JPS5826297A - 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 The present invention relates to a neutron shielding material comprising boron and/or an inorganic boron compound and clay powder.

In recent years, with the development of the nuclear power industry, radiation shielding in nuclear facilities has become important. The purpose of this radiation shielding is to keep the amount of radiation received by the human body below the permissible level by using a certain kind of shielding material, and also to prevent the structural materials and equipment materials of nuclear facilities from being damaged by radiation, heated by radiation, and activated. Prevent radiation exposure to measuring equipment? The goal is to keep the ground low. For example, in the case of nuclear reactor shielding, gamma rays and neutrons coexist, and secondary radiation must also be taken into account. Since r-rays and neutrons have different attenuation characteristics depending on materials, combinations of various materials are being considered as shielding materials. Currently, concrete is a commonly used shielding material that is effective against both r-rays and neutrons. Additionally, water is widely used as a neutron shielding material. Water is circulated and used to cool the reactor body of the neutron breeder reactor. Water is widely used to increase the water content in shielding concrete, thereby enhancing the shielding effect of concrete. As substances similar to water, hydrocarbon compounds with relatively few impurities and a relatively large number of hydrogen atoms (for example, paraffins, polyethylene resins) are used in the form of blocks or thick plates.

On the other hand, from the standpoint of radiation absorption, elements with a large atomic number are effective at attenuating gamma rays, and elements with a large pre-elastic scattering cross section for neutrons are suitable for attenuating fast neutrons into slow neutrons. There is. When fast neutrons become thermal neutrons or slow neutrons due to scattering, they are easily absorbed by atomic nuclei, and elements with large absorption cross sections increase the absorption effect. For these reasons, even if neutrons are absorbed, secondary gamma rays must not be emitted, or even if they are emitted, the energy must be extremely low.

As mentioned above, it is important for neutron shielding materials to contain as many elements as possible that have effective shielding performance, but when it comes to shielding design, there are issues with optimal design from the viewpoints of weight, volume, cost, etc. exist. In particular, lightweight, low-volume neutron shielding materials are needed in place of concrete, lead, water, etc., as shielding materials for ships with limited weight and volume, such as nuclear-powered ships.

In addition, in the field of nuclear medicine, such as radiography for detecting defects in materials using neutron beams or treatment of malignant tumors using thermal neutron beams, effective radiation shielding structures that suit the purpose are required. Therefore, there is a need to develop a neutron shielding material that is lightweight, has a low volume, and is easy to install.

Currently, as a neutron shielding material that meets these demands, a composite molded product of boron or an inorganic boron compound and an ethylene resin is widely used because of its shielding effect and light weight. However, it takes time to prepare materials and install, and it is limited to objects with a certain shape, so it is difficult to shield parts with complex shapes.
It is difficult to deal with sudden changes in shielding design or temporary shielding in emergencies, and there is an urgent need to develop shielding materials with excellent workability.

Based on the above, the present inventors conducted various searches in order to obtain a neutron shielding material with excellent safety and ease of construction.
The inventors have discovered that a neutron shielding material consisting of 0 to 200 parts by weight of clay powder can be easily applied even to complex-shaped objects, and have thus arrived at the present invention.

The boron used in the present invention has a density of 1,739
7 cm3 of amorphous boron (amorphous) to crystalline boron (density
There are up to 2.33 g 7 cm3), but amorphous ones are particularly preferable because they are easy to obtain in powder form. As for the purity, it is sufficient if the concentration of simple boron is around 96 to 97. In addition, as a grain powder, the average grain size of the electric sewing is 05 to 500.
A micron diameter is desirable, and a 30 to 300 micron diameter is particularly preferred.

Furthermore, among the inorganic boron compounds used in the present invention, inorganic boron compounds that do not contain metal are desirable. Representative examples of desirable inorganic boron compounds include boron carbide, boron nitride, boric anhydride, orthoboric acid, metaboric acid, and tetraboric acid. Among these inorganic boron compounds and boron, boron nitride is preferred. These inorganic boron compounds are preferably in powder form with a weight average diameter of 0.5 to 500 microns.
Particularly suitable are those having a diameter of 30 to 300 microns.

Regarding boron nitride, which is a preferred inorganic boron compound, the density is 1.88 to 2°27.9 depending on the degree of crystal development.
7α3, a weight average diameter of 0.5 to 6.0 microns, a surface area of 14 to 35rn2/9 is desirable, and especially a true density of 1.7g10n3 or more and a weight average diameter of: 0
A diameter of micron or larger is preferable. Further, it is optimal to use a material containing a large amount of 4Bto, which has a large neutron absorption cross section.

In addition, the clay powder used in the present invention generally has naturally occurring fine aluminum silicate as its main component,
Any material may be used as long as it has plasticity when water is added to the fine powder and kneaded. In particular, clays with high plasticity such as Honbushi clay and Laminar clay are desirable, but if whiteness is required, kaolin clay with high plasticity is suitable. The average particle size of this clay powder is 1 to 20 microns, particularly preferably 5 to 15 microns.

The mixing ratio of powdered clay to 100 parts by weight of boron and/or inorganic boron compound is 10 to 200 parts by weight,
Particularly desirable is 30 to 100 parts by weight. If the mixing ratio of powdered clay to 100 parts by weight of boron and/or inorganic boron compound is less than 10 parts by weight, the plasticity and bonding strength will decrease, and as the mixed material obtained by the treatment described below dries, boron and/or inorganic boron As the compound falls off significantly, the shielding effect during construction decreases.

On the other hand, if the amount is more than 200 parts by weight, in order to reduce the neutron intensity to 1/100, for example, it is necessary to coat the object to be shielded to a thickness of 10 mm or more, which increases the weight of the shielding material and makes it lightweight. Sexuality becomes poor.

To produce the neutron shielding material of the present invention, the boron and/or inorganic boron compound and a powder clay V-type blender,
This can be accomplished by substantially uniform mixing using mixers such as screw mixers and ball mills. In producing this mixture, the boron and/or inorganic boron compound and clay powder may be mixed together in a ball mill or ground, or one of them may be ground and the other mixed. Mixing and pulverization may be performed while sequentially adding the components.

The mixture thus obtained is further mixed with water, soap, or a surfactant to the extent that it has enough plasticity to be applied to other shapes by applying the kneaded mixture to the fingertips using a mixer such as a plastic bender or a kneader. By uniformly kneading the mixture while adding water, it is possible to obtain a mixture that can be applied to objects to be shielded. When producing this mixed wire, boron and/or inorganic boron compound powder and water or water containing soap or a surfactant may be sequentially added to powdered clay that has been kneaded in advance and kneaded until uniform. . By using the kneaded product obtained in this way, it is possible to easily perform shielding work on objects to be shielded that have complicated shapes by painting or filling the gaps in the shaped shielding material.

The mixed material obtained by treating the shielding material obtained by the present invention with water or water containing soap or a surfactant as described above can be used as a joint material in addition to being applied as an irregularly shaped material and used for embedding. Not only can it be used as a pouring material, but it can also be used as a pouring material by increasing the amount of water. Furthermore, it can also be used as a shaped shielding material by molding and sintering. In addition, if the above-mentioned mixed wire has dried during storage and its plasticity has decreased at the time of construction, by adding an appropriate amount of water and kneading it again, the plasticity will be restored and construction will become possible. Also,
The kneaded product not only has excellent neutron shielding power, but also has an amorphous shape, which makes it particularly useful for shielding complex-shaped objects as described above, as well as for temporary shielding against neutron leakage in emergencies.

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

Example 1 100 parts by weight of boron nitride powder (particle size 200 mesh passes, particle diameter 1 to 10 microns, secondary particle density)
, 9 fl 7 cm3) and 30 parts by weight of Kibushi clay powder (particle size 200 mesh, 5 in2 content 5
5% by weight, AI! 203 content: 35% by weight, crystal water content: 12% by weight) was mixed while being ground in a ball mill for 2 hours. The resulting mixture was kneaded for 20 minutes while sequentially adding 70 parts by weight of water using a kneader with a set of screws (diameter 15 omyn) to produce a plastic, irregularly shaped material.

In order to see the neutron shielding power of this material, the opening is 2 with 5 fins.
The mixture was applied uniformly onto a 0 m x 20 cTn wire mesh to a thickness of 5 sea breams. This sample was irradiated with thermal neutrons emitted from a trigger type nuclear reactor, and a transmission experiment was performed. The neutron intensity after transmission was 1/100, indicating good shielding ability.

Example 2 Instead of the Kibushi clay powder used in Example 1, white kaolin (particle size: 200 mesh, SiO2 content: 60% by weight, Al2O3 content: 25% by weight, crystal water content: 12% by weight)! 200 parts by weight and 10
0 parts by weight of the boron nitride used in Example 1 was placed in a vertical screw set stirrer, and 100 parts by weight of water was added.
After stirring for a period of time, a fluidized kneaded product was obtained. This kneaded material was poured into a wooden mold of 10 m x 20σ and 3 crn in depth.

After drying at room temperature, the mold was cut out and the neutron shielding ability was measured using the same method as in Example 1. The neutron intensity was 1/20.
0, indicating good shielding ability.

Patent applicant: Showa Denko Co., Ltd. Agent: Patent attorney Sei Kikuchi

Claims (1)

[Claims] 100 parts by weight of boron and/or inorganic boron compound and 1
A neutron shielding material comprising 0 to 200 parts by weight of clay powder.