JPS5933874B2 - Neutron shielding material - Google Patents

Description

[Detailed description of the invention] The present invention relates to a neutron shielding material.

The areas where radiation emitted from radioactive materials are shielded include nuclear reactors and other facilities that handle radioactive materials, as well as containment vessels and transportation containers for radioactive materials. Large materials, such as water, hydrocarbons with relatively high hydrogen atom densities such as polyethylene, polybutene, and paraffins, have been used alone or in combination with inorganic compounds such as boron or lithium compounds.

However, among these conventional materials, there are extremely few that have both workability, durability, and self-extinguishing properties by combustion in the event of a fire.

For example, water is a cheap and relatively good neutron shielding material, but since it is a liquid at room temperature and pressure, it requires an enclosed container to be used as a shielding material in a certain place, making it difficult to use in complex structures. Not only that, but the pressure also increases as the temperature rises, making it impossible to use open threads.

Thermoplastic resins such as carbon fiber, polyethylene, polypropylene, and polybutene, and hydrocarbons such as paraffin generally have a high hydrogen atom density, but have the disadvantage that they soften and flow when heated.

Furthermore, instead of thermoplastic resins, it is possible to use thermosetting resins that do not soften even when heated, but since the hydrogen atom density of these resins is lower than that of thermoplastic resins, they are not suitable alone as neutron shielding materials. However, even if the thermosetting resin is encapsulated with water, the book evaporates over time in the atmosphere.
The disadvantage is that it can only be used in specific locations.

In addition, the above-mentioned hydrocarbons and trees themselves are flammable and do not have so-called self-extinguishing properties, which poses a safety problem in the event of a fire.

Therefore, the object of the present invention is to improve the shortcomings of these conventional neutron shielding materials, and to provide a neutron shielding material that has excellent heat resistance, flame resistance, and versatility.

Another object of the present invention is to provide a neutron shielding material that is easy to mold, has excellent workability, and has good neutron shielding ability.

The present invention aims to achieve the above object, and the neutron shielding material of the present invention has an unsaturated polyester resin of 20 to
60% by weight, 10 to 40% by weight of polyethylene powder, and 15 to 55% by weight of aluminum hydroxide.

Further, a curing catalyst is appropriately added during curing.

The thermosetting resin used in the implementation of the present invention is the main raw material of the shielding material of the present invention, and may be any one known per se, such as unsaturated polyester resin, phenol resin, epoxy resin, urethanized vinyl ester resin, etc. It is desirable to have a hydrogen atom density as high as possible and excellent heat resistance, and unsaturated polyester resin is one of the most preferred thermosetting resins in the present invention.

Further, polyethylene powder is one of the resins with the highest hydrogen atom density, along with polypropylene, and is blended in order to increase the hydrogen atom density of the shielding material and increase the neutron shielding effect.

The polyethylene powder may be manufactured by any of the high-pressure method, medium-pressure method, and low-pressure method.

Moreover, those having a molecular weight of 1,000 to 60,000 are used, and those having a particle size of 80 mesh or less are preferably used.

Furthermore, the present invention uses aluminum hydroxide.

This aluminum hydroxide Al(OH)3 imparts flame retardancy to the shielding material without producing toxic gas, and promotes self-extinguishing ability.

For each of these substances used in the present invention, as specifically shown in the examples, in order to achieve the objectives of the present invention such as heat resistance while maintaining performance as a neutron shielding material,
There is an optimal blending ratio that balances each individual.

That is, in the present invention, unsaturated polyester resin 20
It is used in a range of 60% by weight.

This is because it is the main material for exhibiting the function of the heat-resistant shielding material of the present invention, and when it is less than 20% by weight, it tends to cause a decrease in the function of the heat-resistant shielding material.

Moreover, when it is 60% by weight or more, the hydrogen atom density is small and the neutron shielding ability is reduced.

Further, polyethylene powder is used in a range of 10 to 40% by weight.

This is because if it is less than 10% by weight, the hydrogen atom density will be low and the neutron shielding ability will be poor, and if it is too much, problems will occur in terms of heat resistance.

Moreover, if it exceeds 40% by weight, uniform mixing with the unsaturated polyester resin becomes impossible, and the shielding effect becomes uneven, which is not preferable.

Further, ichalium hydroxide is used in a range of 15 to 55% by weight.

If the aluminum hydroxide content is less than 115% by weight, the self-extinguishing property of the shielding material will be poor, and if it is more than 55% by weight, the neutron shielding ability will decrease and it will become too heavy, causing problems in terms of workability and handling. remains.

The neutron shielding material of the present invention consists of unsaturated polyester resin (liquid), polyethylene powder and aluminum hydroxide (
(in powder form) to form a mixture, and this mixture is thoroughly stirred and molded and hardened.

In this case, a curing catalyst is preferably added to the mixture, and the amount of the curing catalyst added is preferably about 0.5 to 5.0% by weight based on 100 parts of thermosetting resin.

The curing catalyst and curing conditions can be appropriately selected depending on the type of thermosetting resin, and known catalysts and curing conditions may be used.

In addition, as a molding method, various molding methods used for general thermosetting resins can be used, and in the case of the casting method, shielding materials of various shapes can be molded by changing the mold. be.

Furthermore, when construction on a complex structure is required, it is preferable to inject directly into the shield part.

Therefore, curing in the present invention may be carried out by pouring the mixture into a mold or by directly injecting it and curing it.

The neutron shielding material of the present invention is characterized by the use of specific components in specific amounts as described above, and has the following effects.

(1) The hydrogen atom density in the resin constituting the shielding material is high, that is, it is not much different from that of polyethylene or water, and has good neutron shielding ability.

This is because neutrons lose their energy due to scattering with hydrogen, and the hydrogen atom density of the shielding material of the present invention is at least s, 5 x 1022 atms/i.

(2) It has excellent heat resistance, with a normal heat resistance temperature of at least 150°C, which is higher than about 80°C or less for polyethylene and polypropylene, and higher than the room temperature of water and paraffin in an open system.

(3) It is heat resistant, that is, it has excellent self-extinguishing properties, so it does not spread like polyethylene, polypropylene, paraffin, and their geothermally curable resins, and does not emit toxic gas, so it can be used in the event of a fire. The level of safety is even higher.

(4) It is easy to mold and machine the molded resin, and can be applied to complex structures, so it has excellent workability, and is also versatile and durable.

Example 1 Unsaturated polyester resin Nister GA l 47 (manufactured by Mitsui Toatsu Chemical Co., Ltd.) 44.5% by weight, polyethylene powder (molecular weight average 20,000, particle size average 32μ22.2)
% by weight and 33.3% by weight of aluminum hydroxide (Hijirai 1-H-30, manufactured by Showa Denko Co., Ltd.), and 1.0% by weight of Niver B (benzoyl peroxide, manufactured by NOF Corporation) based on the resin. The mixture was added, stirred, and molded and cured.

The performance of the obtained resin was as shown in Table 1.

For comparison, Table 1 also shows the performance when polyethylene, water and unsaturated polyester resin (Nister GA147) were used individually.

These results show that the hydrogen atom density of the shielding material of the present invention is comparable to that of polyethylene or water, and that it has excellent heat resistance and self-extinguishing properties.

Example 2 50% by weight of unsaturated polyester resin Nystar D172 (manufactured by Mitsui Toatsu Chemical Co., Ltd.), different proportions of polyethylene powder (molecular weight average 20,000) and aluminum hydroxide (same as Example 1) were molded. After curing, the hydrogen atom density, which is involved in neutron shielding performance, was investigated and the results shown in Figure 1 were obtained.

As a catalyst, the same benzoyl peroxide as in Example 1 (!) was used in an amount of 1.5% by weight based on the resin.

Example 3 Unsaturated polyester resin Nister R280 (manufactured by Mitsui Toatsu Chemical Co., Ltd.): polyethylene powder (molecular weight average 20,
000) = 2:1 mixture in various proportions with aluminum hydroxide (same as in Example 1) and carried out in the same manner as in Example 2 to make molding resins, and ASTM D635-6
When a heat resistance test was conducted according to 8T, the results shown in Table 2 were obtained.

Moreover, when the results of the shielding material of the present invention are plotted in the second layer, the results are as shown in FIG.

As understood from Figure 1 above, increasing the proportion of aluminum hydroxide decreases the hydroxyl atom density of the resin.
Although the performance as a neutron shielding material decreases, as shown in FIG. 2, the self-extinguishing time is shortened and the flame resistance is increased depending on the amount of aluminum hydroxide added.

Therefore, in order to obtain a shielding material intended by the present invention, such as heat resistance, while maintaining a high level of performance as a neutron shielding material, a balanced ratio of each of the above-mentioned components is required.

Example 4 Urethane vinyl ester resin diluted with styrene (Nister H7000 manufactured by Mitsui Toatsu Chemical Co., Ltd.) 35% by weight, polyethylene powder (average molecular weight 30.000, average particle size 30μ)
) to a mixture consisting of 35% by weight of aluminum hydroxide (same as in Example 1) and 30% by weight of aluminum hydroxide (same as in Example 1), after adding 1.0% by weight of a curing agent (Percure, manufactured by NOF Corporation) to the above mixture, stirring; Molded and hardened.

The performance of the obtained molded hardened phase is shown in Table 3.

For comparison, the third coating also includes the performance when molded and cured using the above urethanized vinyl ester resin alone.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between hydrogen atom density and specific gravity with respect to the ratio of polyethylene powder and aluminum hydroxide.
The figure shows the relationship between the proportion of aluminum hydroxide and the autolysis time.

Claims (1)

[Claims] 1. A neutron shielding material obtained by curing a mixture containing 20 to 60% by weight of unsaturated polyester resin, 10 to 40% by weight of polyethylene powder, and 15 to 55% by weight of aluminum hydroxide.