JPS61213695A - 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) This invention relates to a neutron shielding material with excellent flame retardancy.

(Prior art) Polyethylene, paraffin, etc. with high hydrogen content have been widely used as neutron shielding materials used in nuclear reactors, etc., but these have low melting points (polyethylene = 50
-100°C, paraffin: 45-60°C), so it cannot be used in a high-temperature atmosphere. They are also flammable and therefore pose a fire hazard. aAs a shielding material that can be used in a humid atmosphere, JP-A-57-173795 discloses a neutron shielding material made from monoolefin copolymer rubber, but the material disclosed here is based on boron compounds (or The amount of lithium compound) added is 250 to 450 weight Ma based on the ioomi part of monoolefin copolymer rubber.
il and very many. This is effective when used in a place where thermal neutrons are dominant, but the performance becomes poor when the neutron energy is high (the spectrum is hard).

At nuclear facilities, accelerators, Cf-252, Am-B
Neutrons from neutron sources such as E and spent fuel have hard energy spectra, and it has been desired to develop a shielding material that is effective as a shielding material against such materials and has excellent heat resistance.

(Purpose of the Invention) This invention was made to solve such conventional problems, and provides a shielding material that has excellent heat resistance and has an excellent shielding effect against neutrons with a hard energy spectrum. It is.

(Structure of the Invention) This invention uses chlorosulfonated polyethylene as a material, and blends 1 to 50% by weight of a boron compound therein. This allows the chlorosulfonated polyethylene to exhibit its own flame retardant properties, while supplementing its thermal neutron absorption ability with the boron compound.

(Example) Chlorosulfonated polyethylene is a crystalline polymer that has been given elasticity by introducing 802 and CQ2, and because it does not contain unsaturated bonds in the molecule, it is resistant to ozone, oxygen, heat, and oxidizing chemicals. It has very good resistance against It has excellent flame retardancy because it contains chlorine in its molecular structure.
There is also almost no chlorine elution. Also, since it is based on polyethylene, the hydrogen atom density is 5~6X102
It has a relatively high density of 2 atoms/C13.

Adding a boron compound to chlorosulfonated polyethylene having such properties can improve its ability to absorb thermal neutrons. As this boron compound,
There are boron carbide, boron nitride, boron oxide, etc., but boron carbide (2,5
1(j/cj) is preferred. This is because the addition amount is the smallest in order to give the shielding material a boron atom density of the predetermined m, and therefore the highest hydrogen atom density can be obtained. The particle size of the boron compound is preferably as small as possible in order to enable uniform dispersion in the shielding material, but a center particle size of about 50 μm is sufficiently practical.

The addition m of the boron compound may be set in accordance with the neutron energy spectrum of the location where the shielding material is used. In order to investigate the relationship between the amount of boron compounds added and their effects, a neutron source with the fission spectrum of uranium-235 was shielded with a 3Qcm thick carbon steel wall, and the neutron beam rate in that state was calculated. 1, and the neutron beam m rate was calculated in a state where the outside of this carbon steel wall was further shielded with a shielding material with a thickness of 10 cm. In addition, as the above-mentioned shielding material,
When the ratio of 84G added to the basic composition of chlorosulfonated polyethylene was varied, the results were shown in Fig. 1.
The results shown in 111 were obtained. In other words, when the amount of 84C added is within the range of 1 to 50% by weight, the dose rate is 0.01.
While it is small at 2 to 0.025, it increases rapidly when it exceeds 50% by weight. Therefore, between additions of 84G
It is necessary to set it within a range of 50% by weight.

Furthermore, a crosslinking aid, carbon black, etc. may be added to the above material in order to improve the mechanical strength and properties of the rubber. The blending amount needs to be small in order to prevent the hydrogen atom density, which is effective in shielding fast neutrons, from decreasing.
0 mff 1 part reinforcing agent (carbon black) 20
It is desirable to use about 1 part of mff, and about 0.5 to 2.0 parts by weight of other parts.

Table 1 shows the amount of boron compound added as a neutron absorber to chlorosulfonated polyethylene in parts by weight, and the ratio of the boron compound is 8.2% by weight for sample 1 and 1.2% by weight for sample 2. This corresponds to 8% by weight. Regarding these shielding materials, a neutron source with a nuclear fission magnitude of uranium-235 is shielded by a 30 cm thick carbon steel wall, and the neutron dose rate in that state is set to 1. The figure shows the results of calculating the neutron dose rate in a state where the outside of the wall of the cell is shielded with the above-mentioned shielding material having a thickness of 10CI+. In addition, in the same table, the hydrogen atom density is (X1Q2
2atog+s/cm3), the boron atom density is (
x 1020 atoms/cm3).

As is clear from the above table in Table 1, all the samples had good neutron shielding performance, and the oxygen index, which is an indicator of flame retardancy, was sufficiently high, indicating that they had excellent flame retardancy.

(Effects of the Invention) As explained above, the present invention uses chlorosulfonated polyethylene as a material and blends 1 to 50% by weight of a boron compound therein, thereby making the most of the characteristics of chlorosulfonated polyethylene. This product has improved neutron shielding performance, and due to its excellent flammability, it can be used in places where there is a risk of fire or high temperatures, where conventional plastic neutron shielding materials cannot be used. Available for use.

[Brief explanation of the drawing]

The drawing is a characteristic diagram showing the relationship between the amount of 84G added and the IIfIL rate. 1...Characteristic curve.

Claims (1)

[Claims] 1. A neutron shielding material made of chlorosulfonated polyethylene and containing 1 to 50% by weight of a boron compound.