JPH0697275B2 - Neutron shielding material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a neutron shielding material that is fluid in an uncured state and is obtained by curing at room temperature.

[Conventional Technology / Problems] Conventionally, as a neutron shielding material, a silicone rubber filled with aluminum hydroxide has been known. The purpose of using aluminum hydroxide for the neutron shielding material is to impart flame retardancy to the neutron shielding material. Further, aluminum hydroxide has a function of decelerating fast neutrons into slow neutrons, that is, thermal neutrons, which is equivalent to silicone rubber.

However, although aluminum hydroxide is stable at room temperature,
When exposed to higher temperatures for a long time, dehydration occurs,
Form alumina. By this decomposition into alumina, hydrogen involved in the moderating action is removed from the aluminum hydroxide, and the moderating effect of fast neutrons to slow neutrons is reduced. Furthermore, the decomposition of aluminum hydroxide becomes faster as the temperature increases, and it is difficult to withstand the 30-year service life of neutron shielding materials in nuclear power plants.

Further, JP-A-53-73000 discloses a radiation-resistant neutron absorption shielding material in which boron carbide particles are mixed and dispersed in polyorganosiloxane. This shielding material obtains a moderating action of fast neutrons to slow neutrons by hydrogen in polyorganosiloxane, and makes boron carbide act to absorb slow neutrons.

Furthermore, the present inventors have applied for a neutron shielding material in Japanese Patent Application No. 61-232215, in which magnesium hydroxide powder and boron carbide powder are added and blended with polyorganosiloxane. This neutron shielding material is excellent in heat resistance and fire resistance, and is a suitable neutron shielding material for producing spent nuclear fuel, high-level radioactive waste after reprocessing, and cask for new fuel protonium.

However, the above-mentioned neutron shielding material is suitable for use in a special site requiring heat resistance, and the combination of magnesium hydroxide and boron carbide provides excellent neutron shielding property, There is a demand for an inexpensive neutron shielding material with excellent neutron shielding properties.

[Means for Solving the Problems] The inventors of the present invention have a neutron shield equivalent to or more than the combination of magnesium hydroxide and boron carbide in a zone where heat resistance is not required, that is, a zone of normal temperature or slightly higher temperature range. As a result of various studies of neutron shielding material having properties, using polyethylene powder instead of magnesium hydroxide powder,
Further, they have found that it is possible to provide an inexpensive neutron shielding material having a neutron shielding property superior to that of a conventional neutron shielding material by using a boron compound powder, and completed the present invention.

That is, the present invention provides (A): general formula [Wherein R is a monovalent hydrocarbon group containing no aliphatic unsaturated bond, R'is a monovalent hydrocarbon group, and n is the viscosity of (A) at 25 ° C.
At 100 to 50,000 cSt], 100 parts by weight of a polyorganosiloxane both ends of which are blocked with a vinyl group represented by the formula (B): (R ″) ₂ containing or not including a SiO unit, ″) ₃ SiO _0.5 unit and SiO ₂ unit (in the formula, R ″ represents a group selected from a monovalent hydrocarbon group not containing an aliphatic unsaturated bond and a vinyl group) and has 2.5 to 10 silicon atoms. Mol% has a vinyl group directly bonded to a silicon atom, and (R ″) ₃ S
0 to 100 parts by weight of polyorganosiloxane copolymer having a ratio of iO _0.5 unit: SiO ₂ unit of 0.4: 1 to 1: 1; (C): general formula [In the formula, R has the same meaning as R in (A), m is a number of 2 or more, a has a value of 1.0 to 2.0, and b is 0.1
Has a value of ˜1.0, (a + b) is 1.9 to 3.0, and has an average of more than 2 hydrogen atoms directly connected to silicon atoms per molecule], and (a) and (B) Hydrogen atom directly bonded to silicon atom for one vinyl group of polyorganosiloxane
Polyorganohydrogen siloxane in an amount sufficient to give 0.5 to 5.0, (D): 5 to 100 parts by weight of polyethylene powder, based on 100 parts by weight of [(A) + (B) + (C)], (E): Polyorganosiloxane composition characterized by comprising 5 to 150 parts by weight of a boron compound powder, and (F): an effective amount of platinum catalyst, based on 100 parts by weight of [(A) + (B) + (C)]. It is to provide a neutron shielding material obtained by curing an object.

[Operation] Since the composition of the present invention does not cure unless (A) and / or (B), (C) and (F) coexist, one of them is housed in another package. , Mix just before use. For example, the first package includes the total amount of (D) and (E) and most of (A) and (B), and the second package includes only (C) or the total amount of (C) and (A) and (B). In part, the third package consists of the total amount of (F) and the balance of (A) and (B),
At the time of use, the above three packages can be mixed and cured.

In the present invention, the monovalent hydrocarbon group represented by R and R'of the vinyl chain end polyorganosiloxane component (A) is an alkyl group (for example, methyl, ethyl, propyl, butyl, hexyl, octyl, and decyl groups). Aryl groups (eg phenyl, tolyl and xylyl groups),
Examples include cycloalkyl groups (eg cyclohexyl and cycloheptyl groups), aralkyl groups (eg benzyl, β-phenylethyl and β-phenylpropyl groups),
As R ', alkenyl groups (vinyl and allyl groups) are further added to the examples. R and R'may be used alone or in combination of two or more, and may be the same or different from each other.

At least 50% of the groups represented by R and R'are selected from the group consisting of methyl and vinyl groups, and in a preferred particular composition all of the groups represented by R and R'are methyl and vinyl groups. .

The value of n is such that the viscosity of component (A) at 25 ° C is 100 to 50,000c.
St, preferably in the range of 500 to 8,000 cSt. When the viscosity of the component (A) is less than 100 cSt, sufficient physical properties cannot be obtained, and when it exceeds 50,000 cSt, handling in an uncured state becomes difficult, which is not preferable.

The polyorganosiloxane copolymer of the component (B) in the present invention is a component for imparting sufficient strength to the composition without containing a reinforcing filler and is a monovalent hydrocarbon containing no aliphatic unsaturated bond. Alternatively, it can be defined as a polyorganosiloxane copolymer containing R ″ groups which can be vinyl groups and at least the abovementioned proportions of R ″ groups are vinyl groups. Non-vinyl R ″ groups are within the same range as the R groups of component (A) and similar groups thereof, and in a preferred embodiment thereof, all monovalent hydrocarbon groups containing no aliphatic unsaturated bond are methyl groups. The vinyl group can be present as part of the (R ″) ₃ SiO _0.5 group, or as part of the (R ″) ₂ SiO group, or both.

The various siloxane units in the copolymer component (B) are selected so that the ratio of (R ″) ₃ SiO _0.5 units: SiO ₂ units is 0.4: 1 to 1: 1. (R ″) ₃ SiO _0.5 Unit: SiO ₂ unit ratio is
If it is less than 0.4: 1, the stability of the component (B) is poor and it is difficult to synthesize it with good control. If it exceeds 1: 1, it is not possible to give good mechanical strength to the cured product, which is preferable. Absent.

The (R ″) ₂ SiO units are present in an amount equal to 0 to 10 mol% based on the total number of siloxane units in the copolymer. Where the silicon-bonded vinyl groups are located in the copolymer Irrespective of whether the silicon-bonded vinyl group is from 2.5 to 1 of the copolymer component (B).
It should be present in an amount equal to 0.0 mol%.

Copolymer component (B) is a solid resinous material, often produced as a solution in a solvent such as xylene or toluene, and generally as a 30-75 wt% solution. In order to facilitate the handling of the composition, this solution of the copolymer component (B) is usually dissolved in part or all of the vinyl chain end polysiloxane component (A), and the solvent is distilled off from the resulting solution. Then, a mixture of the component (A) and the copolymer component (B) may be prepared, or the component (B) from which the solvent has been removed in advance may be used.

The amount of the component (B) is 0-100 in 100 parts by weight of the component (A).
Parts by weight, preferably 10 to 80 parts by weight.

When mechanical strength is required for the neutron shielding material, sufficient strength cannot be obtained without the reinforcing filler unless the component (B) is blended in an amount of 10 parts by weight or more. It is not preferable because it becomes impossible to fill the polyethylene powder and the boron compound powder necessary for shielding the intended neutrons. Further, when the amount of the component (B) exceeds 100 parts by weight, the viscosity of the composition in an uncured state becomes high and it is difficult to handle.

The polyorganohydrogensiloxane of the component (C) in the present invention reacts with the components (A) and (B) to form a reticulated polysiloxane, and therefore the average of 2 in the molecule.
It has more than silicon-bonded hydrogen atoms. Such a polyorganohydrogen siloxane may have a siloxane skeleton which may be linear, branched or cyclic, and may be a polymer composed of only siloxane units having a silicon bond,
It may be a copolymer of this with one or more of triorganosiloxy units, diorganosiloxane units, monoorganosiloxy units and SiO ₂ units. Examples of R are the same as those of R in the component (A), and one or two or more thereof may be used in combination, but they are easy to synthesize and have good physical properties after curing with a relatively low viscosity. Therefore, a methyl group and a phenyl group are preferable, and a methyl group is particularly preferable. In order to have an average of more than 2 silicon-bonded hydrogen atoms in one molecule, m
Is required to be 2 or more, preferably in the range of 4 to 1,000. When m is less than 4, volatility is high, and when it exceeds 1,000, synthesis and handling are difficult. If a is less than 1.0 or b is more than 1.0, it is difficult to synthesize. a
When it exceeds 2.0, the desired m cannot be obtained while the component (C) has the necessary silicon-bonded hydrogen atoms, and when b is less than 0.1, the number of m for giving the desired silicon-bonded hydrogen atoms is large. As a result, it becomes difficult to handle the component (C). a +
If the sum of b is less than 1.9, it is difficult to synthesize with good control, and if it exceeds 3.0, the required degree of polymerization cannot be obtained.

The amount of component (C) is such that the amount of hydrogen atoms directly bonded to silicon atoms contained in component (C) is 0.5 to 5.0 per one vinyl group contained in components (A) and (B). That's enough. If it is less than 0.5, a rubber-like elastic body cannot be obtained,
If it exceeds 5.0, it is not preferable because it causes foaming and deterioration of mechanical properties.

The component (D) used in the present invention is polyethylene powder. The particle size of polyethylene powder is usually 600 μm or less, preferably around 250 μm. This polyethylene powder has a larger number of hydrogen atoms per unit weight than polyorganosiloxane, and has a moderating effect of fast neutrons to slow neutrons superior to that of polyorganosiloxane.

The amount of the component (D) is 5 to 100 parts by weight, preferably 10 to 10 parts by weight based on 100 parts by weight of the total amount of the components [(A) + (B) + (C)].
It is in the range of 80 parts by weight. If the added amount of the component (D) is less than 5 parts by weight, a sufficient hydrogen atom increasing effect cannot be obtained, and if it exceeds 100 parts by weight, the component [(A) + (B) +
(C)] becomes difficult to knead, which makes the on-site injection work impossible, and also reduces the strength of the cured composition, which is not preferable.

The component (E) used in the present invention is a boron compound powder such as boric acid powder, boron oxide powder and boron carbide powder. Boron atoms in these boron compound powders act to shield slow neutrons, that is, thermal neutrons.

Total amount of component [(A) + (B) + (C)] of component (E)
5 to 150 parts by weight, preferably 15 to 140 parts by weight per 100 parts by weight
The range is parts by weight. If the added amount of the component (E) is less than 5 parts by weight, a sufficient slow neutron shielding effect cannot be obtained, and if it exceeds 150 parts by weight, the component [(A) + (B) +
(C)] becomes difficult to knead, which makes it impossible to perform on-site injection work and reduces the strength of the cured composition, which is not preferable.

The mixing ratio of the component (D), that is, the polyethylene powder and the component (E), that is, the boron compound powder, depends on the moderating characteristics of the slow neutrons of the fast neutrons of the neutron shielding material, the absorbability of the slow neutrons, that is, the thermal neutrons, the application, the cost, and the like. It is to be understood that various changes can be made to the above.

The platinum catalyst component (F) used in the present invention includes all known platinum catalysts that are effective in effecting the reaction between silicon-hydrogen bonds and silicon-bonded vinyl groups. Examples of the component (F) include platinum black, platinum-olefin complex, platinum-vinylsiloxane complex, platinum-phosphine complex and platinum-phosphite complex. Regardless of the platinum catalyst used, the catalyst is generally used in an amount sufficient to provide 10 ^-3 to 10 ^-6 gram atoms of platinum per mole of silicon-bonded vinyl groups in the composition.

[Examples] The present invention will be further described with reference to the following examples (hereinafter, simply referred to as "examples" unless otherwise specified). All parts in the examples are parts by weight. In the examples, Me is a methyl group, Vi
Indicates a vinyl group.

Example 1 65 parts of polydimethylsiloxane having a viscosity of 3,000 cSt at 25 ° C. and blocked with vinyl groups at both ends, and 60 mol% of SiO ₂
Units, 37.2 mol% Me ₃ SiO _0.5 units and 2.8 mol% MeVi
35 parts of a copolymer composed of SiO units were mixed to obtain a vinyl group-containing polyorganosiloxane mixture. This mixture was charged into a closed kneader, and 74 parts of polyethylene powder having a particle size of about 250 μm and 20 parts of boric acid powder having a particle size of 300 to 500 μm were charged and mixed under a closed condition until uniform.

Me ₃ SiO [Me ₂ SiO] ₆ [MeHSiO] ₆ · SiMe ₃ 5 parts and platinum-tetramethyltetravinylcyclotetrasiloxane complex were added and mixed in the amount of 50 / 1,000,000 parts converted to platinum atoms,
A composition of the invention was obtained. This composition is degassed to a thickness of 130 m
The rubber-like cured material (neutron shielding material) according to the present invention was obtained by casting in a m-shaped mold and leaving it at 30 ° C. for 24 hours.

Example 2 A neutron shielding material was obtained in the same manner as in Example 1 except that the content of polyethylene powder was 13 parts and the content of boric acid powder was 144 parts.

The properties of the cured bodies obtained in Examples 1 and 2 are described below: [Effects of the Invention] The neutron shielding material of the present invention uses polyethylene powder having a larger number of hydrogen atoms per unit weight than polysiloxane, and thereby obtains a deceleration effect of fast neutrons to slow neutrons superior to conventional shielding materials. Further, by using the boron compound powder, it is possible to provide an inexpensive neutron shielding material having a good slow neutron shielding effect.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location // (C08L 83/07 83:05 8319-4J 23:04) 7107-4J (72) Inventor Hisashi Okuda 4-13-1-105 Tokodai, Ishioka-shi, Ibaraki (72) Inventor, Yuzuru Kaneko 2-7-15 Shiba, Minato-ku, Tokyo Takachiho Electric Co., Ltd. (56) Reference JP-A-63-85497 ( JP, A) JP 62-217199 (JP, A) JP 62-12896 (JP, A) JP 60-194394 (JP, A)

Claims (9)

[Claims] 1. (A): General formula [Wherein R is a monovalent hydrocarbon group containing no aliphatic unsaturated bond, R'is a monovalent hydrocarbon group, and n is the viscosity of (A) at 25 ° C.
At 100 to 50,000 cSt], 100 parts by weight of a polyorganosiloxane whose both ends are blocked with a vinyl group represented by: (B): (R ″) ₂ SiO unit
(R ″) ₃ SiO _0.5 unit and SiO ₂ unit (in the formula, R ″ represents a group selected from a monovalent hydrocarbon group not containing an aliphatic unsaturated bond and a vinyl group), and has 2.5 ˜10 mol% has a vinyl group directly linked to silicon atom, and the ratio of (R ″) ₃ SiO _0.5 unit: SiO ₂ unit is 0.4: 1 to 1: 1. Polyorganosiloxane copolymer 0 to 100% by weight Part, (C): general formula [In the formula, R has the same meaning as R in (A), m is a number of 2 or more, a has a value of 1.0 to 2.0, and b is 0.1
Has a value of ˜1.0, (a + b) is 1.9 to 3.0, and has an average of more than 2 hydrogen atoms directly connected to silicon atoms per molecule], and (a) and (B) Hydrogen atom directly bonded to silicon atom for one vinyl group of polyorganosiloxane
Polyorganohydrogen siloxane in an amount sufficient to give 0.5 to 5.0, (D): 5 to 100 parts by weight of polyethylene powder, based on 100 parts by weight of [(A) + (B) + (C)], (E): Polyorganosiloxane composition characterized by comprising 5 to 150 parts by weight of a boron compound powder, and (F): an effective amount of platinum catalyst, based on 100 parts by weight of [(A) + (B) + (C)]. Neutron shielding material obtained by curing an object. 2. The neutron shielding material according to claim 1, wherein the amount of (B) is 10 to 80 parts by weight. 3. The first package is the total amount of (D) and (E) and most of (A) and (B), and the second package is the only amount of (C) or (C) and (A) and ( The neutron shielding material according to claim 1, wherein a part of (B), the third package comprises the entire amount of (F) and the rest of (A) and (B). 4. At least 50 mol% of R, R'and R "
The neutron shielding material according to claim 1, wherein is a methyl group. 5. The neutron shielding material according to claim 1, wherein R, R'and R "are methyl groups and vinyl groups. 6. The viscosity of (A) is 500 to 8,000 cS at 25 ° C.
The neutron shielding material according to claim 1, which is t. 7. A first claim in which m is 4 to 1,000.
The neutron shielding material according to the item. 8. The neutron shielding material according to claim 1, wherein the particle size of the polyethylene powder is 600 μm or less. 9. The neutron shielding material according to claim 1, wherein the particle size of the boron compound powder is 500 μm or less.