EP0125889B1

EP0125889B1 - Radiation shielding putty-like composition

Info

Publication number: EP0125889B1
Application number: EP84303164A
Authority: EP
Inventors: Akimasa C/O Danichi-Nippon Cables Ltd. Sugiyama; Jinichi Dainichi-Nippon Cables Ltd. Taniguchi; Kazuyuki C/O Dainichi-Nippon Cables Ltd. Ogura
Original assignee: Mitsubishi Cable Industries Ltd
Current assignee: Mitsubishi Cable Industries Ltd
Priority date: 1983-05-12
Filing date: 1984-05-10
Publication date: 1987-11-19
Also published as: JPH0223837B2; JPS59208500A; DE3467655D1; EP0125889A1

Description

This invention relates to a radiation shielding putty-like composition.
In order to avoid radiation leakage through various openings, including openings provided for electric cables or piping through room walls or vessels walls in nuclear power stations, it has been ordinary in the art to fill fibrous lead, either per se or bagged, directly into such openings. However, this method of filling opening with fibrous lead is laborious and troublesome and moreover, openings cannot be sealed tightly because only about 50% of the space can be filled. On the other hand, US-A-3 114721 (which was concerned with powdered tungsten in a curing resin) referred to a lead powder-containing, curable resin composition as being known. Even though the application of such a composition is relatively easy the radiation shielding effect attainable therewith is still unsatisfactory since the lead powder content in said composition is limited so as to allow for curing after application. It is generally known that radiation shielding effect is proportional to the surface density which is the product of the density of a shielding material used for filling and its thickness. Moreover, said composition, after curing is difficult to remove, whereby trouble may be faced in installing additional electric cables and piping.
An object of the invention, which has been made to solve the above problems in radiation shielding, is to provide a radiation shielding putty-like composition which contains an inorganic powder, such as a high density metal or high density metal oxide powder, in a high content and which is therefore excellent in radiation shielding effect, along with easy application to a variety of openings owing to its being putty-like. This putty-like composition is excellent in its shape maintaining ability, that is, moldability and dimensional stability after mold, and also may be noncuring and then can easily be removed when necessary after application.
In US-A-3102024 there is disclosure of incorporation of a high percentage of metal powder in a greasy and apparently non-curing binder. A high density is achieved by coalescing at least some of the metal particles together by extruding the material at high pressure.
In contrast, the present composition contains additionally a fibrous component, and parameters of its ingredients and of the total composition are defined so as to give the desirable properties mentioned above, particularly that of dimensional stability. According to the invention, a radiation shielding putty-like composition comprises a dense inorganic powder in a binder, the binder having, at 25°C, a viscosity in the range of not less than 1 x10⁴ centistokes to an unworked penetration of not less than 100, there being for each 100 weight parts of binder 1,200-4,000 weight parts of the inorganic powder having a density of not less than 5 g cm-³ and a particle size such that 95% thereof passes a 200-mesh sieve, and 0.1-50 weight parts of a fiber having a diameter of 0.05-50 pm and an average length of 0.1-50 mm, the composition having a density of not less than 4 g cm-³ and a consistency of 1-25 (as defined in Japanese Industrial Standard JIS 5752).
The binder to be used in the present invention is viscous, having, at 25°C, a viscosity in the range of not less than 1 x104 centistokes to an unworked penetration, as measured in accordance with JIS K 2220-1980, Section 5.3.4, of not less than 100. With binders having a viscosity, at 25°C, of less than 1 x 10⁴ centistokes, it is difficult to obtain putty-like composition with good shape maintaining ability. With binders having an unworked penetration of below 100, the composition obtained upon incorporation of a sufficient amount of inorganic powder to produce radiation shielding effect will have difficulty in being integrated as putty, therefore, the amount of inorganic powder which can be incorporated is limited. The binder preferably has a viscosity at 25°C in the ra_'1ge of 5x 10⁴ centistokes to an unworked penetration of not less than 150, more preferably in the range of not less than 1 x 10⁵ centistokes to an unworked penetration of not less than 200.
As such viscous binder, generally preferred are a grease, an organic or inorganic polymer, and a mixture of a grease and such polymer.
The grease is generally a substance which is viscous and liquid, or semisolid at ordinary temperature and is prepared by dispersing a thickener in a natural or synthetic oily dispersion medium, namely base oil. As the above base oil, there are used, for instance, transformer oil, spindle oil, cable oil, insulating oil, machine oil and other petroleum-based oils, rosin oil, castor oil, olive oil, whale oil and other natural oils, polybutene, chlorinated paraffin, polyethylene glycol and other synthetic polymer oils. As the thickener, there are used, for example, metal soaps which are barium, strontium, zinc, lead, cadmium, potassium, sodium, calcium, lithium, aluminum and other metal salts of fatty acids, and non-soap thickeners such as bentonite, silica gel and copper phthalocyanine. Mixtures of two or more of the above-mentioned thickeners may naturally be used.
Such grease thus includes, among others, soap-containing greases such as sodium soap greases, calcium soap greases, lithium soap greases, aluminum soap greases and barium soap greases, and non-soap greases such as bentonite greases and silica gel greases. Especially preferred are, for instance, lithium soap greases, aluminum soap greases, bentonite greases and silica gel greases because they give compositions good shape maintaining ability. In addition to the above generally known greases, such greases as described in Hiroshi Horiguchi: "Lubricants and Greases", pages 402-419, Sankyo Shuppan K. K., 1970, may also be used.
The above-mentioned organic or inorganic polymer includes, among others, petroleum hydrocarbon oils, olefin polymer oils such as polybutene, polyalkene glycol oils, halogenated hydrocarbon oils such as chlorinated paraffin, liquid rubbers such as liquid chloroprene rubber, liquid butadiene rubber and liquid nitrile rubber, silicone oils, and water glass.
The radiation shielding putty-like composition according to the invention contains, per 100 weight parts of the above binder, 1,200-4,000 weight parts, preferably 1,300-3,000 weight parts, more preferably 1,500-2,000 weight parts, of an inorganic powder. The inorganic powder functions as the radiation shielding material. Therefore, when the content of the inorganic powder is too low, the radiation shielding effect is insufficient. Conversely, when said content is too high, the resulting composition will not have putty-like properties. It is required that the density of the inorganic powder should be not less than 5, preferably not less than 7, and especially desirable not less than 9. As such inorganic powder, there may be used any of inorganic powders which are compatible with the above-mentioned binder. Generally used are powders of metals or metal oxides, more specifically, lead, zinc, iron, zirconium and copper, oxides, of these and other various compounds. Preferred are lead powder and lead oxide powder since they have a density of not less than 9.
These powders should preferably have a particle size as small as possible so that they can be incorporated in the composition in large amounts. Thus, generally used are those powders that have a particle size such that at least 95% thereof passes a 200-mesh sieve of the JIS Z 8801 Standard Sieve series, more preferably such that not less than about 90% passes a 350-mesh sieve. Furthermore, the use of a mixture of a coarser powder and a finer powder having a particle size such that at least 90% passes a 350-mesh or finer sieve makes it possible to incorporate the inorganic powder in the composition in larger amounts, since such inorganic powder mixture is dispersed in the composition in a manner such that finer powder particles are packed among coarser powder particles.
The radiation shielding putty-like composition according to the invention further contains, per 100 weight parts of the binder, 0.1-50 weight parts, preferably 1-20 weight parts, more preferably 2-6 weight parts, of a fiber so that the composition, after application at the site requiring shielding, has good dimensional stability. Said fiber may be either an inorganic fiber or an organic fiber. For the reason mentioned above, the fiber should have a diameter in the range of 0.05-50 pm preferably 3-30 um, more preferably 5-20 pm, and an average length in the range of 0.1-50 mm, preferably 0.5-20 mm, more preferably 1-10 mm. Such fiber, which may be an inorganic one or an organic one, includes inorganic fibers such as asbestos, rock wool, glass wool, carbon fiber, and iron, copper and other metal fibers, and organic fibers such as polyamide fiber, fluororesin fiber and phenol-based polymer fiber, but is not limited to these. An excessively large amount of fiber is not preferable since it reduces the putty-like properties of the composition.
In addition to the above-mentioned binder, inorganic powder and fiber, the putty-like composition according to the invention may, as necessary, contain an appropriate amount of flame retardant such as aluminum hydroxide, a colorant and other ingredients.
The method of producing the radiation shielding putty-like composition according to the invention is not critical. Thus, for instance, said composition can be obtained by uniformly kneading the required components _'in the conventional manner using, for example, a kneader or a roll.
The radiation shielding putty-like composition according to the invention, which has the above-mentioned composition, generally has, at room temperature, a consistency as prescribed in JIS A 5752 of 1-25, preferably 3-18, more preferably 5-15, and a density of not less than 4, preferably not less than 6, more preferably not less than 6.5.
The composition according to the invention may further contain a vinyl chloride resin plasticizer such as dioctyl phthalate, and/or other additives ordinarily used for synthetic resin and rubbers provided that the physical characteristic requirements mentioned above are satisfied.
The radiation shielding putty-like composition according to the invention, which contains such high density inorganic powder as a metal or metal oxide powder at such high addition level has an excellent radiation shielding effect and, in spite of its high density, is putty-like and has good shape maintaining ability.
Therefore, it can easily be applied to a variety of openings where there is a danger of radiation leakage. Furthermore, since the composition is noncuring any after-treatment following application is not required. In addition, once applied, the composition can be removed easily as necessary.
The following examples, which by no means limit the present invention, will illustrate the invention in more detail. Since it is known that the radiation shielding effect of a composition is generally proportional to the surface density, as mentioned previously, the density data alone are shown in the examples.

Example, Comparative Example

The components given in the table were kneaded together on a roll to produce radiation shielding putty-like compositions. The compositions of the invention sach contains a lead or lead oxide powder or some other metal oxide powder in a large amount. Although it has a high density as shown in the table, each composition has a moderate consistency and a high shape maintaining ability and therefore is excellent in applicability and workability. Further, it is nonhardening and can be easily removed after application.
Following sufficient manual kneading, each composition was molded into a 1 cm cube to test its moldability, then left for 1 month at room temperature to test dimensional stability. By these two tests the shape maintaining ability of the compositions were rated by the following criteria, and shown in the table below.

S-The composition is well integrated into a putty, has a moderate consistency and therefore can easily be shaped into a cube. The shape of the cube is maintained very well.
E-The composition is slightly inferior for integration into a putty as compared with S, but is very good in moldability into a cube and for dimensional stability of the cube.
G-The composition can be integrated into a putty and, for practical purposes, is good in moldability into a cube and for dimensional stability of the cube.
F-The composition can, with some difficulty, be integrated into a putty and is modable into a cube. However, the cube undergoes deformation when subjected to slight external force.
P-The composition has an excessive flowability and cannot be integrated into a putty, hence can hardly be shaped into a cube.

The nonhardening property was regarded as good if the composition showed a change in consistency of not more than 3.0 after standing at room temperature for 1 month. The initial consistency was measured 24 hours after preparation of. the putty by kneading.

Claims

1. A radiation shielding putty-like compositon which comprises a dense inorganic powder in a binder characterized in that the binder has, at 25°C, a viscosity in the range of not less than 1 x 10⁴ centistokes to an unworked penetration of not less than 100, in that for each 100 weight parts of binder there are 1,200-4,000 weight parts of the inorganic powder, the powder having a density of not less than 5 g cm-³ and a particle size such that at least a 95% portion thereof passes a 200-mesh sieve, in that there is also present in the composition 0.1-50 weight parts of a fiber having a diameter of 0.05-50 pm and an average length of 0.1-50 mm, and in that said composition has a density of not less than 4 g.cm-³ and a consistency of 1-25 (as defined in Japanese Industrial Standard JIS 5752).

2. The radiation shielding putty-like composition according to Claim 1, which comprises per 100 weight parts of the binder, 1,300-3,000 weight parts of the inorganic powder and 1-20 weight parts of the fiber.

3. The radiation shielding putty-like composition of Claim 1 or Claim 2, wherein the binder has, at 25°C, a viscosity in the range of not less than 1 x10⁵ centistokes to an unworked penetration of not less than 200.

4. The radiation shielding putty-like composition according to Claim 1, Claim 2 or Claim 3, wherein the inorganic powder has a particle size such that not less than a 90% portion thereof passes a 350-mesh sieve.

5. The radiation shielding putty-like composition according to any one of the preceding claims wherein the fiber has a diameter of 3-30 µm and an average length of 0.5-20 mm.

6. The radiation shielding putty-like composition according to any one of the preceding claims, wherein the binder is a noncuring one.