US3754141A - Shipping and storage container for high power density radioactive materials - Google Patents

Abstract

A shipping and storage container for radioactive material, particularly high thermal producing fissile material, which includes a cylindrical inner metal container for retaining the radioactive material, an alpha contamination barrier of polyvinyl chloride surrounding said inner container, a cylindrical outer metal container enclosing said inner container and barrier with inner surfaces spaced from the inner container walls and from said barrier, and finely divided heat absorbing and transferring or conducting magnesium oxide filling the space intermediate said barrier and the inner surfaces of the outer metal container.

Description

r...-Iv'"..1 ea 9.111

OR 3a75 19l 1-l United States Pf Leebl et al.

[ SHIPPING AND STORAGE CONTAINER FOR HIGH POWER DENSITY RADIOACTIVE MATERIALS [75] Inventors: Robert G. Leebl, Arvada, Colo.;

Robert L. Sandvig, Rapid City, S. Dak.; Edward Vejvoda, Boulder, C010.

[73] Assignee: The United States of America as represented by the United States Atomic Energy Commission, Washington, D.C.

[22] Filed: July 12, 1972 [21] Appl. No.: 270,885

[52] US. Cl 250/507 [51] Int. Cl. G2lf 3/00 [58] Field of Search 250/108 R, 108 WS,

[56] References Cited UNITED STATES PATENTS Bruno et al. 250/108 R Nash et al. 250/108 R Princiotta et al. 250/108 R Primary Examiner-James W. Lawrence Assistant Examiner-Davis L. Willis AttorneyRoland A. Anderson [5 7 ABSTRACT A shipping and storage container for radioactive material, particularly high thermal producing fissile material, which includes a cylindrical inner metal container for retaining the radioactive material, an alpha contamination barrier of polyvinyl chloride surrounding said inner container, a cylindrical outer metal container en closing said inner container and barrier with inner surfaces spaced from the inner container walls and from said barrier, and finely divided heat absorbing and transferring or conducting magnesium oxide filling the space intermediate said barrier and the inner surfaces of the outer metal container.

3 Claims, 2 Drawing Figures Patented Aug. 21, 1973 3,754,141

SHIPPING AND STORAGE CONTAINER FOR HIGH POWER DENSITY RADIOACTIVE MATERIALS BACKGROUND OF INVENTION Radioactive materials may be stored in appropriate containers for various reasons between uses thereof or between production and use and must often be shipped or transported from one location to another while so stored. These materials, because of their radioactivity and any other inherent toxicity must be stored in a container which will reliably contain the same regardless of the environmental conditions under which the storage and/or shipping container may be subjected. In turn, it is also desirable, that whichever materials that the storage or shipping containers are formed of are not such that will produce or give off material or gases which may contaminate the radioactive material and which might prevent its use for an intended purpose.

The storage and shipping of radioactive material becomes increasingly more difficult when the material exhibits a high degree of radioactivity together with a high production of thermal energy. Materials which may withstand a certain amount of radioactivity at low temperatures may rapidly degrade under the combined effects of heat and radiation. Thus, the storage of such materials as fissile plutonium dioxide with high specific power outputs may prevent storage or shipping of this material in ordinarily acceptable container configuration and materials or require its shipping or storage in uneconomically small quantities. For example, polyvinyl chloride bags or sheets used either alone or in combination with other containers to hold radioactive materials, when subjected to temperatures above about 200F in alpha and gamma radiation, rapidly degrade with appreciable decrease in strength and contaminant capabilities. In addition, during such degradation of polyvinyl chloride, both hydrogen gas and hydrochloric vapors are evolved which may react with the radioactive material to contaminate the same as well as attack the container. Further, the so degraded polyvinyl chloride becomes more permeable to air and moisture which in turn may cause additional decomposition or contamination of the radioactive material, particularly under the high temperature conditions resulting from the high thermal energy production of high specific power radioactive materials. In addition, the degradation and failure of the polyvinyl chloride bag used to remove a radioactive material container from a glovebox line would permit the spread of radioactive contamination from the outside surface of the container and the inside surface of the polyvinyl chloride bag as well as other parts of the storage system.

It would be desirable to provide a storage and shipping container which is of simple and relatively low cost construction and which will provide the desired long term protection of high specific power radioactive materials without release or contamination of such.

SUMMARY OF INVENTION In view of the above, it is an object of this invention to provide a storage and shipping container which is of simple and low cost construction.

It is a further object of this invention to provide a storage and shipping container which utilizes a polyvinyl chloride alpha radiation contamination barrier.

It is a further object of this invention to provide a high specific power plutonium oxide storing and shipping container utilizing relatively low cost and reusable materials.

Various other objects and advantages will appear from the following description of the invention and the most novel features will be pointed out hereinafter in connection with the appended claims. It will be understood that various changes in the details, materials and arrangements of the parts, which are herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art.

The invention comprises a radioactive-materialenclosing inner metal container, a polyvinyl chloride alpha radiation barrier enclosing said inner container, a metal outer container surrounding and spaced from said inner container and said barrier, and heat absorbing and transferring or conducting magnesium oxide powder filling the space intermediate said outer container and said polyvinyl barrier to maintain the barrier in close contact with said inner container and for absorbing and transferring or conducting heat away from the latter.

DESCRIPTION OF DRAWING The invention is illustrated in the accompanying drawing wherein:

FIG. I is a cross-sectional view of the storage and shipping container of this invention; and

FIG. 2 is an elevation side view partially in cross section of a shipping system utilizing the container of FIG. 1.

DETAILED DESCRIPTION The storage and shipping container 10 shown in FIG. 1 may be used or employed to hold radioactive material for appreciable time periods without significant degradation of the container materials and without release or contamination of the radioactive material itself or the component parts of the shipping system. This successful containment of radioactive material is achieved for long periods of time even using radioactive material having high thermal energy production and high specific power with significant amounts of even highly corrosive forms of plutonium.

The storage and shipping container arrangement 10 includes a cylindrical or tubular inner or primary container 12 having a central bore or cavity open at one end and closed at the other for receiving the radioactive material 14 therein. The open end of container 12 is closed by an appropriate removable cover 16 which may be suitably attached to container 12 by the threaded portions shown, or the like, to form a complete, enclosed chamber for retention of material 14. An appropriate gasket or an unperforate liner I8 may be provided between the end cap or cover 16 and container 12, either as shown or within the threaded portions or other mating portions thereof, to prevent release of material I4 from container 12 and to hermetically seal or contain any gas pressure buildup which may occur within container 12 from radioactive decay of material 14 or from increased heat buildup therein and resulting expansion of enclosed gases or solids. Gasket or liner 18 may be formed from polytetrafluoroethylene thread gasket material, which will also act to inhibit galling or other damage to the threads that could lead to a failure of the seal between end cap 16 and container 12 should such damage occur and permit reuse of the container and cover. The container 12 with end cap 16 should preferably be made of a corrosion resistant and heat conductive material which is also not subject to objectionable heat degradation and which is compatible with the radioactive material 14 being contained under all environmental conditions to which the container and radioactive material may be subjected. Fro plutonium oxide containment, the container and end cap are preferably made from 300 series stainless steel. For convenience, container 12 may be made from commercially available stainless steel pipe threaded at one end and sealed at the other end with a welded plate while end cap 16 may be a conventional threaded stainless steel pipe cap.

A polyvinyl chloride bag or container 20, shown with exaggerated thickness for illustration purposes, of appropriate shape is disposed about and in close or in an initial relatively close contact with the outer surfaces of inner container 12 and end cap 16 and the open end or ends or openings of bag 20 closed and sealed by application of heat or a sealant or by an appropriate clamping member 22 or tightly encircling sealing tape. The bag 20 should be made of a polyvinyl chloride film or sheet having a sufficient thickness to provide an alpha contamination barrier and is preferably of thickness of from about 0.01 inch to 0.015 inch, for convenience of handling. Bag 20 may be a tube of polyvinyl chloride sheet sealed and clamped or closed at both ends or it may be in the form of a container as shown in FIG. 1 having a single open end for receiving container 12 which is then sealed by clamp 22. Clamp 22 may be any appropriate device or material which will gather and hold the polyvinyl chloride film and seal the same about said opening and may be of such as pigmented vinyl plastic adhesive tape or the like, or the barrier may be heat sealed to itself. The polyvinyl chloride bag is a convenient mechanism to remove the primary container from a glovebox or other handling container and to serve as the initial alpha radioactivity containment barrier.

The polyvinyl chloride alpha barrier enclosed inner cylindrical or tubular container 12 is then positioned within a cylindrical or tubular outer container 24 with all inner surfaces thereof spaced from all outer surfaces of inner container 12 and end cap 16 and from the outer surfaces of barrier 20. The remaining internal cavity or space in container 24 is completely filled and gravity or otherwise tamped with finely divided heat absorbing and transmitting or conducting magnesium oxide 26 about the outer surfaces of and in intimate contact with barrier 20 so as to maintain barrier 20 in close contact with container 12 and end cap 16 for ready absorption and transfer or conduction of heat away from container 12, end cap 16 and barrier 20. Container 24 is enclosed and sealed by an appropriate cover or lid 28 using suitable crimping or other closure techniques and, if desired, suitably sealed by appropriate sealants, gaskets or the like. The finely divided magnesium oxide 26 is preferably in a powder or particle form of less than about 200 microns (new US. Standard sieve size) in size and of high purity to insure high levels of heat absorption and transferability or conductivity. Commercially available magnesium oxide sand of 80 mesh with less than 2 percent silicon has been found to be particularly appropriate. Greater particle sizes may be used, however, with decreasing thermal absorption and transfer or conductivity capabilities. Magnesium oxide powder of about 180 micron size gravity tamped to achieve a good level of contact between particle surfaces exhibits a thermal conductivity of about 0.392 Btu/ft-hr-F. Such magnesium oxide powder is also non-burning, relatively stable, provides shock absorption, and exhibits a high melting point, all of which characteristics are desirable in the storage and shipping container 10. Container 24 may be made of any appropriate metal, such as steel, which will provide good thermal conductivity as well as sufficient strength to retain the materials enclosed therein under the environmental conditions to which they are to be subjected, and for convenience, may be a commercially available steel can. it is generally desirable that container 12 be spaced from all inner surfaces of container 24 by at least about 1 inch to provide sufficient shock absorbing capabilities and a desired temperature gradient between the radioactive material 14 and the exterior of container 10.

A storage and shipping container 10 was made by utilizing a 1.5 inch as nominal diameter series 300 stainless steel pipe threaded at one end and sealed at the other end with a welded plate, the pipe and plate having wall thicknesses of about 0.145 inch and an overall length of about 6.5 inches as inner container 12. A standard threaded stainless steel pipe cap with a polytetrafluoroethylene gasket was threaded over the open end of container 12 after filling the interior thereof with about 800 grams of plutonium oxide, which may include americium-24l oxide or other radioactive materials. The loaded container 12 was then enclosed within a polyvinyl chloride tube of about 0.01 inch film thickness and the ends thereof gathered and sealed by adhesive-backed, pigmented vinyl plastic tape, thus facilitating removal of container 12 from a glovebox and protection of personnel from alpha radioactivity. The bagged container was then placed into a standard No. mild steel can having approximately 4 inches outside diameter by 9 inches in height after disposing and gravity tamping about 1 inch of magnesium oxide powder at the bottom thereof. The can, that is outside container 24, was then filled in the spaces between its inner surfaces and the outer surfaces of the barrier 20 with additional finely divided magnesium oxide and the same gravity tamped. A cover was then crimped and sealed over the can to complete the storage and shipping container 10.

Storage and shipping containers as so described were filled with radioactive plutonium oxide materials having specific powers from about 2 to about 7 watts per kilogram with corresponding total power thermal output of from about 1.5 to about 5.5 watts. The maximum temperature of the container 10 enclosing the highest specific power radioactive material was about 1 10F. It was found that the polyvinyl chloride barrier 20 did not change in texture, appearance or apparent strength even when subjected to a temperature at the outside of container 12 of about 148F for about hours and a temperature of about 122F for about 200 hours. The storage and shipping container 10 constructed as described may contain radioactive material producing up to 9 or [0 thermal watts without producing a temperature greater than 200F at the exterior surface of container 12, and at such temperature the polyvinyl chloride, even in the radiation environment, is not noticeably degraded over long periods of exposure time.

Storage and shipping container 10 may be positioned within a standard, commercially available shipping container system, as shown in FIG. 2, to provide complete and acceptable radiation and other protection under all situations. This shipping container system may include an inner container 30 and cover 32 for receiving and holding container 10, an outer container 34 and cover 36, and an intermediate shock absorbing medium 38 and 40 disposed about container 30 on all sides thereof. Such a shipping system may meet all requirements of safe conductance of radioactive materials in normal channels of transportation.

What is claimed is:

l. A plutonium oxides shipping package comprising a cylindrical gas-tight inner container of heat conductive and corrosion resistant metal for retaining plutonium oxides having heat output of up to about thermal watts, a flexible alpha contamination barrier of polyvinyl chloride of from about 0.01 inch to 0.015 inch thickness completely enclosing and in intimate heat conducting contact with cylindrical outer surfaces with all inner surfaces spaced from all outer surfaces of the inner metal container and with inner cylindrical surfaces spaced at least one inch from outer cylindrical surfaces of the inner metal container, and solely finely divided heat conducting magnesium oxide of about 80 mesh filling the space intennediate said polyvinyl chloride barrier and inner surface of the outer metal container and maintaining said barrier in said intimate heat conducting contact with said outer surfaces of the inner metal ontainer for conducting heat away from the latter.

2. A shipping package as claimed in claim 1 wherein said inner container comprises complementary screwthreaded interfitting side wall portions with a joint therebetween and a polytetrafluoroethylene gasket sealing the joint between said portions.

3. A shipping package as claimed in claim 1 wherein said inner container has an inner diameter of about 1.5

of said inner container, a cylindrical outer container of inches and a wall thickness of about 0.15 inches.

heat conducting metal enclosing said inner container

Claims (2)

1. 2. A shipping package as claimed in claim 1 wherein said inner container comprises complementary screw-threaded interfitting side wall portions with a joint therebetween and a polytetrafluoroethylene gasket sealing the joint between said portions.
2. 3. A shipping package as claimed in claim 1 wherein said inner container has an inner diameter of about 1.5 inches and a wall thickness of about 0.15 inches.

Images