COMPOSITE MATERIAL FOR NEUTRON SHATTERING AND SUBCRITICALITY MAINTENANCE, METHOD FOR PRODUCING IT AND USES THEREBY

Description

TECHNICAL FIELD

[0001] The present invention relates to a composite material for neutron shielding and maintaining subcriticality which exhibits particularly high-performance thermomechanical properties.

[0002] The invention also relates to a manufacturing process and the use of such a composite material for neutron shielding and maintaining subcriticality, particularly in the nuclear industry and, more specifically, as a component of packaging intended for the transport, storage and / or disposal of radioactive materials, particularly nuclear fuels. PREVIOUS STATE OF THE ART

[0003] The neutron shielding and subcriticality maintenance composite materials used in the nuclear industry, particularly those intended for radioactive material packaging, must exhibit a number of properties to meet complex specifications required to ensure the safe transport, storage and / or disposal of such packaging.

[0004] These composite materials must be capable of slowing down and capturing neutrons very effectively, both to provide effective neutron shielding and to maintain subcriticality within the packaging and / or a network of packaging, to prevent the neutrons formed there from triggering nuclear chain reactions, particularly when the radioactive materials are fissile. For these composite materials to be able to slow down neutrons and then capture them, they must be highly hydrogenated and contain a compound, for example, one containing boron, which performs the actual neutron capture.

[0005] These composite materials must also have a low density, so as to add as little weight as possible to the packaging for which they are intended, and be self-extinguishing, meaning they must stop burning as soon as the flames are extinguished. This last characteristic is particularly important in the context of fire testing related to accidental transport conditions, which is required by current regulations to which the packaging must be subjected.

[0006] The formulations for obtaining these composite materials must, in addition, be able to be poured directly into a mold or into a structure forming the transport, storage and / or warehousing packaging and allow, after hardening, to obtain composite materials free from defects such as voids and / or cracks in order to avoid any risk of neutron leakage.

[0007] These composite materials must also exhibit good resistance to aging at relatively high temperatures under normal transport, storage, and / or handling conditions. Indeed, the presence of radioactive materials in packaging can generate significant temperatures within the composite materials, typically at least 130°C, and even reaching 160°C to 170°C.

[0008] The neutron shielding and subcriticality maintenance composite materials used in the nuclear industry are classically obtained from a polymerizable formulation comprising a thermosetting resin and an inorganic filler.

[0009] In particular, document US 7,160,486, which is referenced [1]in the remainder of this description, describes a neutron shielding and subcriticality maintenance composite material which exhibits resistance to thermal aging at relatively high operating temperatures, it being specified that the operating temperatures correspond to the temperatures to which the packaging and, therefore, the composite materials they contain are subjected during transport, storage and / or warehousing under the effect of the temperature of the radioactive materials they contain which can reach 170 °C.

[0010] The composite material described in the document [1]is obtained from a formulation employing a composition comprising a vinylester resin and an inorganic filler capable of slowing down and absorbing neutrons, this inorganic filler comprising at least one inorganic boron compound and at least one hydrogenated inorganic compound. In particular, the weight percentages of vinylester resin and inorganic filler may be between 25% and 40% by weight and between 60% and 75% by weight, respectively, relative to the total weight of the composition.

[0011] The US document 7,399,431, which is referenced [2] in the remainder of this description, also describes a composite material for neutron shielding and maintaining subcriticality.

[0012] The composite material described in the document [2]is obtained from a formulation employing a composition that includes a vinyl ester resin, an inorganic filler capable of slowing down and absorbing neutrons, and at least one polyamide. This composition may include, in particular, from 30% by weight to 45% by weight of vinyl ester resin and from 10% by weight to 30% by weight of polyamide, relative to the total weight of the composition.

[0013] Experimental data show that the composite material described in this document [2] exhibits resistance to thermal aging which, at operating temperatures of 160 °C and 170 °C, is slightly improved compared to that of the composite material described in the document [1] and this with a lower density.

[0014] The document JP S57 147095, which is referenced [3]in the remainder of this description, also describes a neutron shielding composite material characterized by thermal resistance at temperatures of 150 °C as well as fire resistance.

[0015] The composite material described in the document [3] is obtained from a formulation employing a composition that includes a halogenated unsaturated polyester resin, a polyolefin-based synthetic resin powder, a zinc borate powder, and, where applicable, aluminum hydroxide and / or antimony oxide powders. This composition may include, in particular, 30% to 80% by weight of halogenated unsaturated polyester resin, 5% to 30% by weight of polyolefin-based synthetic resin, and 8% to 70% by weight of such inorganic fillers, relative to the total weight of the composition.

[0016] If the composite materials described in these documents [1] has[3] prove satisfactory for making parts intended for packaging for storage, warehousing and / or transport in radioactive ways and adapted to operating temperatures of 150 °C, 160 °C, or even 170 °C, however it becomes necessary to propose composite materials which can withstand higher operating temperatures, in particular around 180 °C, and which can be used for a long time, as the storage and / or warehousing of packaging under air can last up to forty years.

[0017] In particular, thermal aging tests have shown that the composite material described in the document [1]It degrades at temperatures of 180°C. In particular, cracks form within the composite material. Such cracks can, on the one hand, weaken the composite material through oxidation caused by atmospheric oxygen that can penetrate these cracks and, on the other hand, create risks of neutron leakage. It should be noted that the term "crack" should be understood as defining any two-dimensional or three-dimensional discontinuity visible to the naked eye.

[0018] The aim of the present invention is therefore to overcome the formation, at temperatures of 180 °C, of ​​such cracks within a composite material and thus to propose a composite material for neutron shielding and maintaining subcriticality which meets all the requirements stated above and which also has particularly high-performance thermomechanical properties with resistance to aging at operating temperatures of 180 °C to allow the storage, warehousing and / or transport of radioactive material loads with a temperature above 160 °C or 170 °C.

[0019] Another objective of the present invention is to provide a method for manufacturing such a composite material, this method being easily implemented in the equipment and tooling of industrial installations currently used for manufacturing thermosetting resin-based composite materials, and in particular those used for manufacturing the composite materials described in the documents [1] has [3]. STATEMENT OF THE INVENTION

[0020] These goals, as well as others, are achieved, firstly, by a composite material for neutron shielding and maintaining subcriticality, which is obtained from a particular formulation.

[0021] According to the invention, this formulation comprises: 100 parts by weight of a composition comprising, the weight percentages being referred to the total weight of the composition: from 30% by weight to 45% by weight of a vinylester resin, from 23% by weight to 58% by weight of an inorganic filler, the inorganic filler comprising at least one hydrogenated compound and at least one boron compound, and from 12% by weight to 32% by weight, of a polyolefin or an olefinic copolymer; from 0.3 parts by weight to 1.4 parts by weight of a polymerization initiator; and from 0.3 parts by weight to 1.4 parts by weight of a polymerization accelerator.

[0022] The neutron shielding and subcriticality maintenance composite material according to the invention makes it possible to manufacture parts specifically intended for the transport, storage, and / or disposal of radioactive materials, parts that are free of defects and, in particular, free of cracks within their structure. This absence of cracks is observed not only after the actual manufacturing of these parts but also after subjecting them to thermal aging tests carried out at a temperature of 180 °C. The risks of degradation of the composite material by oxidation and / or potential neutron leakage from such a composite material are thus completely eliminated. Moreover, and unexpectedly and surprisingly, after these thermal aging tests, the parts are characterized by a particularly limited surface oxidation layer that changes very little over time.

[0023] The neutron shielding and subcriticality maintenance material according to the invention also has the advantage of being particularly attractive from an economic point of view, the compounds used to manufacture it being available at a controlled cost.

[0024] The neutron shielding and subcriticality maintenance composite material is obtained from a formulation which comprises 100 parts by weight of a particular composition to which are added 0.3 parts by weight to 1.4 parts by weight of a polymerization initiator and 0.3 parts by weight to 1.4 parts by weight of a polymerization accelerator.

[0025] This particular composition includes: 30% by weight to 45% by weight of a thermosetting vinyl ester resin, 23% by weight to 58% by weight of an inorganic filler, the inorganic filler comprising at least one hydrogenated compound and at least one boron compound, and 12% by weight to 32% by weight of a polyolefin or an olefinic copolymer.

[0026] It is specified that the expression "from... to..." which has just been quoted and which is used in this application must be understood as defining not only the values ​​of the interval, but also the values ​​of the bounds of this interval.

[0027] Thermosetting resin is a vinyl ester resin.

[0028] According to the invention, the thermosetting resin is a vinyl ester resin. The choice of a vinyl ester resin makes it possible to further improve, if necessary, the resistance to thermal aging at high temperatures of the neutron shielding and subcriticality maintenance composite material obtained from a formulation comprising such a resin.

[0029] Polyester resin classically results from the polycondensation of at least one dicarboxylic acid or at least one of its derivatives, such as a carboxylic acid anhydride or a diester, with an organic compound having two or more hydroxyl groups (glycol or diol) (polyol).

[0030] In a variant not part of the invention, the polyester resin is unsaturated and results from the polycondensation of a dicarboxylic acid with a glycol, at least one of these compounds having an ethylenic bond capable of reacting subsequently with a vinyl, acrylic or allylic compound.

[0031] In this variant, which is not part of the invention, the following polyester resins can be used: from saturated dicarboxylic acids or anhydrides such as adipic acid, isophthalic acid, orthophthalic acid, terephthalic acid and orthophthalic anhydride, or from unsaturated dicarboxylic acids or anhydrides such as maleic acid, fumaric acid, citraconic acid, metaconic acid, itaconic acid and maleic anhydride, and glycols such as propylene glycol (propane-1,2-diol), propane-1,3-diol, dipropylene glycol, diethylene glycol, neopentyl glycol and bisphenol A, or oxyethylated or oxypropylated glycols of the oxyethylenated ethylene glycol type.

[0032] In a preferred embodiment, which is not part of the invention, the polyester resin is not halogenated, unlike the polyester resin used in the formulation from which the composite material described in document [3] is obtained. The use of a non-halogenated polyester resin helps to limit the risks to the health of operators and to the environment.

[0033] In a more preferred embodiment, which is not part of the invention, the polyester resin is chosen from polyester resins obtained from, on the one hand, maleic acid, isophthalic acid, orthophthalic acid or fumaric acid and, on the other hand, one of the glycols that have just been mentioned, namely propylene glycol, propane-1,3-diol, dipropylene glycol, diethylene glycol, neopentyl glycol or bisphenol A.

[0034] More preferably, according to this variant, which is not part of the invention, the polyester resin is chosen from polyester resins obtained from: of maleic acid and propylene glycol, isophthalic acid and neopentyl glycol, orthophthalic acid and neopentyl glycol, fumaric acid and bisphenol A, and fumaric acid and propane-1,3-diol.

[0035] Vinyl ester resin can be produced by esterifying one or more epoxy resins with an unsaturated carboxylic acid. The epoxy resin may have a bisphenol A or novolac macromolecular motif. The unsaturated carboxylic acid can be either acrylic acid or methacrylic acid, with methacrylic acid being advantageous because it is richer in hydrogen.

[0036] According to an advantageous variant, the vinyl ester resin is chosen from the group consisting of bisphenol A type epoxyacrylates and epoxymethacrylates, novolac type epoxyacrylates and epoxymethacrylates, halogenated bisphenol A-based epoxyacrylates and epoxymethacrylates and mixtures of two or more of these.

[0037] Vinylester resin can also be a non-epoxy vinylester resin resulting from the reaction of an isophthalic polyester with a urethane.

[0038] Vinyl ester resins suitable for preparing the composition implemented within the framework of the present invention may, in particular, be the vinyl ester resins described in the documents [1] And [2] and, more specifically, vinyl ester resins that correspond to the semi-developed formulas noted (I) to (IV) in the document [2].

[0039] In a preferred variant, the vinylester resin comprises a novolac-type epoxy resin.

[0040] Such vinyl ester resins are notably marketed under the names Derakane Momentum ™< 470-300 and Derakane ™< 470HT-400 by the company Ineos.

[0041] As previously stated, the composition comprises 30% by weight to 45% by weight of thermosetting resin, relative to its total weight.

[0042] According to an advantageous variant, and in order to optimize the flowability of the formulation for its hardening, the weight percentage of thermosetting resin in the composition is 32% by weight to 45% by weight, preferably 35% by weight to 44% by weight, relative to the total weight of this composition.

[0043] In particular, when the thermosetting resin is a vinyl ester resin, optimal flowability is obtained with a weight percentage of vinyl ester resin in the composition ranging from 40% by weight to 45% by weight, relative to the total weight of the composition.

[0044] The composition implemented within the framework of the present invention also comprises from 23% by weight to 58% by weight, relative to the total weight of the composition, of a particular inorganic filler.

[0045] This particular inorganic charge comprises at least one hydrogenated compound and at least one boron compound.

[0046] The hydrogenated inorganic compound(s), whose role is to slow down the neutrons, can be chosen from among the hydroxides and in particular from magnesium hydroxide Mg(OH) 2 and alumina hydrates Al(OH) 3 or AIO(OH).

[0047] The alumina hydrates Al(OH) 3 and AlO(OH) are particularly preferred in the sense that these hydrogenated compounds also confer particularly high self-extinguishing properties to the composite material according to the invention.

[0048] The inorganic boron compound(s), whose role is to absorb neutrons once slowed down by the hydrogenated inorganic compound(s), can notably be chosen from boric acid H3BO3, colemanite Ca2O14B6H10, zinc borates such as 2ZnO.3B2O3.3,5H2O, 4ZnO.B2O3.H2O, 2ZnO.3B2O3 and 3ZnO.2B2O3, boron carbide B4C, boron nitride BN and boron oxide B2O3.

[0049] In one embodiment of the invention, the inorganic boron compound(s) also comprise hydrogen, which has the effect of improving the self-extinguishing properties of the composite material according to the invention. Such hydrogenated boron compounds can advantageously be selected from hydrated zinc borates such as 2ZnO.3B2O3.3,5H2O or 4ZnO.B2O3.H2O.

[0050] As previously stated, the composition comprises from 23% by weight to 58% by weight of inorganic filler, relative to its total weight.

[0051] According to an advantageous variant, the weight percentage of inorganic filler in the composition is 30% by weight to 50% by weight, relative to the total weight of this composition.

[0052] According to a preferred variant, the weight percentage of inorganic filler in the composition is 32% by weight to 44% by weight, relative to the total weight of this composition.

[0053] The weight percentages of hydrogenated inorganic compounds, on the one hand, and of boron, on the other hand, can be advantageously adapted according to the properties, among the shielding and / or subcriticality properties, which are sought for the composite material in question.

[0054] In one embodiment of the invention, the composition comprises, relative to the total weight of this composition: from 20% by weight to 55% by weight, advantageously from 25% by weight to 45% by weight and, preferably, from 27% by weight to 38% by weight of one or more hydrogenated compounds, and from 3% by weight to 28% by weight, advantageously from 5% by weight to 15% by weight and, preferably, from 6% by weight to 9% by weight of one or more boron compounds.

[0055] In a particular embodiment, the inorganic charge comprising at least one hydrogenated compound and at least one boron compound is in a divided form, for example in the form of granules, grains, beads, powders, flakes..., which are hereinafter referred to by the generic term particles.

[0056] In one particular variant, this inorganic charge is in the form of particles whose largest dimension is at most equal to 5 mm, the size of these particles being measured by laser diffraction.

[0057] This larger dimension of the inorganic charge particles can in particular be between 1 µm and 1 mm, advantageously between 5 µm and 500 µm and, preferably, between 10 µm and 200 µm.

[0058] The composition implemented within the framework of the present invention further comprises, from 12% by weight to 32% by weight, relative to the total weight of the composition, of a thermoplastic polymer selected from a polyolefin and an olefinic copolymer.

[0059] Polyolefin is advantageously chosen from polyethylene (PE) and polypropylene (PP) and is preferably polyethylene (PE).

[0060] The olefinic copolymer is a polymer resulting from the copolymerization of at least two distinct monomers, one of these monomers being an olefinic monomer.

[0061] The olefinic copolymer is advantageously a copolymer of ethylene and vinyl acetate (EVA).

[0062] As will be seen in the examples below, the weight percentages selected for each of the compounds forming the composition make it possible to prepare a formulation which, after hardening, leads to obtaining a composite material which meets all the requirements for a neutron shielding and subcriticality maintenance material (neutron slowing, capture of the latter, self-extinguishing, low density...) and which also exhibits high resistance to thermal aging at an operating temperature of 180 °C.

[0063] In particular, it should be noted that a polyolefin or olefinic copolymer content of less than 12% by weight, relative to the total weight of the composition, results in composite materials exhibiting cracks visible to the naked eye after a thermal aging test conducted at 180 °C. Similarly, a polyolefin or olefinic copolymer content exceeding 32% by weight, relative to the total weight of the composition, results in composite materials that no longer meet the self-extinguishing criterion.

[0064] According to an advantageous variant, the weight percentage of polyolefin or olefinic copolymer in the composition is 15% by weight to 29% by weight, preferably 16% by weight to 28% by weight, relative to the total weight of this composition.

[0065] In one embodiment of the invention, the polyolefin or olefinic copolymer is in the form of particles, i.e. in a divided form as previously described for the inorganic filler.

[0066] In an advantageous variant, at least 50% by number of the polyolefin or olefinic copolymer particles have an average size, denoted dso, ranging from 10 µm to 150 µm and preferably from 30 µm to 120 µm, this average particle size being measured by laser diffraction.

[0067] The composition just described may also include, in addition, one or more additives such as, for example, a chain limiting agent, a chain transfer agent, a formulation polymerization rate adjustment agent, a flame retardant, an antioxidant, a colorant and / or a pigment.

[0068] The formulation for obtaining the composite material according to the invention comprises, for 100 parts by weight of the composition just described: from 0.3 parts by weight to 1.4 parts by weight of a polymerization initiator, and from 0.3 parts by weight to 1.4 parts by weight of a polymerization accelerator.

[0069] The polymerization initiator, whose function is to ensure the start of the polymerization of the formulation, can be chosen from among the organic peroxides, while the polymerization accelerator, whose function is to accelerate this polymerization, can be chosen from among the cobalt salts.

[0070] The use of multiple polymerization initiators and / or accelerators is entirely feasible. However, it should be noted that the weight proportion ranges defined above for the polymerization initiator and accelerator apply regardless of whether there is one or more polymerization initiators and / or accelerators.

[0071] In particular, the implementation of two polymerization accelerators will be illustrated in the detailed description of specific embodiments that follows.

[0072] The present invention relates, secondly, to a method of manufacturing a composite material for neutron shielding and maintaining subcriticality from the formulation as described above.

[0073] According to the invention, this method comprises the following successive steps (1) to (3): (1) the preparation of a composition obtained by mixing the following compounds, the weight percentages being referred to the total weight of the composition: 30% to 45% by weight of a vinylester resin, 23% to 58% by weight of an inorganic filler, the inorganic filler comprising at least one hydrogenated compound and at least one boron compound, and 12% to 32% by weight of a polyolefin or an olefinic copolymer; (2) the preparation of a formulation obtained by mixing: 100 parts by weight of the composition prepared in step (1), 0.3 parts by weight to 1.4 parts by weight of a polymerization initiator, and 0.3 parts by weight to 1.4 parts by weight of a polymerization accelerator; and (3) the molding of the formulation prepared in step (2).

[0074] The manufacturing process according to the invention is therefore a process whose implementation is particularly simple, rapid, and economical. The process according to the invention makes it possible to obtain a composite material with a shape (design) specifically adapted to the packaging for which it is intended. Furthermore, this process can be easily implemented in facilities currently dedicated to the manufacturing processes of composite materials such as those described in the documents [1] has [3].

[0075] The characteristics described above in connection with the composition and, in particular, the characteristics relating to the thermosetting resin, the inorganic filler (hydrogenated and boron compounds), the polyolefin or olefinic copolymer, the polymerization initiator, the polymerization accelerator and any additives, are of course applicable to the present manufacturing process of the composite material.

[0076] Step (1) of the manufacturing process according to the invention, which makes it possible to prepare the composition described above, is carried out by mixing all the compounds entering into the composition, namely the vinyl ester resin, the inorganic filler comprising at least one hydrogenated compound and at least one boron compound, the polyolefin or olefinic copolymer, and the possible additive(s).

[0077] Step (2) of the manufacturing process according to the invention, which allows the formulation described above to be prepared, is carried out by mixing the composition obtained at the end of step (1), the polymerization initiator and the polymerization accelerator.

[0078] The polymerization initiator and the polymerization accelerator can be introduced into the composition simultaneously or successively. In the latter case, the polymerization initiator is introduced last.

[0079] The mixing carried out in steps (1) and (2) of the manufacturing process according to the invention can be done manually or by means of a mixer.

[0080] Step (3) of the manufacturing process, which makes it possible to obtain the neutron shielding and subcriticality maintenance composite material according to the invention, is carried out by molding the formulation obtained at the end of step (2).

[0081] In one variant, this formulation can be poured into a mold.

[0082] In a second embodiment of the invention, this formulation can be poured directly into the packaging intended for the transport, storage, and / or disposal of radioactive materials. Such packaging may, for example, include peripheral compartments into which the formulation obtained at the end of step (2) is poured.

[0083] Step (3) of molding the formulation as obtained at the end of step (2) is advantageously carried out at room temperature, i.e. it can be carried out at a temperature between 18 °C and 25 °C.

[0084] At the end of this molding step (3), during which the polymerization of the formulation occurs, the neutron shielding and subcriticality maintenance composite material according to the invention is obtained.

[0085] The mechanism of this polymerization reaction is radical.

[0086] Thirdly, the present invention relates to the use of the neutron shielding and subcriticality maintenance composite material as defined above, the advantageous characteristics of this composite material being able to be taken alone or in combination.

[0087] The composite material according to the invention can in particular be used for the manufacture of a part of a package intended for the transport, storage and / or disposal of radioactive materials.

[0088] Fourth, the invention relates to packaging for the transport, storage and / or warehousing of radioactive materials.

[0089] According to the invention, this transport, storage and / or holding package for radioactive materials comprises a neutron shielding and subcriticality maintenance composite material as defined above, the advantageous characteristics of this composite material being able to be taken alone or in combination.

[0090] Other advantages and features of the present invention will become clearer from the following description, which relates to examples of manufacturing composite materials according to the invention and reference materials, including a composite material obtained from a composition conforming to that described in the documents [1] And [2] and two composite materials obtained from a composition of the type described in the document [3], as well as to the evaluation of their respective thermomechanical properties.

[0091] Of course, these particular embodiments of the invention are given only as an illustration of the object of the invention and do not, in any case, constitute a limitation of this object. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] THE figures 1A, 1B and 1CThese correspond respectively to the photographic images of the composite material plates M2, M3 and M4' as obtained at the end of the thermal cycle implemented to evaluate their resistance to thermal aging conducted at 180 °C. Figures 2A and 2B correspond respectively to the images taken using a scanning electron microscope (SEM) of a section of the composite material plates M1 and M4 as obtained at the end of the thermal cycle implemented to evaluate their resistance to thermal aging conducted at 180 °C. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS -A- Obtaining composite materials M1 to M8 and M4'

[0093] Formulations F1 to F8 and F4' from which composite materials M4, M4' and M5 to M7 according to the invention were obtained, as well as reference composite materials M1 to M3 and M8, were prepared from compositions C1 to C8 and C4' described below. Compounds used

[0094] The compounds used for the preparation of compositions C1 to C8 and C4' are as follows: as a thermosetting resin: a vinylester resin comprising a novolac-type epoxy resin marketed by Ineos under the name Derakane™< Momentum 470-300 (noted 470-300), and a vinylester resin comprising a novolac-type epoxy resin marketed by Ineos under the name Derakane™< 470HT-400 (noted 470HT-400); as a polyolefin: a high-density polyethylene marketed by Celanese under the name Gur®< 4050-3-PE-UHMW, noted HDPE, which is in the form of a powder whose particles have a particle size characteristic dso of 60 µm as measured by laser diffraction;and as an inorganic filler: as a hydrogenated compound: an alumina hydrate Al(OH)3, noted as ATH, marketed by the company Nabaltec under the name Apyral®< 20X which is presented in the form of a powder whose particles have an average size of 8 µm as measured by laser diffraction, and as a boron compound: a zinc borate 2ZnO.3B2O3.3,5H2O marketed by the company Borax under the name Firebrake®< ZB which is presented in the form of a powder whose particles have an average size of 9 µm as measured by laser diffraction. Preparation of compositions C1 to C8 and C4'

[0095] Compositions C1 to C8 and C4' were prepared by mixing a vinyl ester resin, polyolefin, hydrogenated compound and boron compound mentioned above in the weight percentages shown in Table 1 below.

[0096] It is specified that composition C1 is identical to the composition of example 2 of the document [1] as well as the composition that led to the composite material known as the "reference material" exemplified in the document [2].

[0097] Compositions C2 and C3 are compositions of the type described in the document [3], It should be noted, however, that the thermosetting resin used here is a vinyl ester resin and not a halogenated unsaturated polyester resin as described in this document. [3]. Preparation of formulations F1 to F8 and F4'

[0098] Formulations F1 to F8 and F4' were prepared by introducing and then mixing, in each of compositions C1 to C8 and C4', a catalytic system comprising, for 100 parts by weight of the composition considered: 0.676 parts by weight of a polymerization initiator formed by a cumyl hydroperoxide marketed by Nouryon under the name Trigonox K-90, 0.768 parts by weight of a polymerization accelerator formed by a cobalt(II) 2-ethylhexanoate marketed by Nouryon under the name Accelerator NL-49PN, and 0.192 parts by weight of a polymerization co-accelerator formed by a N,N- diethylacetoacetamide marketed by Akzo Nobel under the name Promotor D. Obtaining composite materials M1 to M8 and M4'

[0099] Each of the formulations F1 to F8 and F4' obtained was degassed under vacuum and then poured, at room temperature (21 °C), into a mold.

[0100] It has been observed that, although these formulations F1 to F8 and F4' all exhibit good flowability, their viscosity increases with the weight percentages of polyethylene (HDPE) and alumina hydrate (ATH).

[0101] After hardening each of the formulations F1 to F8 and F4' at room temperature (21 °C) for a period of between 10 min and 40 min, the composite materials M1 to M8 and M4' were obtained respectively. -B- Evaluation of the properties of composite materials Resistance to thermal aging at 180°C

[0102] The resistance to thermal aging of composite materials M1 to M8 and M4' at an operating temperature of 180 °C was evaluated by placing samples in the form of square plates of 12 cm on each side and 10 mm thick of each of these composite materials M1 to M8 and M4' in a furnace and subjecting them to a thermal cycle comprising the following successive steps (a) to (d): (a) a first temperature rise from ambient temperature (25 °C) to a first plateau temperature of 80 °C, at a rate of 10 °C / h, (b) a maintenance of the temperature at this first plateau temperature of 80 °C for 8 h, (c) a second temperature rise from this first plateau temperature of 80 °C to a second plateau temperature of 180 °C, at a rate of 10 °C / h, and (d) a maintenance of the temperature at this second plateau temperature of 180 °C for 24 h.

[0103] At the end of step (d), the plates were removed from the oven and cooled to room temperature.

[0104] As the photographic images of Figures 1A to 1C , the M2 composite material plates ( Figure 1A ), on the one hand, and M3 ( figure 1B ), on the other hand, exhibit numerous cracks that are visible to the naked eye, unlike the M4' composite material plate ( Figure 1C ) which is completely devoid of it.

[0105] Referring to the SEM image of the Figure 2B We observe that the crack present in the M4 composite material plate is partially filled. These fillings are formed by polyethylene, which is present in the F4 formulation and which melted during the thermal cycle, creating bridges at the cracks. These bridges have the advantage of limiting the flow of oxygen from the air into these cracks and preventing their propagation, contrary to what can be observed in the SEM image of the Figure 2A which shows a larger crack, and in particular a wider one than that of the Figure 2B , and furthermore not filled, and therefore liable to propagate, within the composite material M1 which conforms to the composite material of example 2 of the document [1] and to the composite material referred to as the "reference material" described in the document [2]. Self-extinguishing

[0106] Self-extinguishing tests were conducted on the M1 to M8 and M4' composite materials to evaluate their behavior under accidental fire conditions.

[0107] These tests were carried out by placing samples of composite materials M1 to M8 and M4' in a fire at 800 °C for 30 minutes. At the end of these 30 minutes, the flames were extinguished and it was observed whether each of the composite materials M1 to M8 and M4' stopped burning immediately or not.

[0108] The results of these tests, which are recorded in Table 1 below, show that the composite materials M1 to M7 and M4' stopped burning when the flames were extinguished, unlike the composite material M8 which only stopped burning after 32 s counted from the extinction of the flames. Table 1 Composition C1 C2 C3 C4' C4 C5 C6 C7 C8 470-300 (in %) 32 40 32 40 40 35 35 40 470HT-400 (in %) 40 HDPE (in %) 0 5 10 18 18 24 29 32 35 ATH (in %) 62 49 52 36 36 30 30 27 19 Zinc borate (in %) 6 6 6 6 6 6 6 6 6 Inorganic charge (in %) 68 55 58 42 42 36 36 33 25 Composite material M1 M2 M3 M4' M4 M5 M6 M7 M8 Theoretical density (in g / cm³) 1,79 1,55 1,57 1,37 1,41 1,33 1,32 1,29 1,22 Cracks visible to the naked eye Yes Yes Yes No No No No No No Self-extinguishing Yes Yes Yes Yes Yes Yes Yes Yes No

[0109] We therefore observe that from a weight percentage of polyethylene which is greater than 32% by weight in the composition, and which is in particular equal to 35% by weight as in the case of composition C8, the composite material M8 no longer meets at least one of the criteria of the specification of composite materials for neutron shielding and maintenance of subcriticality, in this case that of self-extinguishing. BIBLIOGRAPHY

[0110] [1] US 7,160,486 B2 [2] US 7,399,431 B2 [3] JP S57 147095 A

Claims

1. A composite material for neutron shielding and for maintaining sub-criticality obtained from a formulation comprising: - 100 portions by weight of a composition comprising, the weight percentages being based on the total weight of the composition: . from 30% by weight to 45% by weight, advantageously from 32% by weight to 45% by weight and, preferably from 35% by weight to 44% by weight, of a vinylester resin, . from 23% by weight to 58% by weight, advantageously from 30% by weight to 50% by weight and, preferably, from 32% by weight to 44% by weight, of an inorganic filler, the inorganic filler comprising at least one hydrogenated compound and at least one boron compound, and . from 12% by weight to 32% by weight, advantageously from 15% by weight to 29% by weight and, preferentially, from 16% by weight to 28% by weight, of a polyolefin or of an olefin copolymer; - from 0.3 portion by weight to 1.4 portion by weight of a polymerisation initiator; and - from 0.3 portion by weight to 1.4 portion by weight of a polymerisation accelerator.

2. The composite material according to claim 1, wherein the vinylester resin is selected from the group consisting of epoxyacrylate and epoxymethacrylate resins of the bisphenol A type, epoxyacrylate and epoxymethacrylate resins of the novolac type, epoxyacrylate and epoxymethacrylate resins based on halogenated bisphenol A and mixtures of two or more thereof.

3. The composite material according to claim 1 or 2, wherein the composition comprises from 35% by weight to 45% by weight and, advantageously, from 40% by weight to 45% by weight, of vinylester resin, relative to the total weight of the composition.

4. The composite material according to any one of claims 1 to 3, wherein the composition comprises, relative to the total weight of the composition: - from 20% by weight to 55% by weight, advantageously from 25% by weight to 45% by weight and, preferably, from 27% by weight to 38% by weight of one or more hydrogenated compounds, and - from 3% by weight to 28% by weight, advantageously from 5% by weight to 15% by weight and, preferably, from 6% by weight to 9% by weight of one or more boron compounds.

5. The composite material according to any one of claims 1 to 4, wherein - the hydrogenated compound(s) are selected from hydroxides, for example Mg(OH)2, Al(OH)3 and AlO(OH), the hydrogenated compound preferably being Al(OH)3 or AlO(OH), and / or - the boron compound(s) are selected from H3BO3, Ca2O14B6H10, zinc borates, B4C, BN and B2O3.

6. The composite material according to any one of claims 1 to 5, wherein the boron compound(s) comprise hydrogen and are advantageously selected from hydrated zinc borates such as 4ZnO.6B2O3,7H2O or 4ZnO.B2O3,H2O.

7. The composite material according to any one of claims 1 to 6, wherein the olefin copolymer is an ethylene and vinyl acetate copolymer and the polyolefin is selected from a polyethylene and a polypropylene, the polyolefin preferably being a polyethylene.

8. The composite material according to any one of claims 1 to 7, wherein the polyolefin or the olefin copolymer is in the form of particles, these particles advantageously having an average size in number dso ranging from 10 µm to 150 µm and, preferably, from 30 µm to 120 µm.

9. A method for manufacturing a composite material for neutron shielding and for maintaining sub-criticality according to any one of claims 1 to 8, this method comprising the following successive steps (1) to (3): (1) preparing a composition obtained by mixing the following compounds, the weight percentages being based on the total weight of the composition: . from 30% by weight to 45% by weight of a vinylester resin, . from 23% by weight to 58% by weight of an inorganic filler, the inorganic filler comprising at least one hydrogenated compound and at least one boron compound, and . from 12% by weight to 32% by weight of a polyolefin or of an olefin copolymer; (2) preparing a formulation obtained by mixing: - 100 portions by weight of the composition prepared in step (1), - from 0.3 portion by weight to 1.4 portion by weight of a polymerisation initiator, and - from 0.3 portion by weight to 1.4 portion by weight of a polymerisation accelerator; and (3) moulding the formulation prepared in step (2).

10. The manufacturing method according to claim 9, wherein step (3) of moulding is carried out at a temperature comprised between 18°C and 25°C.

11. A use of a composite material for neutron shielding and for maintaining sub-criticality according to any one of claims 1 to 8 for the manufacture of a part of a package intended for the transport, warehousing and / or storage of radioactive materials.

12. A package for the transport, warehousing and / or storage of radioactive materials comprising a composite material for neutron shielding and for maintaining sub-criticality according to any one of claims 1 to 8.