Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste – By fixation in stable solid media
Reexamination Certificate
1999-12-16
2004-06-01
Silverman, Stanley S. (Department: 1754)
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
By fixation in stable solid media
C588S008000
Reexamination Certificate
active
06743963
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to methods for treating radioactive-containing waste materials. More specifically, the present invention relates to the prevention of radon emissions. More particularly, the present invention relates to the prevention of radon emissions by encapsulating the radon in radon-generating waste matter using a chemical additive and by adjusting the shape of the carrier which stores the radon-generating waste matter.
BACKGROUND OF THE INVENTION
Radioactive materials are a major concern in the U.S. One of the more common radioactive materials is radon. Radon is a pervasive pollutant. Radon (Rn) is a naturally occurring element that is formed upon the radioactive decay of radium-226. Radon is tasteless, odorless and colorless. It exists as a gas in the form of three natural isotopes—Rn-219, Rn-220, and Rn-222. The former two isotopes have half-lives of the order of seconds and thus are of little concern. However, Rn-222 decays in a slower process that is characterized by a considerably longer half-life of 3.82 days. Radon decay proceeds with emission of alpha particle radiation through a series of solid, short-lived radioisotopes (e.g., polonium-218 and polonium-214) that are collectively referred to as radon “daughters” or progeny.
These radon daughters, which are unstable isotopes in their own right, are responsible for most of the radiation dose associated with high radon levels in the air. Most radon gas that is inhaled is generally exhaled as well because its radioactive half-life is long as compared to the residence time of the gas in the lungs. However, the above-mentioned alpha-emitting polonium isotopes are solids rather than gases, and a fraction of these radon daughters are deposited on the surfaces of the airways deep in the lung when air is inhaled. The radon progeny deposited in this manner subsequently decay by emission of short-range but slow-moving and powerful alpha particles capable of damaging cells which they encounter. This alpha radiation dose is delivered to stem cells present in the epithelium that comprises the surface of the air passages in the lungs.
Radon gas in lungs is believed to be the second leading cause of lung cancer. Early United States Environmental Protection Agency (EPA) estimates indicated that in the Unites States alone 5,000 to 20,000 lung cancer deaths a year are attributable to “natural” radon from all sources, and more recent estimates tend to be larger, e.g., between 10,000 and 40,000 lung-cancer deaths each year. Extensive surveys of radon levels in homes and schools are under way at EPA's urging, based on its finding that some 10% of the nation's homes exceed its 4 picoCuries per liter (pCi/L) action level. Congress has recently identified a long-term goal of reducing indoor radon concentrations to typical levels in the outside environment (0.1-0.7 pCi/L), and EPA is publicizing radon mitigation measures and establishing the groundwork for eventual regulations dealing with allowable levels of radon in indoor air and drinking water.
The prior art has proposed several solutions in dealing with radon and radon emissions. Most of these solutions are directed to preventing radon emissions from entering an individual's home. One such solution has been to line the floor or ground below the home with a plastic covering designed to prevent radon from entering through the ground or floor. However, these coverings only provide partial protection, and any slit or tear in the cover will permit the radon to enter the building.
U.S. Pat. No. 5,399,603 discloses attempts to overcome these deficiencies by using a polymer sealant to coat the ground or floor. While these sealants are more effective at preventing radon emissions from penetrating into the home, they suffer some of the same problems that if part of the floor or ground is not coated, the radon emissions are still able to enter through these openings.
Additionally, the above solutions are directed to preventing naturally occurring radon emissions from entering a home. Workers who work with radon-contaminated waste also need to be protected from the emissions. The choices available for preventing radon emissions from radon-generating waste matter are much more limited. U.S. Pat. Nos. 4,897,221 and 4,980,090 are directed to the treatment of radon-contaminated waste. These references admix the waste with a shielding material, such as ceramic, enamel, concrete or metal, and place the admixture into a centrifuge to mix and encapsulate the waste within the shielding material. The encapsulated waste is then placed in a vault. However, the problems with this method are that the radon emissions are still able to escape the shielding material, which is the reason these wastes are placed into a vault.
Accordingly it is an object of the present invention to provide methods useful for treating waste material containing radioactive wastes. These methods would prevent radon emissions while obviating the need for protective vaults and would permit the wastes to be formed into products that could be used without fear of harming members of the public.
SUMMARY OF THE INVENTION
The present invention is directed to methods for treating radioactive materials contained within a variety of different waste materials. More specifically, the present invention is directed to the prevention of radon emissions wherein radon-emissions are minimized by admixing the radon-generating waste with a shielding material and then forming the admixture into geometric-shaped objects which minimize the surface area of the object with respect to the volume of the object, thereby reducing any radon emissions emanating from the object.
Additionally, the radon-generating waste may be admixed with a chemical additive which encapsulates the radon. Then, the encapsulated radon is admixed with a shielding material and formed into objects. These objects may further be shaped into geometric objects having a high ratio of volume to surface area to ensure that any radon which may not be encapsulated has less area from which to leave the object.
Finally, a polymer sealant optionally may be used to further prevent radon emissions from radon-generating waste which has either been encapsulated or formed into geometric shapes or both.
Accordingly it is an object of the present invention is to provide methods useful for treating waste material containing radioactive wastes.
It is another object of the present invention to provide a method of reducing radon emissions from radon-generating wastes by adding a chemical additive to the waste to encapsulate the radon prior to admixing the radon with a shielding material.
It is another object of the present invention to provide a method of reducing radon emissions from radon-generating wastes by adjusting the geometry of the shielding material into which the radon-generating waste is placed.
It is another object of the present invention to provide a method of reducing radon emissions from radon-generating wastes by both adding a chemical additive to the waste to encapsulate the radon and adjusting the geometry of the encapsulated waste.
It is another object of the present invention to provide a method of reducing radon emissions from radon-generating wastes by further using a polymer sealant to prevent radon emissions from radon-generating wastes.
These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.
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Boddeker Steve
Bolch W. Emmett
Centofanti Louis
Harder George
Johnson Edward M.
Kilpatrick & Stockton LLP
Perma-Fix Environmental Services, Inc.
Silverman Stanley S.
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