Patent Number: 044366558
Section: summary

DESCRIPTION The present invention relates to a process for purifying fluids in general, however contaminated, that is, those contaminated by radioactive substances or non-radioactive substances, such as toxic or chemically active compounds and the like, as well as for conditioning the concentrates resulting from such a process. The invention also relates to a plant for carrying out this process. The present invention is of particular application to water containing radioactive substances in solution and, or in dispersion and, or in suspension, such as for example water for re-use (water of the storage baths for irradiated nuclear fuel elements, cooling water for nuclear reactors etc.) and waste radioactive water (end products of chemical processes, drainage water, solutions resulting from decontamination operations, etc) The volume of radioactive water (water to be re-used+ waste water) to which the invention may be applied is 80-90% of the total quantity of radioactive water which is produced. From a purely chemical point of view, the radioactive water which is normally re-used consists of dilute solutions of inorganic substances of an ionic nature with a low activity. Radioactive liquid wastes may be considered as dilute aqueous solutions of inorganic and organic substances of an ionic and/or molecular nature which also contain colloidal dispersions as well as substances in solid suspension, the radioactive content of which may vary within very wide limits. Various systems and plants are known for purifying radioactive water of low and medium level activity; it is well-known that this purification is in fact carried out by means of various processes (chemical precipitation, evaporation, ion exchange, etc.) all of which tend to produce a reduction in volume with formation of concentrates containing almost all the original radioactivity. All these processes for purifying radioactive water thus present the problem of the further handling of these concentrates, this being necessary to reduce them to a form suitable for their subsequent, final discharge. This handling involves high risks due to the presence of the original radioactive substances in a considerably concentrated form (by at least a factor of 10.sup.3), which renders necessary the use of costly technical devices to allow the handling of such concentrates in safety. In particular, as is known, the ion-exchange treatment involves the regeneration of the exchange beds, which is effected, in the usual purifying columns, by feeding the regenerating liquid through the exchange beds in the columns in the same direction (when a compound bed is used, the regenerant liquid is conveyed in the same direction for the regeneration of anionic resin and in the counter direction for the regeneration of cationic resin) as that of the preceding feed of the liquid to be purified; the radioactive substances which have been retained by the exchange beds are hence taken up in liquid form in the regeneration liquid; this latter is concentrated in radioactive material at the outlet from the regenerated column and hence requires a subsequent conditioning process or process for "rendering insoluble" to transform the greater part of this liquid into an insoluble solid, in that, only the insoluble solid state of the radioactive waste can have those characteristics of mechanical strength and chemico-physical resistance which are absolutely necessary to ensure that environmental polution will not occur, in time, in the place of its final discharge (depths of the sea, underground bunker and the like). The above-mentioned "rendering insoluble" however, presents serious disadvantages in that, precisely because it involves the handling of these liquids which are concentrated in radioactive substances, it can be achieved only by recourse to costly precautionary measures such as the use of sealed and shielded environments, equipment for remote-control manipulation and viewing, as well as plant for ventilation, fire precautions and for collecting possible leakages of radioactive liquids, etc.; similar, costly preventive measures may also be necessary even earlier, or during the purification stage of the liquids to be decontaminated, particularly for the shielding and remote-control of the purification installations for these liquids. The object of the present invention, is, therefore, to avoid the aforementioned disadvantages of the prior art by providing a process and a plant which allow fluids to be purified, however contaminated, and which, at the same time, resolve the problem of rendering the resulting concentrates from the treatment insoluble, without any further handling of the concentrates themselves. The principle on which the present invention is based consists essentially in the use of expendable collecting means for the substances contaminating the fluid to be treated, these collecting means being entirely encapsulated (the encapsulating is initially effected by leaving inlet ports and possibly outlet ports open for the fluid as well as possibly vents for air) within suitable containers, in a solid inert matrix, the thickness of which acts as a biological shield and, or as a mechanically and chemically resistant coating. The outer container, the said encapsulating matrix and the encapsulated collecting means constitute a single unit which will hereinafter be called a "preconditioned cartridge". The use of the preconditioned cartridge is as follows: first stage: the fluid to be treated is purified, with retention of the contaminating substances within the preconditioned cartridge; PA0 second stage (possible): the residual decontaminated liquid present in the cartridge is removed by lowering of the pressure; PA0 third stage: the contaminating substances are rendered insoluble by the passage into the cartridge containing them of a suitable material which can render them insoluble, and the encapsulation of the collecting means in the inert matrix is completed. At the end of the process, the preconditioned cartridge and the substances which have been rendered insoluble are biologically shielded and/or have a mechanical strength and chemical resistance such as to render them suitable, without any further handling, for their final discharge, whether in the earth or in the sea, in complete safety. The principle explained above may be applied to fluids of any nature in that it is sufficient, at the time, to define and to precondition a suitable type of cartridge and then to insert it in a respective plant. The process of the present invention is substantially characterised by the fact that it includes the operations of: preconditioning collection means for the substances contaminating the fluid to be treated by totally encapsulating them, except for inlet and possible outlet ports for the fluid, in a solid inert matrix which acts as a biological shield and, or as a coating which is resistant to chemical action and to mechanical pressure; purifying the fluid, with retention of the contaminating substances in the said preconditioned means; and conditioning the contaminating substances or rendering them insoluble within the preconditioned means, by passing substances adapted to render the contaminating substances insoluble by encapsulating them into these means, with subsequent encapsulation of the said ports of the preconditioned means in a solid inert matrix having the aforementioned function. The preconditioned means according to the present invention may take various forms according to the characteristics of the fluid to be purified; these may therefore, as will be better shown below, consist of beds of decontaminating-concentrating material, of meshed filtering means, of receptacles provided with internal agitators, and the like. The operation of purification may also be carried out by different processes according to the characteristics of the fluid to be treated; thus, this latter may be passed through cartridges with decontaminating-concentrating beds and, or through cartridges with filters and, or through decanting means from which the solid which sediments in them is discharged into cartridges with agitators; in other words the purification of the fluid may be carried out, according to the case, by using the various types of cartridge either alone or in any mutual combination. Even the rendering-insoluble operation may be carried out by different processes according to the type of preconditioned cartridge which is to be subjected to the operation itself. The plant for carrying out the process according to the present invention is, in its turn, essentially characterised by the fact that it includes: preconditioned collecting means for the substances contaminating the fluid to be treated, which means are entirely encapsulated except for inlet and possible outlet ports for the fluid, in a solid inert matrix which acts as a biological shield and, or as a coating resistant to chemical action and to mechanical pressure; one or more stations for purifying the fluid in which this latter is purified with retention of the contaminating substances in the said preconditioned means; and one or more stations for conditioning the contaminating substances or rendering them insoluble within the said collecting means, in which substances suitable for rendering the contaminating substances insoluble by encapsulating them are introduced into these means, with subsequent encapsulation of the said ports of the preconditioned means in a solid inert matrix having the above-mentioned function.