EP0724271A1 - Process and device for treating radioactive waste by hydraulic binding agent - Google Patents

Abstract

Aqueous slurries of radioactive waste in individual containers (2) are first homogenised separately using a portable agitator (18), then pumped to a common vessel (3) where the mixture is again homogenised, successive quantities being then pumped from vessel (3) to a mixer (6) where they are mixed with appropriate doses of hydraulic binder before being moulded into solid blocks in reusable mould (8). The blocks are placed in a container (24) for storage. Samples taken from vessel (3) are analysed to enable their water content, pH etc. to be adjusted to ensure that the binder solidifies the slurry mixture. Appts. is also claimed and comprises a series of chambers, where containers (2) are stored, opened to enable their contents to be agitated, and enclosing vessel (3) and mixer (6), which is located above mould (8) and container (24). Container (24) is movable from the final chamber (23) on a roller track (29).

Description

The invention relates to a method and an installation for the treatment of radioactive residues in the form of sludge, ash, concentrates, corundum and various detritus, consisting in immobilizing them by means of a hydraulic binder in order to obtain a solid block. of defined mechanical resistance. This invention will therefore find its application in the context of the reprocessing of radioactive waste.

Whether in nuclear power plants or in nuclear waste treatment plants, many precautions must be taken with regard to the quality of the effluents discharged into the environment from these plants or factories. Thus, these effluents must be rid of all radioactive particles in order to store them in safe places where they are not likely to contaminate the environment.

Thus, for the treatment of these effluents, chemical precipitation, of the flocculation or other type, is carried out in order to remove the particles in the form of sludge.

Furthermore, the other types of residue, such as evaporator concentrates, ash and other products used in the treatment, by spraying or filtration, for example, corundum, sand, etc. are also collected and then stored.

In this regard and with regard more particularly to radioactive sludge, it is stored in metal drums or cellars which, themselves, are stored in hangars or, simply, in the open, knowing that in no case such barrels cannot be buried because of the significant risks of contamination represented by their contents. Indeed, such metal drums have a limited lifespan so that it is necessary, periodically, to transfer their contents into new drums. It is thus understood that this sludge is considered to be particularly bulky, so much so that, in certain countries, comprising either a regulation which does not favor the environment, or insufficient means of control, this sludge radioactive yet dangerous in all respects, are simply dumped in nature.

The solution according to the invention is a sludge treatment process consisting in immobilizing them in such a way that it is possible to store them without risk of contamination precisely thanks to the stability of the solid block resulting from this sludge immobilization process.

To this end, the invention relates to a process for treating radioactive residues in the form of sludge, ash, concentrates, corundum and various detritus, consisting in immobilizing them by means of a hydraulic binder, characterized in that mixes several types of radioactive residues which are distinguished by different water contents so as to obtain a sludge to be treated having an optimum water content corresponding, substantially, to the amount of water necessary for the hydration of the components of the hydraulic binder for curing the mixture.

Advantageously, throughout the treatment process, the sludge and then the slurry-hydraulic binder mixture are kept under agitation in order to obtain and then maintain a certain level of homogeneity.

• des moyens d'agitation pour homogénéiser les résidus radioactifs contenus dans des fûts destinés à constituer un lot de boues à traiter ;
• un conteneur dans lequel sont déversés, après homogénéisation, les résidus radioactifs contenus dans les fûts ;
• des moyens d'agitation ayant pour fonction d'homogénéiser le lot de boue introduite dans le conteneur ;
• une unité de malaxage ainsi qu'une unité de moulage ;
• et des moyens de pompage permettant, respectivement, de prélever le contenu des fûts en vue de l'introduire dans le conteneur puis de prélever une quantité déterminée de boue homogénéisée contenue dans ce conteneur en vue de la transférer vers l'unité de malaxage.

The invention also relates to an installation for implementing the above method. Thus, this installation includes:

• stirring means for homogenizing the radioactive residues contained in drums intended to constitute a batch of sludge to be treated;
• a container into which the radioactive residues contained in the drums are poured, after homogenization;
• stirring means having the function of homogenizing the batch of sludge introduced into the container;
• a kneading unit as well as a molding unit;
• and pumping means making it possible, respectively, to take the contents of the drums in order to introduce it into the container and then to take a determined quantity of homogenized sludge contained in this container in order to transfer it to the mixing unit.

The advantages obtained thanks to this invention consist precisely in that by transforming the radioactive sludge into an immobilized compact block which, moreover, homogeneous and, therefore, chemically and mechanically stable, it is possible, without risk for the environment, to bury these blocks arranged in a confining envelope.

Consequently, the present invention, through the process and the installation allowing its implementation, makes it possible to envisage a real treatment of this radioactive waste.

• la figure 1 est une vue schématisée et en plan de l'installation permettant la mise en oeuvre du procédé de traitement de résidus radioactifs tels que des boues ;
• la figure 2 est une vue en élévation de l'installation telle que représentée dans la figure 1.

The invention will be better understood on reading the description which follows, accompanied by drawings illustrating an exemplary embodiment.

• Figure 1 is a schematic plan view of the installation allowing the implementation of the process for treating radioactive residues such as sludge;
• FIG. 2 is an elevation view of the installation as shown in FIG. 1.

The present invention consists of a process for the treatment of radioactive residues such as chemical co-precipitation sludge or evaporator concentrate, ash, sand and other spray treatment products which are found, whether in a nuclear power plant or at a nuclear waste reprocessing plant and generally all producers of radioactive waste.

As visible say Figures 1 and 2 of the accompanying drawings, the invention also relates to an installation for the implementation of this treatment process.

In fact, according to this process, the residues which are in the form of fine particles must be distributed, in a homogeneous manner, in a liquid medium constituted, essentially, by water. Thus, in the case of sludge treatment, this is firstly homogenized by stirring because, as will appear further in the description, 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 further in the description. In fact, such dry residues are, according to a feature of the invention, mixed with sludge to be treated in order to obtain a water content in the desired proportions.

It is understood that the method is applied systematically to the treatment of sludge, whether it is sludge such as recovered through a settling tank or the like or obtained by water supply or corresponding to a mixture of sludge and dry residue.

Ultimately, once this radioactive sludge is homogenized as perfectly as possible, we just add, according to the process, a hydraulic binder in proportions that are a function of the mechanical strength of the solid block that will result after drying.

This mixture of radioactive sludge and hydraulic binder is again made homogeneous by agitation, precisely so that this homogeneity is obtained in this solid block, after setting of said hydraulic binder.

In fact, the present invention, through the process, aims to achieve an optimum from the point of view of the yield: quantity of sludge treated - final volume of sludge immobilized, and, at the same time, the quantity of hydraulic binder spoils.

Thus, starting from mechanical considerations, we know 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, ultimately, the hardening of the mixture.

Consequently, if the sludge to be treated has a low water content, it is necessary to add water which can be described as appropriate to the mixture in order to obtain the desired result. Under these conditions, it can be seen that, relative to the volume of the solid block obtained, the volume of sludge treated has not been optimized. In fact, by operating in this way, a given quantity of clean water added to the mixture was treated unnecessarily.

In the same way, by treating sludge with a high water content, ie greater than the amount of water necessary for the hydration of the optimum volume of the hydraulic binder allowing the desired mechanical resistance to be obtained, there is no other solutions than putting more hydraulic binder capable of capturing this excess water. Consequently, the quantity of hydraulic binder finally wasted is greater than that actually necessary, not to mention that, here again, this results in a solid block of unnecessarily increased volume compared to the quantity of residues actually treated.

The solution according to the invention consists in carrying out one or more mixtures of different types of residues which are distinguished, precisely, by their water content to obtain a slurry whose water content is that necessary for the hydration of the amount of hydraulic binder that must be added to this sludge to immobilize it in the form of a block that meets, from the point of view of mechanical strength, the required requirements.

Concretely, with sludge with a high water content, it is possible, for example, to mix sludge with low water content or even simply add "dry" residues of the sand or ash type.

According to the process, it is also planned, before mixing the hydraulic binder and after homogenization of the sludge, to carry out physico-chemical analyzes of the latter. In particular, a measurement of the pH is carried out as well as a measurement of the content in water. Depending on these measures, it is thus possible to readjust the pH, if necessary, or even modify the water content of the 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 one or more samples of an imposed volume, to which is added a prefixed quantity of hydraulic binder. This mixture based on a sample of sludge is contained in a mold which, after immobilization of this sludge, allows easy demolding.

This immobilized mud sample (s) is then analyzed. On the basis of the results of the latter, the necessary readjustment is carried out whether from a point of view of the water content of the sludge or the quantity or nature of the hydraulic binder that there is. place to implement. Such sample tests are repeated as many times as necessary.

Preferably, these tests on samples are followed by a full-scale test. Thus, adjusted and homogenized sludge, the quantity of sludge corresponding to the volume of the solid block that is to be produced is sampled. To this given quantity of sludge is added the hydraulic binder in proportions 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, particularly if it is less than the desired water content.

It is only after observation of a satisfactory result at the level of these full-scale tests that the sludge treatment process enters the continuous operating phase until the total treatment of a given batch of sludge.

It should, in fact, be observed that the tests, whether in reduced size or in real size, lead to results which are strictly dependent on the physical and chemical characteristics of the batch of mud which will have been previously prepared and corresponding to a mixture of different types of mud and other radioactive residues. In final, a batch of mud corresponds to the quantity of mud prepared in a container of a determined volume.

According to a first embodiment from such a batch of mud, it is possible to design a given number of blocks of immobilized mud of a predetermined volume. More precisely, the following operations are repeated a number of times: a defined quantity of mud is taken from the batch prepared for introduction into a mixer into which the hydraulic binder is also poured. After homogenization, the mixture is poured into a recyclable container: at this time, a handling hook is also introduced into this mud-hydraulic binder mixture; after verification of setting, the immobilized block is removed from the recyclable container and is introduced into a storage container which may contain several of these blocks.

According to a second embodiment, more corresponding to the installation illustrated in the attached figures, the batch of prepared and homogenized sludge is mixed using a hydraulic binder whose characteristics and quantities have been determined through tests on samples, this in order to come fill almost all of a specific containment container, in particular in fiber concrete meeting the physical and mechanical characteristics of nuclear storage. Finally, this container constitutes, in this case, a lost formwork and its internal wall is lined with a sheet of compressible material, for example made of polystyrene capable of showing the dimensional variations of the block being solidified.

As already specified above, the present invention also relates to an installation allowing the implementation of the process which has just been described.

This installation, more particularly shown in FIGS. 1 and 2, essentially comprises stirring means 1 making it possible to homogenize the sludge previously contained in drums 2. This installation is also provided with a container 3 in which are discharged, 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 again introduced stirring means 5 which, again, have the function of homogenizing the batch of sludge introduced into this container 3.

This installation is also provided with a kneading unit 6 into which is introduced, according to a discontinuous cycle, a given quantity of sludge from the container 3, as well as the volume of hydraulic binder allowing, finally, to immobilize this defined amount of mud. In addition, under this kneading unit 6 is arranged a molding unit 7 at which there is at least one container 24 capable of containing said immobilized hydraulic binder-binder mixture.

Advantageously, this installation also includes pumping means 9, 10, making it possible, respectively, to take the contents of the drums 2 with a view to introducing it into the container 3, then to take a determined quantity of homogenized sludge contained in this container 3 in order to transfer it to the kneading unit 6.

Figures 1 and 2 schematically illustrate the entire installation. Thus, it can be seen that this installation comprises, first of all, an intermediate airlock 11 in which the drums 2 are arranged, defining a batch of sludge to be treated 4 and coming from a storage room 12. Downstream of this intermediate airlock 11 is located the barrel opening airlock 13 in which the barrels 2 will be opened successively in order to homogenize their content which will then be removed via the pumping means 9 in order to transfer it to the container 3 located at an airlock 14 downstream.

It should be noted that when opening a drum 2, a certain number of operations are carried out, such as visually checking the contents of the drum and measuring the quantity of mud contained in the latter. . Solid waste is also removed from it, where appropriate. Note, moreover, that on this open barrel 2 is placed a specific cover 15 capable of being crossed by the rod 16 of a turbine 17 connected to a portable mixer 18, the assembly constituting the stirring means 1 .

Furthermore, between the barrel opening airlock 13 and the airlock 14 in which the container 3 is located there is a control and test airlock 19. Inside this airlock are carried out the various radiological and pH for example, as well as tests on samples to check the compatibility of the sludge with the hydraulic binder.

As provided for in the process, once the batch of sludge is perfectly homogenized in the container 3, this by means of appropriate stirring means 5 which, here again, can be in the form of a portable mixer 20, it a given quantity is taken from it in order to transfer it to a mixing unit 6. This is, in fact, located in an airlock 21 downstream of the airlock 14 and includes a mixer 22 surmounting a support frame 23 under which can be placed a specific storage container 24 into which the homogenized mud-hydraulic binder mixture is poured in order to harden it.

One can also imagine, according to another embodiment not shown, to have, under the support frame 23 a container 24 in which one comes to deposit blocks of immobilized mud, after hardening in a recyclable mold. In this regard, this recyclable mold can be placed under the mixer 22, on a support structure mounted inside the container 24.

The movements of the container 24 are facilitated by a raceway 29 on which it rests by means of suitable rolling means.

Once this container 24 is filled, it is closed by means of a cover, while the space preserved between this cover and the said solid block (s) is filled with an appropriate filling mortar.

Note that at each of these airlocks 11, 13, 14, 19 and 22, ventilation means can be fitted. Such ventilation means are, of course, specific to the field concerned. Thus, they necessarily include filtration means avoiding contamination of the outside atmosphere.

To return more particularly to the hydraulic binder used in the treatment process according to the invention, it is preferably a mortar without shrinkage ready to use depending on the characteristics of the waste. To this mortar can be added a number of additives necessary for the chemical stability of the immobilized sludge.

As for the container 24, these are preferably concrete containers made of metallic fiber concrete capable of ensuring, at least partially, the function of confinement. Furthermore, the packaging and / or treatment of solid waste taken from the 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 carried out in airlocks adjacent to those previously mentioned. In addition, this installation will preferably be completed by a specific room containing the radiological monitoring devices.

The advantages resulting from the present invention consist, of course, in that we are able, for the first time, to offer a real treatment of radioactive sludge which, being, until then, stored in drums, represented a huge risk to the environment. Indeed, these barrels were liable to break through over time, under the action of corrosive agents.

Claims (9)

Process for the treatment of radioactive residues in the form of sludge, ash, concentrates, corundum and various detritus, consisting in immobilizing them by means of a hydraulic binder in order to obtain a solid block of defined mechanical resistance, characterized in that one mixes several types of radioactive residues which are distinguished by different water contents so as to obtain a sludge to be treated having an optimum water content corresponding, substantially, to the amount of water necessary for the hydration of the components of the hydraulic binder to ensure hardening of the mixture. Treatment method according to claim 1, characterized in that: - A batch (4) of sludge to be treated is formed from radioactive residues in the form of sludge of different qualities contained in separate drums (2); the contents of each of these drums (2) are successively homogenized before being transferred to a container (3) capable of containing the entire batch (4) of sludge to be treated; - After homogenization of the mixture of sludges contained in this container (3), a quantity determined therefrom is determined as a function of the volume of the solid block to be formed, in order to pour it into a mixer (22); - The amount of hydraulic binder is introduced into this mixer (22) to guarantee, after hardening, the immobilization of the amount of sludge it contains; - After homogenization of the mud-hydraulic binder mixture, it is poured into a container (24) constituting a confinement envelope. Method according to claim 2, characterized in that before a predetermined quantity of sludge is drawn up for transfer to the mixer (22), the procedure is carried out an analysis 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; - a hydraulic binder compatibility test is carried out on one or more samples of the latter taken from said container (3); - some of the physical and / or chemical parameters of the sludge are readjusted according to the results on the sample (s); - these operations are repeated, as necessary, before carrying out a full-scale test at the end of which the said physical and / or chemical parameters of the sludge are again liable to be readjusted. Installation for implementing the method according to claims 1 to 3, characterized in 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 are poured, after homogenization, the radioactive residues contained in the drums (2); - Stirring means (5) having the function of homogenizing the batch (4) of sludge introduced into the container (3); - a kneading unit (6), as well as a molding unit (7); - And pumping means (9, 10) allowing, respectively, to take the contents of the drums (2) in order to introduce it into the container (3), then to take a quantity homogenized sludge contained in this container (3) in order to transfer it to the mixing unit (6). Installation according to claim 4, characterized in that it comprises, at least: - an intermediate airlock (11) in which the drums (2) are arranged intended to constitute a batch (4) of sludge to be treated; - a barrel opening airlock (13) in which the barrels (2) are opened successively in order to homogenize their content which is then removed via the pumping means (9) in order to transfer it to the container (3) located in an airlock (14) downstream; - a mixing airlock (21) grouping the mixing unit (6) as well as the molding unit (7). Installation according to any one of claims 4 or 5, characterized in that it further comprises a control airlock (19), preferably located between the barrel opening airlock (13) and the airlock ( 14) containing the container (3). Installation according to any one of claims 4 to 6, characterized in that the mixing unit (6) comprises a mixer (22) surmounting a support frame (23) under which a specific storage container (24) can be placed ) into which the homogenized mud-hydraulic binder mixture is poured in order to harden it. Installation according to any one of Claims 4 to 6, characterized in that the mixing unit (6) comprises a mixer (22) surmounting a support frame (23) under which a container (24) can be placed in which the immobilized sludge blocks will be placed, after hardening in a recyclable mold, the latter being placed, under the mixer (22), on a support structure mounted inside said container (24). Installation according to one of claims 7 or 8, characterized in that the container (24) is mounted on a raceway (29) facilitating its movement and its positioning under the mixer (22).

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