Cleaning and liquid contact with solids – Processes – Using sequentially applied treating agents
Reexamination Certificate
1999-11-02
2001-05-15
Carrillo, S. (Department: 1746)
Cleaning and liquid contact with solids
Processes
Using sequentially applied treating agents
C134S011000, C134S026000, C134S028000, C134S031000, C134S032000, C134S033000, C134S034000, C134S036000, C134S037000, C423S003000, C423S004000, C423S020000, C976SDIG003, C976SDIG003
Reexamination Certificate
active
06231683
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the cleaning of radioactively contaminated material and, more particularly to the cleaning of radioactively contaminated plastics material.
BACKGROUND OF THE INVENTION
Before consignment of radioactively contaminated material to a waste disposal site, for example, a waste landfill site, it must be ensured that the contamination of the material is below the specified disposal limits of the site. It is therefore often necessary to treat the contaminated materials before disposal in order to ensure that the contamination levels are within the disposal limits.
Products, for example gloves and sheets, made of plastics material are widely used in the processing and handling of radioactive material. Difficulties have been experienced in cleaning such material sufficiently to enable it to be disposed of safely.
Attempts to clean contaminated plastics material by simply subjecting the material to a nitric acid leaching operation, followed by at least one washing cycle have proved to be unsatisfactory. It was found that the material had not been cleaned sufficiently to enable safe disposal.
A known process for cleaning contaminated waste plastics material is described in International Publication No. 95/16997. This process comprises washing the material in water which contains a strong base, such as soda or potash in aqueous solution. Optionally, a wetting agent, preferably non-foaming, may also be added to the water. During the washing operation a saponification reaction occurs so that the material is subjected to a selective chemical treatment whereby certain surface agents, for example, plasticisers, which contain most of the contaminants are attacked. The washed material is then rinsed in water.
A disadvantage of this process is that the contaminants, such as uranic substances, are not rendered soluble and this presents certain difficulties in their recovery. Recovery must be effected by a solid-liquid separation process, such as filtration, followed by either direct leaching of the uranic substances from the filter, or by physical removal of the solids from the filter and then leaching the uranic substances from the removed solids.
It is an object of the present invention to provide a method of cleaning radioactively contaminated plastics material which is efficient and enables the treated material to be disposed of safely.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of cleaning plastics material contaminated with radioactive substances comprises the step of contacting the plastics material with a decontaminating liquid comprising an aqueous solution of nitric acid which contains a NOx generating agent.
Preferably the NOx generating agent comprises a nitrite.
Advantageously, the NOx generating agent comprises sodium nitrite.
Alternatively, the NOx generating agent may comprise a ferrous metal.
Preferably the method includes the step of agitating the decontaminating liquid.
The method may include the further step of washing the plastics material following contact thereof with the decontaminating liquid.
The method may comprise the steps of placing the contaminated plastics material in a rotatable vessel having one or more apertures, subjecting the material to a leaching cycle comprising supplying the decontaminating liquid to the inside of the vessel, and rotating said vessel whereby said decontaminating liquid is agitated and mixed with the contaminated material, terminating the rotation of the vessel and discharging the decontaminating liquid therefrom.
The method may further comprise subjecting the material to a washing cycle comprising supplying a washing liquid to the inside of the vessel, rotating said vessel to enable the washing liquid to mix with the material, terminating the rotation of the vessel and then discharging the washing material therefrom.
Preferably the material is subjected to at least one further washing cycle.
The material may be subjected to three washing cycles.
Suitably the contaminated material may be held in a container having one or more perforations.
The decontaminating liquid may have a nitric acid molar concentration having a value within a range of 3M to 5M, the preferred value being 4M.
The material to be cleaned may be contaminated with uranic substances.
An advantage of the method according to the present invention is that it is compatible with processes used in the nuclear industry for the recovery of uranium and for its reincorporation in the uranium fuel cycle.
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European Patent Office Search Report for PCT/GB98/01212 pp. 1-9, Mar. 1999.*
GB Search Report for PCT/GB98/01212 pp. 1-3, Aug. 1998.
Armit James Clark
Rushton Alan
Beyer Weaver & Thomas LLP.
British Nuclear Fuels PLC
Carrillo S.
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