Patent Grant
9126230
A method and an apparatus using aqueous fixatives for fogging of ventilation ductwork, enclosures, or buildings containing dust, lint, and particulates that may be contaminated by radionuclides and other dangerous or unsafe particulate contaminants, which method and apparatus are capable of (1) obtaining full coverage within ductwork and buildings, (2) penetrating and fixing the lint, dust and large particles present in ductwork and buildings so that no airborne particles are released during or after the application of the fixative.
The method and apparatus of the present invention is motivated by the need for safe and effective Deactivation and Decommissioning (D&D) of ventilation ductwork, enclosures, and buildings containing dust, lint, and particulates that prevents the release of radionuclides and other dangerous or unsafe particulate contaminants. Numerous examples exist of using fogging techniques to fix radionuclide contamination for a variety of situations. However, these techniques tend to work only on thin layers of contamination, and historically, they have not been effective on large particles such as lint and dust trapped in ducts of interest. The invention described herein is novel and has not been attempted before.
Contamination control is crucial during D&D activities, as well as during modifications to existing systems. In several of the older processing facilities, it is well known that contamination, in some cases substantial contamination, is present throughout the exhaust ductwork due to the years of processing in glove boxes, etc. A critical area of concern during the decommissioning of radioactive facilities is the prevention of the spread of radiological contamination. This is more serious for areas where large accumulations of radioactive dust and lint are present that have the potential to “go airborne”, such as disposal site exhumation, laundry facilities, exhaust ventilation ducting and exhaust stacks. In a recent demolition of large ventilation ducting (about 10-ft cross section and 100-ft long) at the US Department of Energy's (DOE's) Brookhaven National Laboratory, a spray coating was applied to the duct from inside using a painter dressed in anti-contamination clothing and an airline respirator system.
A different scenario at the U.S. DOE's Idaho National Laboratory (INL) required that a backhoe operator be placed in a contamination proof, positive pressure cab to prevent airborne contamination. In the case of the Idaho example, the required change of operators (required every two hours due to limitations using positive pressure system), and the anti-contamination clothing alone amounted to thousands of dollars per day.
In another case at the Idaho Site, there were significant accumulations of lint at a radioactive laundry. Traditional methods of capturing the lint prior to decommissioning, like simple glycerin fogging methods, were not successful, because they did not penetrate and bind the lint (see
There have been attempts of applying a coating in the past. However, these attempts have not been successful in penetrating and adhering contaminated lint and dust to the ductwork. As a result, that contamination was not fixed and ultimately became airborne when it was disturbed. Improved capture coating formulation will penetrate large amounts of lint and dust present in the ductwork and make the lint and dust, and any radioactive contaminants trapped in the lint and dust, adhere to the substrate material to allow ducting to be removed and compacted without spreading contamination. Since a “fog” acts as a gas, it can be introduced into the ductwork at a very low pressure and low velocity and will travel throughout the ducting with only an entry and exit point. The fogging has a number of operational advantages over spraying, which requires a spray hose and nozzle to be inserted and moved along the ducting. The spraying method has the potential of disturbing the contamination during the spraying itself, which depends on the pressure and velocity at which it is implemented.
The current glycerin-based capture coatings are formulated to remain tacky for prolonged periods, allowing any re-suspended contaminant particles to become captured when they contact the surface. However, this coating is formulated only to remove airborne contaminants and will not soak into the lint and dust deposited on the ducting surface. By formulating a new capture coating (containing surfactants and other components) and ensuring the delivery method supplies adequate amounts of the coating, as well as providing adequate coverage of the entire surface area of the ductwork, this new capture coating will reduce or eliminate the requirement for glovebags and extensive contamination control during cutting and removal of ductwork. This control is achieved by fixing the contaminants to the surface of the duct so that the danger of creating airborne contaminants is reduced.
There are a number of technologies that have been used for this application with limited success. They are:
The invention proposed herein addresses the deficiencies of and greatly enhances the performance of fogging methods in terms of reducing or eliminating contamination and increasing worker safety, particularly where capture coatings are to be fogged into dusty areas and ductwork. While testing has been performed to prevent the generation of airborne radioactive contamination, none dealt directly with the problem of penetrating significant quantities of dust and lint, and then capturing them in one step. A fog behaves similar to a gas. As a consequence, it can be introduced into ductwork at low pressure and low velocity. The approach was to use a more sophisticated solution containing a sticky base and a surfactant to increase the penetration and capture of dust and lint. A wide range of laboratory tests were conducted with the following criteria to improve the fogging fixative:
The fogging technology has the potential to be applied across a variety of industries.
The proposed invention described herein, mainly using latex paint as one of the constituents of the aqueous fixative solution, while very simple, has not been used before. It will
It is the object of this invention to provide a method and an apparatus for fogging ventilation ductwork, enclosures, rooms, or buildings containing dust, lint, and particulates with aqueous fixatives that will prevent or reduce the amount of lint, dust, and large particles released as airborne particles during or after the application of the fixative.
It is another object of this invention to provide aqueous fixative solutions that will fog, wet, penetrate, and bind lint, dust, and particulates within ductwork, enclosures, or buildings.
The method and apparatus of the preferred embodiment of the present invention is to use an aqueous solution comprised of Ammonium Lauryl Sulfate (ALS), sodium lauryl sulfate (SLS), glycerin, and latex paint that can be used to fog ductwork, enclosures, rooms, or buildings with a coating that will wet, penetrate, and bind large amounts of lint, dust, or particulates residing in the structures to the substrate material and prevent or minimize the release of airborne particulates containing radionuclides or other dangerous or unsafe contaminant particulates during or after the application of the fixative. This solution is comprised of a surfactant to aid wetting and penetration of the lint and dust, a binder to stabilize loose or respirable particles, and an agent to aid in fogging and enhance adhesiveness. Since a fog behaves similar to a gas, it can be safely introduced into ductwork at low pressure and low velocity. The addition of latex paint greatly improves the performance of the fogging solutions used presently in these applications. The initial application of this invention is for the safe removal and compaction of ductwork containing radionuclides during D&D operations without spreading airborne contamination.
FIGS. 12/1 and 12/2 show the coverage of coupons for the Fogging Solution (#212) used in the test (top) and for the conventional solution (bottom) in a laboratory fogging test obtained at 1.5 h (same as test box), 4.0 h, 8 h, and 16 h after fogging began.
The method and apparatus of the present invention is motivated by the immediate and ongoing need to decommission DOE facilities, which may have ductwork, enclosures like hot cells, and buildings that may be contaminated with radionuclides or other dangerous or harmful chemicals.
The purpose of fogging is to penetrate and coat the dust and lint present in the duct to minimize the airborne contamination released during D&D activities.
The PAG shown uses kilowatt-sized ultrasonic transducers to generate a fog in the ductwork. This equipment was used to evaluate the new aqueous fixatives described herein.
Laboratory Tests of Fogging Solutions. A series of laboratory tests were performed to develop new formulations for the capture coatings using sophisticated binders and surfactants that perform better than the representative baseline coatings for penetrating dust, lint, and other particulates. Different surfactants, binders, and other components were tested on laboratory samples of lint, dust, and simulated contamination independently and in combination.
Initial scoping studies consisted of spraying many different types of these solutions onto pads of lint contained in plastic beakers from a height of 20 inches. The distance and amount of spray (via number of pumps) were held constant.
A pneumatic nebulizer, which is used in inhaler devices in the medical industry, was then used to simulate in the laboratory an industrial fogging method during the evaluation of the most promising fixative solutions.
The results are presented and discussed below. For reference the Baseline/Conventional Fogging Solution was died red. The Fogging Solution #204 was died blue and the Fogging Solution #212 was dyed yellow. In
Additional penetration testing was performed to evaluate the absorption characteristics of the new formulations.
Fogging Test in a Waste Container.
On 26 Feb. 2007, the Idaho National Laboratory (INL) performed a fogging test in a 6-ft by 6-ft by 4-ft waste container 90 as a precursor to fogging a small hot cell and agreed to use our Fogging Solution #206, which was named #212 for these tests, vice a traditional glycerin fogging solution. A 4- to 8-h test was planned, but had to be cut short to 1.5 h. This was the first test of the new fogging solution used with full-scale fogging equipment 91 in a large container. Because of our ad hoc participation, no attempt was made to optimize the fogging operations. The solutions were not optimized for use in the commercial fogging equipment, but the results of this pilot scale test showed (1) that the solution was able to fog and (2) that the fogging was able penetrate the lint coupons placed in the waster container. As will be discussed, further laboratory testing of this solution at 1.5 h, 4 h, 8 h, and 16 h with the nebulizer confirmed the shortened pilot scale test results and showed that the longer periods produced excellent penetration and capture.
As illustrated in the pilot scale testing, the fogging solutions developed from the laboratory tests can be implemented operationally using commercially available fogging equipment. Two different types of fogging equipment were used in our laboratory and field tests. Current commercial passive aerosol generating (PAG) equipment utilize large ultrasonic transducers (see
Over 50 fogging formulations were developed and tested in the laboratory and compared against the conventional glycerin baseline formulation called solution #201 in our tests. Of these, three are particularly noteworthy and were described herein as fogging solution #206, which is very similar to solution #212, and solution #203. Solution #204 was also found to be effective. Fogging solution #212 was used in a full-scale test to determine its performance in a waste container used to simulate a hot cell. Table 3 summarizes the % by volume of the chemical additives used in the fogging solutions that greatly outperformed the baseline solution #201.
While fogging solutions #206 and #212 performed the best, other fogging solutions performed satisfactorily as well. As stated above, these new coatings contain a surfactant to aid wetting and penetration of the lint and dust, a binder to stabilize loose or respirable particles, and an agent to aid in fogging and enhance adhesiveness. While we found these specific solutions to perform well, we would expect that these same solutions would perform acceptably if the chemical additives were added in different percentages. If the percentages are changed the resulting fogging solution must be able to
While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes in the methods and apparatus disclosed herein may be made without departing from the scope of the invention which is defined in the appended claims.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/456,001 filed Oct. 28, 2010, and is hereby incorporated by reference.
This invention was made with government support under Contract Number DE-AC07-ID14517 awarded by the United States Department of Energy. The government has certain rights in this invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4529449 | Baustert et al. | Jul 1985 | A |
| 4800063 | Mierswa et al. | Jan 1989 | A |
| 5523513 | Milner | Jun 1996 | A |
| 5878355 | Berg et al. | Mar 1999 | A |
| 6153809 | Singh et al. | Nov 2000 | A |
| 6504077 | Purohit et al. | Jan 2003 | B1 |
| 7166758 | Nunez et al. | Jan 2007 | B2 |
| 7951227 | Weatherman et al. | May 2011 | B2 |
| 20020192803 | Rogers et al. | Dec 2002 | A1 |
| 20040115423 | Rouppert et al. | Jun 2004 | A1 |
| 20060217584 | Nunez et al. | Sep 2006 | A1 |
| Entry |
|---|
| Conley et al., “Use of Fixatives to Accelerate Building Decontamination and Decommissioning (D&D)—9047,” WM2009 Conference, Mar. 1-5, 2009, Phoenix, AZ, 7 pages. |
| Harper et al., “Decontamination and Decommissioning of the 2000 Complex Facilities at Oak Ridge National Laboratory—11199,” WM2011 Conference, Feb. 27-Mar. 3, 2011, Phoenix, AZ, 9 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 61456001 | Oct 2010 | US |
