en) * | 1994-02-10 | 1997-05-28 | 理化学研究所 | Method and apparatus for removing surface deposits by laser |
| WO1995024279A1 (en) * | 1994-03-10 | 1995-09-14 | Ishikawa, Toshiharu | Film removing device |
| GB9407058D0 (en) * | 1994-04-09 | 1994-06-01 | British Nuclear Fuels Plc | Material removal by laser ablation |
| GB9412238D0 (en) * | 1994-06-17 | 1994-08-10 | British Nuclear Fuels Plc | Removing contamination |
| JP3461948B2 (en) * | 1995-02-06 | 2003-10-27 | 株式会社東芝 | Underwater laser processing method |
| US5790620A (en) * | 1995-01-31 | 1998-08-04 | Kabushiki Kaisha Toshiba | Underwater laser processing method and apparatus |
| TW284907B (en) * | 1995-06-07 | 1996-09-01 | Cauldron Lp | Removal of material by polarized irradiation and back side application for radiation |
| US5780806A (en) * | 1995-07-25 | 1998-07-14 | Lockheed Idaho Technologies Company | Laser ablation system, and method of decontaminating surfaces |
| DE102005009324B9 (en) * | 2005-02-24 | 2008-05-21 | Technische Universität Dresden | Method and device for decontamination of surfaces |
| FR2887161B1 (en) * | 2005-06-20 | 2007-09-07 | Commissariat Energie Atomique | METHOD AND DEVICE FOR LASER ABLATION OF A SURFACE LAYER OF A WALL, SUCH AS A PAINT COATING IN A NUCLEAR PLANT |
| JP5500620B2 (en) * | 2009-04-28 | 2014-05-21 | 独立行政法人日本原子力研究開発機構 | Decontamination apparatus and decontamination method |
| US10112257B1 (en) | 2010-07-09 | 2018-10-30 | General Lasertronics Corporation | Coating ablating apparatus with coating removal detection |
| US9895771B2 (en) * | 2012-02-28 | 2018-02-20 | General Lasertronics Corporation | Laser ablation for the environmentally beneficial removal of surface coatings |
| KR101437384B1 (en) * | 2013-01-31 | 2014-09-15 | 대한민국 | The method for removing lacquer and soot of lacquer gilding surface by Nd:YAG Laser |
| EP3706140A1 (en) | 2019-03-06 | 2020-09-09 | Evekinger Rohr- und Profilwerke GmbH | Device and method for decontaminating a wall surface of in particular a hollow body |
| FR3100002B1 (en) | 2019-08-21 | 2021-11-19 | Onet Tech Cn | Process for decontaminating by pulsed laser a metal part comprising on its surface a layer of metal oxides |
| 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 |
| DE102021110458B4 (en) | 2021-04-23 | 2022-12-29 | Evekinger Rohr- Und Profilwerke Gmbh | Device for treating an inner wall surface of a hollow body |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1382915A (en) * | 1972-04-25 | 1975-02-05 | British Nuclear Fuels Ltd | Decontamination of fuel element sheaths |
| LU71852A1 (en) * | 1975-02-14 | 1977-01-05 |
-
1983
- 1983-03-30 CA CA000424947A patent/CA1198482A/en not_active Expired
- 1983-04-06 DE DE8383103326T patent/DE3368800D1/en not_active Expired
- 1983-04-06 EP EP83103326A patent/EP0091646B1/en not_active Expired
- 1983-04-07 JP JP58062057A patent/JPS58187898A/en active Granted
- 1983-04-11 KR KR1019830001506A patent/KR840004610A/en not_active Application Discontinuation
- 1983-04-12 ES ES521391A patent/ES8703050A1/en not_active Expired
- 1983-04-13 FR FR8306046A patent/FR2525380A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| ES521391A0 (en) | 1987-01-16 |
| EP0091646A1 (en) | 1983-10-19 |
| DE3368800D1 (en) | 1987-02-05 |
| ES8703050A1 (en) | 1987-01-16 |
| EP0091646B1 (en) | 1986-12-30 |
| FR2525380B1 (en) | 1985-04-19 |
| KR840004610A (en) | 1984-10-22 |
| FR2525380A1 (en) | 1983-10-21 |
| JPH0145039B2 (en) | 1989-10-02 |
| JPS58187898A (en) | 1983-11-02 |
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