JPS6385497A - Neutron shielding material - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a neutron shielding material that is fluid in an uncured state and is obtained by curing at room temperature. This invention relates to neutron shielding materials for producing casks for processed high-level radioactive waste and new fuel protonium.

[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 decomposition of aluminum hydroxide is far from being achieved at high temperatures, making it difficult to decompose aluminum hydroxide.
The service life of 20 years is unbearable.

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.

By the way, the above-mentioned cask is required to have heat resistance and fire resistance, that is, long-term stability at 150 to 200°C and fire resistance at 800°C for 30 minutes.

Neutron shielding materials containing aluminum hydroxide are able to achieve almost satisfactory fire resistance at 800°C, which is required in anticipation of instantaneous high temperatures, i.e., fire; however, as mentioned above,
Long-term stability cannot be achieved. Furthermore, since this shielding material does not contain a slow neutron absorber, its shielding effect is poor.

Furthermore, the current situation is that neutron shielding materials containing boron carbide cannot provide satisfactory fire resistance.

Therefore, an object of the present invention is to provide a neutron shielding material that is stable for a long period of time at temperatures up to about 200°C and exhibits little deterioration even at instantaneous temperatures of up to about 800°C.

[Means for solving the problem] As a result of various studies, the present inventors used magnesium hydroxide powder instead of aluminum hydroxide powder, and further added B4C powder to shield slow neutrons. The inventors have discovered that the above-mentioned problems can be solved by using the present invention, and have completed the present invention.

That is, the present invention is based on the general formula (A) [wherein R is a monovalent hydrocarbon group containing no aliphatic unsaturated bond, R' is a monovalent hydrocarbon group, and n is a compound having a viscosity of (A) of 25
100 parts by weight of a polyorcasiloxane whose both ends are capped with a vinyl group represented by (B) 2(R″)2s; o units, or not included,(
R''), 5iOo, s units and 5i02 units (in the formula, R''
represents a group selected from a monovalent hydrocarbon group containing no aliphatic unsaturation and a vinyl group), and consists of 2 silicon atoms.
, 5 to 10 mol% of the polyorganosiloxane copolymer has a vinyl group directly bonded to the silicon atom, and the ratio of (R''>38 iOo-s units:5i02 units is 0.4:1 to 1:1) 0 to 100 parts by weight, (C) general formula [wherein R has the same meaning as R in (A), In
is a number of 2 or more, a has a value of 1.0 to 2.0,
b has a value of 0.1 to 1.0, and (a+b) is 1.9 to
3.0 and has an average of more than 2 hydrogens directly bonded to silicon atoms per molecule], and <1 vinyl group of the polyorganosiloxanes of A) and (B) is Polyorganohydrogensiloxane in an amount sufficient to provide 0.5 to 5.0 directly bonded hydrogen atoms, (D): [(A)+(B)+(C)] 10
5 to 100 parts by weight of magnesium hydroxide powder to 0 parts by weight, 0.1 to 50 parts by weight of B4C powder to 100 parts by weight of (E): [(A>+(B)10(C)), F): An effective amount of a platinum catalyst.Relating to a neutron shielding material obtained by curing a polyorganosiloxane composition.

[Function] The composition of the present invention has (A) and/or (B) and (C)-
Since curing will not occur unless 7= and (F) coexist, either of them may be stored in separate packaging and mixed immediately before use. 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 all of (C) and (A) and (B). part, third
The package consists of the entire amount of (F) and the balance of (A) and (B), and the three packages can be mixed and cured at the time of 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, 1-helyl and xylyl groups),
Examples include cycloalkyl groups (e.g. cyclohexyl and cycloheptyl groups), aralkyl groups (e.g. pencil, β-phenylethyl 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, and in particular preferred 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 1oo to 5.
0,0OOc,SL, preferably 500-8,00
This is a range of 0 cSt. The viscosity of component (A) is 100
If it is less than cSt, sufficient physical properties cannot be obtained, and 50,00
If it exceeds 0 cSt, it becomes difficult to handle in an uncured state, which is not preferable.

The polyorcassilokine 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 carbonized component that does not contain aliphatic unsaturated particles. R” which can be hydrogen or a vinyl group
may be defined as a polyorcasiloxane copolymer containing R'' groups in which at least the aforementioned proportion of the R'' groups are vinyl groups. Similar groups, in its preferred 1A embodiment, all of the monovalent hydrocarbon groups that do not contain aliphatic unsaturation are methyl groups. The vinyl group is (R”)s S
i as part of the Oo-s group or (R″)2Si
It can be present as part of the O group or both.

Various siloxane units in the copolymer component (B) are (R″
>3SiOo, the ratio of s units:5i02 units is 0.4. +
Choose a ratio of 1 to 1:1. (R″)3S io
If the ratio of o, s units: S i 02 units is less than 0.4:1, the stability of component (B) will be poor and it will be difficult to synthesize it in a well-controlled manner; if it exceeds 1:1, the cured product will deteriorate. It is undesirable because it cannot provide good mechanical strength.

The (R'')2SiO units are present in an amount equal to 0 to 10 mol%, based on the total number of siloxane units in the copolymer. Silicon-bonded vinyl groups are located in the copolymer. Regardless of location, 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% by weight solution. To facilitate handling of the composition, 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. Component (A) and copolymer component (B)
You may 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 by weight, preferably 10 to 80 parts by weight.

If mechanical strength is required for the neutron shielding material, the component (B
), sufficient strength will not be obtained without a reinforcing filler, and if a reinforcing filler is used in combination, the filling of magnesium hydroxide powder and B4C powder required for neutron shielding as intended by the present invention will be reduced. or undesirable to become impossible. Moreover, when the amount of component (B) exceeds 100 parts by weight,
The uncured composition has a high viscosity and is difficult to handle.

The polyorganohydrogensiloxane of component (C) in the present invention reacts with components (A) and (B) to form a network 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-
It may be a polymer consisting only of siloxane units having hydrogen bonds, or a copolymer of this with one or more of triorganosiloxy units, diorganosiloxy units, monoorganosiloxy units, and S i 02 units. R
The same as R in component (A) is exemplified, and one type or two or more types may be used in combination, but it is easy to synthesize, has a relatively low viscosity, and has good physical properties after curing. Methyl group and phenyl group are preferable, and methyl group is particularly preferable. - In order to have more than 2 silicon-bonded hydrogen atoms on average in a molecule, from the viewpoint of ease of synthesis, 0 must be 2 or more, preferably 4
~1, , OOO. When (2) is less than 4, the volatility is high, and when it exceeds 1.000, synthesis and handling become difficult. It is difficult to synthesize those with a of less than 1.0 and those with l) of more than 1.0. When a exceeds 2.0, component (C) has the necessary silicon-bonded hydrogen atoms and the desired "
0 cannot be taken, and if b is less than 0.1, the number of n becomes large to provide the desired silicon-bonded hydrogen atom.
Component (C) becomes difficult to handle. The sum of a ten is 1.
Those less than 9 are difficult to synthesize with good control;
．． If it exceeds 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 the mechanical properties may not deteriorate, which is not preferable.

Component (D) used in the present invention is magnesium hydroxide powder. The average particle size of magnesium hydroxide is usually 50 μm or less. This is because magnesium hydroxide powder with a particle size exceeding 50 μm is not currently available. This magnesium hydroxide powder is used to impart fire resistance to neutron shielding materials.

Furthermore, magnesium hydroxide exhibits superior long-term stability to aluminum hydroxide, and has the same effect of moderating fast neutrons on slow neutrons as the polyorganosiloxane used in the present invention.

The amount of component (D) is the component [(A)+(B)+(C
) 5 to 100 parts by weight per 100 parts by weight of the total amount of
Preferably it is in the range of 40 to 80 parts by weight. If it is less than 5 parts by weight, sufficient fire resistance cannot be obtained, and if it exceeds 100 parts by weight, it becomes difficult to knead with the components [(A) + (B) + (C)], which makes it difficult to inject on-site. This is not preferable because it makes it impossible to work and also reduces the strength of the cured composition.

Component (E) used in the present invention is B4C powder.

This B4C acts to shield slow neutrons, that is, thermal neutrons.

The amount of component (E) is the component [(A)+(B)+(C
)] is in the range of 0.1 to 50 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight. 1.0
If it is less than part by weight, sufficient low-speed neutron shielding effect cannot be obtained;
In addition, if it exceeds 100 parts by weight, the component [(A)
(C)] becomes difficult, which makes on-site injection work impossible and reduces the strength of the cured composition, which is undesirable.

The blending ratio of component (D), that is, magnesium hydroxide powder, and component (E), that is, B4C powder is determined based on the neutron shielding material's slow neutron moderation properties of fast neutrons, flame retardance, and absorption of slow neutrons, that is, thermal neutrons. It should be understood that variations may occur depending on factors such as cost and cost.

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 component (F) include platinum black, platinum-olefin complexes, platinum-vinylsiloxane complexes, platinum-phosphine complexes, and platinum-phosphite complexes. Regardless of the type of platinum catalyst used, the catalyst is 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 commercially available acid.

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

Tuna-L 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% 81 parts 2 units, 37.2 mol% Me3S
35 parts of a copolymer consisting of io O-5 units and 2.8 mol % McViSiO units were mixed to obtain a vinyl group-containing polyorcasiloxane mixture. This mixture was charged into a closed kneader, and 60 parts of magnesium hydroxide powder having an average particle size of 1 μm and 4 parts of B4C powder were charged and mixed under closed conditions until uniform.

To this, Ne, SiO[Me2SiO]6[MellSi
O] 6.5ide, 5 parts and platinum-te1-lamethylte-Lapinylcyclote-I-comb 1 50/1,000,000 parts of Kokizan precious wood were added and mixed to obtain the composition of the present invention. Na. This composition was defoamed to a thickness of 1.30
Pour into mm mold! 1"shi, '3 (1"(,:te24
By standing for a period of time, a comb-shaped cured product (neutron shielding material) according to the present invention was obtained.

The properties of the obtained cured product are described in 1) and 1ζ below at 20°C and 20'C: When 10c+n) was heated at 800°C for 30 minutes, the temperature was 1.5cm from the heating direction. ．． However, no deterioration layer (carbonization) was formed, and the cured product had good flame retardancy. When the hydrogen content of this test piece was measured with the hydrogen content before heating being 100, the results shown in FIG. 1 were obtained. From Figure 1, it can be seen that the test piece with a thickness of 10 CI 11 was about 4 cm before heating.
A decrease in hydrogen was observed up to m, but no decrease in hydrogen was observed in the remainder.

In addition, the same polyorcasiloxane as above except that magnesium hydroxide and B < C was not added.
When a heating test for 30 minutes at 0° C. was conducted in the same manner as described above, the thickness of the deteriorated layer (carbonized layer) was 3CI11, which was approximately twice the thickness of the test piece of the neutron shielding material of the present invention.

Next, the obtained cured body is subjected to medium-fast neutrons, thermal neutrons and γ
Describe the results of irradiation with radiation consisting of a line.

1 1.5X10153.2X10151.7X10
″10 1.5X10'ε 3.2X10161.
7X10'20 3.0X10ISe, 4xto+b
3.3X10' There was no change in the appearance of the cured product under any of the above conditions, and there was no decrease in mass.

Next, the neutron shielding properties of the cured product obtained as described above were tested using a neutron shielding test apparatus equipped with a neutron source, and the cured product showed good neutron shielding properties.

Example - 1-L 55 parts of polyorganosiloxane having a viscosity of 4,500 cSt at 25°C and having both ends blocked with vinyl fibers and consisting of 6 mol% diphenylsiloxane units and the remainder dimethylsiloxane units, and 52.5 mols. % of 5i02 units, 44.5 mol% of Me+SiO units, and 35.0 mol% of McViSiOjF- units. 90 parts of a 50% toluene solution of a co-wheel body were mixed and the pressure was gradually reduced. 1. Toluene was distilled off by heating to 30° C. with 1-1 g of OOmm to obtain a vinyl group-containing polyorcasiloxane mixture. This mixture was charged into a closed kneader, and magnesium hydroxide powder with an average particle size of 1 μm was
0 parts and 10 parts of B4C powder were charged and mixed in a closed state until uniform.

To this Me2SiO fuels iO' 3 7
, 5 parts and 30/1 million parts of the same platinum catalyst used in Example 1 in terms of platinum atoms to obtain the composition of the present invention. This composition was defoamed, cast into the same mold as in Example 1, and left at 50° C. for 6 hours to form a rubber-like cured product.

This cured product was subjected to the same heating test and neutron shielding test as in Example 1, and the same good results as in Example 1 were obtained.

"Effects of the Invention" Magnesium hydroxide powder used in the neutron shielding material of the present invention has higher temperature resistance than aluminum hydroxide powder, that is, it is stable even at temperatures of about 200°C and instantaneous temperatures of about 800°C. , problems such as decomposition of aluminum hydroxide can be solved. Also, magnesium hydroxide\ and 13. By using C in combination, it is possible to obtain a good slowing effect of fast neutrons on slow neutrons and a good effect of shielding slow neutrons.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the results of measuring the hydrogen percentage of a cured test piece with the hydrogen content before heating being 100.

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″), SiO_0_._5 units and SiO_2 units (
In the formula, R'' represents a group selected from a monovalent hydrocarbon group containing no aliphatic unsaturated bond and a vinyl group), and 2.5 to 10 mol% of the silicon atoms are vinyl groups directly bonded to the silicon atom. group, (R″)_3SiO_0_. 0 to 100 parts by weight of a polyorganosiloxane copolymer in which the ratio of _5 units: SiO_2 units is 0.4:1 to 1:1, (C): General formula {(R)_a(H)_bSiO_[_4_-_ (_a_
+_b_)_]_/_2}_m [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, b has a value of 0.1 to 1.0, (a + b) is 1.9 to 3.0, and one molecule has an average of more than two hydrogens directly bonded to silicon atoms] polyorganohydrogensiloxane in an amount sufficient to provide 0.5 to 5.0 hydrogen atoms directly bonded to a silicon atom for each vinyl group of the polyorganosiloxanes (A) and (B), (D): 5 to 100 parts by weight of magnesium hydroxide powder per 100 parts by weight of [(A)+(B)+(C)], (E):
For 100 parts by weight of [(A)+(B)+(C)], B_
A neutron shielding material obtained by curing a polyorganosiloxane composition comprising: 0.1 to 50 parts by weight of 4C powder; and (F): an effective amount of a platinum 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 amount of magnesium hydroxide powder is [(A)+(B)+(
C)] 40 to 80 parts by weight per 100 parts by weight of the neutron shielding material according to claim 1. 9. The neutron shielding material according to claim 1, wherein the magnesium hydroxide powder has a particle size of 50 μm or less. 10.The amount of B_4C powder is [(A)+(B)+(C)]1
The neutron shielding material according to claim 1, wherein the amount is 0.5 to 10 parts by weight per 00 parts by weight.