TECHNICAL FIELD
The present invention relates generally to cleaning radioactive contamination using dry ice blasting.
BACKGROUND
Radionuclides or radioactive materials are generated by fission and activation in reactors, including power reactors, research (non-power) reactors, naval and marine-type reactors, plutonium production reactors, and marine fuel cells of nuclear facilities such as nuclear power plants, nuclear research facilities, nuclear propulsion facilities, and government facilities including Department of Energy (DOE) facilities, naval facilities and nuclear submarines. These radioactive materials may contaminate various components of the nuclear power plant including spare parts, hand tools, equipment, motors, etc., used in the operation and maintenance of the nuclear power plant, or other power plant components such as ducts, pipes, vessels, and tanks which may be exposed to coolant, liquid, ion-exchange resins or other media which may be contaminated with radioactive material. Contaminated components must be stored under controlled conditions until the radioactivity of the contaminant decays away, or be disposed of as radioactive waste. The length of time a contaminated component must be stored is defined by the half-life of the radioactive material in the contaminant. For example, components contaminated with cobalt-60 must be stored for a minimum of 5.27 years, e.g., for the half-life or cobalt-60, for the radioactivity of the cobalt-60 to completely decay, resulting in transformation of the cobalt-60 to the stable isotope nickel-60.
The volume of radioactive waste in the form of contaminated components which must be stored and/or disposed of may be reduced by cleaning the contaminated components sufficiently to remove and contain the radioactive contaminants such that the cleaned components may be released for continued use. However, cleaning the radioactive contaminants using existing processes generally employs some form of solvent or other carrier during the cleaning processes, which generates a contaminated carrier that requires secondary decontamination, cleaning and/or controlled disposal and may leave a residue requiring secondary cleaning or increase corrosion susceptibility of the component. The radioactive contaminant may be deposited on the contaminated component in a form such as sludge, resin or crud, where removal by solvent methods may be ineffective and abrasive removal methods, which may use an abrasive media such as grit or sand, may be employed. Abrasive removal methods may be detrimental to the component being cleaned and may generate incremental waste in the form of contaminated abrasive grit. Additionally, abrasive cleaning methods may be unacceptable because of the potential to cause the radioactive contaminant to become embedded in the component as a result of the abrasive cleaning process, such that the component may be clean smearable, e.g., no radioactive contaminant may be wiped from the surface of the component during a smear or wipe test, but remains contaminated by a fixed contaminant in the form of the radioactive material which has become embedded in the component. A component with fixed contamination must be stored for the duration of the half-life of the radioactive contaminant until radioactive decay is complete. Some contaminated components, such as electronics, electrical tools, motors, etc., may be rendered inoperative by solvent or abrasive cleaning methods.
SUMMARY
A system and method for cleaning components contaminated with radioactive materials is provided herein using dry ice blasting to remove the radioactive contaminant from the contaminated component in a chamber including a directed air flow. The removed contaminant is transported by the directed air flow for collection in a HEPA filter. During the cleaning process, the dry ice used for the blasting process sublimates into gaseous carbon dioxide such that no incremental contaminated cleaning media or residue is generated during decontamination of the component. Multiple cleaning cycles, if required, can be completed without interim rinsing or other interruption of the cleaning process. By containing the radioactive contaminant within a chamber and using a directed air flow to transport the contaminant to the HEPA filter, free release of the radioactive contaminant is prevented. Because the dry ice is non-corrosive, non-abrasive and environmentally neutral, damage to the component being cleaned and decontaminated is prevented or substantially avoided. Because dry ice sublimates on impact, cleaning of electrical components without compromising electrical function is enabled.
The HEPA filter including the removed contaminant in a concentrated form may be removed for controlled storage and/or disposal as radioactive waste. By concentrating the removed contaminant in a smaller volume in the HEPA filter, the volume of radioactive waste which must be stored or disposed of is substantially reduced in comparison with the radioactive waste volume which would be generated by disposal of the uncleaned contaminated component. Because of sublimation of the dry ice, the radioactive contaminant remains in a dry, solid form during removal and containment. Additionally, the cleaned and decontaminated component can be released for reinstatement to use, eliminating the cost associated with replacement of the component.
The above features and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a method for removing radioactive contamination from a component;
FIG. 2 is a schematic illustration of a first example system for removing radioactive contamination from a component using the method of FIG. 1;
FIG. 3 is a schematic illustration of a second example system for removing radioactive contamination from a component using the method of FIG. 1; and
FIG. 4 is a schematic illustration of an optional configuration of the system of FIG. 3.
DETAILED DESCRIPTION
Referring to the drawings wherein like reference numbers represent like components throughout the several figures, the elements shown in FIGS. 1-4 are not necessarily to scale or proportion. Accordingly, the particular dimensions and applications provided in the drawings presented herein are not to be considered limiting. FIG. 1 is a schematic illustration of a method generally indicated at 100 for removing radioactive contamination from a contaminated component. FIG. 2 is a schematic illustration of a first example system generally indicated at 10A for removing radioactive contamination using the method 100 of FIG. 1, wherein the contaminant is present on a surface defined by the component, and the component at least partially defines a cleaning chamber through which air flow is directed through the chamber and through a HEPA filter to collect contaminants removed by dry ice blasting during the cleaning process.
Referring to FIGS. 1 and 2, in step 105 of the method 100, a contaminated component, identified in a non-limiting example in FIG. 2 as a component 60, or contaminated portion of the component, identified in FIG. 2 as a substrate or surface 62, is isolated or contained in a chamber 12 for cleaning In the example shown in FIG. 2, the component 60 may be a duct 70 or portion of the duct, and the contaminated portion of the component 60 may be the internal wall surface 62 of the duct 70. The chamber 12 may be formed by sealing the duct 70 or a portion thereof at a first end using a sealing element 66, which may be a shut-off integral to the duct or may be a sealing element configured for temporary installation into the duct to create a substantially air tight seal between the chamber 12 and another portion of the duct. The chamber 12 includes an air outlet 76, which in the example of FIG. 2 may be defined by a portion of the duct 70 sealed at a sealing interface 68 to form a substantially air tight seal with an outgoing air passage 18 and to enclose the chamber 12. The outgoing air passage 18 may be configured as a conduit, hose, or duct, and may be flexible, adjustable and/or reconfigurable to be readily adapted for sealing to different types and configurations of a contaminated component 60. Other openings, registers, joints or other potential air leak paths in the duct 70 between the sealing element 66 and the air outlet portion 76 may be sealed to seal the chamber 12 to be substantially air tight.
In the example shown in FIG. 2, an access 24 to the chamber 12 is defined by the duct 70. The access 24 is of sufficient size to insert a dry ice blasting unit 30A operatively attached to a dry ice blasting device 30 by a flexible supply line 74 into the chamber 12 and duct 70. A cover 72 may be configured to receive the supply line 74 such that the supply line 74 may movably pass through the cover 72. The cover 72 is configured to seal to the duct 70 so as to enclose the access 24, and the cover 72 may be referred to herein as a duct enclosure. The cover 72 may be further configured to receive an incoming air passage 16 such that air 14 may flow from the incoming air passage 16 into the chamber 12. The incoming air passage 16 is in fluid communication with the outgoing air passage 18. The incoming air passage 16 may be configured as a conduit, hose, or duct, and may be flexible, adjustable and/or reconfigurable to be readily adapted for connection to different types and configurations of a chamber 12 and/or duct enclosure 72. The “air” in the examples described herein may be air as that term is commonly understood, e.g., consisting primarily of a combination of oxygen, carbon dioxide and nitrogen, or may be a gas of controlled composition. For example, the “air” may be predominantly nitrogen or another inert gas composition.
The chamber 12 formed by the duct 70, the sealing element 66, the duct cover 72, and enclosed by the outgoing air passage 18, contains or isolates the contaminated surface 62 of the duct 70. The example shown in FIG. 2 is not intended to be limiting. For example, the access 24 may be defined by an end opening of the duct similar to the air outlet 76 and distal from the air outlet 76 such that the contaminated surface 62 is isolated in the duct portion between the duct end defining the access 24 and the distal duct air outlet 76. In this example, the cover 72 and incoming air passage 16 may be configured similar to the outgoing air passage 18 to seal to the perimeter of the duct opening, while including a port or opening to receive the supply line 74.
In an illustrative example, the surface 62 may be contaminated by a radioactive contaminated material 64 attached to the duct wall surface 62 which may be a residue of fluid flowing through the duct 70. The radioactive contaminated material 64 may be referred to herein as a radioactive contaminant, or as the contaminant. For example, the contaminant 64 may be comprised of ion-exchange resin of the type used in nuclear power plants to purify water used in the power plant, which has been contaminated by radioactive material present in the water and/or power plant. For example, the resin may be contaminated with cobalt-60, which may be present in the water as a product of neutron activation of components in the nuclear reactor cooled by the water. Cobalt-60 is a synthetic radioactive isotope of cobalt characterized by a half-life of 5.27 years, which decays by beta minus decay to the stable isotope nickel-60. The residue of resin and cobalt-60 may form a sludge-like radioactive contaminant 64 on the surface 62 of the duct 70, which must be removed from the surface 62 to reduce the level of radioactive contamination in the duct 70 and/or to prevent deterioration in performance of the duct 70 by build-up of the sludge contaminant 64 reducing the effective cross-section and fluid transfer capacity of the duct or insulating the duct 70 to affect heat transfer characteristics of the duct 70.
Still referring to FIGS. 1 and 2, at an optional step 110, a pre-cleaning measurement of radiation or radioactive material present on the contaminated surface 62 may be taken, using known techniques including but not limited to smear or wipe tests. The level of radioactive contamination may be measured, for example, in disintegrations per minute (dpm). Pre-cleaning measurements may be used, for example, to determine a decontamination factor (DF) after cleaning, by comparing the radiation level measure at step 110 with a radiation level measured after cleaning at an optional step 140. The pre-cleaning measurement step 110 may be completed after isolating the contaminated surface 62 in the chamber 12, or may be completed prior to step 105 or at another time in the method 100 prior to cleaning and decontamination of the surface 62.
At step 115, the ice blasting device 30 is configured for cleaning the contaminant 64 from the contaminated surface 62. In the example shown in FIG. 2, the ice blasting device 30 may be configured to pelletize dry ice from a dry ice source 32 and to feed the dry ice pellets using a carrier medium, such as pressurized air or nitrogen, through a conduit (not shown) in the supply line 74 to the blasting unit 30A, to be expelled in a high velocity blast stream (not shown) from a nozzle 34 movably attached to the blasting unit 30A. The supply line 74 may be configured to provide electrical power to the blasting unit 30A and/or transmit control signals, recorded images or other information between the blasting unit 30A and the blasting device 30. The dry ice pellet stream provides a blasting media for removal of the contaminant 64 from the contaminated surface 62 within the duct 70. The blasting unit 30A includes a propelling mechanism 42 for moving the blasting unit 30A in the duct 70, such that the blasting unit 30A can be repositioned to clean all portions of the contaminated surface 62. The propelling mechanism 42 may include one or more wheels or tracks for engaging the surface 62. The wheels or tracks may be modified or configured to assist with movement of the blasting unit 30A in the duct 70. In one example, the propelling surface(s) of the mechanism 42, e.g., the wheel surface(s), may be coated to resist adhesion of the sludge contaminant 64 to the propelling surface, and to facilitate traction against the contaminated surface 62. The blasting unit 30A may include a positioning mechanism 38 operatively connected to the nozzle 34 and configured to move to nozzle 34 to direct the dry ice blast stream at the surface 62. The positioning mechanism 38 and nozzle 34 may be configured such that the nozzle 34 may be one or more of rotated, articulated, extended and contracted to modify the direction of the dry ice blast stream. The blasting device 30 may include a controller 36 in electrical communication with the blasting device 30 and configured to control operation of the blasting device 30 including the blasting unit 30A, which may include remotely or robotically controlling movement of the blasting unit 30A in the duct 70 and movement of the blasting nozzle 34 and controlling the size and velocity of dry ice pellets in the dry ice blasting stream blasted from the nozzle 34. The blasting unit 30A may include a light source 44 for lighting the chamber 12, and/or a camera 46 for monitoring the dry ice cleaning process within the duct. The controller 36 may be configured to control the operation of the light source 44 and camera 46, which may include modifying the position of each of these. The controller 36 may include a display (not shown) for monitoring camera images. The controller 36 may be operatively connected to the blasting device 30A via the supply line 74. In another example, the blasting unit 30A and the controller 36 may be configured for wireless communication. Configuring the dry ice blasting device 30 to clean the contaminant 64 from the contaminated surface 62 at step 115 may include adjusting one or more of the dry ice pellet size, the size, range and/or velocity of the dry ice pellet stream (the blasting stream), the carrier fluid (compressed air, nitrogen, etc.) as required to clean the particular contaminant 64 from the particular contaminated surface 62.
At step 120 of FIG. 1, and prior to initiating cleaning of the contaminated surface 62 at step 125, a directed air flow 14 is created in the chamber 12. As shown in FIG. 2, the directed air flow 14 is generated by an air flow device 22 which directs the air flow 14 through the incoming air passage 16 and the chamber 12 in the direction indicated by the arrows identifying the air flow 14 to exit the chamber 12 via the outgoing air passage 18. The air flow 14 is directed through a filter 26 contained in a filter housing 28 and the filtered air is recirculated to the chamber 12 via the air flow device 22 in fluid communication with the outlet side of the filter 26 and filter housing 28. The air flow device 22 may be an air handling device of any configuration suitable to create a directed air flow 14 of sufficient pressure and velocity to entrain and transport contaminant 64 removed from the surface 62 during the dry ice blasting from the chamber 12 through the outgoing passage 18 and to the filter 26 for entrapment and collection. For example, the air flow device 22 may include or be configured as a blower, fan, compressor, rotary vane or screw pump, etc., to provide the directed air flow 14. The air flow 14 may be contained in a closed recirculating system, or may be supplemented by air provided through an air intake 20, which may be provided as make-up air or to maintain an air pressure in and/or air flow rate through the chamber 12 and/or the filter 26. The example shown in FIG. 2 is non-limiting, and other configurations are possible. For example, the system 10A may be configured for non-recirculating air flow, such that the air flow device 22 and filter housing 28 are not in fluid communication with each other. In a non-recirculating configuration, the air flow 14 may be created with air incoming through the air intake 20, and the filtered air may exit through the outlet side of the filter 26 and filter housing 28 for direct venting out of the system 10A. Alternatively, the filtered air exiting the filter 26 may be directed through another conduit (not shown) for remote venting and/or additional processing. A non-recirculating air flow configuration may be preferred, for example, to provide remote venting of the exiting air flow, which may substantially consist of carbon dioxide generated from sublimation of the dry ice during the blast cleaning, and/or nitrogen where nitrogen is used as a carrier medium for the dry ice, to minimize oxygen depletion in the workspace surrounding the filter 26.
In the examples shown in FIGS. 2-4, the filter 26 may be configured as a high efficiency particulate air filter (HEPA filter) having a minimum particle removal efficiency sufficient to entrap and contain the particles of radioactive contaminant 64 removed during the dry ice blast cleaning of method 100. In one example, the HEPA filter 26 may have a minimum particle removal efficiency of not less than 99.97% for 0.3 micron particles and a maximum pressure drop when clean of 250 Pascal when operated at rated airflow capacity. The HEPA filter 26 may be configured with a rigid casing extending the full depth of the filter medium (not shown), which may be a paper-based medium. In one example, the filter medium may be approximately 0.381 mm thick and may be constructed from ultra fine glass fibers which may be held together with an organic binder, such that the small fiber and high packing density of the media allow for efficient collection of submicron particles, including the radioactive contaminant particles 64 blasted from the surface 62 of the contaminated component 60, which in the present example is configured as the duct 70. The filter media of the filter 26 may be pleated to provide a large surface area to volume flow rate, and corrugated separators may be used to strengthen the filter 26 and prevent the filter media from collapsing. The HEPA filter 26 may be configured as a cartridge type filter which may be inserted into the filter housing 28, then removed as a unit for controlled radioactive waste storage and/or disposal of the used filter 26 and the contaminant 64 entrapped therein from the dry ice blast cleaning of the surface 62. Entrapping and containing the contaminant 64 in the filter 26 concentrates the contaminant 64 to substantially reduce the volume of radioactive waste which must be processed as radioactive waste as a result of the decontamination method 100 to the filter 26 and contained contaminant 64. In contrast and comparison with other methods which may use a solvent, abrasive cleaning media, or other cleaning media which must be collected as radioactive waste with the removed contaminant 64 and subsequently cleaned or disposed of at higher cost and/or volume of radioactive waste, the dry air blast cleaning method 100 provides an advantage of effective decontamination with minimum radioactive waste generation due to sublimation of the dry ice blasting media concentration of the contaminant 64 in the filter 26, reducing the radioactive waste volume and associated radioactive waste processing costs.
The example of a filter 26 and filter housing 28 shown in FIGS. 2-4 is not intended to be limiting. Other configurations of the filter 26 and/or filter housing 28 are possible. Filtering mechanisms having a minimum particle removal efficiency sufficient to entrap and contain the particles of radioactive contaminant 64 removed during the dry ice blast cleaning of method 100 other than HEPA-type filters may be used, which may include, for example, non-HEPA filters or other particle classification methods such as air classification. In another example, the system 10A, 10B, 10C may include a series of HEPA filters 26 arranged in one or more banks or arrays (not shown) to provide multiple or redundant filtering of the air flow 14, as may be required to remove the radioactive contaminant 64 from the air flow 14 and/or to achieve a minimum or target decontamination factor (DF). The decontamination factor, as that term is used in the art of radiological protection (RP), is a measure of the effectiveness of a decontamination process, such as the decontamination process illustrated by the method 100 of FIG. 1. The DF is a ratio of the radioactivity level prior to decontamination divided by the radioactivity level after decontamination. For example, for the cleaning method 100 applied to a component 60, the DF may be expressed as the ratio of the original contamination level of the contaminated surface 62 of the component 60 measured prior to cleaning, as described for step 110, to the remaining contamination level of the surface 62 measured after dry ice blast cleaning In an illustrative example, where the duct surface 62 has been contaminated with resin containing cobalt-60 as described previously, decontamination of the duct 70 using the method 100 of FIG. 1 effectively reduces the level of radioactive contamination from 100,000 disintegrations per minute (dpm) to zero dpm, e.g., to a level where the radioactive contamination after cleaning is reduced to a level which registers a zero reading using a measurement method such as smear or wipe testing, to achieve a DF of greater than 100. The system 10A (and 10B, 10C shown in FIGS. 3-4) may include a mechanism (not shown) for monitoring the filter 26 during the cleaning and decontamination process to determine the need for filter replacement, for example, when the filter 26 is reaching its capacity to entrap and contain contaminant 46. In one example, the mechanism may monitor pressure drop across the filter 26 as an indication of spent capacity. The monitoring mechanism may provide an alert to indicate that the filter 26 may be removed and replaced at intervals during the cleaning process when the filter 26 approaches or reaches its containment capacity. The alert may be provided in a visual, audible or other form and/or may be communicated to the controller 36 or other monitoring function such as an operations control function of the power plant including the system 10A, 10B, and 10C.
Still referring to FIGS. 1 and 2, at step 125 of the method 100, the contaminated surface 62 of the component 60, which in the example of FIG. 2 is the duct 70, is cleaned and decontaminated using the dry air blasting device 30 and blasting unit 30A. Dry ice from the dry ice source 32 is pelletized into dry ice pellets and propelled using a pressurized medium (carrier gas) such as air or nitrogen to the blasting unit 30A to provide a dry ice blasting stream (not shown) containing dry ice pellets and characterized by a blast velocity, e.g., the velocity of the dry ice pellets and/or the carrier gas in the blasting stream. The size of the pellets provided by the blasting device 30 may be controlled in a predetermined range such that the blasting stream may be characterized by a pellet size or pellet size range. The dry ice blasting stream is directed at the contaminated surface 62, where a scrubbing mechanism of the dry ice particles on impact with the contaminant 64 on the surface 62 acts to dislodge and/or remove the contaminant 64 from the surface 62. The dislodged contaminant particles 64 are entrained in and transported by the air flow 14 out of the chamber 12 via the outgoing air passage 18 and to the filter 26, where the contaminant particles 64 are entrapped and contained by the filter 26. The kinetic energy of the high speed dry ice pellets in combination with the pressurized carrier gas entraining the dry ice pellets results in one or more of fracturing, scrubbing, dislodging, and removal of the contaminant 64 from the surface 62 to decontaminate the duct 70.
The dry ice pellets sublimate into carbon dioxide on impact with the contaminant 64 and/or surface 62, e.g., the dry ice pellets on impact convert directly from the solid physical state into the gaseous state without any melt liquid being produced. Cleaning and decontaminating using dry ice blasting in a directed air flow 14 thus has the advantage that no residue of the dry ice blasting medium remain on the surface 62 and the gaseous carbon dioxide produced from sublimation of the dry ice along with the carrier gas from the blasting stream are readily removed in the air flow 14. Because no residue of the cleaning medium, e.g., the dry ice and the carrier gas, remains in the chamber 12 or on the surface 62, no subsequent rinsing or secondary operations are required to ensure removal of the cleaning medium. The dry ice blasting stream, which sublimates on contact or impact, is substantially non-abrasive and therefore abrasive damage to the surface 62 is prevented or substantially avoided during the cleaning process. The contaminant is dislodged and removed from the surface 62 without leaving any contaminant residue. Because the dry ice blasting is non-abrasive, and the dry ice sublimates on contact with the contamination, the contamination does not become embedded in the surface 62 or component 60, thereby preventing the formation of a fixed contaminant. The cleaning medium is essentially inert and does not present a secondary source of contamination of the surface 62, e.g., the cleaning medium is substantially inert relative to the surface 62 and does not present a corrosion-inducing or other potentially reactive substance relative to the surface 62. The pellet size and blast velocity of the dry ice blasting stream may be adjusted as required to effectively dislodge and remove the contaminant 64 from the surface 62 to clean and decontaminant the component 60. The characteristics of the dry ice blasting stream required for decontamination using the method 100 may be determined by the type of contaminant 64, the characteristics of the surface 62 and/or the component 60, including the configuration, material, function and operation of the surface 62 and the component 60. For example, the dry ice blasting stream may be selectively adjusted for the configuration of the duct 70 such that a smaller pellet size and/or higher blast velocity may be used when cleaning less accessible areas such as corners, bends, seams or other surface portions defined by small radii, recesses, or other less accessible portions as compared with the substantially flat or continuous wall surface areas of the duct 70, where a different combination of pellet size and/or blast velocity may be selected for use.
During the cleaning step 125, the dry ice blasting unit 30A is repositioned in the duct 70 and the blast nozzle 34 is repositioned as needed to clean the contaminated surface 62 isolated or contained in the chamber 12. Step 125 may be completed in one pass, e.g., in one cleaning cycle of the surface 62, such that each portion of the surface 62 is subjected to a single episode or single cleaning event. Depending on the characteristics of the contaminant 64, the component 60, the surface 62, the blasting stream, etc., more than one cleaning cycle of the surface 62 may be performed, and/or one or more portions of the surface 62 may be subjected to more than one cleaning episode during the cleaning cycle. The dislodged contaminant 64 is collected by the HEPA filter 26 at a collection and containment step 130. The filter 26 may be removed when its containment capacity is reached and replaced with another filter 26. At a radioactive waste processing step 135, the removed filter 26 including the entrapped radioactive contaminant 64 is processed as radioactive waste, which may include controlled storage and/or disposal of the filter 26 and contained contaminant 64.
At an optional step 140, post-cleaning measurement of the contaminant level present on the cleaned and decontaminated surface 62 may be performed, using a technique such as a smear or wipe test, or other known method, to determine the post-cleaning condition of the surface 62 and component 60, the DF factor, etc., to measure the effectiveness of the decontamination method 100 using the system 10A.
Referring now to FIG. 3, shown is a second example system 10B for removing radioactive contamination from a surface 62 of a component 60. The system 10B includes a blasting cabinet 50 defining a cleaning chamber 12. The blasting cabinet 50 may include a chamber access 24 configured as an opening through which a contaminated component 60 may be placed in the chamber 12 for cleaning The cabinet 50 may be supported by supports 48, to elevate the cabinet 50 as required to provide a directed air flow 14 through the chamber 12 as shown, and/or to position the chamber access 24 at an accessible working height for an operator (not shown).
The chamber 12 includes a perforated surface 56 defining a plurality of perforations or openings through which air may flow. In one example the perforated surface 56 is a grating defining a plurality of openings approximately ½″ square. The grating 56 is of sufficient size and strength and operatively attached to the cabinet 50 to support the component 60 being cleaned. The grating 56 may be configured to be a removable grating, such that gratings of different configurations, including gratings having openings of various configurations and sizes, may be used according to the requirements of the method 100 and the component 60 being decontaminated.
The system 10B is configured to establish a directed air flow 14 through the chamber 12. As shown in FIG. 3, an incoming air passage 16 is sealably connected to the cabinet 50 in fluid communication with the chamber 12 and configured to provide an incoming directed air flow 14. The incoming air flow 14 may include make-up air provided through an air intake 20. The directed air flow is created by an air flow device 22, which in the example shown is in fluid communication with the chamber 12. The air flow device 22 may include a vane system 80 configured to generate a directed air flow 14 in the direction of the arrows shown in FIG. 3, such that air entering the chamber 12 through the incoming air passage 16 flows through the chamber 12 in the direction of the air flow arrows 14 and through the openings in the grating 56 to be drawn through the vaning system and exited through an air outlet 76. The air outlet 76 is sealably connected to an outgoing air passage 18 such that the air flow 14 is directed to and through a filter 26 in fluid communication with the outgoing air passage 18 and the air outlet 76.
As described previously related to system 10A of FIG. 2, the air flow device 22 is configured to create a directed air flow 14 of sufficient pressure and velocity to entrain contaminant 64 removed from the surface 62 of a contaminated component 60 cleaned by dry air blasting in the chamber 12 and to transport the entrained contaminant 64 to the filter 26 for entrapment and collection. The air flow 14 may include air drawn into the chamber 12 through the chamber access 24 by the air flow device 22. The cabinet 50 including the chamber access 24, incoming air flow 16 and air flow device 22 may be configured to generate air flow 14 in a flow pattern, which may be a laminar flow pattern, such that contaminant 64 entrained in the air flow 14 is contained within the chamber 12 of the cabinet 50 and directed through the grating 56 to prevent free (airborne) release of the contaminant 64 outside of the chamber 12.
The cabinet 50 and/or air flow device 22 may include two or more air outlets 76, each of which may be in fluid connection with one or more filters 26, which may be HEPA filters. The number or air outlets 76 and the number and arrangement of filters 26 may be varied dependent upon the characteristics of one or more of the contaminant 64, the contaminated component 60, the grating 56, the dry ice blasting stream (not shown) and the directed air flow 14 included in a cleaning cycle using the system 10B and the method 100. The system 10B in FIG. 3 shows, by way of example, a plurality of air outlets 76. When not in use, the air outlet 76 may be sealed using a sealing device 78, which in the example shown may be an attachable cap configured to provide an air tight seal of the outlet 76.
In the example shown in FIG. 3, the air flow 14 is circulated through the chamber 12, where contaminants 64 blasted from the component 60 become entrained in the air flow 14 and are transported via the outgoing air passage 18 to the filter 26 for entrapment and removal as previously described. The air flow 14 is recirculated via the incoming air passage 16 and may be supplemented with air introduced through the air intake 20 to provide an air pressure and/or air flow rate required to perform the cleaning method 100. As described previously for FIG. 2, other configurations of the air flow system are possible. For example, the system 10B may be configured for non-recirculating air flow, such that the filtered air exiting the filter 26 is vented away from the cabinet 50, either by direct venting or through another conduit (not shown) configured to vent the filtered air flow 14 remotely. The system 10B may include a plurality of filters 26 and/or filter housings 28 such that each air outlet 76 is vented to a separate filter or bank of filters. The outgoing air passages 18 from each of the air outlets 76 may be configured in fluid communication with a shared filter system comprising a bank of filters 26 in a filter housing 28. The configurations described herein are intended as non-limiting and other air flow configurations may be possible.
The system 10B may include a dry ice blasting device 30 including a blasting unit 30B operatively connected to the blasting device 30 by a flexible supply line 74. As described previously related to FIG. 2, the dry ice blasting device 30 may be configured to pelletize dry ice from a dry ice source 32 and to feed the dry ice pellets using a pressurized carrier medium to the blasting unit 30B, to be expelled in a high velocity blast stream (not shown) from a nozzle 34 attached to the blasting unit 30B. A controller 36 may be configured to control the size and velocity of the dry ice pellets and other characteristics of the blasting stream.
Referring now to FIGS. 1 and 3, the cleaning method 100 may be used with the cleaning system 10B to clean and decontaminate a component 60 contaminated with a radioactive contaminant 64. The component 60 may be, for example, a component part of the power plant system, a tool, which may be a standard hand tool, specialty (dedicated use) tool, power tool, a motor, a component including a motor or other electrical equipment, electronic component, or other component used in the operation and/or maintenance of a power plant or other nuclear-related facility which may have become contaminated by a radioactive contaminant 64. As described previously related to FIG. 1, in a first step 105 the contaminated component 60 is placed in the chamber 12. The component 60 may be supported by the grating 56 or otherwise positioned in the chamber 12. For example, the component 60 may be suspended in the chamber 12 to facilitate cleaning of all surfaces of the component 60 with minimal repositioning of the component 60 during the cleaning process. The suspension system (not shown) may be configured such that the component 60 may be repositioned by adjustment of the suspension system, which may be adjustable using controls located outside the chamber 12 and the cabinet 50, such that an operator (not shown) is not required to access the chamber 12 to reposition the suspended component 60 during the cleaning process. The grating 56 may be optional in the example where the component 60 is suspended during cleaning, such that the chamber 12 is in direct fluid communication with the vaning system 80 of the air flow device 22. At an optional step 110, the level of radioactive contamination of the component 60 may be measured.
At step 115, the dry ice blasting device 30 and the blasting unit 30B may be configured for use in cleaning and removing the contaminant 64 from the contaminated component 60, which may include selecting a dry ice pellet size, a blasting stream velocity, or other characteristics of the blasting stream appropriate to clean the type and configuration of the contaminant 64 and considering the type and configuration of the component 60. For example, some components 60 may include surfaces 62 internal and external to the component 60 which may require dry ice blasting, and may be of various configurations and materials such that the characteristics of the blasting stream must be modified during the cleaning cycle and for the particular surface configuration and material represented by the portion of the component 60 being cleaned. For example, during cleaning of a component 60 including electronics or other materials sensitive to low temperatures, the temperature of the air flow 14 and/or the blast carrier gas may be adjusted to minimize thermal shock of the electronic or temperature sensitive material by exposure to the extremely low temperature of the dry ice prior to sublimation.
At step 120, a directed air flow 14 is created in the system 10B as previously described, having a sufficient pressure, flow rate, velocity and/or flow rate to entrain contaminant particles 64 dislodged and removed from the component 60, and to transport the removed contaminant particles 64 to the filter 26 while preventing free release of the contaminant 64 through the chamber access 24. At step 125, the component 60 is cleaned using the dry ice blasting unit 50B. In the example shown, the dry ice blasting unit 50B may be configured as a manually operated blasting unit or gun, such that an operator may manually control, reposition, adjust and direct the dry ice blast stream at the surfaces 62 of the component 60 requiring decontamination. The operator (not shown) may be covered with protective clothing of the type used related to dry ice operations and for radiological protection (RP). The chamber access 24 may be draped or curtained (not shown) to minimize air loss and prevent free release of the contaminant 64 through the chamber access 24. The drape or curtain may be configured to allow the operator and/or the blast unit 30B access to the chamber 12 and component 60 during the cleaning operation. Non-limiting examples of the drape or curtain may include a split drape which may define glove holes, or a strip curtain. In another configuration, the blasting device 30 of the system 10B may include a blasting unit 10C shown in FIG. 4. The blasting unit 30C may be mounted via a mounting interface 40 inside the chamber 12, and configured with a nozzle position mechanism 38. In this configuration, the operator may direct the movement of the nozzle 34 and control the dry ice blasting stream using the controller 36 or otherwise remote control. The operator may access the component 60 through the chamber access 24 during the cleaning operation, for example, to reposition the component 60 relative to the mounted nozzle 34 and blasting unit 30C.
At step 130, the contaminant 64 dislodged and removed from the component 60 during the blasting step 125 is entrained in the directed air flow 14 and drawn by the air flow device 22 through the grating 56, the vaning system 80, the air outlet 76 and the air outlet passage 18 to the filter 26, to be entrapped and contained by the filter 26. As described previously related to FIG. 2, the filter 26 may be configured as a HEPA filter, which may be removed from the filter housing 28 when spent, e.g., when the filter is nearing or at containment capacity, and at step 135 the filter 26 including the entrapped contaminant 64 may be processed (stored and/or disposed of) using methods known for the processing of radioactive waste. At optional step 140, post-cleaning measurement of the contaminant level present on the cleaned and decontaminated surface 62 may be performed, using a technique such as a smear or wipe test, or other known method, to determine the post-cleaning condition of the surface 62 and component 60, the DF factor, etc., to measure the effectiveness of the decontamination method 100 and the system 10B.
Referring now to FIG. 4, shown is a system 10C in an optional configuration of the system 10B of FIG. 3 and including a dry ice blasting unit 30C mounted within a sealable chamber 12 defined by a cabinet 50A and controllable from outside the chamber 12. A directed air flow 14 may be generated in the chamber 12 using the air flow system including the air flow device 22, air passages 16, 18, HEPA filter 26 and air outlet 76 as described for system 10B, such that the generated air flow 14 is sufficient to entrain contaminant 64 removed from the component 60 during the cleaning method 100 and to transport the removed contaminant 64 to the filter 26 for entrapment and collection. As previously described in an alternate configuration of system 10B, system 10C of FIG. 4 may include a dry ice blasting unit 30C configured for mounting in the interior of the cabinet 50A, e.g., within the chamber 12. The mounting interface 40 may include a nozzle positioning mechanism 38 which may be remotely controllable using a controller 36 in direct or wireless communication with the positioning mechanism 38. The cabinet 50A may include an access closure 58 which may be generally configured as a sealable door to seal the chamber access 24 during cleaning of the component 60 with the dry ice blasting unit 30C. The cabinet 50A may include an access panel 52 including access holes 54 which may incorporate gloves (not shown) sealably attached to the access panel 52 and configured for protection of the operator from the dry ice blasting stream and the radioactive contaminant 64, for example, during repositioning of the component 60 in the chamber 12 during cleaning In another example, an operator, wearing protective gloves for example, may access the chamber 12 through the access holes 54.
The systems 10A, 10B and 10C are non-limiting examples, and it would be understood that additional configurations of the radioactive decontamination system described herein are possible. For example, the blasting device 30 may include a plurality of blasting units 30n, which may each be configured to concurrently or consecutively direct blasting streams at a component 60 or component surface 62 contained in the chamber 12. By way of example, the blasting cabinet 50A may be configured with a plurality of blasting units 30C to expand the area of the chamber 12 to which a dry ice blast stream may be directed, thereby reducing the need to reposition the component 60 during cleaning to reach all contaminated surfaces or portions with a dry ice blasting stream. Other system configurations are possible. For example, the system 10A shown in FIG. 2 may be used to clean a component 60 other than a duct 70, where the component 60 defines the chamber 12 or a portion of the chamber 12 to enclose or isolate the contaminated portion or surface 62 of the component 60. For example, the component 60 may be configured as a pipe, vessel, tank or other structure which may have an internal surface or portion contaminated such that the contaminated portion of or the pipe, vessel, tank, or other structure may be sealed or isolated to form the chamber 12. In another example, the method 100 and system 10A-10C may be configured for decontamination of a larger fixed permanent structure, such as a large generator, housing or other structure, and may include forming a chamber 12 using a tent or other temporary enclosure draped over or containing the large structural component 60 and sealed sufficiently to generate a directed air flow therein. In this example, an operator in protective clothing, which may include breathing apparatus, and a dry ice blasting device 30 and or blasting unit 30B (for example) may be located within the chamber 12 to clean the component 60 using the method 100.
The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims.
Patent Application
20130263890
