Electrodecontamination of contaminated surfaces

The present application claims the benefits of U.S. Provisional Application Ser. No. 60/486,493, filed Jul. 10, 2003, entitled “Electrodecontamination for Mitigation of Airborne Contamination”, which is incorporated herein by this reference.

The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract Nos. DE-FG03-00ER82934 and DE-FG02-03ER83591 awarded by the Department of Energy.

The invention relates generally to decontamination of objects and surfaces and particularly to electrolytic decontamination of radioactive contaminated surfaces.

Radioactive contamination of objects can occur in a wide variety of applications, such as nuclear-powered utility power plants, submarines, and ships, nuclear weapons production plants and storage facilities, petrochemical plants and refineries, and uranium mines and refineries. In these applications, various types of equipment, including piping, vessels, pumps, valves, and the like, are exposed to surface contamination by man-made or naturally occurring radionuclides, such as radioactive isotopes of plutonium, uranium, cesium, cobalt, zirconium, strontium, radium, polonium, thorium, and daughter products of uranium and plutonium.

Surface contamination by radioactive materials is normally of two types. One type of surface contamination is known as smearable contamination. In smearable contamination, the radioactive materials on the surface can be removed by hand wiping the surface with a non-abrasive pad. Another type of surface contamination is known as fixed contamination. In fixed contamination, the radioactive materials have penetrated into microcracks, microcrevices, and other surface defects and irregularities and/or are chemically bonded to the surface. As a result, the materials are not removed simply by hand wiping the surface with a non-abrasive pad.

Currently available decontamination methods can be classified broadly under two categories: mechanical and chemical. Mechanical methods typically require surface abrasion to remove radioactive materials. Chemical methods, in contrast, typically require a chemical reaction to remove the radioactive materials from the surface.

Commonly used mechanical decontamination methods include vacuum cleaning, hydroblasting, sandblasting, blasting with other abrasives, flame cleaning, scraping, and scabbling. Mechanical decontamination methods can have drawbacks. Although they can remove both fixed and smearable contaminants, removed radioactive material is typically dispersed into the surrounding atmosphere, not only presenting a significant health hazard to decontamination personnel but also spreading to and contaminating other areas. Many of the mechanical methods are labor intensive, increasing both the cost of decontamination and decontamination personnel exposure time to radioactive materials. The complexity ofmany surface contours and shapes often renders decontamination by mechanical means difficult or impractical.

Commonly used chemical decontamination methods include water washing, steam cleaning, scrubbing with detergents, acids, caustics, and solvents, electro-chemical stripping, and strippable coatings. The water washing, steam cleaning, and scrubbing techniques can have drawbacks. They can require long treatment times to adequately decontaminate a surface because of low ion exchange rates and the need to apply chemical solutions at elevated temperatures, increasing the complexity and cost of the decontamination system.

Electro-chemical stripping and strippable coatings can overcome some of these drawbacks. In electrochemical stripping, the contaminated surface (which is conductive) is configured as an anode or cathode while an opposing electrode is configured as the cathode or the anode, respectively. An electrolyte solution is applied to the surface and the surface subjected to a voltage and therefore electrical current. Surface contaminants are electrolytically stripped from the surface into the electrolyte. Although electro-chemical stripping works well for objects that are fully immersed in an electrolyte bath, it does not work well for stationary surfaces or objects too large for full immersion in the bath. When applied to a surface, the liquid electrolyte, under the force of gravity, typically runs down the surface and becomes an uncontrolled carrier of the radioactive materials to other locations. Moreover, electrolytes can endanger personnel through their use of hazardous chemicals. Strippable coatings, in contrast, are viscous chemical formulations that are applied to the contaminated surface and capture the contaminants. After curing, the coating may be removed by stripping the coating off of the surface. Although strippable coatings are effective for smearable contaminants, they can have a very low removal rates for fixed contaminants.

These and other needs are addressed by the various embodiments and configurations of the present invention. The present invention removes contaminants from contaminated surfaces-using a combination of electrochemical and strippable coating techniques.

In one embodiment, a method for treating (e.g., decontaminating) an object is provided. The method includes the steps of:

(a) applying a gel-like material to a contaminated surface of the object;

(b) passing an electrical current through the applied gel-like material to drive the contaminants into the applied gel material.

(c) curing the gel-like material to form a cured, strippable layer of the material; and