JPS63173000A - Neutron shielding material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a neutron shielding material that is fluid in an uncured state and can be obtained by curing at room temperature.

[Prior Art/Problems] Conventionally, silicone rubber filled with aluminum hydroxide has been known as a neutron shielding material.

The purpose of using aluminum hydroxide as a neutron shielding material is to impart flame retardancy to the neutron shielding material.

Additionally, aluminum hydroxide has the same effect as silicone rubber in moderating fast neutrons into slow neutrons, that is, thermal neutrons.

However, although aluminum hydroxide is stable at room temperature,
Prolonged exposure to higher temperatures causes dehydration,
Forms alumina. This decomposition into alumina removes hydrogen involved in the moderation effect from aluminum hydroxide, reducing the moderation effect of fast neutrons on slow neutrons. Furthermore, the higher the temperature, the faster aluminum hydroxide decomposes, making it difficult to withstand the 30-year service life of neutron shielding materials in nuclear power plants and the like.

Further, Japanese Patent Application Laid-open No. 53-73000 discloses a radiation-resistant neutron absorption shielding material in which boron carbide particles are blended and dispersed in polyorganosiloxane. This shielding material uses hydrogen in polyorganosiloxane to slow down fast neutrons to slow neutrons, and also uses boron carbide to absorb slow neutrons.

Furthermore, the present inventors filed a patent application in Japanese Patent Application No. 61-232215 for a neutron shielding material made by adding and blending magnesium hydroxide powder and boron carbide powder to polyorganosiloxane.

This neutron shielding material has excellent heat resistance and fire resistance, and is suitable for producing casks for spent nuclear fuel, high-level radioactive waste after reprocessing, and new fuel protonium.

However, the above-mentioned neutron shielding materials are suitable for use in special parts characterized by heat resistance, and the combination of magnesium hydroxide and boron carbide provides excellent neutron shielding properties, but There is a need for inexpensive neutron shielding materials with excellent neutron shielding properties.

[Means for Solving the Problems] The present inventors have developed a method for neutron shielding that is equivalent to or better than the combination of magnesium hydroxide and boron carbide in a zone where heat resistance is not required, that is, a zone between room temperature and a slightly higher temperature range. As a result of various studies on neutron shielding materials that have properties, we decided to use polyethylene powder instead of magnesium hydroxide powder.
Furthermore, the present inventors have discovered that by using boron compound powder, it is possible to provide a neutron shielding material that has better neutron shielding properties than conventional neutron shielding materials and is inexpensive, leading to the completion of the present invention.

That is, the present invention provides (A) in the general formula 1, R is a monovalent hydrocarbon group containing no aliphatic unsaturated bond, R' is a monovalent hydrocarbon group, and n is a viscosity of (A) of 25
The number is 100 to 50,000 aSt at °C] A 100-layer polyorganosiloxane capped at both ends with a vinyl group, (B): (R″) Contains or does not contain a tsio unit,
(R″>38iO0, unit and 5ift unit (where R
'' indicates a monovalent hydrocarbon group containing no aliphatic unsaturated bond and a group derived from a vinyl group), and 2.5 to 10 mol% of the silicon atoms have a vinyl group directly bonded to the silicon atom. , (R″)3SiOo, 0 to 100 parts by weight of a polyorganosiloxane copolymer having a ratio of s units:Sio□ units of 0.4:1 to 1:1, (C) 2 general formula [wherein R has the same meaning as R in (A), the ring is a number greater than or equal to 2, a has a value of 1.0 to 2.0, and b
has the value of o, i ~ t, o, and (a+b) is 1.9 ~
3.0 and has an average of more than 2 hydrogen atoms directly bonded to silicon atoms per molecule], and the number of silicon atoms per vinyl group of the polyorganosiloxanes (A) and (B) is polyorganohydrogensiloxane in an amount sufficient to provide 0.5 to 5.0 directly bonded hydrogen atoms, (D): [5 to 100 parts by weight of polyethylene powder per 1100 parts by weight of (A) + (B) + (C); Parts by weight, (E): [5 to 150 parts by weight of boron compound powder, based on 1100 parts by weight of (A) + (B) + (C), and (F):
It is an object of the present invention to provide a neutron shielding material obtained by curing a polyorganosiloxane composition characterized by comprising a platinum catalyst as an effective lid.

[Function] The composition of the present invention will not cure unless (A) and/or (B), (C), and (F) coexist, so any one of them cannot be housed in a separate package. For example, the first package contains all of (D) and (E) and most of (A) and (B), and the second package contains only (C) or only (C). The whole quantity and a part of (A> and (B)), the third package consists of the whole quantity of (F) and the remainder of (A) and (B),
The above three types of packaging can be mixed and cured during use.

In the present invention, the monovalent hydrocarbon groups represented by R and R' of the vinyl chain end polyorganosiloxane component (A) include alkyl groups (for example, methyl, ethyl, propyl, butyl, hexyl, octyl, and decyl groups). , aryl groups (e.g. phenyl, tolyl and xylyl groups), cycloalkyl groups (e.g. cyclohexyl and cycloheptyl groups), aralkyl groups (e.g. benzyl, β-phenyle-thyl and β-phenylpropyl groups),
Examples of R' include alkenyl groups (vinyl and allyl groups). R and R' may each be used alone or in combination of two or more, and may be the same or different.

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

The value of n is the viscosity of component (A) at 25°C of 100 to 5.
0.0OOcSt, preferably 500-8.000cS
This is the range where t is reached. The viscosity of component (A) is 100eSt
If it is less than 50.000eS, sufficient physical properties cannot be obtained.
If it exceeds t, it becomes difficult to handle in an uncured state, which is not preferable.

The polyorganosiloxane copolymer as component (B) in the present invention is a component that provides sufficient strength to the composition without containing a reinforcing filler, and is a monovalent hydrocarbon that does not contain aliphatic unsaturated bonds. or R can be a vinyl group
'' groups, and at least the aforementioned proportion of the R'' groups are vinyl groups. R'' groups that are not vinyl groups are of the same scope as the R group of component (A) and groups thereof, and in a preferred embodiment, all of the monovalent hydrocarbon groups that do not contain aliphatic unsaturation are It is a methyl group.The vinyl group is (R″)ss
It can be present as part of the ioe, , group, or as part of the (R″)zsio group, or both.

Various siloxane units in the copolymer component (B) are (R”
LSioo, s unit: Ratio of S i Ox unit is 0.4
:1 to 1:1. (R″)3SiO
0,.

Unit:SiO, if the unit ratio is less than 0.4:1, the component (
The stability of B) is poor, making it difficult to synthesize in a well-controlled manner, and when the ratio exceeds 1:1, good mechanical strength cannot be imparted to the cured product, which is not preferred.

(R">28io units are present in a wall equal to 0 to 10 mol%, based on the total number of siloxane monomers in the copolymer. Where silicon-bonded vinyl groups are located in the copolymer, Regardless, the silicon-bonded vinyl groups should be present in an amount equal to 2.5 to 10.0 mole percent of copolymer component (B).

Copolymer component (B) is a solid resinous material, often prepared as a solution in a solvent such as xylene or toluene, and generally as a 30-75% solution by weight.6 Composition Handling To facilitate this, this solution of copolymer component (B) is usually dissolved in some or all of the vinyl chain-terminated polysiloxane component (A), and the solvent is distilled off from the resulting solution to remove component (B). A) and copolymer component (B)
You may also prepare a mixture of the components (B) from which the solvent has been removed in advance.
) may be used.

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

When mechanical strength is required for neutron shielding materials.

If 10 parts by weight or more of component (B) is not added, sufficient strength will not be obtained without a reinforcing filler, and if a reinforcing filler is used in combination, the polyethylene powder and boron compound powder necessary for the neutron shielding intended in the present invention will be obtained. If the amount of component (B) exceeds 100 parts by weight, the viscosity of the uncured composition increases, making it difficult to handle.

The polyorganohydrogensiloxane of component (C) in the present invention reacts with components (A) and (B) to form a linear polysiloxane, and therefore has an average of 2
It has more than one silicon-bonded hydrogen atom. The siloxane skeleton of such polyorganohydrogensiloxane may be chain, branched, or cyclic, and silicon-
R may be a polymer consisting only of siloxane units with hydrogen bonds, or a copolymer of this with one or more of triorganosiloxy units, diorganosiloxy units, monoorganosiloxy units, and SiO2 units. is the same as R in component (A), and 1
Although a species or a combination of two or more species may be used, methyl groups and phenyl groups are preferred, and methyl groups are particularly preferred because they are easy to synthesize, have relatively low viscosity, and provide good physical properties after curing. , - In order to have an average number of silicon-bonded hydrogen atoms in the molecule exceeding 2, the number of scales must be 2 or more, preferably 4 to 1, for ease of synthesis.
The range is 000. - is less than 4, volatility is high;
If it exceeds t, o o o, synthesis and handling become difficult. It is difficult to synthesize those where a is less than 1.0 or b is more than 1°0. When a exceeds 2.0, component (C)
cannot have the desired - value while having the necessary silicon-bonded hydrogen atoms, and if b is less than 0.1, the number of - to provide the desired silicon-bonded hydrogen atoms becomes large, resulting in component (C) becomes difficult to handle. If the sum of a+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. This is a sufficient amount to reduce the number to 0. If the number is less than 0.5, a rubber-like elastic body cannot be obtained, and if it exceeds 5.0, foaming may occur or mechanical properties may deteriorate, which is not preferable.

Component (D) used in the present invention is polyethylene powder. The particle size of the 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 better effect of moderating fast neutrons on slow neutrons than polyorganosiloxane.

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

The boron compound powder of component (E) used in the present invention is, for example, boric acid powder, boron oxide powder, and boron carbide powder. The boron atoms in these boron compound powders act to shield slow neutrons or thermal neutrons.

The amount of component (E) is the component [(A)+(B)+(C
)] is in the range of 5 to 150 parts by weight, preferably 15 to 140 parts by weight, based on 100 parts by weight. Component (E)
If the amount added 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, which makes on-site injection work impossible and reduces the strength of the cured composition, which is undesirable.

In addition, component (D), that is, polyethylene powder and component (E
) That is, it should be understood that the blending ratio of the boron compound powder can be varied depending on the neutron shielding material's slow neutron moderation characteristics, slow neutron, i.e. thermal neutron absorption, use, cost, etc.

The platinum catalyst component (F) used in the present invention includes all known platinum catalysts that are effective for carrying out the reaction between silicon-hydrogen bonds and silicon-bonded vinyl groups. , platinum-olefin complexes, platinum-vinylsiloxane complexes, platinum-phosphine complexes, and platinum-phosphite complexes. Regardless of the type of platinum catalyst used, the catalyst usually contains sufficient I to provide 10-3 to 10-6 gram atoms of platinum per mole of silicon-bonded vinyl groups in the composition.
Use with.

[Example] The present invention will be further explained with reference to Examples (hereinafter simply referred to as "Examples" unless otherwise specified). In addition, all parts in the examples indicate parts by weight. , Me is a methyl group,
Vi represents a vinyl group.

65 parts of polydimethylsiloxane, which has a viscosity of 3,000 cSt at 25°C and is capped at both ends with vinyl groups;
0 mol% 5iOz units, 37.2 mol% M e 3
S i Oo , s units and 2.8 mol% MeVi
35 parts of a copolymer consisting of SiO units were mixed to obtain a vinyl group-containing polyorganosiloxane mixture. This mixture was placed in a tight funnel type Nigu, and 74 parts of polyethylene powder with a particle size of around 250 μm and 20 parts of boric acid powder with a particle size of 300 to 500 μm were charged and mixed under a tight funnel until uniform.

To this, MeSiO[MetSiO]s[Mellsi
o]s.5ides and 50/1,000,000 parts of platinum-tetramethyltetravinylcyclotetrasiloxane complex in terms of platinum atoms were added and mixed to obtain a composition of the present invention. This composition was defoamed, cast into a mold with a thickness of 130 cm, and left at 30° C. for 24 hours to obtain a rubber-like cured product (neutron shielding material) according to the present invention.

Faith? A neutron shielding material was obtained in the same manner as in Example 1 above, except that the amount of U-polyethylene powder was 13 parts and the amount of boric acid powder was 144 parts.

The properties of the cured bodies obtained in Examples 1 and 2 are described below: No.-1-1 In the table, μ represents the linear absorption coefficient.

[Effects of the Invention] The neutron shielding material of the present invention uses polyethylene powder that has a higher number of hydrogen atoms per unit weight than polysiloxane, thereby achieving a better effect of moderating fast neutrons into slow neutrons than conventional shielding materials. Furthermore, by using boron compound powder, it is possible to provide an inexpensive neutron shielding material that has a good slow neutron shielding effect.

Claims (1)

[Claims] 1. (A): General formula ▲ Numerical formula, chemical formula, table, etc. ▼ [In the formula, R is a monovalent hydrocarbon group that does not contain an aliphatic unsaturated bond, and R' is a monovalent hydrocarbon group. Hydrogen group, n is the viscosity of (A) 25
100 parts by weight of a polyorganosiloxane with both ends capped with a vinyl group represented by (B): (R″)_2 containing or not containing SiO units;
(R″)_3SiO_0_._5 units and SiO_2 units (wherein R″ represents a group selected from a monovalent hydrocarbon group and a vinyl group that does not contain an aliphatic unsaturated bond),
A polyorganosiloxane in which 2.5 to 10 mol% of the silicon atoms have vinyl groups directly bonded to the silicon atoms, and the ratio of (R″)_3SiO_0_._5 units:SiO_2 units is 0.4:1 to 1:1. 0 to 100 parts by weight of copolymer, (C): general formula (R)_a(H)_bSiO_4_-_(_a_+_b
_)_/_2 [wherein, 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. has a value of 1 to 1.0, (a+b)
is 1.9 to 3.0, and each molecule has an average of more than two hydrogens directly bonded to silicon atoms], and the vinyl group 1 of the polyorganosiloxanes (A) and (B) polyorganohydrogensiloxane in an amount sufficient to provide 0.5 to 5.0 hydrogen atoms directly bonded to silicon atoms per 100 parts by weight of (D):[(A)+(B)+(C)] , 5 to 100 parts by weight of polyethylene powder, (E): 5 to 150 parts by weight of boron compound powder per 100 parts by weight of [(A)+(B)+(C)], and (F): effective amount of platinum. A neutron shielding material obtained by curing a polyorganosiloxane composition comprising a catalyst. 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 contains the total amount of (D) and (E) and (A) and (
Most of B), the second package is only (C) or the whole amount of (C) and a part of (A) and (B), the third package is the whole amount of (F) and the remainder of (A) and (B) A neutron shielding material according to claim 1 consisting of: 4. The neutron shielding material according to claim 1, wherein at least 50 mol% of R, R', and R'' are methyl groups. 5. R, R', and R'' are methyl groups and vinyl groups. A neutron shielding material according to claim 1. 6. The viscosity of (A) is 500 to 8,000 at 25°C
The neutron shielding material according to claim 1, which is cSt. 7. The neutron shielding material according to claim 1, wherein m is 4 to 1,000. 8. The neutron shielding material according to claim 1, wherein the polyethylene powder has a particle size of 600 μm or less. 9. The neutron shielding material according to claim 1, wherein the boron compound powder has a particle size of 500 μm or less.