JPH0385498A - Neutron shielding material - Google Patents

Abstract

PURPOSE:To enable filling and plastering a neutron shielding material to a complicatedly shaped object to be shielded, by obtaining a plastic shielding material of high neutron shielding ability, which is a kneaded body with 100 parts weight of a polyisobutylene and 1 to 50 parts by weight of an inorganic boronic compound. CONSTITUTION:100 parts by weight of a polyisobutylene of which an gaverage molecular weight as a clay is around 24,000 to 80,000, for instance, and of which density is more than 0.920g/ml, and 1 to 50 parts by weight of an inorganic boronic compound powder are heated up to around 70 to 150 deg.C and kneaded together. In this occasion, the kneading work is preferably performed in a depressurized atmosphere of lower than 200mgHg, for uniform density and constitution are hard to be kept by kneading work under an ambient pressure. A neutron shielding material obtained by this way, has high neutron shielding ability and plasticity under room temperature, easily fluidizes when heated, can be easily filled or plastered to a complicatedly shaped object to be shielded, and has very good processability. Moreover, the material does not easily flow out of its receptacle even when the receptable opens, is comparatively safe against a fire and can be very freely mixed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a neutron shielding material. Specifically, the present invention relates to a neutron shielding material that has excellent neutron shielding properties, is plastic at room temperature, easily fluidizes when heated, and can be easily applied to shielded objects having complex shapes.

(Prior Art) Radiation shielding is an important issue in nuclear facilities and in the handling of radioactive materials in order to protect the human body and reduce radiation that may interfere with measurements. The radiation that poses a particular problem of shielding are gamma rays and neutrons, which have large penetrating power.

For the former, elements with large atomic numbers such as lead are effective, and the shielding measures are different between the two, and the present invention is aimed at shielding the latter.

Since hydrogen atoms have a large shielding effect against fast neutrons, hydrocarbon compounds containing relatively large amounts of water and hydrogen are known as shielding materials. It is also known that boron atoms are excellent against slow or thermal neutrons, and for this reason, polyethylene with a high hydrogen atom density and other plastics have traditionally been used as neutron shielding materials by mixing or mixing boron or boron compounds. Used in combination.

For example, JP-A-58-133349 discloses a composition in which polyethylene is blended with an inorganic boron compound and a zinc sulfide phosphor to provide radiation sensing performance. This composition contains an inorganic boron compound in high-density polyethylene, and has excellent neutron blocking properties.
Polyethylene itself is solid at room temperature and has an extremely high viscosity when melted, so although it can be used in plate or block form, it has the disadvantage that it is difficult to fill it into places with complex shapes. have Japanese Patent Publication No. 56-131849
The publication discloses blending chlorinated polyethylene with an inorganic boron compound, but this also has similar drawbacks. JP-A-58-28298 discloses blending liquid paraffin with boron and/or an inorganic boron compound. This has the feature that it can be easily applied even to objects with complicated shapes, which is the object of the present invention. However, since liquid paraffin is a relatively low-molecular paraffin with a carbon number of 10 to 50, there is a risk of ignition when heated. Moreover, the density of liquid paraffin is generally 0.86~
0.88g/mj and polyethylene (density 0.92g/m
As shown in Table 1, the hydrogen atom density is lower than that of polyethylene, and its shielding properties against fast neutrons are accordingly inferior. Furthermore, since the viscosity of liquid paraffin is as low as 10 to 100 centipoise (c, p,) at room temperature, it is necessary to incorporate large amounts of expensive boron and/or inorganic boron compounds (120 parts or more per 100 parts of liquid paraffin). It has drawbacks such as difficulty in maintaining a constant shape when pasted. Japanese Patent Publication No. 59-42280 (Japanese Patent Publication No. 53-105700) discloses a plastic shielding material containing polyethylene, low molecular weight polyethylene, polybutene, liquid paraffin, and a radiation shielding substance such as boron. The polybutene used here has a molecular weight of 50
0 to 2,500, and the density of polybutene in this range is generally 0.86 to 0.90 g/mj, which is lower than polyethylene.As seen in Table 1, the hydrogen atom density is lower than that of polyethylene, making it difficult to flow. Like paraffin, it is disadvantageous in terms of fast neutron shielding properties. Not only that, this shielding material also contains low molecular weight liquid paraffin, which poses a fire risk.Furthermore, it requires special technology and is expensive as it requires a large number of components with significantly different viscosities. It takes. Finally, the well-known water has a high hydrogen density, poses no fire hazard, and is an excellent neutron shield, but it is too fluid and can leak if the container is punctured. be.

As explained above, polyethylene has a high hydrogen atom density and has excellent neutron blocking properties, but since it is a solid, shielding materials containing polyethylene and boron compounds cannot be used in the construction of shielding objects with complex shapes. , especially difficult to construct on-site.

In addition, polybutene and liquid paraffin have a low hydrogen atom density, which is disadvantageous in terms of shielding properties, and because they contain relatively low molecular weight hydrocarbons, there is a high risk of fire.
Moreover, since it has high fluidity, there are restrictions on the blending ratio to maintain plasticity. In addition, water has a high fluidity and there is a risk of leakage.

(Problems to be Solved by the Invention) In view of the above circumstances, the present invention has excellent neutron shielding properties, has plasticity at room temperature, is easily fluidized by heating, and can be easily applied to shielded objects with complex shapes. Provides a neutron shielding material that has excellent workability that can be filled or pasted, does not easily leak out even when a container is opened, is relatively safe against fire, and is extremely easy to formulate. The purpose is to

(Means for solving the problem) As a result of the inventors' intensive research to solve the above problem,
100 parts by weight of polyisobutylene having a viscosity average molecular weight in the range of 20.000 to go, ooo and a density of 0.920 g/mj or more and powdered inorganic boron compound 1
A composition containing ~60 parts by weight has excellent neutron shielding properties, has plasticity at room temperature, and is easily fluidized by heating.
It has workability that allows it to be easily filled or attached to shielded objects with complex shapes, and has a viscosity that prevents it from easily flowing out even when the container is opened, making it relatively safe against fire. They discovered this, established an easy method for blending the composition, and completed the present invention.

The polyisobutylene referred to herein refers to a polymerized product of inbutylene using a cationic catalyst, and the viscosity average molecular weight refers to a value measured by the Flory method. The viscosity average molecular weight is 2
0,000~so,o.

O1 likes t, <! Those in the range of tao, ooo-80,000 are preferred. If it is lower than 20,000, it has high fluidity and poor shape retention after filling or pasting, and if it is higher than go or ooo, it has poor flexibility when an inorganic boron compound is blended, and it is difficult to cover complex-shaped objects. construction becomes difficult.

Further, if the density is less than 0.920 g/mJ, the neutron shielding property is inferior to that of polyethylene.

The viscosity average molecular weight used in the present invention is 20,000 to go,
Polyisobutylene with a density of 0.920 g/m1 or more is catalyzed by a Lewis acid such as aluminum chloride, and in a liquid phase at a temperature of 0° C. or less in a hydrocarbon solvent inert to the catalyst, about 1 Obtained by time polymerization. Alternatively, easily available products such as "Tetrax 5T" or "Tetrax 6T" (trade name) (manufactured by Nippon Petrochemical Co., Ltd., each with a viscosity average molecular weight of 50.00
0. and so, ooo1 density is 0.923g/
mj) etc. can be used.

The inorganic boron compound may be any inorganic compound with a high boron content, such as boric anhydride (boron dioxide), boron carbide, boron nitride, orthoboric acid, metaboric acid, tetraboric acid,
Alternatively, boron-containing ores can be used. All inorganic boron compounds are blended in powder form. The particle size of the powder is not particularly limited, but in order to homogeneously contain it in the composition, the smaller the particle size, the more preferable it is, for example, a particle size of 3 to 200 microns is preferable. The blending amount of these components is 1 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of polyisobutylene. If the amount is less than 1 part by weight, the shielding properties against low-velocity and thermal neutrons will be poor, and if it exceeds 50 parts by weight, the flexibility will be poor and the fluidity during heating will be poor, making it difficult to apply shielding to complex-shaped objects. .

Neutron shielding properties are generally proportional to the density of hydrogen atoms or boron atoms, and are not affected by the structure of the compound. Hydrogen atoms have excellent shielding properties against fast and medium-speed neutrons, and the latter boron atoms play the role of absorbing slow and thermal neutrons slowed by hydrogen, so it is necessary to use them in combination, but the neutron shielding properties of the mixture are In order to increase this, it is preferable to increase the atomic density of each constituent component as much as possible. The constituent components of the present invention have a viscosity average molecular weight of 20.000 to so, ooo, and a density of 0.
As shown in Table 1, polyisobutylene of 920 g/ml or more has a hydrogen atom density of 7.9 x 1022 pieces/c.
As high as m3, 7.9 x 1022 pieces/cm' for regular polyethylene and 8.2 x 10'' pieces/cm for high density polyethylene.
It has a hydrogen atom density almost equal to m3, and therefore has excellent neutron shielding properties as well as polyethylene. Furthermore, while polyethylene is solid, it is semi-solid at room temperature and has the characteristic of being fluidized by heating.

On the other hand, the hydrogen atom density of liquid paraffin and polybutene, which also have fluidity, is 7.4 to 7.8X1, respectively.
0" pieces/cm3% 7.4~7.7X1022 pieces/cm'
neutron shielding properties are disadvantageous. Moreover, since these have too high fluidity, it is necessary to mix a large amount of boron and/or an inorganic boron compound in order to maintain the shape, in excess of that required for the purpose of shielding.

(Left below) As described above, the neutron shielding material according to the present invention has a hydrogen atom density equivalent to that of a known neutron shielding material containing polyethylene, and on the other hand, it has plasticity at room temperature and has a certain degree of flexibility necessary to maintain its shape. It has high hardness and flexibility, easily becomes fluidized by heating, and can be easily filled or attached to objects with complex shapes.

The construction performance for complex-shaped objects, which is one of the features of the present invention, is not a problem that can be solved only by adjusting the flexibility as described above. For example, paraffin wax is solid at room temperature, but when heated during construction, it easily melts and becomes fluid, so it can be filled into any complex shape and can easily return to its original shape after cooling. It appears that the purpose of the present invention can be achieved in terms of workability such as maintenance. However, paraffin wax contracts unevenly when it cools and solidifies, so if it is poured into a cylindrical can, for example, it solidifies from the periphery, creating a cavity in the middle, which tends to cause uneven neutron shielding properties, which is the object of the present invention. It is unsuitable as a component of neutron shielding materials.

In addition, the viscosity average molecular weight blended in the present invention is from 20.000 to
polyisobutylene with a flash point of 240 to 250°C (J I
S- to -225COO method) and has a much lower molecular weight than liquid paraffin (molecular weight 140-700) and bobten (molecular weight 500-2.5001 flash point 1130-23
It is safer from the risk of fire compared to the known tron shielding materials that contain 0°C).

Next, a method for manufacturing the neutron shielding material of the present invention will be explained. That is, the viscosity average molecular weight is 24.000 to so, o
oo, and 100 parts by weight of polyisobutylene having a density of 0.920 g/mj or more and powdered inorganic boron compound 1-
To mix 50 parts by weight, both are heated to 70-150 DEG C. in a kneader such as a Brabender and kneaded until uniform. At this time, it is preferable to perform the kneading under reduced pressure of 200 mmHg or less. If it is carried out under normal pressure, air will be mixed in, making it impossible to maintain a uniform composition.

As described above, the neutron shielding material of the present invention has excellent neutron shielding properties, has plasticity at room temperature, easily becomes fluidized by heating, and can be easily filled or attached to shielded objects C with complicated shapes. It has excellent workability, does not easily leak out even when a container is opened, is relatively safe against fire, and is extremely easy to mix.

Next, the present invention will be explained in more detail with reference to Examples.

[Example] 100 g of polyisobutylene with a viscosity average molecular weight of 50,000 ("Tetrax 5T", density 0.923 g/Cm3, manufactured by Nippon Petroleum Chemical Co., Ltd.), anhydrous ferlic acid (manufactured by Wako Pure Chemical Industries, Ltd.) ,
27 g of the mixture (particle size: 100 tons) was put into a kneader (planetary mixer manufactured by Bengami Seisakusho), heated to 120°C, then reduced to 100 mmHg, and kneaded for 1 hour to obtain a neutron shielding material. The density of this material was 1.03 g/cm3, and the neutron removal cross section ΣR, which is a measure of hydrogen atom density and neutron shielding property, was determined as shown in Table 2.

The amount of neutron attenuation can be calculated based on this value using the following formula.

I=Ioe-ΣRX Here, ■ indicates the intensity after a fast neutron incident with intensity I0 passes through a shielding material of thickness X.

In addition, in order to evaluate the ease of construction of this product on objects with complex shapes, we measured the viscosity at 100°C ('Pf1, the softness and shape retention at the temperature of hot fluid pouring, and the third evaluation method). It is clear from these tables that the obtained neutron shielding material has a large neutron removal cross section, and also has the practical physical properties aimed at by the present invention, such as heating fluidity, softness at room temperature, Shape retention is also moderate.

(Evaluation method) The viscosity here is 10 according to J Is-2283.
This is the kinematic viscosity at 0°C. Softness is JIS-220
The penetration rate is 7 (100 g, 5 seconds). Shape retention is achieved by shaping the neutron shielding material into a 1cm square cube at room temperature.
The degree of shape retention was evaluated on the following three levels.

A: Good consistency as putty. It is easy to form into a cube, and the shape is maintained extremely stably.

B: It has a consistency as a putty, and has moldability and stability into a cube.

C The fluidity is too high and the shape cannot be maintained.

The procedure of Example 1 was repeated except that 70 g of anhydrous fluoric acid was used. The results are shown in Tables 2 and 3.
It has a high viscosity and lacks heat fluidity, making it difficult to fill objects with complicated shapes.

- 100 g of polyisobutylene with viscosity average molecular weights eo and ooo ("Tetrax 6T" (density 0.923 g/cmr1, manufactured by Nippon Petrochemical Co., Ltd.), 100 g of halogen anhydride (manufactured by Wako Pure Chemical Industries, Ltd., granules) The operation of Example 1 was repeated using 10 g of 1,004 chrome (diameter: 1,004 km), and the results are shown in Tables 2 and 3.Similar to Example 1, the neutron removal cross section was large, and the heating fluidity, which is a practical physical property, was The softness and shape retention at room temperature are also moderate.

Fruit 1 100 g of polyisobutylene with a viscosity average molecular weight of 30,000 ("Tetrax 3T" (density 0.923 g/cm3, manufactured by Nippon Petrochemical Co., Ltd.), oxalic anhydride (manufactured by Wako Pure Chemical Industries, Ltd., The operation of Example 1 was repeated using 27 g of particles with a particle size of too microns, and the results are shown in Tables 2 and 3.Similar to Example 1, the neutron removal cross section is large and the heating fluidity has practical physical properties. The properties of softness, softness at room temperature, and shape retention are also moderate.

The procedure of Example 3 was repeated except that 150 g of anhydrous fluoric acid was used, and the results are shown in Tables 2 and 3. It had good shape retention but lacked heat flowability.

- Polybutene with a number average molecular weight of 3,600 (Shiraishi Polybutene Hv-30001 density 0.910 g/cm3, Nippon Petrochemical Co., Ltd.! 11) 100 g 1 anhydrous oxalic acid (manufactured by Wako Pure Chemical Industries, particle size 100 The operation of Example 1 was repeated using 10 g of micron) and the results are shown in Tables 2 and 3. The softness was too high and the shape could not be maintained.

Comparative Example 3 was repeated except that 70 g of anhydrous fluoric acid having a specific gravity of 1''2 was used, and the results are shown in Tables 2 and 3. Similar to Comparative Example 3, the softness was too high and the shape could not be maintained.

Money Exchange U- A composition obtained by kneading 100 g of paraffin wax and 10 g of anhydrous fluoric acid (manufactured by Wako Pure Chemical Industries, Ltd., particle size too microns) according to the procedure of Example 1 was directly mixed while hot.
A 3 cm deep iron container was filled to the brim, left to cool, and the surface was observed. It froze with a hole in the middle.

(Effects of the Invention) As described above in detail with reference to examples, the present invention provides shielded objects that have excellent neutron shielding properties, have plasticity at room temperature, easily become fluid when heated, and have complex shapes. Neutrons have excellent workability and can be easily filled or pasted into containers, do not easily leak out when the container is opened, are relatively safe from fire, and are extremely easy to mix. It is now possible to provide shielding materials.

(Margin below)

Claims (1)

[Claims] 100 parts by weight of polyisobutylene having a viscosity average molecular weight in the range of 20,000 to 80,000 and a density of 0.920 g/ml or more and powdered inorganic boron compound 1
~50 parts by weight of a neutron shielding material.