Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F1/00—Shielding characterised by the composition of the materials
  • G21F1/02—Selection of uniform shielding materials
  • G21F1/04—Concretes; Other hydraulic hardening materials
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F1/00—Shielding characterised by the composition of the materials
  • G21F1/02—Selection of uniform shielding materials
  • G21F1/08—Metals; Alloys; Cermets, i.e. sintered mixtures of ceramics and metals
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F1/00—Shielding characterised by the composition of the materials
  • G21F1/02—Selection of uniform shielding materials
  • G21F1/10—Organic substances; Dispersions in organic carriers
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F5/00—Transportable or portable shielded containers
  • G21F5/005—Containers for solid radioactive wastes, e.g. for ultimate disposal
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F5/00—Transportable or portable shielded containers
  • G21F5/06—Details of, or accessories to, the containers
  • G21F5/12—Closures for containers; Sealing arrangements

Definitions

• the present invention is in the field of nuclear waste packaging devices intended to be transported, stored or stored. It relates in particular to a device for packaging nuclear waste comprising radioactive materials and chemically aggressive species.
• Nuclear waste disposal devices must meet strict regulatory criteria, in particular to ensure, in most circumstances, the radiation protection of the public and the operators who handle them.
• the patent application FR 2801133 describes a device for the packaging of nuclear waste consisting of radioactive materials of low and medium activity.
• This device comprises a container in concrete reinforced with metal fibers whose inner wall delimits a cavity in which is housed a metal drum. It is provided with an opening in the container and the barrel, which opening may be closed by a cover to ensure the containment of radioactive material.
• radioactive materials are said to be "homogeneous", ie in the form of nuclear waste which is liquid or which has a certain fluidity (such as for example a liquid effluent, a concentrate or a mud), their conditioning in such a device comprises two steps.
• the nuclear waste is mixed with a hydraulic cement mortar to form a slurry.
• This grout is introduced into the metal drum, in which, after solidification, it forms a cementitious matrix coating the waste.
• the metal drum is placed in the container and a completion mortar is poured so as to fill all the empty spaces of the packaging device.
• This device for the conditioning of radioactive materials has several disadvantages.
• the solidification of the cement slurry is accompanied by a rise in temperature (due to the heat of hydration) that can reach up to 96 ° C in the heart of the cement matrix.
• a failure in this structure is not easily detectable before use and can be detrimental in the long term to the good mechanical strength of the packaging device as a whole.
• the operating protocol of this device requires to work in two different workshops and adapted to each of the two packaging packages, with transfers between these workshops requiring heavy handling operations, which increases the risks for operators (especially a risk of injury related to the actual handling or risk of irradiation related to the nature of the nuclear waste in case of mishandling).
• such a packaging device may be unsuitable when the radioactive materials are accompanied by chemically aggressive species with respect to the packaging device, which is most often the case for so-called "homogeneous" nuclear waste.
• the cementitious matrix always contains a quantity of water present in the form of interstitial solution which is most often alkaline.
• This solution may allow radioactive materials and / or chemically aggressive species to migrate and come into contact with the metal drum and / or the concrete container. By their chemical aggressivity, these species can cause in the more or less long term the degradation and weakening of the packaging device.
• the interstitial solution may consist of an alkaline solution of sulphate ions which can interact with the calcium aluminate of the cement and form within the cement matrix a calcium sulphoaluminate called ettringite.
• ettringite a calcium sulphoaluminate
• any aforementioned deterioration and embrittlement of an element of the packaging device can lead to the loss of containment of the waste and / or materials it contains. It must therefore, as far as possible, be limited or even prevented.
• One of the aims of the invention is therefore to provide a device for the conditioning of nuclear waste which preserves a structural integrity and a mechanical resistance making it possible to ensure the confinement of this waste over a period of at least a hundred years, especially when these wastes include chemically aggressive species.
• Another object of the invention is to provide a method of packaging nuclear waste using the device of the invention.
• the object of the invention thus relates to a device for the packaging of nuclear waste, comprising a concrete container whose inner wall delimits a cavity in which is housed a metal vessel, the device being characterized in that it further comprises a container which is made of thermoplastic polymer spherolitic morphology. This container is placed inside the metal tank and is intended to receive the waste.
• nuclear waste refers to waste from the nuclear industry which necessarily include radioactive material and possibly chemically aggressive species.
• at least one of the nuclear waste can constitute both a radioactive material and a chemically aggressive species.
• these nuclear waste is embedded in a cement matrix when they are contained in the packaging device of the invention.
• thermoplastic polymer spherulitic morphology a semi-crystalline thermoplastic polymer comprising essentially spherulites, the latter being polycrystalline aggregates consisting of radial crystallites, separated by the amorphous phase, which grow from a center to occupy the space offered.
• a spherulite is generally in the form of a disk or sphere whose contour is polygonal or essentially circular.
• thermoplastic polymer gives it optimum resistance to all organic solvents and alkaline products.
• the thermoplastic polymer is essentially (ie more than 80%) consisting of spherulites of average diameter greater than 50 microns, preferably between 100 microns and 500 microns diameter.
• the average diameter can be measured by electron microscopy after cryofracture of the thermoplastic polymer.
• such a diameter gives the thermoplastic polymer excellent mechanical properties such as a Young's modulus greater than 550 MPa. (preferentially between 750 MPa and 1500 MPa, even more preferably between 750 MPa and 1000 MPa), a maximum impermeability with water transfer fluxes lower than 10 ⁇ 3 mol / m 2 / day and a permeation coefficient at 1 less than 10 ⁇ 12 m 2 / s.
• This diameter is preferably obtained thanks to the implementation of a rotomoulding process for producing the thermoplastic polymer, a process which makes it possible to attain spherulites of average diameter greater than 50 ⁇ m, preferably between 100 ⁇ m and 500 ⁇ m.
• thermoplastic polymer according to the invention confers on the container several advantages, namely that, by means of numerical modeling, the applicants have been able to observe that over a period of at least less than a hundred years such a container:
• this thermoplastic polymer is chosen from polyethylene, polypropylene, a thermoplastic elastomer (such as an elastomer of the family of styrene-ethylene-butadiene or styrene-propylene-butadiene copolymers).
• the thermoplastic polymer of the invention is of the metallocene type.
• metallocene polymer for the sake of brevity, such a polymer will be called "metallocene polymer" in the following description.
• the metallocene polymer is metallocene polyethylene.
• a metallocene polymer is characterized in that it was obtained during a metallocene catalyzed polymerization reaction.
• EP 1 400 566 A1 describes the metallocene polyethylene, and by analogy the method of obtaining a metallocene polymer according to the invention and its physicochemical characteristics. This document (especially paragraphs 14 and 15) is as such included by reference to this description.
• the metallocene polymers are distinguished by a great uniformity both in the length of the polymer chains (which are essentially linear) and in the position of lateral groupings (which are usually small).
• the microstructure of these metallocene polymers makes it possible to obtain crystallite thicknesses at least 1.5 times greater than those obtained with Ziegler Natta catalysts and medium diameter spherulites. greater than 50 microns, preferably between 100 microns and 500 microns, such a diameter guaranteeing the mechanical properties described above.
• the metallocene polymer also has at least one of the following characteristics:
• metallocene polymer Another particularity of the metallocene polymer is its ability to crosslink in an anaerobic atmosphere with self-healing properties when the material was previously in an aerobic environment.
• the applicants have found that the use of a metallocene polymer, in place of a conventional thermoplastic polymer, confers on the conditioning device of the invention various properties such that: a better distribution of the temperatures leading to a decrease of the thermal gradients caused by the thermal shock, ii) an improvement of the mechanical resistance (in particular an increase of approximately 20% of the criterion of Drucker-Prager), iii) the best preservation on a period of at least a hundred years of structural characteristics (such as the average size of spherulites obtained through the rotational molding process) and physicochemical properties of the polymer (especially its fluidity).
• metallocene polymer may also be present in the metallocene polymer.
• Still others result from the action of radioactive materials on the metallocene polymer which can be oxidized at the surface and sub-surface of the container, such oxidation resulting from the radio-initiated decomposition of hydroperoxides in the presence of oxygen in the air initially present in the polymer and / or in the metal drum.
• the direct consequence of this oxidation is the formation of compounds such as alcohols, carbonyls and transvinylenes.
• carbonyls and transvinylenes are responsible for chain cleavage of the metallocene polymer (which has the effect of reducing the ductility of the latter), they remain attached to the metallocene polymer chains and therefore do not migrate into the metallocene polymer. rest of the conditioning device. Moreover, they do not affect the elastic modulus and the threshold at the flow of the metallocene polymer, which makes it possible to guarantee the structural integrity of the container.
• the oxygen will become rare due to oxidation reactions. Gradually, these reactions will give way to crosslinking reactions causing a "scarring" of the metallocene polymer with a bonus of its mechanical properties and impermeability.
• the concentration of oxygen in the form of bubbles present in the metallocene polymer is also reduced as possible, that is to say advantageously less than 1% by volume.
• the metallocene polymer according to the invention comprises at least one compound capable of attracting and / or fixing among the waste those which are presented under the strain of the chains of this polymer and at least the shear stress of the crystallites. ionic form (in the manner of ion exchange resins).
• such a compound is chosen from silica (optionally in the form of a ball or tube), imogolite, allophane, vanadium pentoxide or a clay which are modified.
• the clay to be modified is a clay of the smectite family such as montmorillonite. It is modified by at least one ion such as an acid or an electrolyte (preferentially dimethyl tallow benzyl ammonium) or with a nanoparticle (such as a carbon nanotube or a nanoalumin), preferably itself chemically modified: ion or nanoparticle inserted between the sheets of the clay, which makes it swell ensuring maximum exfoliation and allows it to be incorporated in the form of nanometric sheets (for example of average size of 2 nm x 200 nm) in the amorphous phase of the metallocene polymer.
• ion such as an acid or an electrolyte (preferentially dimethyl tallow benzyl ammonium) or with a nanoparticle (such as a carbon nanotube or a nanoalumin)
• a nanoparticle such as a carbon nanotube or a nanoalumin
• the article by Benfarhi et al. (J. Phys. IV France 124 (2005) 75-80) describes the procedure for performing the modification of a clay by an ion, then the incorporation of the clay thus modified into a polymer. It is as such included by reference to this description.
• This dispersion increases the tortuosity of the diffusion paths within the metallocene polymer and generates ionic attractors, which makes it possible to trap the radioactive materials and / or the chemically aggressive species which are in ionic form and which are likely to pass through the wall of the container.
• the invention also relates to a method in which nuclear waste is conditioned by means of the packaging device of the invention, the method comprising the following successive steps:
• the metal tank is assembled around the polymer container so as to enclose the latter
• the concrete container is molded around the metal vessel comprising the container, the nuclear waste is introduced into the container, the packaging device is closed by closing the opening of the metal vessel with a tape and then closing the opening of the container with a plug leading to provoke in the medium term (generally less than 5 years) an anaerobic atmosphere to stabilize and crosslink the thermoplastic polymer container in the long term (generally from 10 years ).
• Figure 1 shows a longitudinal sectional view of the packaging device of the invention.
• Figure 2 shows a longitudinal sectional view of the upper part of this device.
• the conditioning device 1 as represented in FIG. 1 is externally in the form of a cylinder of axis of symmetry 11. It is here illustrated in its final configuration in which it constitutes a hermetic waste containment enclosure. nuclear waste capable of receiving radioactive materials and chemically aggressive species, these waste being embedded in a cement matrix (waste and matrix not shown in the figure).
• Chemically aggressive species most often include at least one species such as boron, chloride, fluoride, sulfate, phosphate.
• the conditioning device 1 comprises a metal tank 2 generally made of carbon steel, the main function of which is to impart good mechanical strength to the conditioning device 1.
• This tank is made from a boiler shell, at the ends of which are welded two curved bottoms.
• the bottom "high” rounded of the tank, in which is made an opening, is welded first. It comprises a flange 13 which allows adjustment at the flange of the container 4 made of polymer.
• This container is then placed in the metal tank 2. Then the bottom “bottom” of the tank is positioned and welded to the ferrule.
• thermoplastic polymer container 4 is located inside the metal tank 2.
• the manufacture of the container 4 of thermoplastic polymer is preferably carried out according to a rotational molding process.
• the base of the container 4 of thermoplastic polymer is sufficiently curved to prevent its alteration by the heat released during the welding of the bottom "bottom".
• the convex nature of the base of the container 4 also makes it possible to reinforce the mechanical strength of the packaging device 1 in its final configuration, since it can dampen or even prevent the impact of the cement matrix against the "bottom” bottom of the container. the metal tank 2 in case of fall of the conditioning device 1.
• the concrete container 3 is molded around the metal tank 2 comprising the container 4. This is done taking care to preserve an opening in the packaging device 1 allowing Subsequent introduction into the vessel 4 of radioactive material and chemically aggressive species.
• the concrete component of the container 3 is a concrete reinforced mechanically by metal fibers (cast iron, steel, or stainless steel) uniformly and randomly distributed in its mass.
• This container 3 has a durable protection function against external aggression (mainly chemical), mechanical reinforcement of the device as well as radioprotective function since it stops the radiation emitted by the radioactive material it contains.
• the metal tank 2 Due to the adhesion of the concrete to the steel, the metal tank 2 has a certain connection with the concrete container 3.
• the outer wall of the metal tank 2 is preferably provided with fastening means which, after solidification of the concrete which covers them, make it possible to reinforce this connection.
• fastening means are for example constituted by "carp tails" 7 positioned on the bottom “bottom” and on the outer wall of the metal vessel 2 and / or by reinforcements 10 located on the curved "high" bottom of the same tank. They make it possible to confer on the packaging device 1 increased mechanical strength and to prevent the metal tank 2 from striking and damaging the concrete container 3, in particular in anticipation of a drop test of a height of 1.2 m. after which the confining nature of the device must be preserved.
• the radioactive materials and the chemically aggressive species can be stored by coating them preferentially in a cement slurry which is then introduced into the container 4 through the aforementioned opening in order to form after solidification a cement matrix.
• step 5 the operator is better protected from the radiation emitted by the radioactive materials (decrease in dose rates). It him allows then pour on the tape 5 and its reinforcements 9 fiber-concrete, of the same composition as the container body 3, to form a plug 6 which permanently closes the opening of the container 3 concrete and ensures the containment optimal waste and materials contained in the conditioning device 1.
• the plug 6 is made of concrete reinforced with metal fibers so that the container 3 has continuity and homogeneity in its composition giving it an optimal mechanical strength.
• This plug has a great solidarity with the rest of the packaging device 1, in particular thanks to the reinforcements 9 of the tape 5 as well as its preferentially conical shape which fits in the toric shape 12 of the opening of the container 3, thereby constituting a natural keying after setting concrete.
• the fact of having a packaging device 1 in one piece as well as its closure mode facilitates and makes safer operation which now includes only one step of handling radioactive materials and chemically aggressive species .
• the diameters of the metal vessel 2 and the thermoplastic polymer container 4 are such that the inner wall of the vessel and the outer wall of the vessel define a well 8 capable of preventing contact between these walls.
• the distance separating the generatrices of these two walls is of the order of 1 cm.
• the elasticity of the thermoplastic polymer makes it possible to avoid any deterioration of the internal wall of the metal tank 2 in the event of impact of the container 4 on this wall due to a fall of the conditioning device 1.
• the wall of the thermoplastic polymer container 4 has a thickness advantageously between 4 mm and 20 mm, more preferably between 10 mm and 15 mm, which makes it possible to reinforce its mechanical strength and to mitigate the harmful effects of the aforementioned thermal shock. on the entire packaging device 1.
• the packaging device of the invention makes it possible to ensure optimum confinement while preserving structural integrity and mechanical strength over a period of at least one hundred years, despite the fact that possible presence of chemically aggressive species. This result is achieved thanks to the original structure of the device and in particular thanks to its thermoplastic polymer container.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Ceramic Engineering (AREA)
• Metallurgy (AREA)
• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Processing Of Solid Wastes (AREA)
• Container Filling Or Packaging Operations (AREA)
• Wrappers (AREA)

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• 2007
  • 2007-12-21 FR FR0708968A patent/FR2925753B1/fr not_active Expired - Fee Related
• 2008
  • 2008-12-19 WO PCT/FR2008/001786 patent/WO2009106730A2/fr not_active Ceased
  • 2008-12-19 AT AT08872827T patent/ATE513299T1/de not_active IP Right Cessation
  • 2008-12-19 EP EP08872827A patent/EP2225762B1/de not_active Not-in-force

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