FR2519580A1 - Resin container for radioactive or toxic wastes - mfd. without residual stress using elastomer core in rigid mould - Google Patents

Abstract

A pure thermosetting resin container, esp. for radioactive and toxic wastes, is mfd. by pouring liquid resin with hardener into the space between an exterior rigid mould and a layer of elastomer covering a second rigid mould, pref. resting on the removable base of the first mould. The elastomer layer absorbs the strains which would otherwise develop in the resin because of shrinkage during hardening. Used for long-term containment of radioactive or toxic wastes, inside outer vessels, disposed of on land or at sea. The continuous layer of pure resin around the waste gives improved resistance to leaching. Because no stress is developed in the resin during hardening, it is less prone to cracking and rupture.

Description

 The subject of the present invention is a method and a device for manufacturing a container made of resin, usable in particular for the packaging of radioactive or toxic waste and a container obtained by this method.

 More precisely, it relates to the manufacture of a container of radioactive waste in pure resin, used in devices for the long-term containment of radioactive waste. It is known that such devices must meet very strict characteristics, in particular with regard to their properties of resistance to leaching by soil or sea water, their resistance to weathering and their mechanical resistance.

 Until now, waste has generally been treated by coating in materials such as glass, bitumen, concrete and thermosetting resins, then stored in containers. Among these materials, thermosetting resins are of great interest because they make it possible, on the one hand, to limit the dimensions of the storage containers and, on the other hand, to obtain the lowest leaching rates.

 Furthermore, it has recently been discovered that by using more in the containment devices for radioactive waste a container made of pure thermosetting resin, the resistance to leaching of the waste is very significantly improved by the presence of this impermeable barrier and continuous of pure thermosetting resin which constitutes the wall of the container (see French patent n ° 80/00230 filed on January 7, 1980 in the name of the ECOPOL Company).

 According to this patent, the containers of pure thermosetting resin can be prepared either by centrifugation or by molding by introducing the thermosetting resin in the liquid state between an external mold and a polypropylene core.

 However, the preparation of such containers by molding poses certain problems because stresses develop during the hardening of the resin; these constraints weaken the resin and cracks can appear in the wall of the container and lead to a rupture of this wall.

 The present invention specifically relates to a method of manufacturing a container made of pure resin which overcomes the disadvantages of previous molding methods.

 The method according to the invention for manufacturing a resin container is characterized in that it consists in pouring a liquid resin into the space between a first rigid mold and a layer of elastic material capable of absorbing the stresses which develop in the resin during its hardening, said layer of elastic material being supported by a second rigid mold, allowing the resin to harden, and demolding the hardened resin container thus obtained.

 Preferably, according to the invention the second rigid mold is placed inside the first rigid mold.

 It is specified that according to the invention, the term “resin” means a liquid mixture of a resin (monomer or prepolymer) and of a compound capable of causing the hardening of the resin and of converting it into solid resin. Thus, when the resin is a polyester resin, the liquid mixture generally comprises an unsaturated polyester resin and a vinyl monomer such as styrene. When the resin is an epoxy resin, the liquid mixture generally comprises an epoxy resin and a hardener constituted for example by a polyamine. When the resin is a vinyl resin, the liquid mixture generally comprises a polyvinyl compound and a vinyl monomer. As a pre-reference, the resin used is thermosetting (polyester or epoxy).

 In the process of the invention, the fact of carrying out the casting and hardening of the resin by inserting in the space delimited between two molds a layer of elastic material, makes it possible to reduce the stresses developed by the withdrawal of the resin during hardening by polymerization and / or crosslinking and thereby reducing the brittleness of the container walls.

 Indeed, it is known that most resins have the disadvantage of giving rise to a relatively large volume shrinkage phenomenon during their hardening by polymerization and / or crosslinking. According to the invention, the drawbacks due to this shrinkage phenomenon are largely eliminated because the layer of elastic material absorbs the shrinkage of the resin.

 The nature of the elastic material and the thickness of the layer are chosen according to the resin used, so that the layer is sufficiently supple to absorb the stresses developed during hardening and sufficiently hard not to be crushed under the effect of hydrostatic and withdrawal pressures developed in the interval between the two molds during the casting and curing of the resin.

By way of example, the elastic material can be a polyether foam or a rubber foam
cabbage. Furthermore, the layer of elastic material may consist of several superimposed sublayers, made of different materials.

 Generally, the layer of elastic material has a thickness of 10 to 60 mm.

 Preferably, when the thermosetting resin is an epoxy resin, a rubber foam is used because this rubber foam is not impregnated with the epoxy resin in the liquid state whereas in the case of a polyether foam , the epoxy resin permeates the polyether foam. Therefore, it is necessary to interpose between the polyether foam and the liquid resin a sheet of a material such as "Terphane".

 According to a preferred embodiment of the process of the invention, more particularly suited to the production of a container open at its upper end, a first mold is used consisting of a container open at its upper end and provided with a removable bottom, and a second mold consisting of a core, the external surface of which is covered with a layer of elastic material, said core being placed inside the container constituting the first mold and resting on the bottom with its bottom removable bottom of said container, and the first mold is filled with liquid resin to a level higher than the upper part of the core constituting the second mold so as to form the side walls of the container between the two molds and to form the bottom of the container above the top of the second mold.

 Thus, the resin container is obtained in the inverted position, which makes it possible to carry out the casting of the container in a single operation and to obtain a uniform wall thickness while avoiding having to ballast the second internal mold.

 Indeed, one could mold the container by pouring the liquid resin between two rigid molds, arranged concentrically with a gap between the bottoms of the two molds to form the bottom of the container; but this procedure has certain drawbacks. In this case, before hardening by polymerization or crosslinking of the resin, a high hydrostatic pressure is obtained at the bottom of the mold, which leads to a deformation of the elastic material and to excess thicknesses on the bottom of the container. In addition, to precisely center the internal mold which tends to float, it is necessary to ballast it with at least 200 kg to make a container with a capacity close to 200 1. Therefore, the thickness of the bottom and walls of the container is hardly homogeneous and reproducible.

 On the other hand, when the two molds of the invention are used to form the container in the inverted position, the bottoms of the two molds can be joined together, which avoids the problems of centering and ballasting of the second internal mold and makes it possible to obtain containers whose bottom and side walls have homogeneous and reproducible thicknesses.

 Finally, in the case where the container is molded in the normal position, it is necessary to carry out the resin casting in two stages to obtain side walls of desired height. In fact, when pouring the liquid resin between two rigid concentric molds, it is necessary first to pour the bottom of the container, then wait for the bottom to harden before pouring the resin constituting the side walls, and d '' generally operate in several stages to adjust the liquid level and obtain the desired height.

 On the other hand, in the preferred embodiment of the process of the invention, the resin is poured in one go without level adjustment, which saves appreciable time during manufacture.

 In addition, clear edges are obtained on the side walls of the container by joining together the bottoms of the two molds. Preferably, to improve the seal, a seal is interposed between the bottom of the first mold and the bottom of the second mold. This seal is constituted for example by a sheet of latex. Thus, a good seal is obtained by crushing on the latex sheet of the lower part of the second internal mold, which is itself screwed in abutment on the first external mold.

 According to the invention, to facilitate demolding of the resin container, the second internal mold preferably has a frustoconical shape and the first external mold has a cylindrical shape of circular section, the second mold resting by its large base on the bottom of the first mold. .

 Furthermore, to also facilitate demolding, the wall of the first mold which will be in contact with the liquid resin is covered with a material which facilitates demolding, such as polyvinyl chloride or Teflon. According to the method of the invention, it is also possible to remove only the internal rigid mold during demolding and thus keep the external rigid mold which reinforces the container.

 According to the process of the invention, the outer wall of the resin container can also be protected by means of an outer casing of plastic material reinforced with glass fibers, for example, of epoxy resin reinforced with glass fibers or in polyester resin reinforced with glass fibers.

 According to a first embodiment, this protection is carried out during the molding of the container.

In this case, the wall of the first mold which will be in contact with the resin is covered with a layer of plastic material reinforced with glass fibers, which will then constitute, after the resin has hardened, the outer protective envelope. According to this first embodiment, this protection can serve, in certain cases, as a first rigid mold; this further facilitates the production of the containers.

 Likewise, according to this first embodiment, only the cylindrical wall of the container is covered with a layer of reinforced plastic, it is then necessary to also reinforce the bottom.

For this, two techniques can be used - bonding on the bottom of the container, by means of the re
pure sine, of a reinforced plastic disc
having a raised edge; - gluing on the bottom of the container, by means of the re
pure sine, of a reinforced plastic disc
whose diameter is at most equal to the internal diameter
laughing cylinder.

 According to a second embodiment, this protection is formed after demolding the resin container. In this case, at least one layer of glass fibers impregnated with liquid resin is deposited on the external surface of the container.

 When the resin container thus obtained is intended for the storage of angular solid radioactive waste, the internal bottom of the container is preferably protected by placing on the bottom a shock absorbing device constituted for example by a first disc formed of a metallic braid in ribbon wound in a spiral, this first disc being surmounted by a second disc constituted by a metal sheet pierced with holes. Thus, if angular metallic solid waste accidentally falls to the bottom of the container during the filling operation, a deterioration of the internal wall of the container is avoided under impact. The shock absorbing device is designed to receive 10 kg objects falling from 1 m in height without them reaching the resin wall of the container.

After coating the waste introduced into the container, there is generally above the coated waste a plug of prefabricated pure resin peddling: - a disc of polymerized resin, a gripping device stuck on this disc or
drowned in its mass.

 The container is then sealed by pouring resin into the residual space between the prefabricated plug, the container and the coating material. The end of the casting is effective when the level of the resin exceeds that of the stopper.

 According to the invention, the resins which can be used for the preparation of the container are advantageously epoxy resins, polyester resins or vinyl resins.

épichlorhydrine bisphénol A

avec n allant de 0 à 10. The epoxy resins used are generally obtained by reaction of epichlorohydrin on bisphenol A according to the following reaction scheme

bisphenol A epichlorohydrin

with n ranging from 0 to 10.

The hardening of these resins can be obtained by reaction with an amine hardener according to the following scheme:

 In the case of polyester resins, it is possible to use a mixture of a polyester resin based on glycol maleophthalate in admixture with styrene.

In this case, the resin is obtained by condensation of two diacids in their anhydrous form, maleic anhydride (I) and phthalic anhydride (II) with propylene glycol (III) according to the reaction scheme (1).

This resin (IV) is mixed in its long two-dimensional form with a monomer (V) such as styrene of formula

ou N représente le résidu maléique de la réaction (1) où P représente le résidu phtalique de la réaction (1) ou G représente le résidu glycol de la réaction (1), et où X représente le styrène.The resin (IV) and the styrene (V) unite by a copolymerization reaction, the styrene (V) forming a bridge between the unsaturated resin units (IV) to give a three-dimensional baked resin which is modifiable (VI). We can represent the resin tVI) in the following way:

or N represents the maleic residue of reaction (1) where P represents the phthalic residue of reaction (1) or G represents the glycol residue of reaction (1), and where X represents styrene.

 In the case of vinyl resins, divinylbenzene and styrene can be condensed, for example.

Other characteristics and advantages of the invention will appear better on reading the description which follows, given of course by way of illustration and not limitation, with reference to the appended drawing in which
FIG. 1 represents a grinding device for implementing the method of the invention, and
- Figure 2 shows a resin container -protected internally and externally according to the invention.

 In Figure 1, we see that the device of the invention comprises a first metal mold 1 consisting of a container in two parts, open at its upper end and provided with a removable bottom which can be secured to the side walls of the mold 1 by a set of screws and nuts. Inside the mold 1 is disposed a second metal mold 3 consisting of a frustoconical core whose large base 3a is opposite the bottom of the first mold. This second mold is covered with a layer 5 of elastic material and with a gripping means 3b to facilitate demolding.

 A sheet 7 of latex is interposed between the removable bottom 1a of the mold 1 and the base 3a of the mold 3 covered with the layer 5 of elastic material and screw-nut systems 9 make it possible to secure the base 3a and the bottom 1a of the second and first molds.

Finally, a sheet 13 of material facilitating the release of the resin is placed on the side wall of the first mold 1. This sheet 13 is obviously useless when the metal mold 1 is kept after manufacture.

 After having secured the two bottoms 1a and 3a of the first and second molds while ensuring good sealing by crushing the latex sheet 7, liquid resin, for example a resin mixture, is introduced into the first cylindrical mold-1 epoxy and amine hardener so as to fill the entire space between molds 1 and 3 and form a layer of resin: liquid above the upper part of the second mold 3. After this operation, where the elastic material 5 absorbs the stresses due to the hydrostatic pressure of the liquid, the resin is left to harden. The presence of the elastic material 5 then makes it possible to absorb the shrinkage of the resin during its hardening. After hardening, the bottom 1a of the first mold 1 is dismantled, then the frustoconical mold 3 is removed, which leads to obtaining d a container made of pure resin 15 having a homogeneous and reproducible thickness on different operations.

By way of example, a 200 l container made of epoxy resin with a wall thickness of about 20 mm was used for the preparation - a first removable external mold 1 made of steel, having
an internal diameter of 590 mm and a height of
850 mm, - a sheet 13 of polyvinyl chloride of a thick
0.5 mm, - a layer 5 of elastic material consisting of a
rubber foam having a thickness of 15 mm, - a frustoconical interior mold 3 of stainless steel,
having at its base an outside diameter of 530 mm and at
its upper part an outside diameter of 510 mm
and a height of 710 mm, and - a latex seal 7 with a thickness of 10 mm.

Under these conditions, it was possible to obtain epoxy resin containers having satisfactory properties and good reproducibility. Generally, we operate at room temperature, which
due to hardening of the resin at a temperature of up to 600C.

For these tests, the epoxy resin used was an XF43l epoxy resin supplied by the Company
CIBA. This resin which is a bis-phenol A of diglycidyl ether obtained by the action of epichlorohydrin on bis-phenol A has an epoxy number of 175, an average molecular weight of 350 and it also contains 10% by weight of dibutyl stearate used as a plasticizing agent. To this epoxy resin, a hardener was added consisting of the product sold by CIBLA under the reference XF348, which is a glycol adduct. bisphenol A and diamino diphenylmethane or 4 4 'methylene dianiline, in the following proportions - resin: 100 parts by weight, - hardener: 60 parts by weight.

 For comparison, other epoxy resin containers have been made, using instead of the device in FIG. 1, two concentric cylindrical molds open at their upper end, leaving a free gap between the bottoms of the two molds. In these tests, rubber foam, polyether foam or two overlapping layers of polyether foam and rubber foam and the thicknesses of the layer or layers of material were used as the elastic material for coating the internal mold. elastic were 10, 50 or 60 mm.

 With this set of molds, the casting was carried out either in two steps by first forming the bottom and forming the side walls of the container 48 hours later, or in one step by ballasting the internal mold with 200 kg lead bricks to compensate for the hydrostatic pressure during filling.

Under these conditions, we had certain difficulties in demolding the containers. In addition, when the casting was carried out at one time, resin thickeners were obtained on the internal wall of the bottom of the container because the polyether or rubber foam crashes under the effect of hydrostatic pressure. Furthermore, it is difficult to center the internal mold with precision since it tends to float # r under the effect of the hydrostatic pressure of the liquid resin.

 On the other hand, when the container is poured in the inverted position by using, moreover, a frustoconical internal mold, these drawbacks are avoided.

 After demolding the container, made of resin, its mechanical properties, in particular its impact resistance, can be improved, by protecting its external wall with a coating of plastic material reinforced with glass fibers. For this purpose, several layers of glass fibers impregnated with the same liquid resin as that used to manufacture the container are deposited on the external surface of the container in order to obtain a total thickness close to 5 mm.

 However, this external protection of the container could also be produced by replacing the sheet 13 of polyvinyl chloride placed on the internal wall of the first mold 1 by a sheet of plastic material reinforced with glass fibers, which then solidifies with the resin of the container during the manufacturing thereof.

 One can also improve the impact resistance of the bottom of the container by arranging inside the latter on its bottom a shock absorbing device.

 Referring to Figure 2, we can see a container with such a shock absorbing device. This container of thermosetting resin 15 has on its outer surface a coating 17 of plastic material reinforced with glass fibers and it is provided with a shock absorbing device 19 arranged on the bottom of the container. This device comprises a first disc 19a constituted by a mattress 3 cm thick formed by a metal braid 3 ci wide wound in a spiral, and a second disc 19b constituted by a steel sheet 2 mm thick, pierced of holes having a diameter of about 20 mm, which is placed on the metal braid 19a.

 In this device, the braid of the mattress 19a makes it possible to distribute over the bottom of the container the pressure caused by the fall of an object of 10 kg falling from a height of 1 m, and the second disc 19b can absorb the shock of an object falling on a sharp angle to prevent the angular part of the object from crossing the metal braid and reaching the pure resin forming the bottom of the container.

 This figure also shows in A and B the two possibilities of the reinforced plastic bottom. Respectively using a disc with raised edge A or a disc with a diameter at most equal to the diameter of cylinder B.

Claims (19)

 1. A method of manufacturing a resin container, characterized in that it consists in pouring a liquid resin into the space between a first rigid mold and a layer of an elastic material capable of absorbing the stresses which develop in the resin during its hardening, said layer of elastic material being supported by a second rigid mold, allowing the resin to harden and demolding the hardened resin container thus obtained.  2. Method according to claim 1, characterized in that the second rigid mold is arranged inside the first rigid mold.  3. Method according to any one of claims 1 and 2, characterized in that the thickness of the layer of elastic material is such that the layer is sufficiently flexible to absorb the stresses # and sufficiently hard not to be crushed under 11 effect of hydrostatic and withdrawal pressures, which develop during the casting and hardening of the resin.  4. Method according to any one of claims 1 to 3, characterized in that the elastic material is a polyether foam or a foam rubber.  5. Method according to any one of claims 1 to 4, characterized in that the first mold is constituted by a container open at its upper end and provided with a removable bottom, in that the second mold is constituted by a core the external surface of which is covered with a layer of elastic material, said core being disposed inside the container constituting the first mold and resting at its bottom on the removable bottom of said container, and in that the the first mold is filled with liquid resin up to a level higher than the upper part of the core constituting the second mold so as to form the side walls of the container between the two molds and to form the bottom of the container above the upper part of the second mold.  6. Method according to claim 5, characterized in that one interposes a seal between the bottom of the first mold and the lower part of the second mold.  7. Method according to claim 6, characterized in that the seal is a latex sheet.  8. Method according to any one of claims 5 to 7, characterized in that the second mold has a frustoconical shape and the first mold has a cylindrical shape of circular section, the second mold resting by its large base on the bottom of the first mold.  9. Method according to any one of claims 1 to 8, characterized in that one covers the wall of the first mold, which will be in contact with the liquid resin, with a material facilitating demolding.  10. The method of claim 9, characterized in that the material facilitating the release is polyvinyl chloride or Teflon.  11. Method according to any one of claims 1 to 10, characterized in that the wall of the first mold which will be in contact with the resin is covered with a layer of plastic material reinforced with glass fibers.  12. Method according to claim 2, characterized in that the first rigid mold is made of plastic material reinforced with glass fibers and in that during demolding, only the second rigid mold is eliminated.  13. Method according to any one of claims 1 to 10, characterized in that, after demolding the resin container, is deposited on the external surface of the container at least one layer of glass fibers impregnated with liquid resin.  14. Method according to any one of claims 1 to 13, characterized in that, after demolding the resin container, there is arranged on the bottom thereof a shock absorbing device.  15. The method of claim 14, characterized in that the shock absorbing device is constituted by a first disc formed of a metal braid in ribbon wound in a spiral, this first disc being surmounted by a second disc formed by a metal sheet pierced with holes.  16. Method according to any one of claims 1 to 15, characterized in that the resin is a thermosetting resin, consisting of an epoxy resin or polyester resin.  17. Device for implementing the method according to any one of claims 5 to 12, characterized in that it comprises - a first mold (1) consisting of a cy container  lindrique of circular section, open at its end  upper unit and provided with a removable bottom (la), - a second mold (3) constituted by a tronconi core  that whose outer surface is covered with a neck  che of an elastic material (5), said core (3)  being placed inside the container (1) made up  killing the first mold and being supported by its gran  base (3a) on the removable bottom (la) of said reci  pient through a gasket é  elastic (7) and - means (9) for securing the removable base  of said container and the frustoconical core.  18. Container of radioactive waste in resin, obtained by the method according to any one of claims 1 to 16, characterized in that it is provided with a shock absorbing device (19) disposed on the inner bottom wall of said container.  19. Container according to claim 18, characterized in that the shock-absorbing device consists of a first disc (19a) formed of a metal braid wound in a spiral, the first disc being surmounted by a second disc (19b) formed by a metal sheet pierced with holes.