Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
  • G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof

Definitions

• the present invention relates to radioactive decontamination of polluted surfaces by deposition of contaminating agents, in particular in the form of dust.
• radioactive decontamination (or D.R.A.) consists in ridding the surfaces of the deposited radioactive dust, or at least ridding it sufficiently to no longer represent a danger for the operator.
• the object of the present invention is to allow radioactive decontamination of surfaces while avoiding the drawbacks and handicaps of the usual practice or of known techniques.
• the adherent film-forming coating which is formed beforehand on the surfaces is, on the one hand, insoluble. without marked solubility - in an aqueous medium having a pH at a value between approximately 6 and 8 and, on the other hand, is perfectly soluble in an aqueous solution having a pH at a value situated outside the range of pre- mentioned, and in that said solution is used as a liquid for washing contaminated surfaces.
• the film-forming coating that is formed is insoluble in water, but on the other hand, is perfectly soluble in water added with a base, so as to preferably have a pH at a value d about 9 or more, and this basic aqueous solution is used as a wash for contaminated surfaces.
• dust is therefore meant to qualify, not only powdery solid fragments, but any other substance, in any form whatsoever (droplets, mist, vapor, etc.) capable of being deposited on the surfaces, by example by condensation.
• the invention results, among other things, from the following considerations: it is clear that the dust which is deposited on the surfaces adhere to it with a resistance to removal which depends on the surface condition of the support.
• a "thin layer” is a layer whose thickness is less than 50 A m approximately and, preferably equal or slightly less than 20 ⁇ m.
• an advantageous implementation of the invention consists in using a liquid varnish which is spread over the surfaces to be coated and which, after drying, will form the desired film.
• the "homogeneous" character of the film is really only necessary if the latter is applied in a thin layer, because it is known that it is difficult, if not impossible, to control the porosity of a heterogeneous film (for example example) in a thin layer.
• the coating film is applied in a thin layer, in which case coatings of heterogeneous character (for example the paints themselves) can in all rigor be used according to the method of the invention.
• coatings of heterogeneous character for example the paints themselves
• the choice of a film-forming coating in a homogeneous thin layer constitutes an implementation of the method according to the invention which is both easy and economical, and therefore particularly advantageous.
• a varnish is prepared composed, as basic constituents, of a resin (or binder) formed by a vinyl copolymer of crotonic acid and a solvent formed by ethyl (or isopropyl) alcohol).
• Adjuvants are then added in an adequate quantity to improve the quality of the varnish, namely: a diluent, such as ethyl glycol acetate (or butyl glycol) as well as a plasticizer, for example phthalate dioctyl (or octyl cebacate)
• a varnish solution comprising, by weight, Approximately 25% of vinyl copolymer of crotonic acid, between 2.5 and 3% of dioctyl phthalate, the remainder being constituted by the solvent (ethyl alcohol) and the diluent (ethyl glycol acetate).
• the diluent and the plasticizer are determined so that after drying, the resin (or "dry extract") is capable of forming, in a single layer and without sagging or the like, a film of minimum thickness offering good protection.
• the varnish once ready, is applied to clean and dry surfaces, preferably by spraying with a pneumatic gun.
• the varnish After drying, the varnish forms a continuous film, without breaking or cracking and with a thickness of about fifteen microns on average.
• the above-mentioned value represents a practical and economic optimum, but by no means a technical minimum necessary for the execution of the method according to the invention.
• the equipment after proper drying of the varnish, the equipment, the surfaces of which are thus coated, can be put into service, and in particular be exposed to an atmosphere having in suspension the radioactive dust.
• the protective resin film will slowly load into dust without, however, deteriorating or deteriorating, since the vinyl copolymer which constitutes it, being insoluble in the usual solvents as well as in any aqueous solution at pH below about 8, therefore remains perfectly stable and chemically inert in contact with the atmosphere prevailing in the enclosures and cells where the material is used.
• a basic aqueous solution having a pH preferably at least one point above the solubility threshold of the resin.
• aqueous solution is prepared containing 3 g of sodium hydroxide (Na OH) per liter of water, corresponding to a pH close to 9.
• a suitable surfactant can be added to give the washing solution an additional detergent action.
• this solution is then projected onto the contaminated surfaces using injection lances.
• the varnish dissolves easily, carrying with it the contaminating dust which had settled there.
• a period of washing which can range from half an hour to an hour and a half approximately depending on the extent of the initial contamination of the surfaces, the latter are completely cleared radioactive dust.
• a new layer of varnish is applied to them and the equipment is ready for a new start-up.
• the dissolution of the varnish in the soda solution has the advantage of being irreversible, that is to say that the varnish, once dissolved, no longer regains its initial film-forming quality, but occurs after water evaporation, in powder form.
• This absence of gelification in the washing solution constitutes an additional advantage for the final conditioning of the contaminated effluents.
• the solid residue which appears in small quantity on these surfaces can be easily removed by simple dry cleaning, for example by light brushing.
• the method according to the invention has many other advantages and advantages, some of which are now mentioned.
• the state of the surface to be decontaminated is perfectly known, given that it consists of the film-forming coating which is completely controlled both in application and in stability and which is can, at the desired time, easily dissolve and eliminate whatever the nature, the quantity, the distribution and especially the adhesion of the contaminants which are deposited there.
• the quantity of base to be used (for example soda) is less important than that consumed with the usual practice because, not only of the less quantity of washing necessary but also because the concentration of liquid sodium hydroxide can be adjusted to its minimum value, sufficient to slightly exceed the pH threshold above which the coating applied is perfectly soluble.
• the residual concentrate composed of the dry extract of the varnish (the resin), soda and contaminants, can be easily calcined and thus waste of a minimum volume is obtained.
• varnish additives having electrostatic properties which oppose by their effects the tendency to deposit dust and thus making it possible to modify in the direction desired the amount of dust deposited, or even their geographic distribution on the surfaces.
• constituent elements of the film-forming material to be applied in particular varnish when this type of product is used, can vary within a wide range of possibilities, among which the skilled person will be able to make a choice according to his wishes or necessities.
• the process according to the invention can be carried out with washing of the contaminated surfaces with a solution not only basic but also with an acid solution.
• temporary film-forming coating will be made accordingly so that it can be removed by dissolving in an acidic washing solution, preferably at a pH of at least 5.
• the washing operation carried out for this purpose can be carried out, not only by jets with a lance, as is imperatively the case in current current practice, but also - (although less easy to implement and may be generally less effective) - statically, in a "dead bath", by immersion in a swimming pool.
• the field of application of the method according to the invention extends beyond the reprocessing of irradiated fuels and in fact relates to radioactive decontamination in general, within the limit however where the contamination originates from the deposition on surfaces, or other supports, of irradiated dust or condensables .
• the method according to the invention can find civil applications, for example in equipment and installations located in sensitive areas in nuclear power plants, or for laboratory devices on which solutions loaded with radioactive particles can flow during manipulations.
• the method according to the invention can also find military applications, in particular of the same type as civil applications for sensitive areas (for example in nuclear-powered submarines) or for various military materials which may be contaminated. by dust from a nuclear explosion, during atmospheric tests, etc.

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• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Food Science & Technology (AREA)
• Physics & Mathematics (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Sampling And Sample Adjustment (AREA)

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• 1982
  • 1982-03-02 FR FR8203561A patent/FR2522869B1/fr not_active Expired
• 1983
  • 1983-02-23 DE DE8383400370T patent/DE3368143D1/de not_active Expired
  • 1983-02-23 EP EP19830400370 patent/EP0090680B1/de not_active Expired
  • 1983-03-02 JP JP3300883A patent/JPS58161897A/ja active Pending

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