FR2728719A1 - METHOD AND INSTALLATION FOR THE TREATMENT OF RADIOACTIVE RESIDUES IN THE FORM OF SLUDGE - Google Patents

Abstract

The invention relates to a method and to an installation for the treatment of radioactive residues, more particularly in the form of sludge. The process is characterized in that the sludge to be treated is first of all homogenized by stirring and then a hydraulic binder is introduced into these sludges in determined proportions with a view to immobilizing them and obtaining a solid block of defined mechanical strength. .

Description

The invention relates to a method and an installation for the

  treatment of radioactive residues. presenting more particularly in the form of sludge. This invention will therefore find its application

  in the context of the reprocessing of nuclear waste.

  Whether in nuclear power plants or in nuclear waste treatment plants, many precautions must be taken in terms of the quality of effluents discharged into the environment from these plants or factories. Thus, these effluents should be removed from any radioactive particles in order to store them in safe places or they are not likely to contaminate the environment. Thus, for the treatment of these effluents. chemical precipitation, such as flocculation or other type, is carried out in order to remove the

particles in the form of sludge.

  Moreover, the other types of residues. such as evaporator concentrates, ashes and other products involved in the treatment process, for example by spraying. sand, are also collected

then stored.

  In this respect and more particularly with regard to sludge

  radioactive material, these are stored in metal drums

  same, are stored in hangars or. simply, in the open, knowing that in no case such drums can be buried because of the significant risk of contamination that represents their content. Indeed, such metal drums have a limited life so that it is necessary, periodically. to transfer their contents into new casks. It is thus understood that these sludges are considered particularly bulky. so much so that in some countries there are either regulations that do not favor the environment or insufficient means of control. these radioactive sludge yet

  dangerous in every way. are simply dumped in nature.

  The solution according to the invention is a method of treating sludge by immobilizing them so that it is possible to escape them into the ground. this without risk of contamination precisely thanks to the

  stability of the solid block resulting from this sludge immobilization process.

  For this purpose, the invention relates to a process for the treatment of radioactive residues that is more particularly in the form of sludge, characterized in that: - these sludges are first homogenized by stirring - and then introduced into these sludges a hydraulic binder in specific proportions to immobilize them and to obtain a solid block

of mechanical strength defined.

  According to another characteristic of this method ,. the sludges to be treated are derived from a mixture of several types of homogenized radioactive residues which are distinguished by different water contents so that these sludge to be treated comprise an optimum water content corresponding substantially to the amount of water required for the hydration of the components of the hydraulic binder to ensure

hardening of the mixture.

  Advantageously, throughout the treatment process, the sludge and then the hydraulic binder mixture are kept under agitation with a view to

  to obtain and maintain a certain level of homogeneity.

  The invention also relates to an installation for implementing the above method. Thus, this installation comprises: stirring means for homogenizing the radioactive residues contained in drums intended to constitute a lot of sludge to be treated; a container into which, after homogenization, the radioactive residues contained in the drums are discharged: stirring means whose function is to homogenize the batch of sludge introduced into the container; a mixing unit and a molding unit, and pumping means making it possible, respectively, to take the contents of the drums with a view to introducing it into the container and then to collect a determined quantity of homogenized mud contained in this container;

  to transfer it to the mixing unit.

  The advantages obtained by virtue of this invention consist precisely in transforming the radioactive sludge into an immobilized compact block which, moreover, is homogeneous and homogeneous. thus chemically and mechanically stable, it is possible, without risk to the environment,

  to bury these blocks once arranged in a confining envelope.

  Therefore, the present invention. through the method and the installation for its implementation, allows to consider a real treatment of these radioactive waste Other purposes and advantages of the present invention will appear in

  course of the following description relating to an embodiment

  which is given only as an indicative and non-limiting example.

  The understanding of this description will be facilitated by referring to

  attached drawings and in which: - Figure 1 is a schematic and plan view of the installation for the implementation of the process for treating radioactive residues such as sludge; FIG. 2 is an elevational view of the installation as

shown in Figure 1.

  The present invention consists in a process for the treatment of radioactive residues such as chemical coprecipitation sludges or evaporator concentrate, ash, sand and other projection treatment products which are found. whether it's in a nuclear power plant or

  at the level of a nuclear waste reprocessing plant.

  As shown in Figures 1 and 2 of the accompanying drawings, the invention relates. also. to an installation allowing the implementation of this

treatment process.

  In fact, according to this method. residues in the form of fine particles must be distributed. homogeneously, in a liquid medium consisting, essentially. by water. So, in the case of sludge treatment. it is first homogenized by stirring because,

  as it will appear further ahead of the description of this

  homogenization will depend on the stability of the product finally obtained. In the case of dry residues, or with low water content, a water supply may be necessary in proportions, which, again, are defined more in

  before in the description. Such dry residues can also, according to a

  feature of the invention, to be mixed with sludge to be treated in order to

  to obtain a water content in the desired proportions.

  In fact, it is understood that the method applies in a systematic way to the treatment of sludge, whether sludge as recovered through a decanter or other or obtained by adduction

  of water or corresponding to a mixture of sludge and dry residues.

  Ultimately, once this radioactive sludge homogenized as perfectly as possible. we add to it, according to the process, a hydraulic binder in proportions that depend on the resistance

  mechanical block solid resulting after drying.

  In fact, this radioactive sludge-hydraulic binder mixture is, again, made uniform by stirring, precisely so that this homogeneity is obtained in this solid block, after taking said hydraulic binder. The present invention. through its process, also aims to achieve an optimum from the point of view of yield: amount of treated sludge - final volume of immobilized sludge, and, at the same time, the

  amount of hydraulic binder spoiled.

  So. Based on mechanical considerations, it is known the proportions of hydraulic binder to be mixed with respect to a given volume of dry residues. It is known, moreover, the volume of water necessary for the hydration of the components of the hydraulic binder and allowing, in the end, the

hardening of the mixture.

  Thus, if the sludge to be treated is low water content, it is necessary to add water that can be qualified as clean to obtain the desired result. Thus, it can be seen that, with respect to the volume of the solid block obtained, the volume of treated sludge has not been optimized. Indeed, by operating. so. we treated. unnecessarily. a given amount of water

clean added to the mix.

  In the same way. by treating sludge with a high water content, which is greater than the quantity of water required for the hydration of the optimum volume of hydraulic binder to obtain the desired mechanical strength, there are no other solutions than to put more hydraulic binder able to capture this excess water. As a result, the amount of hydraulic binder finally spoiled is greater than that actually needed, besides. again, the result is a solid block of unnecessarily increased volume compared to the amount of residue

actually treated.

  The solution according to the invention is to proceed to a mixture of different types of residues which are distinguished, precisely, by their water content to obtain a sludge whose water content is that required for the hydration of the amount of hydraulic binder that must be added to these sludge to immobilize them in the form of a block responding, from the point of view

  mechanical strength, the requirements.

  Concretely. for sludge with a high water content, it is possible, for example, to mix sludge of low water content or to add to it,

  simply, "dry" residues of the sand or ash type.

  According to the method. it is also planned, before spoiling the hydraulic binder and after homogenization of the sludge, to perform physico-chemical analyzes thereof. In particular, a pH measurement is performed as well as a measurement of the water content. Depending on these 6 measurements, one can, thus, readjust, if necessary, the pH or modify the

water content of sludge.

  In addition, it is planned to check the compatibility of the sludge with the hydraulic binder. For this purpose, homogenized sludge is taken from a sample of a prescribed volume, to which is added a prefixed amount of hydraulic binder. This mixture based on a sample of sludge is contained in a mold which, after immobilization of

  these sludge, allows easy demolding.

  This sample of immobilized sludge is then analyzed. On the basis of the results of the latter, it would be necessary to readjust whether it is from the point of view of the water content of the sludge or the amount of hydraulic binder that should be put implemented. Such tests on

  Samples are repeated as many times as necessary.

  Preferably, this test on a sample is followed by a full-scale test. Thus, sludge adjusted and homogenized, it is taken the amount of sludge corresponding to the volume of the solid block that is desired to achieve. To this quantity of sludge is added the hydraulic binder in proportions such as determined through the test carried out beforehand on a sample. It should be noted that, at this stage, the water content can still be readjusted, especially if

  this is less than the desired water content.

  It is only after a finding of a satisfactory result in these life-size tests that the sludge treatment process enters the continuous operating phase until the total treatment of a given batch of sludge. It suits. indeed, to observe that tests. whether it is reduced in size or in real size. lead to results that are strictly dependent on the physical and chemical characteristics of the sludge lot that will have been previously prepared and corresponding to a mixture of different types of sludge and other radioactive residues. Ultimately, a lot: 35 of mud is the amount of slurry prepared in a container of a

determined volume.

  From such a batch of sludge it is possible to design a given number of blocks of immobilized sludge of a predetermined volume. More specifically, the following operations are repeated a number of times: a defined quantity of sludge is taken from the batch prepared for introduction into a mixer in which the hydraulic binder is also poured. After homogenization, the mixture is poured into a recyclable mold; at this moment, a handling hook is also introduced into this hydraulic sludge-binder mixture; after curing, the immobilized block is removed from the recyclable mold and is introduced into a storage container which can

contain many of these blocks.

  As already stated above, the present invention also relates to an installation for carrying out the process which

just described.

  This installation, more particularly represented in FIGS. 1 and 2, essentially comprises. stirring means 1 for homogenizing the sludge previously contained in drums 2. This installation is further provided with a container 3 in which are poured, after homogenization, the sludge contained in several drums 2

  and corresponding to a batch 4 of sludge to be treated.

  In this container 3 are introduced, again. stirring means D which, again, have the function of homogenizing the batch of introduced sludge

in this container 3.

  This facility is equipped. in addition. a mixing unit 6 in which is introduced, in a discontinuous cycle, a given amount of sludge from the container 3. and the volume of hydraulic binder allowing, finally, to immobilize this defined amount of sludge. In addition, under this mixing unit 6 is disposed a molding unit 7 at which there is a recyclable mold 8 able to contain

  said hydraulic slurry-binder mixture for hardening.

  Advantageously, this installation also includes pumping means 9, 10 permitting. respectively. to take the contents of the drums 2 in order to introduce it into the container 3, then to take a determined quantity of homogenized sludge contained in this container 3 with a view to

  transfer to the mixing unit 6.

  Figures 1 and 2 schematically illustrate the entire installation. Thus, it is found that this installation comprises. firstly, an intermediate lock 11 in which are disposed the drums 2. defining a lot of sludge to be treated 4 and coming from a storage room 12. Downstream of this intermediate lock 11 is the opening lock chamber of barrels 13 in which the drums 2 will be successively opened in order to homogenize their contents, which will then be taken by means of the pumping means 9 in order to transfer it to the container 3 situated at the level of an airlock 14 downstream. It should be noted that when opening a drum 2, a number of operations are carried out such as the visual inspection of the contents of the drum and the measurement of the amount of sludge contained in the drum. . It is removed, too. where appropriate, solid waste. Note, moreover, that on this open shaft 2 is placed a specific cover 15 to be traversed by the rod 16 of a turbine 17 connected to a portable mixer

  18. the assembly constituting the stirring means 1.

  Otherwise. between the barrel opening chamber 13 and the chamber 14 in

  which is the container 3 is a control chamber and test 19.

  Inside this chamber are carried out the various measurements, radiological and pH for example. as well as sample testing to check the

  sludge compatibility with the hydraulic binder.

  As provided in the process. once the batch of sludge is perfectly homogenized in the container 3. this by means of appropriate stirring means 5 which, again, can be in the form of a portable mixer 20. a quantity is taken in order to to transfer it into a kneading unit 6. This is located, in fact, in an airlock 21 downstream of the lock 14 and comprises a kneader 22 surmounting a support frame 23 under which can be placed a container 24 in which will be arranged the immobilized mud blocks, after curing in the recyclable mold 8. In this respect, this recyclable mold 8 is placed under the mixer

  22, on a support structure 25 mounted inside the container 24.

  In reality. to carry out the demolding operations, the container 24 is extracted from the support frame 23. It is again introduced and, therefore, placed under the mixer 22, at the end of this demolding operation and a

  once the block of immobilized mud disposed in the bottom of this container 24.

  This can, indeed, be able to contain many of these blocks of mud immobilized. Furthermore, it should be noted that by molding inside this container 24, it avoids any risk of contamination of the lock 21 in case of possible splashing. The movements of the container 24 are facilitated thanks to a raceway 29 on which

  it rests by means of appropriate rolling means.

  Once this container 24 filled with solid blocks, it is closed by means of a lid. while the preserved space between this lid and

  said solid blocks are filled with a suitable coating mortar.

  Note that at each of these locks 11. 13, 14, 19, and 22, 3 can be arranged ventilation means 26. Such ventilation means 26 are, of course, specific to the field concerned. So, they involve, necessarily. filtration means avoiding contamination

from the outside atmosphere.

  To return more particularly to the hydraulic binder used in the context of the treatment process according to the invention, it is preferentially a mortar with no shrinkage ready for use. To this mortar may be added a number of adjuvants necessary for the

  chemical stability of immobilized sludge.

  As for the containers 24 in which these immobilized mud blocks are arranged, it is preferentially. fiber concrete concrete containers even to ensure. at least partially, the function of containment. In addition, the packaging and / or treatment of solid waste taken from drums 2 or the packaging and decontamination of the latter once emptied, will be carried out according to traditional methods in the field considered. These operations are likely to be conducted in locks 27 adjacent to those previously mentioned. In addition, this installation will be supplemented, preferably, by a

  specific room containing radiological control devices.

  The advantages of the present invention consist, of course, in that one is able. for the first time, to offer a real treatment of radioactive sludge. being, until then, stored in drums. represented a huge risk to the environment. Indeed, these barrels were likely to pierce in time, this under the action

corrosive agents.

  Although the invention has been described with respect to a particular embodiment, it is understood that it is in no way limited and that various modifications of shapes, materials and combinations thereof can be made. various elements. without departing from the frame and

the spirit of the invention.

Claims (9)

claims   1. A process for treating radioactive residues, more particularly in the form of sludge, characterized in that - these sludges are firstly homogenized by stirring; - Then introduced into the sludge a hydraulic binder in specific proportions to immobilize them and obtain a solid block of mechanical strength defined.   2. Treatment process according to claim 1, characterized in that the sludge to be treated is derived from a mixture of several types of homogenized radioactive residues which are distinguished by different water contents so that said sludge to be treated contains a content corresponding optimum water, substantially. the amount of water needed to hydrate the components of the hydraulic binder to ensure hardening of the mixture.   3. Treatment method according to any one of claims 1 and   2, characterized by the fact that: - a batch (4) of sludge to be treated starting from radioactive residues in the form of sludge of different qualities contained in drums (2) distinct; - The contents of each of these drums (2) are homogenized successively before being transferred to a container (3) capable of containing the entire batch (4) of sludge to be treated after homogenization of the sludge mixture. contained in this container (3), a quantity is deducted as a function of the volume of the solid block to be formed, in order to discharge into a mixer (22): - is introduced into this mixer (22) the amount of hydraulic binder to guarantee, after hardening. the immobilization of the quantity of sludge it contains; - After homogenization of the sludge-hydraulic binder mixture, it is poured into a mold from which is taken, after hardening, the solid block to deposit it in a container 24 constituting an envelope confinement.   4. Method according to claim 3, characterized in that before sampling a quantity of mud determined for its transfer into the mixer (22). an analysis is made of certain chemical and / or physical characteristics of the batch (4) of sludge contained in the container (3) - some of the parameters such as pH and water content are readjusted; performs a hydraulic mud compatibility test sludge to be treated on a sample thereof taken from said container (3); some of the physical and / or chemical parameters of the sludge are readjusted based on the results on the sample; - these operations are repeated, as necessary, before carrying out a full-scale test at the end of which the said physical parameters   and / or chemical sludge are again likely to be readjusted.   5. Installation for the implementation of the process according to the   Claims 1 to 4, characterized by the fact that it comprises:   - stirring means (1) for homogenizing the radioactive residues contained in drums (2) intended to constitute a batch (4) of sludge to be treated; a container (3) into which, after homogenization, the radioactive residues contained in the drums (2) are discharged; - stirring means (5) whose function is to homogenize the batch (4) of sludge introduced into the container (3); - a mixing unit (6) and a molding unit (7); and pumping means (9, 10) making it possible, respectively, to take the contents of the drums (2) in order to introduce it into the container (3), then to take a determined quantity of homogenized mud contained   in this container (3) for transfer to the mixing unit (6).   6. Installation according to claim 5. characterized in that it comprises, at least: - an intermediate lock (11) (in which are arranged the drums (2) intended to constitute a batch (4) of sludge to be treated - an airlock for drums (13) in which the drums (2) are successively opened in order to homogenise their contents, which is then withdrawn via the pumping means (9) in order to transfer it to the container (3) located in a lock (14) downstream - a mixing lock (21) grouping the mixing unit (6) as well as the molding unit (7).   7. Installation according to claim 6, characterized in that it further comprises a control chamber (19), preferably located between the   opening of the barrels (13) and the lock (14) enclosing the container (3).   8. Installation according to claim 6, characterized in that the mixing unit (6) comprises a mixer (22) surmounting a support frame (23) under which can be placed a container (24) in which the blocks will be arranged of immobilized mud after curing in a recyclable mold (8). this being placed, under the mixer (22), on a   support structure (25) mounted inside said container (24).   9. Installation according to claim 8, characterized in that the container (24) is mounted on a raceway (29) facilitating its   movements and its positioning under the mixer (22).