US3780309A

US3780309A - Insulated container for radioactive and like substances

Info

Publication number: US3780309A
Application number: US00059037A
Authority: US
Inventors: C Bochard
Original assignee: Robatel SLPI SA
Current assignee: Robatel SLPI SA
Priority date: 1970-07-28
Filing date: 1970-07-28
Publication date: 1973-12-18
Anticipated expiration: 1990-12-18

Abstract

A double-walled container for radioactive material having an outer metal casing and an inner wall of lead and, in the space between the walls, an insulating material which is a solid mass of a mixture of hydrated alumina and hydrated iron oxide. The solid mass of insulating material may be formed in the space by pouring a mixture of an aqueous suspension of alumina trihydrate and particulate mild steel or iron into the space and allowing the mixture to set. The insulating material is effective in removing heat from the lead shield and in preventing heat reaching the lead shield from a source external of the container.

Description

United States Patent Bochard 1 Dec. 18, 1973 [5 INSULATED CONTAINER FOR 3,569,714 3 1971 Anderson et al 250/108 R RADIOACTIVE AND LIKE SUBSTANCES 3,453,160 7/1969 Darling ct all. 250/108 WS X 3,466,444 9/1969 Lusk t. 250/108 WS [75] Inventor: Camille Bochard, Lyon (Rhone),

France [73] Assignee: Robatel S.L.P.l., Geneve (Rhone),

France [22] Filed: July 28. 1970 [21] Appl. No.: 59,037

[52] US. Cl. ..250/507 [51] Int. Cl. G21f l/00 [58] Field of Search 250/108 R, 108 WS, 250/108 FS [56] References Cited UNITED STATES PATENTS 2,773,459 12/1956 Sechy 250/108 WS X 2,726,339 12/1955 B0rst..... 250/108 WS 2,992,175 7/1961 Borst i 250/108 R X. 3,558,526 1/1971 Hall et a1. 250/108 R X Primary ExaminerArchie R. Borchelt Attorney-Alexander and Dowell [57 I ABSTRACT A double-walled container for radioactive material having an outer metal casing and an inner wall of lead and, in the space between the walls, an insulating material which is a solid mass of a mixture of hydrated alumina and hydrated iron oxide. The solid mass of insulating material may be formed in the space by pouring a mixture of an aqueous suspension of alumina trihydrate and particulate mild steel or iron into the space and allowing the mixture to set. The insulating material is effective in removing heat from the lead shield and in preventing heat reaching the lead shield from a source external of the container.

7 Claims, 2 Drawing Figures INSULATED CONTAINER FOR RADIOACTIVE AND LIKE SUBSTANCES This invention is concerned with an insulated container for radioactive and like substances.

Conventional containers for radioactive and like sub stances are double walled, the inner wall being formed of lead to provide the necessary gamma-radiation shielding, and the outer wall being a metal casing which provides protection against impacts, and the space between the inner and outer walls is filled with an insulating material. It has been found that for completely satisfactory results the insulating material must have apparently contradictory properties. The first requirement is that under normal working conditions, the insulating material must be a very good heat conductor so as to remove heat evolved by the radioactive or like substance contained in the container so as to prevent any overheating of the lead shielding. A contrary requirement, however, is that in the event of an accidental outbreak of fire in the vicinity of the container, the insulating material should have very poor heat conductivity so as to act as a heat barrier and effectively reduce the risk of any accidental melting of the lead shielding. Once the outbreak of fire has finished, the insulating material should have sufficient heat conductivity to remove the heat evolved by the contents of the container to substantially the same extent as in normal operation.

We have now developed an insulating material which substantially meets these requirements, which can be used at high temperatures, and which has very good mechanical strength. I

I will explain the invention with reference to the accompanying drawing which illustrates one practical embodiment of the invention, and will summarize in the claims the essential features of the invention for which protection is desired.

In said drawing:

FIG. 1 is a horizontal sectional view through a container before pouring the mixture of insulating material therein.

FIG. 2 is a section similar to FIG. 1, after the insulating material has been poured.

As shown in the drawing the inner vessel 1 is adapted to receive the radioactive or like substance. A lead shield 2 surrounds the said vessel 1 as shown. An outer metal casing 3 surrounds the lead shield 2 and is spaced therefrom, as shown, to form an annular space 4 around the lead shield 2, said outer metal casing 3 being provided with safety openings 3a, as shown in FIG. 1. The insulating material mixture 5 according to the invention is poured into the annular space 4 to fill said space with insulating material 5 as shown in FIG. 2, and thereafter the openings 3a are closed by means of caps 6.

According to the present invention, the inter-wall insulation material 5 is made by introducing a mixture of an aqueous suspension of alumina trihydrate (A1 3H O) and particulate mild steel or iron into the space 4 between the outer and

inner walls

3 and 2 and allow ing the mixture to set. The water (of the suspension) oxidises the iron particles and the resulting reaction yields a hydrated iron sesquioxide (Fe O nI-I O); the final product is, therefore, a solid mass of a mixture of hydrated alumina and hydrated iron sesquioxide which has very good mechanical strength and good thermal conductivity.

Advantageously, an appropriate quantity of calcium sulphate hemihydrate (CaSO. VzH O) is-addcd to the mixture. The use of calcium sulphate or wet plaster as insulating material has already been suggested, for example in US. Pat. No. 3,466,662 issued to Paul Blum on Sept. 9, 1969. However, adding wet plaster to the alumina trihydrate-particulate iron mixture apparently helps to achieve outstandingly good results, for as in the case of the Blum patent above mentioned, hydration of the calcium sulphate leads to homogeneous hardening of the mixture; also, the increase in volume consequent upon the hardening or setting of the plaster helps to bond the inner lead shielding wall 2 to the inside of the outer metal casing 3. Also, because of the good contact thus produced between the inner surface of the outer wall 3 and the outer surface of the inner wall 2, there is an appreciable improvement in heat transfer. More particularly, the setting of the plaster 5 leads to the formation of a crystal lattice which accelerates oxidation of the iron or steel powder and the formation of a very strong solid block.

In order to accelerate oxidation a flow of wet, and preferably warm, air is advantageously introduced into the space 4 between the outer and

inner walls

3 and 2 before the normal safety openings 3a from this space are closed by caps 6. This flow of warm wet air can be followed by a current of dry warm air so as to at least partly dry the mixture, which finally has the form of a rigid porous block 5.

However, because of the presence of the hydrated alumina, an insulating block 5 of this kind contains a considerable quantity of water which in the event of an accidental temperature rise (accidental outbreak of fire) turns into steam, so that the lead shielding 2 cannot be damaged. Normal removal of the heat evolved by the radioactive material in the container proceeds very satisfactorily during normal use of the package. Even after having lost its water of crystallisation in the form of steam through the safety openings 3a, the insulating material 5 according to the invention retains sat isfactory mechanical strength and still has a heat con ductivity coefficient sufficient to ensure removal of the heat from the radioactive contents after such an accidental external fire.

The proportions by weight of a preferred starting mixture are, for example, as follows:

Alumina trihydratc 35% Iron powder 25% Calcium sulphate 15% Water 25% The density of the resulting insulating material is about 2.2, although properties of the product can be adjusted appreciably by variation of the proportions in the starting mixture. Other compounds adapted to form a crystal lattice which can support the other two ingredients of the mixture can be used instead of calcium sulphate hemihydrate.

I claim:

1. In a double-walled container for radioactive and like substances having an outer metal casing and a spaced inner wall of lead constituting a radiation shield and, in the space between the outer and inner walls, an insulating material, the improvement wherein the insu lating material comprises a solid mass containing at least 35 percent by weight of hydrated alumina.

6. The container as set forth in claim 1, wherein the insulating material also comprises approximately 15 percent of a compound adapted to form a crystal lattice; and wherein the said solid mass also contains hydrated iron sesquioxide.

7. The container as set forth in claim 6, wherein said compound is calcium sulphate hemihydrate; and wherein the hydrated iron sesquioxide contains at leat 25 percent by weight of iron powder.

Claims

2. The container set forth in claim 1, wherein the insulating material also comprises approximAtely 15 percent of a compound adapted to form a crystal lattice.
3. The container set forth in claim 2, wherein said compound is calcium sulphate hemihydrate.
4. The container as set forth in claim 1, wherein the said solid mass also contains hydrated iron sesquioxide.
5. The container as set forth in claim 4, wherein the hydrated iron sesquioxide contains at least 25 percent by weight of iron powder.
6. The container as set forth in claim 1, wherein the insulating material also comprises approximately 15 percent of a compound adapted to form a crystal lattice; and wherein the said solid mass also contains hydrated iron sesquioxide.
7. The container as set forth in claim 6, wherein said compound is calcium sulphate hemihydrate; and wherein the hydrated iron sesquioxide contains at leat 25 percent by weight of iron powder.