EP3038113B1 - Use of a material comprising a solid matrix of a siliconised polymer and inorganic fillers such as neutron-absorbing material - Google Patents

Description

TECHNICAL AREA

The invention relates to the field of neutron protection, also called neutron shielding.

More specifically, it relates to the use of a material comprising a solid matrix based on a silicone polymer (resin or elastomer) as well as fillers dispersed in this matrix as a neutron-absorbing material.

This material, besides being capable of slowing down and capturing neutrons very efficiently, has remarkable properties of resistance to high temperatures and, in particular, resistance to thermal aging, and has, among other additional advantages, being able to present itself under a number of conditions. flexible or rigid form depending on the use for which it is intended.

Therefore, it is particularly useful for the manufacture of neutron shielding elements which are intended to be used in environments where high temperatures, such as those found in nuclear power plants and irradiated nuclear fuel plants.

These neutron protection elements can be of any size (whether in terms of length, width or thickness) and of any geometrical configuration and can be both flexible elements such as seals (for example, sealing ) or coatings (eg, sleeves or sleeves for cables, pipes, vats or the like) than rigid elements such as doors, frames, walls, partitions, screens or cabinets.

STATE OF THE PRIOR ART

A material is called neutron when it is able to slow down and capture neutrons.

For a material to be able to slow down and capture neutrons, it should contain light nuclei, ie typically hydrogen atoms, which will slow down neutrons by an elastic scattering mechanism , and nuclei "greedy" in neutrons, such as boron, cadmium or lithium, which will capture the neutrons thus slowed down.

• un matériau neutrophage rigide, qui est obtenu par polymérisation/ réticulation d'une résine polyester insaturé dans laquelle ont été préalablement incorporées des particules de polyéthylène pour augmenter le taux d'hydrogène de la résine, ainsi qu'un composé boré, lithié ou cadmié (voir US-A-4,134,937 , ci-après référence [1]) ;
• un matériau neutrophage rigide, qui est obtenu par durcissement d'un mortier comprenant des granulats d'un composé boré inorganique tel que la colémanite, du ciment alumineux et de l'eau (voir EP-A-0 106 759 , ci-après référence [2]):
• un matériau neutrophage rigide, qui est obtenu par polymérisation/ réticulation d'une résine polyester insaturé ou d'une résine vinylester dans laquelle ont été préalablement incorporés un composé inorganique hydrogéné du type hydroxyde d'aluminium ou de magnésium, ainsi qu'un composé inorganique de bore du type acide borique, colémanite ou borate de zinc (voir WO-A-03/030183 et WO-A-03/050822 , ci-après références [3] et [4]) ;
• un matériau neutrophage souple, qui est obtenu par vulcanisation d'un élastomère, typiquement un caoutchouc silicone bi-composant, dans lequel ont été préalablement incorporés un composé écran aux rayonnements γ (par exemple, du carbure de tungstène), un composé absorbant les neutrons/bloquant les rayonnements γ (par exemple, du carbure de bore), un composé thermoconducteur (par exemple, du diamant), un composé résistant à la chaleur (par exemple, de la silice), un composé absorbant les neutrons/électroconducteur (par exemple, du sulfate de baryum) et un composé absorbant l'hydrogène sous forme gazeuse (par exemple, du palladium spongieux) (voir WO-A-02/101756 , ci-après référence [5]) ; et
• un matériau neutrophage souple, qui est obtenu par vulcanisation d'un polydiméthylsiloxane auquel ont été ajoutés un polypropylène, de l'hydroxyde d'aluminium et du carbure de bore (voir KR 1019980078181 B1 , ci-après référence [6]).

It has been proposed:

• a rigid neutrophage material, which is obtained by polymerization / crosslinking of an unsaturated polyester resin in which polyethylene particles have been previously incorporated to increase the hydrogen content of the resin, and a borated, lithiated or cadmium compound ( see US Patent 4,134,937 , hereinafter reference [1] );
• a rigid neutrophage material which is obtained by curing a mortar comprising aggregates of an inorganic boron compound such as colemanite, aluminous cement and water (see EP-A-0 106 759 , hereinafter reference [2] ):
• a rigid neutron-absorbing material which is obtained by polymerization / crosslinking of an unsaturated polyester resin or a vinylester resin in which a hydrogenated inorganic compound of the aluminum hydroxide or magnesium type has been previously incorporated, as well as an inorganic compound of boric acid type, colemanite or zinc borate (see WO-A-03/030183 and WO-A-03/050822 , hereinafter references [3] and [4] );
• a flexible neutrophage material, which is obtained by vulcanization of an elastomer, typically a two-component silicone rubber, into which a γ-radiation shielding compound (for example, tungsten carbide), a neutron absorbing compound, has been previously incorporated; γ blocking (e.g., boron carbide), a thermally conductive compound (e.g., diamond), a heat-resistant compound (e.g., silica), a compound neutron absorbing / electroconductive (e.g., barium sulfate) and hydrogen-absorbing compound in gaseous form (e.g., sponge palladium) (see WO-A-02/101756 , hereinafter reference [5] ); and
• a soft neutrophage material which is obtained by vulcanizing a polydimethylsiloxane to which polypropylene, aluminum hydroxide and boron carbide have been added (see KR 1019980078181 B1 , hereinafter reference [6] ).

It happens that the neutrophage materials which are obtained by polymerization / crosslinking of a thermosetting resin, such as those proposed in references [1], [3] and [4], are necessarily rigid materials and can not be used for the manufacture of flexible neutron protection elements. It is the same for materials obtained by hardening a mortar, such as that proposed in reference [2].

On the other hand, the neutrophage materials which are obtained from a silicone elastomer, such as those proposed in references [5] and [6], are necessarily flexible materials and can not therefore be used to produce elements of rigid neutron protection. In addition, the material described in reference [5] has a low hydrogen content because, on the one hand, the silicones are compounds that are not very rich in hydrogen and, on the other hand, the other components of this material are free of hydrogen. However, a low hydrogen content is detrimental to the ability of the material to slow neutrons and, therefore, to play satisfactorily the role of neutron screen.

The inventors have therefore set themselves the goal of providing a neutron-absorbing material which is, in general, devoid of the various limits presented by the neutrophage materials proposed to date.

More specifically, they have set themselves the goal of providing a material which, in addition to having outstanding neutron-absorbing properties, is also capable of withstanding very high temperatures, i.e., temperatures of 150 to 200 ° C. continuous and from 250 to 300 ° C peak, and can also be in both flexible and rigid form so as to be used in as many applications as possible.

In addition, they have set themselves the goal that the manufacture of this material is simple to implement and can be carried out at costs compatible with an industrial scale operation.

STATEMENT OF THE INVENTION

These and other objects are achieved by the present invention which proposes the use of a material comprising a solid matrix based on a silicone polymer in which a hydrogenated inorganic filler and a borated inorganic filler are dispersed as a material. neutrophage, the silicone polymer being a polysiloxane which is formed by one or more siloxane repeating units and characterized in that in said siloxane repeating units the silicon atom is bonded to one or two aromatic groups.

The inventors have, in fact, found that the dispersion, within a matrix based on a silicone polymer, of inorganic fillers, respectively hydrogenated and borated, makes it possible to obtain a material which combines neutrophage and high temperatures particularly interesting and this silicone polymer is a silicone resin or a silicone elastomer.

It is therefore possible, by playing on the fact that silicone resins lead to rigid materials while silicone elastomers lead to flexible materials, to give this material rigidity or, conversely, a flexibility perfectly adapted to the use for which it is intended.

In what precedes and what follows, the expression " based on a silicone polymer ", as applied to the solid matrix, means that this matrix has a polysiloxane for majority component, that is to say that this polysiloxane represents more than 50% by weight of the mass of said matrix.

In the context of the invention, it is preferred that the solid matrix comprise, as polymer, only this polysiloxane but it goes without saying that it can perfectly consist of a mixture of several different polysiloxanes or a mixture of one or more polysiloxanes and one or more other non-polysiloxane polymers, suitable for facilitating the use of the material or for imparting particular properties depending on the use for which it is intended, provided, of course, that this or these non-polysiloxane polymers are compatible with said polysiloxane (s).

According to the invention, the solid matrix comprises a polysiloxane which is formed by one or more siloxane repeating units in which the silicon atom is bonded to one or two aromatic groups, so that the material is as resistant as possible neutron and gamma irradiation.

dans laquelle :

• R¹ représente un groupe aromatique, tandis que
• R² représente un groupe alkyle comprenant de 1 à 4 atomes de carbone, c'est-à-dire méthyle, éthyle, propyle, isopropyle, n-butyle, isobutyle ou tert-butyle, ou bien un groupe aromatique.

More preferably, it is preferred that this polysiloxane be formed of one or more siloxane repeating units which each correspond to formula (I) below:

in which :

• R ¹ represents an aromatic group, while
• R ² represents an alkyl group comprising from 1 to 4 carbon atoms, that is to say methyl, ethyl, propyl, isopropyl, n- butyl, isobutyl or tert- butyl, or an aromatic group.

The aromatic group (s) present in the polysiloxane are typically phenyl, benzyl, o-tolyl, m-tolyl, p-tolyl, o-xylyl or mesityl groups, phenyl being particularly preferred.

Most preferably, the polysiloxane is a homopolymer, i.e. it consists of only one repeating siloxane unit, which corresponds to formula (I) above, in which R ¹ is phenyl, while R ² is methyl or phenyl. In other words, the polysiloxane is a poly [methyl (phenyl) siloxane] or a poly (diphenylsiloxane).

The hydrogenated inorganic filler is advantageously chosen from metal hydroxides, which, in addition to slowing the neutrons very effectively, have the advantage of giving the material an excellent fire resistance.

As examples of metal hydroxides that may be used, there may be mentioned aluminum hydroxide (Al (OH) ₃ , also called alumina hydrate), magnesium hydroxide (Mg (OH) ₂ , also called hydrated magnesia) and their mixtures.

As for the borated inorganic filler, it is advantageously chosen from zinc borates such as Zn ₂ O _14.5 B ₆ H ₇ , Zn ₄ O ₈ B ₂ H ₂ or Zn ₂ O ₁₁ B ₆ , disodium tetraborate decahydrate ( Na ₂ B ₄ O ₇ • 10H ₂ O or borax), boron carbide (B ₄ C), boron oxide (B ₂ O ₃ ), boric acid (H ₃ BO ₃ ), colemanite ( Ca ₂ O ₁₄ B ₆ H ₁₀ ) and mixtures thereof.

Preferably, the hydrogenated inorganic filler is aluminum hydroxide, while the boron inorganic filler is a zinc borate because of the flame retardant properties of this type of compound and, more particularly, a zinc borate containing aluminum oxide. hydrogen such as Zn ₂ O _14.5 H ₇ B ₆ or Zn ₄ O ₈ B ₂ H ₂ .

According to the invention, the amount of hydrogenated inorganic filler is preferably selected so that, taking into account the quantities of hydrogen also present in the polysiloxane, the material has an atomic concentration of hydrogen ranging from ²⁸ 3,2.10 atoms / m ³ to 6.3.10 ²⁸ atoms / m ³ and more preferably 4.1.10 ²⁸ atoms / m ³ to 6.10 ²⁸ atoms / m ³ .

Moreover, the amount of boron inorganic filler is preferably chosen so that the material has a boron atomic concentration ranging from 1.9 × 10 ²⁷ atoms / m ³ to 1.8 × 10 ²⁸ atoms / m ³ and, more preferably, from 2.1.10 ²⁷ atoms / m ³ to 9.10 ²⁷ atoms / m ³ .

In addition to the hydrogenated inorganic filler and borated inorganic filler, the solid matrix may contain other adjuvants in order to modify the behavior of the material during its use or its properties of use, such as fillers (inorganic or organic) stabilizers, plasticizers, dyes, pigments, antistats, etc.

In particular, the solid matrix may contain inorganic fillers of the silica type, natural or synthetic, or carbon black to increase the hardness of the material.

In accordance with the invention, the material is preferably used for the manufacture of neutron shielding elements (i.e. as a component of these protective elements) and, more preferably, as elements of Neutron protection for nuclear power plants or reprocessing plants for the reprocessing of spent nuclear fuel.

• le mélange d'une résine silicone ou d'un élastomère silicone avec une charge inorganique hydrogénée, une charge inorganique borée ;
• le dégazage, par exemple sous vide, du mélange ainsi obtenu ;
• la mise en forme du mélange ainsi dégazé ; puis
• la réticulation de la résine silicone ou de l'élastomère silicone présent dans le mélange ainsi mis en forme.

A material, as previously defined, can be prepared by a process comprising:

• mixing a silicone resin or a silicone elastomer with a hydrogenated inorganic filler, a borated inorganic filler;
• degassing, for example under vacuum, of the mixture thus obtained;
• shaping the mixture thus degassed; then
• the crosslinking of the silicone resin or of the silicone elastomer present in the mixture thus shaped.

If necessary, an accelerator or a crosslinking catalyst selected from the compounds conventionally used to accelerate or catalyze the crosslinking of silicones (metal salts, for example platinum or tin, organostannous compounds, peroxides, etc.) can be added to resin mixture or silicone elastomer / hydrogenated inorganic filler / borated inorganic filler. The shaping of the mixture can be achieved by all the techniques conventionally used for shaping materials based on silicone resins or silicone elastomers, such as casting molding, compression molding or injection molding. .

For the molding of neutron protection elements of large thickness, it is preferred to use a silicone resin or a silicone elastomer without solvent. Typically, the resins and elastomers without solvent are in the form of viscous liquids whose volatile mass is less than 10%, or even 5%, of the total mass of these resins or elastomers. Indeed, the use of this type of silicone greatly limits the amount of volatiles to be removed during the implementation of the material and, thereby, the creation within this material pores suitable for constitute pockets for the gaseous hydrogen likely to be produced by radiolysis of the material under the effect of ionizing radiation.

It goes without saying that the use of a silicone resin or a silicone elastomer without solvent can also be envisaged to produce neutron protection elements which are neither made by molding nor thick.

• une première étape d'une durée typiquement de 10 à 16 heures, pendant laquelle le mélange résine ou élastomère silicone/charge inorganique hydrogénée/charge inorganique borée est soumis à une température qui ne dépasse pas 150°C et qui est idéalement comprise entre 100 et 150°C, de manière à obtenir une densification déjà importante de la résine ou de l'élastomère par réticulation partielle mais tout en limitant les risques de déshydratation des charges inorganiques hydrogénée et borée ; et
• une deuxième étape d'une durée typiquement de 1 à 5 heures, pendant laquelle le mélange résine ou élastomère silicone/charge inorganique hydrogénée/charge inorganique borée est soumis à une température supérieure à 150°C et qui est idéalement comprise entre 150 et 200°C, de manière à achever la réticulation de la résine ou de l'élastomère et à conférer au matériau des propriétés optimales de résistance thermique.

In the case where the material is made from a silicone resin or a silicone elastomer heat curable (also called HTV silicone elastomer for "High Temperature Vulcanization"), the crosslinking of the resin or elastomer is of preferably, carried out in two steps:

• a first step of a duration typically of 10 to 16 hours, during which the resin mixture or silicone elastomer / hydrogenated inorganic filler / borated inorganic filler is subjected to a temperature which does not exceed 150 ° C and which is ideally between 100 and 150 ° C, so as to obtain an already substantial densification of the resin or of the elastomer by partial crosslinking but while limiting the risks of dehydration of the hydrogenated and borated inorganic fillers; and
• a second step of a duration typically of 1 to 5 hours, during which the resin mixture or silicone elastomer / hydrogenated inorganic filler / borated inorganic filler is subjected to a temperature above 150 ° C and which is ideally between 150 and 200 ° C, so as to complete the crosslinking of the resin or elastomer and to impart to the material optimum properties of thermal resistance.

In the case where the material is made from a cold-crosslinkable silicone elastomer (also called RTV silicone elastomer for " Room Temperature Vulcanization "), the crosslinking of this elastomer is preferably carried out while maintaining the silicone / silicone elastomer mixture. hydrogenated inorganic filler / inorganic filler borated at room temperature (23-25 ° C) for a period of typically 24 hours. A complementary heat treatment, for example a few hours at a temperature between 100 and 150 ° C, can then be applied to the material for increase its hardness and thus confer optimal mechanical properties, for example for subsequent machining.

Other features and advantages of the invention will appear better on reading the additional description which follows, which relates to examples of preparation of useful materials according to the invention and demonstration of their properties.

Of course, these examples are given only by way of illustration of the object of the invention and do not constitute in any way a limitation of this object.

BRIEF DESCRIPTION OF THE FIGURES

• The figure 1 illustrates the evolution of the atomic concentration in hydrogen, denoted [H] _at and expressed in number of atoms / cm ³ , of a rigid material useful according to the invention over time, expressed in hours, as determined by elemental analyzes (chemical assay) of samples of this material having been maintained for 24 hours, 96 hours and 500 hours at 150 ° C (curve) and by calculations performed from an accelerated aging test (symbol ◆).
• The figure 2 illustrates the evolution of the Young modulus in flexion, denoted E and expressed in MPa, of a rigid material useful according to the invention over time, expressed in hours, when this material is maintained for 90 hours at 150 ° C. (curve A) or for 170 hours at 250 ° C (curve B).
• The figure 3 illustrates the evolution of the maximum bending stress, denoted σ _max and expressed in MPa, of a rigid material useful according to the invention over time, expressed in hours, when this material is maintained for 90 hours at 150 ° C. (curve A) or for 170 hours at 250 ° C (curve B).
• The figure 4 illustrates the evolution of the atomic concentration in hydrogen, denoted [H] _at and expressed in number of atoms / cm ³ , of a flexible material useful according to the invention over time, expressed in hours, as determined by chemical determination of samples of this material having been maintained for 24 hours, 96 hours and 500 hours at 150 ° C (curve) and by calculations performed from an accelerated aging test (symbol ◆).
• The figure 5 illustrates the evolution of the elongation at break, denoted A and expressed in%, of a flexible material useful according to the invention over time, expressed in hours, when this material is maintained for 500 hours at 150 ° C. (curve A) and for 200 hours at 250 ° C (curve B).
• The figure 6 illustrates the evolution of Young's tensile modulus, denoted E and expressed in MPa, of a flexible material useful according to the invention over time, expressed in hours, when this material is maintained for 500 hours at 150 ° C. (curve A) and for 200 hours at 250 ° C (curve B).

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS EXAMPLE 1 Preparation of a Rigid Material Useful According to the Invention

• 40% en masse d'une résine silicone à motif répétitif méthyl(phényl)-siloxane sans solvant (référence Silres™ H62 C-société Wacker Chemie AG) ;
• 17% en masse de borate de zinc de formule Zn₂O_14,5H₇B₆ (référence Firebrake™ ZB - société Borax) ;
• 43% en masse d'hydroxyde d'aluminium (référence SH150 - société Rio Tinto Alcan).

A mixture is prepared in a turbine mixer comprising:

• 40% by weight of a silicone resin with repeating unit methyl (phenyl) -siloxane without solvent (reference Silres ™ H62 C-company Wacker Chemie AG);
• 17% by weight of zinc borate of formula Zn ₂ O _14.5 H ₇ B ₆ (reference Firebrake ™ ZB - Borax company);
• 43% by weight of aluminum hydroxide (reference SH150 - Rio Tinto Alcan company).

This mixture is degassed under vacuum at 50 ° C, then poured into square molds, 10 cm square and 1 cm thick.

The molds thus filled are placed in an oven heated at 120 ° C. for 16 hours and then at 200 ° C. for 2 hours to induce the crosslinking of the silicone resin.

After demolding, the density of the plates of the material thus obtained is measured according to the conventional technique of weighing in air / weighing in water. This density is equal to 1.7 and is consistent with the theoretical density. The material therefore contains no porosity.

Furthermore, the plates are subjected to tests in order to assess the ability of the material to retain over time, on the one hand, its properties neutrophages, and, on the other hand, its mechanical properties, when maintained at high temperatures.

The ability of the material to retain its neutrophage properties is assessed by an accelerated aging test to simulate the behavior of the material if it were maintained for 100,000 hours (more than 11 years) at 150 ° C. Briefly, this test consists in keeping the material plates for several hundred hours in an oven heated to 120 ° C, 150 ° C, 180 ° C or 205 ° C, to be measured at time intervals the mass of the plates and to establish, for each of these temperatures, a curve representing the mass loss of the material as a function of the residence time in the oven. A master curve corresponding to the loss of mass undergone by the material for a heating of 100,000 hours at the temperature of 150 ° C. is then constructed by translation of the three other curves with respect to that obtained for heating at 150 ° C. Thus to form a single continuous curve, which amounts, in logarithmic time scale, to multiply the aging times by an acceleration coefficient, respectively by 0.1 for the temperature of 120 ° C, by 1 for the temperature of 150 ° C, 45 for the temperature of 180 ° C and 90 for the temperature of 205 ° C.

In addition, elemental analyzes are carried out on plates of the material to determine the atomic hydrogen concentration of this material before it is placed in an oven and after a residence of 24 hours, 96 hours and 500 hours in an oven heated to 150 ° C.

Considering the most severe case, namely that the loss of mass undergone by the material would correspond to a loss of water, it is possible to estimate the quantity of hydrogen remaining in the material after several years of aging at the temperature of 150 ° vs.

The ability of the material to retain its mechanical properties is, in turn, appreciated by a thermal aging test which consists in keeping the plates of the material for 90 hours in an oven heated to 150 ° C or for 170 hours in a heated oven at 250 ° C and follow the evolution over time the evolution of the flexural Young's modulus and the maximum bending stress of the material, which is measured according to the NF EN ISO 178 standard.

The results of these tests are illustrated on the Figures 1, 2 and 3 .

As shown in figure 1 , which represents the evolution of the atomic hydrogen concentration [H] _at (in number of atoms / cm ³ ) of the material over time (in hours), as determined by the elementary analyzes (curve) and by Calculations made from the accelerated aging test (symbol ◆), the atomic hydrogen concentration of the material decreases slightly when it is subjected to a temperature of 150 ° C for a very prolonged period of time. As a result, its neutrophage properties are remarkably well preserved.

Moreover, as shown by figures 2 and 3 , which respectively represent the evolution of Young's modulus in bending E (in MPa) and that of the maximum bending stress σ _max (in MPa) of the material over time (in hours), as obtained when this material is maintained for 90 hours at 150 ° C (A curves) or for 170 hours at 250 ° C (B curves), holding the material for several tens of hours at a temperature of 150 ° C or 250 ° C n does not cause significant degradation of its mechanical properties.

EXAMPLE 2 Preparation of a flexible material useful according to the invention

• d'une part, on remplace la résine silicone, qui est utilisée dans cet exemple, par un élastomère silicone liquide à motif méthyl(phényl)siloxane, également sans solvant (référence Elastosil™ RT 601- société Wacker Chemie AG) ; et
• d'autre part, la réticulation (ou vulcanisation) de l'élastomère silicone est réalisée en laissant les moules pendant 24 heures à température ambiante et en les plaçant ensuite dans une étuve que l'on chauffe d'abord pendant 1 heure à 100°C, puis pendant 1 heure à 150°C.

The procedure is as in Example 1 above except that:

• on the one hand, the silicone resin, which is used in this example, is replaced by a liquid silicone elastomer having a methyl (phenyl) siloxane unit, also without a solvent (reference Elastosil ™ RT 601-Wacker Chemie AG); and
• on the other hand, the crosslinking (or vulcanization) of the silicone elastomer is carried out by leaving the molds for 24 hours at room temperature and then placing them in an oven which is first heated for 1 hour at 100 ° C. C, then for 1 hour at 150 ° C.

After demolding, the plates of the material thus obtained are subjected to thermal aging tests in order to assess the ability of the material to retain over time, on the one hand, its neutrophage properties, and on the other hand, its mechanical properties, when maintained at elevated temperatures.

The ability of the material to retain its neutrophage properties is appreciated by an accelerated aging test identical to that described in Example 1 above.

The ability of the material to retain its mechanical properties is, in turn, appreciated by a thermal aging test which consists of keeping the plates of the material for 500 hours in an oven heated to 150 ° C or for 200 hours in a heated oven at 250 ° C and to follow the evolution over time of the elongation at break A and the modulus E in tension of the material which is measured according to standard NF EN ISO 527-1.

The results of these tests are illustrated on the figures 4 , 5 and 6 .

As shown in figure 4 , which represents the evolution of the atomic hydrogen concentration [H] _at (in number of atoms / cm ³ ) of the material over time (in hours), as determined by the elementary analyzes (curve) and by calculated from the accelerated aging test (symbol ◆), the quantity of hydrogen atoms lost by this material is very small (less than 5%) when it is subjected to a temperature of 150 ° C during a very prolonged period of time. As a result, the neutrophagic properties of the material are remarkably well preserved.

Moreover, as shown by Figures 5 and 6 , which respectively represent the evolution of the elongation at break A (in%) and that of the Young's modulus in traction E (in MPa) of the material over time (in hours), as obtained when this material is maintained for 500 hours at 150 ° C (curves A) and for 200 hours at 250 ° C (curves B), the mechanical properties of the material stabilize after a hundred hours of aging at 150 ° C.

These figures also show that the elongation at break of a material based on a silicone elastomer remains high compared to that of materials based on a thermosetting resin and whether it is a resin unsaturated polyester, vinylester, epoxy or even silicone. This reduces the risk of cracking of the material by thermal expansion when it is exposed to significant temperature variations.

REFERENCES CITED

1. [1] US Patent 4,134,937
2. [2] EP-A-0 106 759
3. [3] WO-A-03/030183
4. [4] WO-A-03/050822
5. [5] WO-A-02/101756
6. [6] KR 1019980078181 B1

Claims (15)

1. Use of a material comprising a solid matrix based on a silicone polymer, in which are dispersed a hydrogenated inorganic filler and a borated inorganic filler, as a neutrophage material, said silicone polymer being a polysiloxane which is formed with one or several siloxane recurrent units and characterized in that the silicon atom is bound to one or two aromatic groups.
2. Use according to claim 1, wherein the polysiloxane is formed with one or several siloxane recurrent units, each fitting the formula (1) hereafter:

   

   wherein:

   R¹ represents an aromatic group, while

   R² represents an alkyl group comprising 1 to 4 carbon atoms or an aromatic group.
3. Use according to claim 1 or claim 2, wherein the polysiloxane is a homopolymer.
4. Use according to claim 3, wherein the polysiloxane is a poly[methyl(phenyl)siloxane] or a poly(diphenylsiloxane).
5. Use according to any of claims 1 to 4, wherein the hydrogenated inorganic filler is selected from among metal hydroxides.
6. Use according to claim 5, wherein the hydrogenated inorganic filler is selected from among aluminium hydroxide, magnesium hydroxide and mixtures thereof.
7. Use according to claim 6, wherein the hydrogenated inorganic filler is aluminium hydroxide.
8. Use according to any of claims 1 to 7, wherein the borated inorganic filler is selected from among zinc borates, boron carbide, boron oxide, boric acid, colemanite and mixtures thereof.
9. Use according to claim 8, wherein the borated inorganic filler is a zinc borate.
10. Use according to any of claims 1 to 9, wherein the material has an atomic hydrogen concentration ranging from 3.2x10²⁸ atoms/m³ to 6.3x10²⁸ atoms/m³.
11. Use according to claim 10, wherein the material has an atomic hydrogen concentration ranging from 4.1x10²⁸ atoms/m³ to 6x10²⁸ atoms/m³.
12. Use according to any of claims 1 to 11, wherein the material has an atomic boron concentration ranging from 1.9x10²⁷ atoms/m³ to 1.8x10²⁸ atoms/m³.
13. Use according to claim 12, wherein the material has an atomic boron concentration ranging from 2.1x10²⁷ atoms/m³ to 9x10²⁷ atoms/m³.
14. Use according to any of claims 1 to 13, wherein the material is a component of a flexible or rigid neutron protection element.
15. Use according to claim 14, wherein the neutron protective element is an element of a nuclear power station or of a plant for processing irradiated nuclear fuels.

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