EP0037312B1 - Container for conditioning radioactive effluents - Google Patents

Description

The present invention relates to containers used for conditioning effluents and radioactive waste.

• - d'une part, de séparer et de confiner sous un volume minimal,
• - d'autre part, de conditionner dans des conditions de sécurité particulièrement strictes.

The development of nuclear energy leads to the production of ever greater quantities of effluents and radioactive waste of all kinds which are appropriate:

• - on the one hand, to separate and confine under a minimum volume,
• - on the other hand, to condition in particularly strict security conditions.

In the first phase of these operations, the effluents will be brought, if they are not already so, in a solid form and they will be coated in a suitable solid matrix capable of withstanding the mechanical, physical or chemical aggressions coming from the radioactive materials themselves. - same or from the outside environment.

In the second phase, the effluents dispersed in said solid matrix will be "conditioned" so as to be able to be preserved for more or less long periods which will be necessary for the evolution of the radioactive material (natural decay in particular).

The present invention consists in the choice of a suitable material which can be used for the conditioning of radioactive effluents dispersed in a solid matrix.

• -de conteneurs en acier noir d'un volume compris entre 50 et 400 I, avec une épaisseur d'acier variant entre 0,6 et 2 mm; ces conteneurs sont fermés avec un couvercle muni d'un joint en caoutchouc, l'extérieur des conteneurs est généralement recouvert d'une peinture ou d'un enduit de 30 à 110 microns d'épaisseur, un revêtement de 100 microns environ sous forme d'acier inoxydable au chrome a été également proposé et utilisé;
• - de conteneurs en acier noir avec un revêtement intérieur en béton, de manière à obtenir une protection biologique efficace contre le rayonnement;
• -de conteneurs en tôle d'acier noir d'une épaisseur pouvant aller jusqu'à 10 mm, permettant de disposer d'un volume de plusieurs mètres cubes, et de forme cylindrique ou parallélépipédique, selon les cas;
• - de conteneurs en béton, avec des épaisseurs de paroi allant de 100 à 350 mm, avec le plus souvent un revêtement en acier à l'intérieur et un ferraillage du béton;
• - de conteneurs en bois avec un conteneur plastique étanche disposé à l'intérieur; - de conteneurs moulés en matière plastiques, souvent avec une armature en fibre de verre (résines polyester armé).
• Tous ces conteneurs, même les plus élaborés, présentent des difficultés techniques, certaines provenant soit de leur dégradation potentielle dans le temps (vieillissement), soit de leur résistance insuffisante à la corrosion, soit d'une sensibilité trop importante vis-à-vis de la température ou des variations de celle-ci, soit enfin d'un poids exagéré.

To carry out said conditioning, the use of steel has been recommended to date, possibly coated with stainless alloys, concrete, wood or even plastics. Thus, when it is desired to condition said radioactive effluents contained in a solid matrix in containers for immediate storage in a suitable site, the use of:

• - black steel containers with a volume of between 50 and 400 I, with a steel thickness varying between 0.6 and 2 mm; these containers are closed with a cover provided with a rubber seal, the outside of the containers is generally covered with a paint or a coating of 30 to 110 microns thick, a coating of approximately 100 microns in the form of chrome stainless steel has also been proposed and used;
• - black steel containers with an inner concrete coating, so as to obtain effective biological protection against radiation;
• -containers made of black sheet steel with a thickness of up to 10 mm, allowing a volume of several cubic meters, and of cylindrical or parallelepiped shape, as the case may be;
• - concrete containers, with wall thicknesses ranging from 100 to 350 mm, most often with a steel coating inside and concrete reinforcement;
• - wooden containers with a waterproof plastic container placed inside; - molded plastic containers, often with a fiberglass frame (reinforced polyester resins).
• All these containers, even the most elaborate, present technical difficulties, some coming either from their potential degradation over time (aging), or from their insufficient resistance to corrosion, or from an excessively high sensitivity towards temperature or variations thereof, or of an exaggerated weight.

It has been found, and this is the object of the present invention, that dense asbestos cement (that is to say by definition in the present application an asbestos cement with a density greater than 1.75 g / cm ³ ) constitutes the material of choice for the constitution of containers usable for the transport and the storage of radioactive products.

The asbestos cement chosen is a material with a high dosage of cement (of the order of 1500 kg per cubic meter), a fine particle size due to the mixture of approximately 85% of cement having approximately 3000 to 4000 cm ² / g BLAINE specific surface area and approximately 15% asbestos at 20,000 cm ² / g and a density greater than approximately 1.75 g / cm ³ obtained by applying a strong compression at the head of the forming machine bonding and densification of successive layers of material. The values given above are average values. Those skilled in the art will be able to adapt, on the one hand, the starting materials and, on the other hand, the conditions of implementation to obtain a material acceptable for the intended application.

Furthermore, the techniques for using this asbestos-cement material, in particular for the production of tubes or pipes, are known and industrialized and make it possible to obtain tubes or pipes having diameters, thicknesses and properties adapted to the problems. of packaging mentioned above.

• - une densité suffisante pour que l'on puisse envisager la réalisation d'une protection biologique raisonnable par utilisation d'une épaisseur d'amiante-ciment comprise entre 30 et 100 mm (cas des déchets β de faible activité spécifique et des déchets émetteurs a);
• - des résistances mécaniques appréciables; ces propriétés seront spécialement intéressantes lors du transport de produits dans des conteneurs en amiante-ciment, ainsi que pour l'empilement des colis et leur enfouissement sous terre, car ces conteneurs devront résister à des efforts ou à des chocs potentiels;
• - une stabilité dans le temps démontrée par des études portant sur près de 70 années;
• - une résistance élevée aux corrosions diverses (eaux souterraines, courants vagabonds, bactéries, gaz carbonique, etc.) que l'on peut rencontrer lors des stockages souterrains;
• - une étanchéité remarquable vis-à-vis des gaz et de l'eau due à une porosité extrêmement fine et au colmatage progressif de ces pores, au cours du temps, sous l'influence d'agents extérieurs (par exemple carbonatation);
• - une très grande résistance (et une bonne stabilité) lors des variations de température. Ainsi, l'amiante-ciment est considéré comme pouvant supporter, sans variation notable de ses propriétés, des températures comprises entre - 50 et +300°C environ.
• L'ensemble de ces propriétés fait ressortir que l'amiante-ciment dense constitue bien un matériau de choix pour diverses réalisations de conditionnement des déchets et/ou des effluents radioactifs dispersés dans une matrice solide.

Among the properties of this asbestos-cement which are particularly advantageous for said packaging, we can mention:

• - a sufficient density so that we can envisage the realization of a reasonable biological protection by using a thickness of asbestos-cement between 30 and 100 mm (case of waste β of low specific activity and emitting waste a );
• - appreciable mechanical resistance; these properties will be particularly advantageous during the transport of products in asbestos-cement containers, as well as for the stacking of packages and their burial underground, since these containers will have to resist efforts or potential shocks;
• - stability over time demonstrated by studies covering almost 70 years;
• - high resistance to various corrosions (groundwater, stray currents, bacteria, carbon dioxide, etc.) that may be encountered during underground storage;
• - a remarkable seal against gases and water due to an extremely fine porosity and the gradual clogging of these pores, over time, under the influence of external agents (for example carbonation);
• - very high resistance (and good stability) during temperature variations. Asbestos-cement is therefore considered to be able to withstand, without significant variation in its properties, temperatures between - 50 and + 300 ° C approximately.
• All of these properties make it clear that dense asbestos-cement is indeed a material of choice for various embodiments for packaging waste and / or radioactive effluents dispersed in a solid matrix.

We have already mentioned the possibility of using asbestos and cement-based materials for certain projects involving radioactive elements. This is the case in particular in the German patent DE-B-1 136 261 and in the French patent FR-A-1 347 402. The German patent DE-B-1 136 261 describes the use of a refractory binder material of complex composition (based on calcium sulphate) mixed with asbestos, but does not describe the use of a dense asbestos-cement as in the present application. French patent FR-A-1 347 402 describes the use of a filling material which consists of fibers impregnated with an adhesive and then compressed in the space between two containers; the material used in French patent FR-A-1 347 402 is therefore not asbestos-cement with a density greater than 1.75 as in the present application and does not play the same role with respect to radiation.

Realization of dense asbestos-cement containers.

Dense asbestos-cement can be used for the production of "containers" intended for transport and / or storage (in particular buried radioactive effluents dispersed in a solid matrix, said radioactive effluents being effluents coming directly from industrial nuclear installations or from intermediate storage facilities.

• - ils sont réalisés à partir de tuyaux en amiante-ciment, éventuellement découpés à longueur, préparés de préférence par le procédé type MAZZA, c'est-à-dire sous forte pression;
• - ils ont de préférence une épaisseur de l'ordre de 30 à 80 mm;
• - il sont pourvus, au voisinage de chacune de leurs extrémités et sur leur face interne, d'au moins un dispositif destiné à favoriser l'accrochage des bouchons, par exemple une gorge ou un pas de vis garni d'un jonc mou en mastic de silicone, permettant de parfaire l'étanchéité;
• - ils sont de préférence pourvus à la face interne de leurs extrémités de chanfrein.

These containers have the following characteristics:

• - They are made from asbestos-cement pipes, possibly cut to length, preferably prepared by the MAZZA type process, that is to say under high pressure;
• - They preferably have a thickness of the order of 30 to 80 mm;
• - They are provided, in the vicinity of each of their ends and on their internal face, with at least one device intended to promote the attachment of the plugs, for example a groove or a thread fitted with a soft mastic ring silicone, allowing perfect sealing;
• - They are preferably provided on the internal face of their chamfer ends.

The present invention therefore relates to a: container of cylindrical shape, for the sealed packaging of radioactive waste, comprising a side wall and near each of the ends, a bottom and a cover, characterized in that it consists of asbestos- dense cement, with a density greater than 1.75 g / cm ³ , that the bottom is a dense asbestos-cement plate held in place in a fastening device by a soft plastic material and that a layer of micro-concrete is poured onto this so-called dense asbestos-cement plate on the inside of the container.

The containers will be made from dense asbestos-cement tubes according to the invention; for this, one end of said tubes will be provided with a bottom of the same nature as the tube and hooking means in the form of a groove at the other end, said hooking means being intended to keep a cover closed.

Thus, these containers are intended to be closed at their two ends by means of a "plug"; one of these fillings can advantageously be made in the factory, so that the container is delivered with a plug and an open end. e plug is advantageously made by pouring, in line with the attachment device or devices formed in the internal face of the pipe, a layer of microbeton the thickness of which is between 50 and 100 mm. The micro-concrete is perfectly compatible in its properties with asbestos-cement and adheres well to the pipe thanks to the attachment device. The rod in silicone sealant or equivalent material, placed in the attachment device, prevents any possible entry of water between the shell of the dense asbestos-cement container and the part of the stopper formed by micro-concrete, which may result from the very slight withdrawal of the latter. The external surface of said micro-concrete is advantageously constituted by a dense asbestos-cement plate which is glued to the pipe, in particular using said chamfer before pouring the micro-concrete. It is possibly possible to perfect the gas-tightness of containers of this type by using along the contiguous parts (between the micro-concrete and the pipe and between the micro-concrete, the pipe and the external asbestos-cement plate) materials such as tars, pitch, plastic resins, etc.

The use of such containers can be provided in two different ways.

The first consists in performing a direct filling either with an active mix containing the waste to be conditioned, or with an inactive coating product after having previously disposed of the solid waste in a minimum volume inside the container. The second consists in fact of a repackaging of waste previously placed in containers of the type of those already used previously, in particular of cylindrical shape with thin wall of steel or plastic. The interior dimensions of the asbestos-cement containers will then be determined in such a way that there is a clearance of the order of 0.5 to 2 cm between the exterior of the container to be reconditioned and the interior of the container. in dense asbestos cement. This interval is intended to facilitate the installation of the first container, the envelope of which cannot be considered as a barrier and also to allow pouring into the free space a fluid material which will fill all the spaces remaining free and which will solidify either by polymerization, either by cooling (for example, polyester or epoxy resins, bitumen or pitch can be used).

This second embodiment makes it possible to superimpose several drums in an asbestos-cement container (the length of which can then advantageously correspond to the standard length of the pipe elements, generally 5 m, or to half this length) and also to reinforce the second technological barrier through the creation of the asbestos-cement and bitumen or asbestos-cement and plastic resin complex around active mix containers.

It is advantageous to provide that the dense asbestos-cement containers according to the invention will be provided with devices facilitating their handling. These devices are very diverse, they can be constituted by metal belts placed at the two ends of the container, either connected to each other by tie rods provided with attachment means, or more simply bolted in asbestos-cement. They can also consist of one or more belts placed in grooves (depth 5 to 6 mm for example) formed in the external peripheral part of the containers. These various metal belts may also allow the lateral gripping of the container using trolleys or gripper handling machines, and also contribute to the resistance to possible shocks which may occur during their handling or transport.

When these containers are used during the transport of effluents dispersed in a solid matrix, they can advantageously receive suitable external protection. This protection, which aims to strengthen the resistance of the containers to shocks and drops, which may occur during transfer, will preferably be removable so as not to cause unnecessary space during storage.

The following are non-limiting examples of the use of dense asbestos-cement for the production of containers according to the invention.

The containers are shown in Figures 1, 2, 3 and 4.

Figure 1 shows a perspective view of a container according to the invention, half of which is provided with a type of external protection, and the other half of which is simply provided with a type of device facilitating its handling.

FIG. 2 represents a section on II-II of the containers of FIG. 1.

• - en 1 le tube d'amiante-ciment, ce tube a, par exemple, un diamètre de 1000 mm, une hauteur de 1250 mm et une épaisseur de 50 mm;
• - en 2, 2', 3, 3' deux fois deux gorges ménagées dans la face interne du tube au voisinage des extrémités de celui-ci; avant le remplissage du conteneur, on réalisera le bouchon inférieur constitué par une épaisseur d'environ 60 mm de micro- béton 4 qui s'accroche au tube d'amiante-ciment au niveau des gorges 2 et 2', et d'une plaque d'amiante-ciment 5 collée sur sa périphérie à un chanfrein ménagé sur le pourtour du tuyau 1, au moyen d'une colle convenable (comme, par exemple, d'une colle époxydée chargée); le bouchon supérieur de même constitution que le bouchon inférieur sera mis en place après le remplissage du conteneur par le matériau solide qui y est conditionné:
• - en 6 et 7 des ceintures inférieures et supérieures qui sont reliées entre elles par des tirants tels que 8; ces ceintures métalliques sont en outre reliées à l'aide de pattes 9 à des ceintures extérieures 10, 11 également métalliques:
• - sous la ceinture inférieure 6, on a soudé deux tunnels métalliques 12 et 13 en tôle d'acier dimensionnés de façon à laisser passer les fourches des chariots élévateurs;
• - tout l'espace délimité par les ceintures 10 et 11 et le conteneur proprement dit est alors rempli à l'aide d'une mousse de polyuréthane.

In Figures 1 and 2, there is shown:

• - In 1 the asbestos-cement tube, this tube has, for example, a diameter of 1000 mm, a height of 1250 mm and a thickness of 50 mm;
• - in 2, 2 ', 3, 3' twice two grooves formed in the internal face of the tube in the vicinity of the ends thereof; before filling the container, we will make the lower plug consisting of a thickness of about 60 mm of micro-concrete 4 which is attached to the asbestos-cement tube at the grooves 2 and 2 ', and a plate asbestos cement 5 bonded on its periphery to a chamfer formed around the periphery of the pipe 1, using a suitable adhesive (such as, for example, a loaded epoxy adhesive); the upper stopper of the same constitution as the lower stopper will be put in place after filling the container with the solid material which is conditioned therein:
• - In 6 and 7 lower and upper belts which are interconnected by tie rods such as 8; these metallic belts are also connected by means of lugs 9 to external belts 10, 11 also metallic:
• - Under the lower belt 6, two metal tunnels 12 and 13 are welded in sheet steel dimensioned so as to let the forks of the lift trucks pass;
• - all the space delimited by the belts 10 and 11 and the container itself is then filled with polyurethane foam.

• - le conteneur a été immergé dans l'eau et on y a introduit une pression d'air de 0,5 bar soit 0,5 105 Pa; aucune fuite n'a été décelée;
• - le conteneur a subi une chute d'une hauteur de 1,5 m sur une dalle en béton; exception faite d'une déformation assez sensible des ceintures métalliques circulaires, aucune détérioration n'est apparue sur le conteneur proprement dit qui est demeuré notamment tout à fait étanche à la même pression de 0,5 bar soit 0,5 105 Pa.

The container thus conditioned was filled with concrete and underwent certain tests which gave the following results:

• - the container was immersed in water and an air pressure of 0.5 bar or 0.5 105 Pa was introduced into it; no leaks were detected;
• - the container was dropped from a height of 1.5 m onto a concrete slab; With the exception of a fairly significant deformation of the circular metal belts, no deterioration appeared on the container itself which remained notably completely waterproof at the same pressure of 0.5 bar, ie 0.5 105 Pa.

Figures 3 and 4 show in section conditioners according to the invention provided with protective means usable for the transport and / or storage of these conditioners.

On the conditioner of FIG. 8, the protection is achieved by means of two circular angles 14 and 15 connected together by tie rods 16. Between the angles and the container, rubber elements 17 have been inserted.

On the conditioner of FIG. 4, protection is achieved by the use of delta-shaped rubber dampers suitably arranged. On the upper face of the conditioner, these dampers are advantageously arranged radially; on the underside of the conditioner, these dampers are arranged so as to leave sufficient passage for the arms of a handling device; moreover, similar dampers are arranged on the periphery of the conditioner in its upper part and in its lower part. All these shock absorbers are held in place by suitable metal elements which allow, by disassembly, the recovery of these shock absorbers.

Claims (6)

1. Container of cylindrical shape for tightly packing radioactive wastes, comprising a lateral wall and close to each of the ends, a bottom and a lead, characterized in that it is constituted by dense asbestos-cement, of density greater than 1.75 g/ cm³, the bottom being a plate of dence asbestos-cement held in position in a fixing device by a soft poured plastic material, and in that a layer of microconcrete is poured on said plate in dense asbestos-cement on the inner side of the container.

2. Container according to claim 1, characterized in that the bottom and/or the lead is/are anchored to said lateral wall by means of at least one groove provided in the inner face of said lateral wall.

3. Container according to any one of claims 1 and 2, characterized in that it is closed after filling by sais lead constituted by a plate of dense asbestos-cement glued by a soft plastic material poured into the anchoring device, and in that said lead rests on a layer of micro-concrete.

4. Container according to any one of claims 2 and 3, characterized in that the soft plastic material is a silicon mastic.

5. Container according to any one of the preceding claims, characterized in that means are provided for handling, constituted by metallic belts or grooves provided in the external lateral wall.

6. Container according to any one of the preceding claims, characterized in that a protection against shocks composed of delta-shaped rubber damping means, is placed on the external lateral face of said container.

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