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
  • G21F9/04—Treating liquids
  • G21F9/06—Processing
  • G21F9/10—Processing by flocculation

Definitions

• the present invention relates to the field of treatment of radioactive waste, in particular of oils and solvents, in particular in nuclear power stations and in military study centers, and relates to a process for reducing waste suitable for this purpose. .
• the invention also relates to a device for implementing this method.
• Contaminated oil is understood to mean an oil containing radioactive substances.
• the decontamination processes of known contaminated oils and solvents are centrifugation, decantation, filtration on rare earths and bacterial destruction.
• DE-A-3 522 126 discloses a process for centrifuging radioactive effluents and drying solid residues.
• JP-A-63 204 198 describes a process for centrifuging and filtering radioactive effluents containing an oily part.
• Also known from WO-A-89 08316 is a process for treating weakly radioactive effluents by preheating eliminating volatile solvents, then by special centrifugation followed by filtration.
• the present invention aims to overcome these drawbacks. Its object is in fact a process for the reduction of radioactive waste, in particular of oils and solvents, in particular in nuclear power stations and in military study centers, characterized in that it consists essentially in pouring said waste in a tank, in which it is subjected to continuous agitation, to preheat it, to carry out a chemical precipitation treatment, to pass the mixture through a centrifuge, to carry out electrostatic or conventional filtration and then to control the level of radioactivity, the treatment being continued continuously until the desired level of decontamination is reached.
• the invention also relates to a device for implementing this process, essentially consisting of a contaminated waste tank connected, by means of supply and return pipes and by a circulation pump, to an element filter, characterized in that it is further provided, between the contaminated waste tank and the filter element, with a centrifuge intended to separate the water possibly contained in the waste and to carry out the separation of large contaminated particles, so as to limit the consumption of filter elements, in that the tank is provided with a mixer and a heating means and in that the filter element consists of at least one collector electrostatic or a conventional filter, all of the elements being controlled and controlled by means of a control panel.
• FIG. 1 is a side elevational view in section of a device for implementing the method according to the invention
• FIG. 2 is a partial plan view of the device
• Figure 3 is a partial schematic view in side elevation and in section showing the operation of an electrostatic collector.
• the process for reducing radioactive waste essentially consists in pouring said waste into a tank 1, in which they are subjected to continuous stirring by means of a mixer 8, to preheat these by means of a heating means 6, to carry out a chemical precipitation treatment, to pass the mixture through a centrifuge 2, by through supply and return lines 4 and a pump 5, to carry out electrostatic or conventional filtration in a filtration element 7, and then to control the rate of radioactivity, all of the operations being controlled and controlled by means of a control panel 9, the treatment being continued continuously until the desired decontamination rate is reached, by return of the treated waste by means of a co Return line 4 to the tank 1.
• the preheating of the waste by the heating means 6 is advantageously carried out at a temperature between 15 ° C and 80 ° C.
• This process is implemented by means of a device essentially consisting of a reservoir 1 of contaminated waste connected, by means of supply and return lines 4 and by a circulation pump 5, to a filtration element 7, this device being characterized in that it is further provided, between the contaminated waste tank 1 and the filter element 7, with a centrifuge 2 intended to separate the water possibly contained in the waste and to carry out the separation of large contaminated particles, in that the tank 1 is provided with a mixer 8 and a heating means 6 and in that the filtration element 7 is constituted by at least one electrostatic collector or a conventional filter, all of these elements being controlled and controlled by means of a control panel 9.
• the filtration element 7 is constituted by one or more electrostatic collectors or by conventional filters, the waste supply of which is carried out, at their lower part, by means of the circulation pump 5, this or these electrostatic collectors being connected in the upper part to the return pipe 4, as shown in FIG. 1 of the accompanying drawings, or the conventional filters being connected in the lower part to the return pipe 4, their supply being done from above.
• This variant embodiment is not shown in the accompanying drawings.
• the conventional electrostatic collector (s) or filters forming the filtration element 7 are preferably provided with removable and interchangeable filter elements made of paper. Thus, by periodically changing the paper filter elements, the contamination accumulated on them can be eliminated in compliance with the regulations in force.
• the heating means 6, the thermostat of which makes it possible to regulate the temperature between 15 ° C and 80 ° C, is intended to maintain a low and constant viscosity of the waste to be treated throughout the duration of the treatment operation and therefore to promote good circulation of this waste in the centrifuge 2 and in the filtration means 7.
• the device is completed by a centrifuge 2 mounted in deflection on the supply line 3 and the outlet of contaminated waste is connected to the tank 1.
• a centrifuge is intended to remove water so that its rate in the waste contaminated is less than 500 ppm. A rate higher than this value would change the insulating characteristics of the oil and interfere with electrostatic filtration.
• FIG. 3 of the accompanying drawings shows a principle of electrostatic filtration as implemented by the invention. It appears from this figure that the particles circulating in an electric field between a positive electrode and a negative electrode are attracted, according to their negative or positive charge, by the two electrodes.
• the charged particles are attracted, according to their polarity, against the corresponding filtering face of the plywood elements 10 and are there retained, so that the contaminated waste is discharged during its passage through the collectors, in porous material such as paper, for example according to the vertical arrows shown in the lower part of FIG. 3, of all or part of the charged particles.
• the circulation of contaminated waste is maintained until a contamination threshold of a value of the same order as that of natural radioactivity is reached, or even lower.
• the decontaminated oils obtained can therefore be treated in existing recycling facilities or for the destruction of used oils, for example by incineration in a cement plant.
• the active particles generally contained in radioactive waste are essentially particles of the type 54Mn, 58Co, 59Fe, 60co, 65zn, 134Cs, 137Cs, and their treatment by application of the process according to the invention by means of the device described above allows a considerable reduction in the volume and weight of the waste in a ratio that can vary between 1 to 1000 and 1 to 3000.
• contamination is mainly due to uranium and other actinides.
• the process according to the invention makes it possible to trap all of these elements.
• the purpose of the chemical reduction treatment in the tank 1 is to change the metal ions into metal elements, which are then retained in the electrostatic collector of the filtration element 7. For example, a cobalt ion ( Co ++) will become (CO °) according to the principle (M ++ + 2e -> M °).
• the method consists in adding to the effluent, beforehand, a so-called entraining salt. The ionic valence of the element will determine the type of trainer to use.
• oils from nuclear power plants are advantageously reduced by using boron salt, such as, in particular, sodium borhydride, added in an amount of 0.001% to 0.2% by weight. It is, however, also possible to use other reducers.
• boron salt such as, in particular, sodium borhydride
• the decontamination of an oil originating from the primary pump of a nuclear power station and having a viscosity of 40 Cst and an activity of 180 Bq / 1 at a value lower than 4 Bq / 1 has been performed as follows:
• NaBH4 sodium borhydride
• the method and the device in accordance with the invention allow decontamination by using only electrical energy which simultaneously warms up and circulates the waste to be decontaminated and fixes the active particles in the filtration element.
• Such a treatment process can be carried out semi-automatically, human intervention being able to be limited to the preliminary chemical treatment and to the replacement of filter papers.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Heat Treatment Of Water, Waste Water Or Sewage (AREA)

Applications Claiming Priority (1)

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• 1995
  • 1995-01-12 US US08/860,873 patent/US5875406A/en not_active Expired - Fee Related
  • 1995-01-12 ES ES95907032T patent/ES2128711T3/es not_active Expired - Lifetime
  • 1995-01-12 WO PCT/FR1995/000041 patent/WO1996021933A1/fr active IP Right Grant
  • 1995-01-12 DE DE69506916T patent/DE69506916T2/de not_active Expired - Fee Related
  • 1995-01-12 EP EP95907032A patent/EP0803127B1/de not_active Expired - Lifetime

Non-Patent Citations (1)

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