EP0055671A1 - Process for fixing radioactive contamination on materials or contaminated wastes and its application - Google Patents

Abstract

1. Process for fixing radioactive contaminants, characterized in that at least one layer of polymerizable resin is sprayed onto the contaminated material at ambient temperature from an electrostatic spray gun.

Description

The present invention relates to a method for fixing radioactive contamination on polluted materials or waste as well as its application.

The handling and packaging of radioactive waste poses many safety problems. It is known to condition radioactive waste, with a view to its storage, in thermosetting resins by coating said waste in polyester or epoxy resins. These processes apply to powders, organic liquids, ion exchange resins as well as large objects. French patents and certificates of addition 2,129,836.73 / 17974, 2,251,081, 2,273,350, 2,361,725, 2,361,724 in the name of the applicant describe these techniques.

However, in the case of very large objects, as occurs during the dismantling of nuclear installations, that is to say during the dismantling, with a view to their storage, of the parts of contaminated nuclear installations, precautions very important must be taken in order to fix the contamination on the parts to avoid contaminating the successive premises where these parts will stay during the various phases of the conditioning process.

The present invention provides a solution to this problem of transferring and handling contaminated objects. The process which is the subject of the invention is easy to carry out, has a low cost price and provides very high safety.

More precisely, the subject of the invention is a method for fixing the radioactive contamination of contaminated materials, characterized in that at least one layer of polymerizable resin is sprayed, using an electrostatic gun, at ambient temperature. on contaminated materials.

• a) économie de matière ;
• b) les pièces à revêtir sont souvent télémanipulées. Le fait que les particules de résine suivent les lignes de champ,diminue beaucoup le nombre de télémanipulations, ce qui conduit à une exploitation plus simple que dans le cas d'une projection classique ;
• c) les pertes en matière étant minimes, les filtres en exploitation dans les cellules de démantèlement où on utilise ce procédé,se colmateront plus lentement que dans le cas d'une projection classique.

The application of the electrostatic gun, which creates an electric field between the nozzle brought to a high potential and the material brought to ground, allows the latter to attract the particles of electrically charged resin and to completely coat said material. The use of the electric field created has a triple advantage:

• a) economy of matter;
• b) the parts to be coated are often remote manipulated. The fact that the resin particles follow the field lines, greatly reduces the number of remote manipulations, which leads to a simpler operation than in the case of a conventional projection;
• c) the losses in material being minimal, the filters in operation in the dismantling cells where this process is used, will clog up more slowly than in the case of a conventional projection.

• - La THT (60 à 90 Kv) a un débit limité à une valeur très faible (60 à 150 µA suivant les types de pistolet) ; l'énergie contenue dans l'étincelle qui se produirait entre buse et masse est de ce fait très faible.

With regard to the equipment used (THT power supply, spray gun, etc.), the elements contributing to safety in use are as follows:

• - THT (60 to 90 Kv) has a flow rate limited to a very low value (60 to 150 µA depending on the types of gun); the energy contained in the spark which would occur between nozzle and ground is therefore very low.

• - Le matériau ou déchet est mis à la masse par contact avec son support, lui-même à la masse ; les charges électriques portées par la résine s'écoulent ainsi à la masse, évitant tout risque de création d'une charge électrostatique qui pourrait amorcer une étincelle. Il a été vérifié que, même si le support est superficiellement recouvert d'une couche correspondant à trente pulvérisations, la qualité de la mise à la masse du déchet n'est pas compromise.

Only the nozzle is brought to the THT, the body of the gun itself being grounded. Experience has shown, moreover, that direct contact of the nozzle by an operator does not present any danger.

• - The material or waste is grounded by contact with its support, itself grounded; the electrical charges carried by the resin thus flow to ground, avoiding any risk of creating an electrostatic charge which could initiate a spark. It has been verified that, even if the support is superficially covered with a layer corresponding to thirty sprays, the quality of the grounding of the waste is not compromised.

Among the resins which can be used, epoxy resins, polyester resins, vinyl resins, mixtures of thermosetting and thermoplastic resins can be considered.

By way of example, mention may be made of the epoxy paint sold under the brand "RIVEPOX ELECTROSTATIQUE 80088" associated with its "Hardener 80057".

Thinners, to adjust the viscosity, can be added to the resins. Depending on the operating conditions, open air or closed premises, these diluents will be chosen to be flammable or not.

By way of example of diluents, mention may be made of the mixture of 1.1.2 trichloro, 1.2.2 trifluoroethane and 1.1.1 trichloroethane, ketone derivatives and diluents E 3 and SC 1 sold by the company BLANCOMME. These diluents are chosen according to their properties, in particular their flash point, their viscosity and their resistivity to obtain a mixture capable of being sprayed by an electrostatic gun.

Adjuvants can also be incorporated into the resins. As adjuvants, powdered metals can be used, for example, aluminum powder, zinc powder, etc., metal oxides such as oxides of zinc, iron, aluminum, titanium etc., salts such as calcium carbonate, fibers for example glass, carbon, boron fibers etc. and mineral beads for example glass or silica beads.

• - une viscosité convenable , par exemple de l'ordre de 30 s à 20°C lorsqu'on la mesure par écoulement en coupe Ford n° 4 ;
• - une constante diélectrique qui permette la charge des particules;
• - une résistivité appropriée qui dépend du type de pistolet utilisé, par exemple une résistivité de 1 à 100MΩ cm. ;
• - une volatilité compatible avec un temps de séchage et de polymérisation de l'ordre de 60 min à la température ambiante ;
• - un point éclair supérieur à 21 °C ; et
• - une bonne compatibilité (corrosion) avec les matériaux contaminés à traiter.

In all cases, the additives used are selected and their quantity is adjusted so that the resin mixture which will be sprayed by the electrostatic gun, presents:

• - a suitable viscosity, for example of the order of 30 s at 20 ° C when measured by flow in Ford n ° 4 section;
• - a dielectric constant which allows the charge of the particles;
• - an appropriate resistivity which depends on the type of gun used, for example a resistivity of 1 to 100MΩ cm. ;
• - a volatility compatible with a drying and polymerization time of the order of 60 min at room temperature;
• - a flash point above 21 ° C; and
• - good compatibility (corrosion) with the contaminated materials to be treated.

Any electrostatic paint having the characteristics-B. 7484.3 MTD The above-mentioned ticks can be used in the process of the invention, for example epoxy - phenolic and epoxy - aminoplast resins, esters of epoxy resins and fatty acids and epoxy resins modified with polyamines or with diisocyanates.

The paints can be sprayed in liquid form in a solvent or in powder form.

According to a first application of the method of the invention, the fixing of the contamination takes place only to ensure a transfer of the materials in complete safety.

In this case, a thin layer of resin is deposited in one or more passes on the material. This deposit can take place in an armored cell or in the open air, depending on the activity. After deposition, the material is transported and conditioned by any known means, such as that described in the French patent for "Process for the storage of large solid radioactive waste".

According to a second application of the invention, usable in particular for parts of low activity, the fixation of the contamination serves at the same time as final packaging. In this case, a suitable number of passes should be provided to ensure a sufficiently thick resin coating. The resin is applied pure or mixed with an inert filler.

The fixation properties of the contamination were determined by comparison of smears carried out on control surfaces soiled by labile contamination, before and after projection.

The layer (s) adhere perfectly after polymerization to the surface of the waste, do not break or flake off if the waste undergoes mechanical deformation after coating, and are resistant to falling.

• - en THT (60 à 90 Kv) à très faible débit (60 à 150 µA suivant le type de pistolet), et
• - en mélange à projeter, à partir d'un réservoir, maintenu à une pression d'air de 0,5 à 6 bars, suivant le type de pistolet.

Generally, the electrostatic projection equipment consists of a gun, the projection nozzle of which is supplied:

• - in THT (60 to 90 Kv) at very low flow rate (60 to 150 µA depending on the type of gun), and
• - as a spray mixture, from a tank, maintained at an air pressure of 0.5 to 6 bars, depending on the type of gun.

Other characteristics and advantages of the invention will appear better on reading the description which follows, given of course by way of illustration and not limitation, with reference to the appended drawing which represents an installation for implementing the method of invention.

In this figure, it can be seen that the installation comprises a closed enclosure 1 constituted by a fume cupboard inside which one can introduce an electrostatic projection gun 3, for example a gun of the Statary type sold by the SAMES Company, under the reference MRV 96.

The nozzle of the electrostatic gun 3 is supplied with electric current by a generator 5 which supplies by the conductor 7 a high voltage (90k-volt) with a current of approximately 0.1 milliampere, and which is connected to the sector by the conductor 9 .

The gun 3 is also supplied with compressed air by line 11 provided with an adjustable pressure gauge 13, and with resin by line 15 connected to a resin tank 17 itself supplied with compressed air by line 19. pressure gauges 21 make it possible to control the pressure in the various circuits of the installation. Inside the fume cupboard 1, the part 3 of contaminated material can be placed on a support and connected to ground by 25. A container 27 is placed below the part 23 to collect the drops of excess resin which are likely to to flow from the part 23 during the projection operation. At its upper part, the fume cupboard 1 is connected to a duct 29 provided with a grid 31 in order to provide ventilation inside the fume cupboard 1 and renew the air.

The nozzle of the gun 3 is chosen according to the shape of the pieces of contaminated material to be treated and it can project either a rounded jet 4 which is suitable for the treatment of pieces of complex shape, or a flat jet for the pieces of large surface .

To implement the method of the invention, the part 23 of contaminated material to be treated is placed in the fume cupboard 1 and the electrostatic gun 3 is supplied, on the one hand, with electric current and, on the other hand, with resin maintaining in the reservoir 17 an air pressure of 0.5 to 6 bars. Thus, the resin is sprayed onto the external surface of the part 23 and the excess resin drops are collected in the container 27.

The following examples illustrate the process of the invention.

Example 1. -

This example is intended to determine the yield of the fixing of the resin.

• a) Sur une pièce de grande surface (2 m²) on projette 49 g de résine époxydique "03FTI" commercialisée par la Société BLANCOMME. On recueille sur le filtre 0,96 g de résine. Pour cette géométrie de pièce 98 % de la résine projetée est donc fixée sur la pièce qui est revêtue d'une couche de résine d'environ 24 pm d'épaisseur.
• b) Sur des pièces de formes diverses (grilles, tubes, plaques etc....) on projette 56 g de résine et on recueille sur le filtre 3,1 g. Pour cette géométrie de pièces le rendement est de 94,5 %.

It was produced in a hood provided with ventilation (1,500 m ³ / hour, vacuum 45 ^m / m), the very high voltage generator (THT) operates at 90 Kv and provides a current of 0.10 mA.

• a) A large surface area (2 m ² ) is sprayed with 49 g of "03FTI" epoxy resin sold by the company BLANCOMME. 0.96 g of resin is collected on the filter. For this part geometry 98% of the sprayed resin is therefore fixed to the part which is coated with a resin layer of approximately 24 μm in thickness.
• b) On pieces of various shapes (grids, tubes, plates, etc.), 56 g of resin are sprayed and 3.1 g are collected on the filter. For this geometry of parts the yield is 94.5%.

Example 2. -

This example is intended to show the efficiency of the process.

Three plates of oxidized steel are prepared on which identical solutions are deposited, each containing 240 μCi of 137Cs.

After drying, the first plate is left intact as a control.

A second layer of resin is deposited on the second plate (approximately 25 to 30 μm).

On the third plate, two layers of resin are fixed (approximately 50 to 60 µm).

After drying, a wet smear is made on the three plates. The results obtained are shown in the table below.

Example 3. -

This example shows the effectiveness of the process when depositing the paint in a thick layer.

Three plates of degreased steel are prepared and the first plate is covered with a layer of powder paint sprayed electrostatically, which consists of the epoxy paint sold by the company BLANCOMME under the reference 95 KT 17 White-red-brown powder .

The spraying is continued for 20 seconds and the curing is carried out hot at a temperature of 180 ° C. A layer is thus obtained whose thickness is 700 microns.

Two layers of paint are deposited on the second plate, making two successive projections, which gives a total thickness of 1 mm.

On the third plate, three layers of paint are successively sprayed and a total thickness of 1.5 mm is obtained.

It should be noted that the purpose of degreasing the plates is to facilitate the attachment of the thick layer of paint. However, this degreasing operation could be replaced by the deposition on the plates of a layer of primer paint, which also makes it possible to ensure the attachment of the paint subsequently deposited in a thick layer.

Claims (7)

1. A method for fixing radioactive contamination, characterized in that at least one layer of a polymerizable resin at room temperature is sprayed onto the contaminated materials using an electrostatic gun. 2. Method according to claim 1, characterized in that the resins which can be polymerized at room temperature are chosen from the group consisting of epoxy resins, polyester resins, vinyl resins, mixtures of thermosetting and thermoplastic resins. 3. Method according to claims 1 and 2, characterized in that at least one diluent is added to the polymerizable resin. 4. Method according to claims 1, 2 and 3, characterized in that at least one adjuvant is added to the resin. 5. Method according to claim 4, characterized in that the adjuvant is iron oxide or zinc oxide. 6. Application of the method according to any one of claims 1 to 5 to the fixing of contamination to ensure the transport of contaminated materials. 7. Application of the method according to any one of claims 1 to 5 to the fixing of the 'contamination to ensure the conditioning and storage.

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