Radiation shielding structure

Abstract: A transparent panel (1) for shielding against harmful radiation consists of a sheet (2) transparent to visible light and which contains lead (Pb) in sufficient amount to stop radioactive radiation (e.g. of an acrylic resin or lead glass), and laminated on at least one face of the sheet (2), with a sheet (3) of transparent material not containing lead which prevents oxidation of the lead. For mounting the panel, it has a gasket (9) retained on the periphery of the panel by an inwardly projecting bead (10) which fits into a groove (8) in the edge of the panel; the outer face of the gasket is seated against a flange (6) around an aperture in the frame (5) of a glovebox or other work station. The outer edge of the panel (1) and inner face of the flange (6) are respectively tapered so that the panel is firmly seated and it is retained by a cover plate (14) bolted (15) to the frame and covering the edge of the panel. The panel remains transparent and is securely and airtightly mounted.

Description: The present invention relates to a transparent radiation-shielding structure which may be used for, for example, a work face of a glove box that is designed to handle radioactive substances safely. We will hereinafter discuss a work-face of a glove box for handling radioactive substances in nuclear facilities as prior art relevant to the present invention. However, it should be noted that the application of the present invention is not necessarily limited thereto and that the invention may be generally applied to radiation-shielding structures that are required to be transparent. Referring to Fig. 2, a conventional glove box 21 has a work-face 22, which is formed with glove ports 23 having gloves (not shown) attached thereto and passing therethrough, and a worker, using the gloves, handles a radioactive substance in the box. The work face 22 of the glove box 21 must be capable of shielding radiation and also transparent to visible light so that the worker can view the inside of the box 21. In addition, the work-face 22 must have a satisfactorily airtight structure. The conventional work face 22 has a double-panel structure comprising an airtight panel 24 made of a transparent acrylate resin material and a radiation-shielding panel 25 of a transparent lead-containing acrylic resin material (or lead glass) that is disposed outside the airtight panel 24, as shown in Fig. 3. The airtight panel 24 is brought into contact with a panel mounting portion 27 through a gasket 26 for an airtight seal that is fitted to the outer peripheral edge of the panel 24. In addition, a retaining plate 29 is pierced by a plurality of bolts 28 that are provided on the panel mounting portion 27, and the airtight panel 24 is fastened with a nut 30 through the retaining plate 29, thereby securing the airtight panel 24 to the panel mounting portion 27. The transparent radiation-shielding panel 25 is disposed outside the airtight panel 24 to shield radioactive rays, e.g., neutron beams or gamma rays, by means of lead that is contained in the radiation-shielding panel 25. The reason why the double-panel structure comprising the airtight panel 24 and the radiation-shielding panel 25 has hitherto been used is that, if the radiation-shielding panel 25 is attached directly to the panel mounting portion 27 through the gasket 26, which is fitted to the outer peripheral edge of the panel 25, to form a single-panel structure, lead (P b ) that is contained in the radiation-shielding panel 25 is oxidized by chemicals, e.g., nitric acid, in the box 21 to form an oxide film on the panel surface, resulting in the panel 25 becoming opaque, so that it becomes difficult to view the inside of the box 21. The above-described prior structure suffers, however, from the problem stated below. Since a gap 31 is present between the airtight panel 24 and the radiation shielding panel 25, which constitute a double-panel structure, the opposing surfaces 24a and 25a of the two panels 24 and 25 become cloudy with moisture or are stained with suspended dust, resulting in a lowering in the transparency. In addition, radiation cannot be shielded at the edge of the gap 31 between the airtight panel 24 and the radiation-shielding panel 25, so that radioactive rays leak therethrough. Further, since two panels 24 and 25 need to be mounted, the efficiency of the assembly operation is low. US-A-2223118 discloses a radiation-shielding panel comprising a transparent glass plate 1 containing lead and laminated on each face of said plate a further transparent glass plate 2 containing no lead. However, US-A-2223118 contains no teaching indicating ways in which it is possible to mount such a panel stably in a shielding structure. Arrangments for mounting a panel in a shielding structure are disclosed in US-A- 3 307 400, US-A- 3 380 303 and LU-A-44 716. It is an object of the present invention to provide a radiation-shielding structure which is designed so that it is possible to shield radiation by means of a single panel and still prevent reduction in the transparency due to oxidation, thereby eliminating the reduction in the transparency due to the gap between two panels of the conventional double-panel structure and leakage of radioactive rays from the peripheral edge of the gap between the two panels, and thus improving the efficiency of the panel mounting operation and preferably the airtightness of the structure, whilst simultaneously providing a radiation-shielding structure which is designed so that it is possible to mount the panel stably in the shielding structure. According to the present invention we provide a radiation-shielding structure including a panel comprising: (a) a transparent plate comprising lead and laminated on at least one face of said plate (b) a further transparent plate made of a material not containing lead; characterised in that it comprises a mounting portion having an aperture for receiving the panel, in that a gasket is fitted to an outer peripheral edge of said panel to hermetically seal the area between said panel and said mounting portion and in that the inner peripheral edge of said mounting portion and the outer peripheral edge of said panel are formed with respective tapers for guiding said panel when it is attached to and detached from said mounting portion, said panel being fitted into said mounting portion through the gasket. The above described radiation-shielding structure is designed so that it is possible to prevent displacement of the gasket in the shielding structure and so that the panel is not damaged by the peripheral retaining plate. In the accompanying drawings: Fig. 1 is a sectional view of one embodiment of the radiation-shielding structure according to the present invention; Fig. 2 is a perspective view of a conventional glove box; and Fig. 3 is a sectional view taken along the line A-A of Fig. 2. One embodiment of the present invention will be described below with reference to Fig. 1. A radiation-shielding panel 1, which constitutes the radiation-shielding structure of the present invention, comprising a plate 2 which contains lead and is transparent to visible light (for example, a transparent lead acrylic resin plate or lead glass plate), and a thin non-lead transparent plate 3 (for example, a transparent acrylate resin plate or glass plate) which is laminated on at least one face of the lead-containing transparent plate 2. Thus, the lead that is contained in the plate 2 shields from radioactive rays, while the non-lead transparent plate 3 prevents the afore described oxidation of the lead in the plate 2 by air or chemicals, which would otherwise form an oxide film on the panel surface and make the panel 1 opaque. It is preferable from the viewpoint of mechanical strength and machinability to employ an acrylic resin containing lead plate as the transparent plate 2 and an acrylate resin plate as the non-lead transparent plate, which is laminated on the lead acrylic resin plate. The outer peripheral edge of the radiation-shielding panel 1 is formed with a taper 4 that serves as a guide when the panel 1 is mounted, and the inner peripheral edge of a panel mounting portion 6 (a flange) of a box frame 5 of a workstation is also formed with a taper 7 as a guide for mounting, so that the radiation shielding panel 1 is fitted into the panel mounting portion 6 by being guided by the tapers 4 and 7. In addition, the outer peripheral edge of the radiation-shielding panel 1 is provided with a gasket fitting recess 8 which is in the form of a groove, and an annular positioning projection 10 that is integrally formed on the inner peripheral edge of the gasket 9 is fitted into the gasket fitting recess 8, thereby enabling the gasket 9 to be attached to the radiation shielding panel 1. The outer peripheral edge of the gasket 9 is provided with a plurality of contact projections 11 having an acute triangle-shaped cross-section so as to enhance the adhesion between the gasket 9 and the panel mounting portion 6 and thereby improving the airtightness. The gasket 9 further has a buffer portion 12, as an integral part thereof, which is interposed between the radiation-shielding panel 1 and a retaining plate 14 (described below) to prevent the radiation shielding panel 1 from being damaged by the retaining plate 14. A plurality of bolts 13 are attached to the peripheral edge of the panel mounting portion 6 by means, for example, of welding. The retaining plate 14 is pierced by the bolts 13 and brought into contact with the boundary between the radiation-shielding panel 1 and the panel mounting portion 6, and the radiation-shielding panel 1 is secured to the panel mounting portion 6 through the retaining plate 14 and the buffer portion 12 of the gasket 9 by nuts 15 that are screwed onto the bolts 13. Although in this embodiment the bolts 13 and the nuts 15 are employed as fastening means for securing the radiation shielding panel 1 through the retaining plate 14, any other fastening means may be employed, as a matter of course. This embodiment, arranged as described above, functions as follows. In the radiation-shielding panel 1, lead that is contained in the lead transparent plate 2 shields radioactive rays, while the non-lead transparent plate 3, which is laminated on at least one side of the lead transparent plate 2, prevents oxidation of the lead in the lead transparent plate 2 by air or chemicals, which oxidation would otherwise form an oxide film on the panel surface and make the panel opaque. Since the work-face comprises only the radiation shielding panel 1, the radiation shielding structure of the present invention is free from the problem of lowering in transparency due to the moisture of suspended dust in the gap between two panels of the conventional double-panel structure, and it is also free from the problem of leakage of radioactive rays through the gap between the two panels of the prior art. In addition, it is possible to improve the efficiency of the panel mounting operation. Since the radiation-shielding panel 1 is fitted into the panel mounting portion 6 by being guided by the tapers 4 and 7, the efficiency of the panel mounting operation is improved and the panel 1 can be mounted even more stably. SInce the positioning projection 10 of the gasket 9 is fitted into the gasket fitting recess 8 in the radiation shielding panel 1, displacement of the gasket 9 is prevented. Since the contact projections 11 of the gasket 9 come into close contact with the inner peripheral edge of the panel mounting portion 6, the airtightness is improved. In addition, since the buffer portion 12 of the gasket 9 is interposed betwee the retaining plate 14 and the radiation-shielding panel 1, there is no danger of the radiation shielding panel 1 being damaged by the retaining plate 14. The present invention provides the following advantages: (1) In the radiation-shielding panel, lead that is contained in the lead transparent plate shields radioactive rays, while the non-lead transparent plate, which is laminated on at least one side of the lead transparent plate, prevents oxidation of the lead in the lead transparent plate, which would otherwise form an oxide film on the panel surface and make the panel opaque. Since the lowering in the transparency due to such oxidation can be eliminated by the radiation-shielding panel only, the radiation shielding structure of the present invention is free from the problem of lowering in the transparency due to the moisture or suspended dust in the gap between two panels of the conventional double-panel structure, and it is also free from the problem of leakage of radiactive rays through the gap between the two panels of the prior art. In addition, since the radiation-shielding panel alone needs to be mounted, the panel mounting operation is easier. (2) Since the radiation-shielding panel is fitted into the panel mounting portion by being guided by the tapers, the efficiency of the panel mounting operation improves and the panel can be mounted even more stably. (3) Since the positioning projection of the gasket is fitted into the gasket fitting recess in the radiation-shielding panel, displacement of the gasket is prevented. (4) Since the contact projections of the gasket come into close contact with the panel mounting portion, the airtightness improves. (5) Since the buffer portion of the gasket is interposed between the radiation-shielding panel and the retaining plate, the radiation-shielding panel is prevented from being damaged by the retaining plate.

Claims: A radiation-shielding structure including a panel (1) comprising: (a) a transparent plate (2) comprising lead and laminated on at least one face of said plate a further transparent plate (3) made of a material not containing lead (3); characterised in that it comprises a mounting portion (6) having an aperture for receiving the panel, in that a gasket (9) is fitted to an outer peripheral edge of said panel (1) to hermetically seal the area between said panel and said mounting portion and in that the inner peripheral edge of said mounting portion (6) and the outer peripheral edge of said panel (1) are formed with respective tapers (4,7) for guiding said panel when it is attached to and detached from said mounting portion (6), said panel being fitted into said mounting portion through the gasket (9). A radiation-shielding structure according to Claim 1, wherein said transparent plate (2) is made of an acrylic resin material containing lead and said non-lead transparent plate (3) is made of an acrylate resin material. A radiation-shielding structure as in Claim 1, further including a retaining plate (14) which covers the boundary between said panel (1) and said mounting portion (6); and fastening means (13) for securing said panel (1) to said mounting portion (6) through said retaining plate. A radiation-shielding structure according to Claim 3, wherein said gasket (9) is integrally formed with a buffer portion (12) which is interposed between said panel (1) and retaining plate (14). A radiation-shielding structure according to any of Claims 1 to 4, wherein the outer peripheral edge of the panel (1) is formed with a gasket fitting recess (8), which is fitted with at least one positioning projection (10) that is integrally formed on the inner peripheral edge of the gasket. A radiation-shielding structure according to any of Claims 1 to 5, wherein the outer peripheral edge of the gasket (9) bears integrally formed contact projections (11) arranged for improving the adhesion between the gasket and the mounting portion (6).

Inventors: KIHARA YOSHIYUKI DORYOKURO KAK, TAKAHASHI YOSHIHARU DORYOKURO, KIHARA, YOSHIYUKI, DORYOKURO KAKUNENRYO KAIHATSU, TAKAHASHI, YOSHIHARU, DORYOKURO KAKUNENRYO KAIHAT.
Applicants: DORYOKURO KAKUNENRYO, DORYOKURO KAKUNENRYO KAIHATSU JIGYODAN
Application year: 1990
Main classification: G21F7
IPC codes: G21F7, G21F1, G21F3, B25J21