CLEANING OF RADIOACTIVE CONTAMINATION USING DRY ICE
A system and method for cleaning components contaminated with radioactive materials uses 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 filter, which may be configured as 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. 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.
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This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/613,075, filed on Mar. 20, 2012, which is hereby incorporated by reference in its entirety.
TECHNICAL FIELDThe present invention relates generally to cleaning radioactive contamination using dry ice blasting.
BACKGROUNDRadionuclides 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.
SUMMARYA 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.
Referring to the drawings wherein like reference numbers represent like components throughout the several figures, the elements shown in
Referring to
In the example shown in
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
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
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
At step 120 of
In the examples shown in
The example of a filter 26 and filter housing 28 shown in
Still referring to
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
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
As described previously related to system 10A of
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
In the example shown in
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
Referring now to
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
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
Referring now to
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
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.
Claims
1. A method of cleaning a component contaminated with a radioactive material, the method comprising:
- containing a component contaminated with a contaminant in a chamber, wherein the contaminant includes a radioactive material;
- generating an air flow through the chamber, wherein the air flow outgoing from the chamber is in fluid communication with a filter;
- cleaning the contaminant from the component with a dry ice blasting stream configured to remove the contaminant from the component such that the removed contaminant is transported by the air flow to the filter;
- filtering the air flow using the filter to entrap the removed contaminant in the filter.
2. The method of claim 1, wherein the filter is configured as a HEPA filter.
3. The method of claim 1, further comprising:
- removing the filter including the entrapped contaminant; and
- processing the filter including the entrapped contaminant as low level radioactive waste.
4. The method of claim 3, wherein processing the filter including the entrapped contaminant includes at least one of controlled storage of the filter and controlled disposal of the filter.
5. The method of claim 1, further comprising:
- measuring the radioactivity of the component prior to cleaning; and
- measuring the radioactivity of the component after cleaning.
6. The method of claim 1, wherein the chamber is at least partially defined by the component.
7. The method of claim 1, wherein containing the component contaminated with a contaminant in the chamber further includes:
- sealing the chamber to isolate the component.
8. The method of claim 1, wherein filtering the air flow using the filter to entrap the removed contaminant in the air flow further includes:
- filtering the air flow through a plurality of filters to entrap and collect the removed contaminant from the air flow.
9. The method of claim 1, wherein the chamber is defined by a cabinet, the method further comprising:
- positioning the component in the cabinet prior to cleaning the component.
10. The method of claim 1, further comprising:
- providing a dry ice blasting unit in the chamber; and
- controlling the dry ice blasting unit to direct the dry ice blasting stream to remove the contaminant from the component.
11. The method of claim 1, wherein cleaning the contaminant with a dry ice blasting stream further includes:
- adjusting one of a dry ice pellet size and a blasting stream velocity of the dry ice blasting stream.
12. A system for cleaning a component contaminated with a radioactive material, the system comprising:
- a chamber configured to contain a contaminated portion of a component, wherein the contaminated portion is contaminated by a contaminant including a radioactive material;
- a dry ice blasting unit configured to provide a blasting stream including dry ice pellets;
- an air flow device configured to generate a directed air flow through the chamber and through a filter in fluid communication with the chamber;
- wherein the system is configured such that contamination removed from the component by the blasting stream of the dry ice blasting unit is transported by the directed air flow to the filter and entrapped by the filter to clean the component of the contaminant including the radioactive material.
13. The system of claim 12, further comprising:
- a controller in operative communication with the dry ice blasting unit;
- wherein the controller is configured to control one or more of a dry ice pellet size, a blasting stream velocity, a blasting nozzle position, and movement of the dry ice blasting unit relative to the component.
14. The system of claim 12, further comprising:
- an incoming air flow passage in fluid communication with the chamber and the air flow device;
- an outgoing air flow passage in fluid communication with the chamber and the air flow device; and
- the outgoing air flow passage is in fluid communication with the filter.
15. The system of claim 12, wherein the filter is configured as a HEPA filter.
16. The system of claim 12, wherein the filter is configured as a plurality of HEPA filters.
17. The system of claim 12, wherein the dry ice blasting unit is remotely controlled.
18. The system of claim 12, wherein the chamber is defined by a cabinet in fluid communication with the air flow device and the filter.
19. The system of claim 12, wherein the component is defined by one of a duct, pipe, vessel, container, and tank.
20. The system of claim 12, wherein the component is configured as one of a tool, an electrical component, and a component part of a nuclear power plant.
Type: Application
Filed: Mar 13, 2013
Publication Date: Oct 10, 2013
Applicant: Mid-American Gunite, Inc. (Newport, MI)
Inventor: Mid-American Gunite, Inc.
Application Number: 13/800,466
International Classification: B24C 3/00 (20060101); B24C 1/00 (20060101);