Hazardous or toxic waste destruction or containment – Processes for making harmful chemical substances harmless,... – By hydropyrolysis or destructive steam gasification – e.g.,...
Patent
1997-07-14
1999-02-23
Mai, Ngoclan
Hazardous or toxic waste destruction or containment
Processes for making harmful chemical substances harmless,...
By hydropyrolysis or destructive steam gasification, e.g.,...
588 20, 208181, 210682, G21F 900
Patent
active
058754067
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to the field of treatment of radioactive waste, particularly oils and solvents, in particular from nuclear power plants and in military research centers, and has for its object a process for reduction of waste suitable for this purpose.
The invention also has for its object a device for practicing this process.
DESCRIPTION OF THE RELATED ART
At present, the elimination of contaminated oils or solvents poses a great problem in nuclear power plants and in military research centers. Active oils used in these power plants are of the mineral or synthetic type. There is meant by contaminated oil an oil containing radioactive substances. Until now, the known processes for the decontamination of contaminated oils and solvents are centrifugation, decantation, filtration over rare earth and bacterial destruction.
To this end, there is known from DE-A 3 522 126, a process for the centrifugation of radioactive wastes and drying the solid residues. Also, JP-A-63 204 198 discloses a process of centrifugation and filtration of radioactive effluents containing an oily portion. There is also known, from WO-A-89 08316, a process for treatment of effluents of low radioactivity by preheating to eliminate volatile solvents, then by special centrifugation followed by filtration. Finally, the publications INSTITUTE OF ELECTRICAL ENGINEERS, STEVENAGE, GB Inspec. No. 3106590 SIMIELE G A et al. "Radioactive decontamination of waste oil by filtration, centrifugation, and chelation" and NUCLEAR AND CHEMICAL WASTE MANAGEMENT, 1987, UK, Vol. 7, No. 3-4, page(s) 257-263, ISSN 0191-815X disclose the decontamination of oily wastes from pressurized water reactors. This process suggests prefiltration which removes large particles, this prefiltration being followed by centrifugation adapted to eliminate water. The oily residue is then treated by chelating agents such as E.T.D.A., and the emulsion is again subjected to centrifugation. However, the use of chelating agents gives rise to serious problem of elimination of wastes from nuclear power plants.
Moreover, these processes are often very long or incomplete, in particular in the case of centrifugation and filtration. Thus, these processes, which are suggested for the treatment of aqueous effluents, permit lowering the radioactivity of the oils but not eliminating or reaching levels equal to natural radioactivity. As a result, these oils, as well as the contaminated solvents, are generally simply stored at the site, awaiting a technical solution, whereby the active wastes encumber the sites and constitute a permanent pollution danger.
SUMMARY OF THE INVENTION
The invention has for its object to overcome these drawbacks.
It thus has for its object a process for the reduction of radioactive wastes, particularly oils and solvents, particularly from nuclear power plants and military research centers, characterized in that it consists essentially in dumping said wastes into a reservoir, in which they are subjected to continuous agitation, preheating them, carrying out a chemical precipitation treatment, passing the mixture into a centrifuge, carrying out electrostatic or conventional filtration and then testing the level of radioactivity, the treatment being performed continuously until the desired level of decontamination is reached.
The invention also has for its object a device for practicing this process, essentially constituted by a contaminated waste reservoir connected by means of forward and return conduits and by a circulation pump, to a filtration element, characterized in that it is provided moreover, between the contaminated waste reservoir and the filtration element, with a centrifuge adapted to carry out separation of water that may be contained in the wastes and to carry out the separation of the large contaminated particles, so as to limit the consumption of the filtering elements, in that the reservoir is provided with a mixture and a heating means and in that the filtration element is constituted by at least one e
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"Method and Apparatus for Waste Oil Regeneration", Chemical Abstracts, vol, 115, No. 22, Dec. 2, 1991.
Bernatom S.A.R.L.
Mai Ngoclan
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