Induced nuclear reactions: processes – systems – and elements – Fission reactor material treatment – Impurity removal
Patent
1993-08-24
1995-06-13
Walsh, Donald P.
Induced nuclear reactions: processes, systems, and elements
Fission reactor material treatment
Impurity removal
376309, 376326, 588 10, G21C 1942
Patent
active
054250722
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of treating a surface, and more particularly a surface contaminated with radionuclides.
2. Discussion of the Prior Art
In the nuclear industry, surfaces of objects including mechanical components and constructional features may become contaminated with radionuclides such as cobalt-60, caesium-137 or strontium-90, or radioactive compounds such as PuO.sub.2 or UO.sub.2. Current practices for treating these surfaces include the use of chemical reagents, and abrasive jets. However, the contaminating radionuclides may penetrate deeply into the surface portion of the components or features and may present difficulties in being removed by these known surface treatments.
A number of alternative surface treatments have been tried by others. One such treatment is described in European patent specification number EP 91646 A1 which discloses a method of removing a radioactive metal oxide from the surface of a radioactive component by means of a laser beam directed at the surface. In UK patent specification number GB 2242060 A a concrete surface contaminated with tritium is treated by irradiating the surface with microwaves in order to vaporise water from the surface thereby removing tritium. German patent specification number DE 3500750 A discloses a method for removing radioactively contaminated surface layers of concrete from a reinforced concrete structure by inductively heating the reinforcing bars within the structure. In a further method, described in Japanese patent specification number JP 3002595 A, a radioactively contaminated concrete surface is removed by irradiating the surface with microwave radiation.
In all of these alternative treatments radioactive contamination is removed from a surface or else the contaminated surface is itself removed. Because of the nature of these treatments, the contamination becomes airborne thus necessitating downstream processing and leading to further complications and expense.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of treating a surface contaminated with radionuclides, the method comprising passing a local area of intense heat across the surface so as to fix or seal the radionuclides therein.
As stated previously, the aforementioned alternative treatments are used to remove contamination from a surface or to remove a surface layer containing contamination. None of these aforementioned treatments provide a method which achieves fixing or sealing of the contamination to a surface as is provided by the present invention. The present invention allows simpler and cheaper treatment.
Desirably, in the present invention, the intense heat has an energy level of at least 150 W/cm.sup.2. Preferably, the intense heat is applied by a laser source, or from a laser source through a fibre optic cable.
The local area of intense heat may be passed, eg in an x-y raster fashion across the surface by moving the object defining the surface and/or by moving a source of the intense heat. A relatively large treatment area may be achieved by overlapping movement of the object and/or the source of the intense heat.
The contaminated surface may comprise a layer applied to an object, for example a paint, or a plastics coating such as an epoxy layer.
At least one layer of a coating material may be applied before or after the application of the intense heat to fix and seal the radionuclides on or in the object by melting the coating material and forming a bond of the coating material to a substrate, or by forming a fused layer comprising the coating material and said substrate material. Examples of coating materials include glass, metal, ceramics, pozzolana and chamotte, or a mixture thereof. A further application of intense heat may be necessary to bond the coating to the surface.
In another application of the invention to a metal surface, the local area of intense heat causes local melting of the metal at the surface which subsequently solidifies as the local area
REFERENCES:
patent: 4565670 (1986-01-01), Miyazaki et al.
patent: 4591454 (1986-05-01), Ohtsuka et al.
patent: 4676586 (1987-06-01), Jones et al.
patent: 4920994 (1990-05-01), Nachbar
patent: 5256848 (1993-10-01), Cartry et al.
patent: 5283010 (1994-02-01), Waring
Li Lin
Modern Peter J.
Steen William M.
British Nuclear Fuels PLC
Voss Fred
Walsh Donald P.
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