U.S. patent number RE29,876 [Application Number 05/820,228] was granted by the patent office on 1979-01-02 for container for transporting radioactive materials.
Invention is credited to Stanton L. Reese.
United States Patent |
RE29,876 |
Reese |
January 2, 1979 |
Container for transporting radioactive materials
Abstract
A container for transporting radioactive materials utilizing a
removable system of heat conducting fins is provided which permits
a substantial reduction in the weight of the container during
transport, increases the heat dissipation capability of the
container and substantially reduces the scrubbing operation after
loading and unloading the radioactive material from the container.
The detachable fins are made of a light weight highly heat
conductive metal such as aluminum or aluminum alloys.
Inventors: |
Reese; Stanton L. (Lakeland,
FL) |
Family
ID: |
26807510 |
Appl.
No.: |
05/820,228 |
Filed: |
July 29, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
109925 |
Jan 26, 1971 |
03727059 |
Apr 10, 1973 |
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Current U.S.
Class: |
250/506.1;
376/272; 976/DIG.348 |
Current CPC
Class: |
G21F
5/10 (20130101); B60P 1/6418 (20130101) |
Current International
Class: |
B60P
1/64 (20060101); G21F 5/00 (20060101); G21F
5/10 (20060101); G21F 005/00 () |
Field of
Search: |
;250/506,507,515,518 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Willis; Davis L.
Attorney, Agent or Firm: Fleit & Jacobson
Claims
It is claimed:
1. A container for transporting radioactive materials which
comprises (a) a body having a beta gamma radiation absorbing
material disposed between a central cavity for holding
.[.radioactovem.]. .Iadd.radioactive .Iaddend.material and an outer
wall of .[.ocrrosion.]. .Iadd.corrosion .Iaddend.resistant
material.Iadd., said outer wall having an essentially smooth
exterior surface, .Iaddend.and (b) heat dissipating fins detachably
mounted on and extending outwardly from said outer wall in
thermally conductive contact therewith, said heat dissipating fins
having a lower density and a higher thermal conductivity than said
corrosion resistant material.
2. The container of claim 1 wherein said cavity is of substantially
the same dimensions as the radioactive material contained
therein.
3. The container of claim 1 wherein said fins are made of aluminum
or aluminum alloys.
4. The container of claim 1 where said beta gamma absorbing
materail is depleted uranium and said corrosion resistant material
is stainless steel.
5. The container of claim 1 which further comprises a jacket for
holding a neutron attenuating substance, said jacket being disposed
between the beta gamma absorbing material and the outer wall.
6. The container of claim 1 wherein said fins are vertically
disposed on plates of the same metal as the fins, said plates being
mounted in heat conductive relationship on .[.the skin of corrosion
resistant metal.]. .Iadd.said exterior surface of said outer
wall.Iaddend..
7. The container of claim 1 wherein said heat dissipating fins are
less corrosion-resistant than said outer wall to decontamination
solutions.
8. The container of claim 1 wherein said heat dissipating fins
sufficiently envelop said outer wall to protect said wall from
environmental contamination during transport.
9. In a container for transporting radioactive materials which
includes a body of beta gamma absorbing material with a central
cavity disposed therein for holding said material, an outer skin of
corrosion-resistant metal surrounding said body, and heat
dissipating fins in heat conductive relationship with said outer
skin, the improvement which comprises .Iadd.providing said outer
skin with an essentially smooth exterior surface and
.Iaddend.removably mounting said fins to said outer skin and
constructing said fins from a lighter weight, greater heat
conductive, less corrosion-resistance metal than said outer
skin.
10. The container of claim 9 wherein said fins are made of aluminum
or aluminum alloy.
11. The container of claim 9 wherein said fins are disposed on
plates of the same metal as the fins, said plates being mounted in
heat conductive relationship on .[.the.]. .Iadd.said .Iaddend.skin
of said corrosion resistant metal. .Iadd. 12. A container for
transporting radioactive materials which comprises (a) a body
having a beta gamma radiation absorbing material disposed between a
central cavity for holding radioactive material and an outer wall
of corrosion resistant material having an essentially smooth
exterior surface and (b) heat dissipating fins extending outwardly
from said outer wall in thermally conductive contact therewith,
said heat dissipating fins having a lower density and a higher
thermal conductivity than said corrosion resistant material, said
dissipating fins being mounted on a support of the same material as
said fins which detachably abuts against said smooth exterior
surface of said outer wall. .Iaddend..Iadd. 13. A container for
transporting radioactive materials which comprises (a) a body
having a beta gamma radiation absorbing material disposed between a
central cavity for holding radioactive material and an outer wall
of corrosion resistant material having an essentially smooth
exterior surface and (b) heat dissipating fins extending outwardly
from flat support members in intimate physical and thermal
conductive contact with said smooth exterior surface, said heat
dissipating fins and said support members having a lower density
and a higher thermal conductivity than said corrosion resistant
material and said heat dissipating fins and support members
substantially enveloping said outer wall. .Iaddend.
Description
The present invention relates to an improved container or packaging
assembly for transporting radioactive materials. More specifically,
the present invention relates to a container or packaging assembly
for transporting heat emitting radioactive materials which has
improved heat dissipating features and which, by virute of its
unique structure, has reduced weight.
Due to the radiation hazard associated with radioactive materials,
it is generally necessary that these materials be packaged in
sturdily constructed containers consisting of materials and design
which will readily attenuate the radiation and dissipate the heat
emitted by the radioactive material being transported. Radiation
attenuation is necessary to biologically shield personnel and the
public from radiation in the course of transport under both normal
conditions of transport and under accident conditions. Heat
dissipation is often necessary to protect the container from damage
and to protect personnel from serious burns while carrying heat
emitting radioactive materials.
In the past it has been the practice to construct heavy shipping
containers for transporting highly radioactive heat emitting
materials with a central cavity considerably larger than that
necessary to obtain the radioactive materials to be transported.
This void space is usually filled with a fluid, such as water,
which circulates through the cavity to an external heat exchanger
to provide cooling. This fluid also frequently serves to absorb
neutrons. The cavity is normally lined with a corrosion resistant
material, such as stainless steel, which is relatively resistant to
decontaminating solutions. The material surrounding the liner is
usually of high density because the ability to attenuate beta gamma
radiation is proportional to the density of the shielding
material.
The outer structure of the container normally includes an external
wall surrounding the liner together with heat dissipating and
impact fins integral with the wall. The outer surface including the
external wall and fins are normally made of the same material, such
as stainless steel or conventional steel coated with stainless
steel. The fins serve to dissipate the heat emitted by the
contained radioactive materials and protect the package against
impact in the event of an accident. The surface of the outer
structure is normally constructed of stainless stell or other acid
resistant material in order to avoid reaction with corrosive
decontaminating solutions, such as nitric acid.
Where highly radioactive materials are to be shipped, such as
irradiated fuel elements or the waste resulting from the recovery
of the fuel values found in irradiated fuel elements, the thick
shielding and heat dissipating requirements for the walls and fins
of the shipping container may result in a container which when
loaded consists of as much as 98 percent shielding and heat
dissipating structure and as little as 2 percent radioactive
material payload to be transported. Unfortunately, containers of
this type, while providing the necessary protection against emitted
radiation, structural integrity, and heat dissipation, are so
extremely heavy that the cost of transporting the radioactive
material is extraordinarily high. Further, transport is often
limited to one fuel assembly on a single legal weight road trailer
at a time.
It is, accordingly, an object of the present invention to provide a
container for transporting radioactive materials which has improved
means for dissipating heat generated by the radioactive
materials.
It is another object of the present invention to provide such a
container for transporting radioactive materials which in addition
to having an improved assembly for dissipating emitted heat is
significantly lighter than previously known containers of this
type.
Still another object of the present invention is to significantly
lessen the time and materials required, compared to present
practice, to remove road dirt and other contamination from the
container proper after transport and to scrub or treat the
container to remove radioactive contamination after loading and
unolading operations.
In accordance with the present invention, these and other objects
are achieved by providing a container for transporting radioactive
materials in which the system of heat dissipating fins externally
located on the container, having generally the configuration of
heat dissipating fins employed in prior structures, is readily
removable or detachable from the external wall of the
container.
Numerous and unexpected advantages are realized by providing
detachable cooling fins which are removable from the outer casing
of the container rather than being an integral part thereof. By
employing removable external fins in accordance with the present
invention, it is possible to construct these fins of not only
lighter materials, but materials which also have superior heat
conducting properties, such as aluminum or aluminum alloys, rather
than the heavier metals such as stainless steel. Stainless steel
has heretofore been the preferred material for the fins in order
that they will be resistant to corrosive cleansing solutions, such
as nitric acid, with which the casing must be decontaminated. By
providing detachable fins that are removable, they can be taken off
the container prior to loading and unloading operations and thereby
avoid the necessity of scrubbing or treating the fins with the
decontaminating solutions. Thus, the fins may be constructed of
materials which would not otherwise be non-corrosive to the
decontaminating solution. Accordingly, the fins can be made of
lighter, more heat conductive materials.
An additional advantage of the present invention is that due to the
improved heat dissipation accomplished by using fins made of a
substantially higher heat conducive material, it is not necessary
to provide for a cooling liquid to circulate within the chamber.
Thus, in addition to permitting a more simplified and therefore
less costly device, the present invention also dispenses with the
need for a central cavity which is substantially larger than the
size of the radioactive materials to be contained therein.
According to this invention, the central cavity into which the
radioactive material is to be placed is substantially no larger
than that necessary to accommodate the largest contemplated load of
radioactive material since there is no requirement for a space
through which to circulate a cooling fluid.
A further advantage of the present invention is that it permits
easier cleaning. The container proper must be meticulously clean
for loading and unloading of the radioactive material since this
operation is performed visually under several feet of water which
must be sparkling clear to permit observation of operations.
Consequently, after detaching the heat dissipation system, the
container proper requires only a minimum of cleaning time and
materials in order to remove dirt, etc. picked up by the outer
shell in transport before it can be loaded or unloaded. What
cleaning is required is done to an essentially smooth, flat
exterior wall surface instead of one containing the many crevices
found in "premanently" finned structures. Similarly,
decontaminating procedures are drastically simplified since it is
no longer necessary to submerge the cooling fins into the
contaminating water during loading and unloading operations. Hence,
only the smooth, flat exterior wall surface of the container, and
not the fin structure, need be scrubbed or treaded for
decontamination.
Still another advantage of the heat dissipation system of the
present invention is that the cooling fins may be designed for
optimum heat transfer with little regard for strength because they
can remain on the carrying vehicle and are thus protected from the
handling injury they would be subjected to were they part of the
container proper which must be moved around in the cleaning,
unloading and loading processes. This design thus permits even
lower weight in the heat dissipation system than would be
practicable were the heat dissipataion system permanently affixed
to the container.
Still another advantage of the detachable fin system design of the
present invention is that although the outer surface of the
container proper may become contaminated with radioactivity from
exposure to the loading or unloading area and this contamination
may exceed the external surface limits for transport permitted by
regulatory authority, the container may still be used since it is
enveloped by the uncontaminated fin system, and the contaminatin is
therefore not accessible on the outside surface of the package as
presented for shipment.
For the purpose of illustrating the foregoing objects and
advantages attendant this invention, preferred and illustrative
embodiments of the invention will hereinafter be described with
reference being had to the accompanying drawings forming a part
hereof, wherein like numerals refer to like parts throughout, and
in which:
FIG. 1 is a perspective view of the inner container having a
smooth, flat exterior wall in which one end is broken away to show
the interior sections of the container and with the heat conductive
fins not shown.
FIG. 2 is a perspective view of a portion of the smooth exterior
wall container of FIG. 1 with the detachable fin system mounted
thereon, the ends being broken away to also show the interior
sections of the container; and
FIG. 3 is a perspective view of another embodiment of the invention
showing the smooth wall container positioned on a road trailer to
be surrounded by the detachable fin system which is actually
mounted on the road trailer, the fin system shown unassembled in
solid lines and shown assembled in dashed lines.
Referring now specifically to FIGS. 1 and 2 of the drawings, the
central cavity 1 carries the radioactive material. It is made only
large enough for easy insertion of the fuel elements or other
radioactive materials to be transported. While a square cross
section is illustrated in the drawings, any configuration, such as
round, may be employed, depending primarily on strength strength
the shape of the material to be contained. The cavity is lined with
a corrosion resistant inner liner 2, such as stainless steel. This
inner liner is surrounded by a beta-gamma radiation shield 3 of
sufficient thickness to be required for the beta-gamma shielding.
However, since the size of the cavity is reduced from what had
normally been required in prior structures, the volume of shielding
material required is smaller to accomplish the same degree of
shielding and, therefore, the total weight is thereby reduced
without sacrificing radiation attenuation. Conventional beta-gamma
radiation shielding materials can be used, however, metallic
uranium depleted in the U-235 isotope is preferred. Further,
depleted uranium having a structural strenght similar to that of
steel is preferred so that the depleted uranium can be either cast
or fabricated into the desired condiguration such that its
structural strenght may be utilized to contribute to the overall
integrity of the package.
The uranium shield is next surrounded with a structurally strong
outer wall 4 which has an exterior surface of corrosion resistant
material, such as stainless steel. An 18-8 stainless steel is often
the preferred material.
If neutron attenuation is required by reason of the nature of the
radioactive material being transported, an additional jacket 5
having an outer wall 6 is provided to accommodate a neutron
attenuator, such as borated water (e.g. a dilute solution of a
soluble boron compound such as sodium borate) or other low density
fluid with suitable neutron attenuation properties. By this
technique the lower density neutron absorbing material is at the
outside of the package and thus adds relatively less weight to this
large volume. A further advantage of this arrangement is that a
reduced thickness of neutron absorbing fluid is required than would
be required if the beta-gamma shield material were not between it
and the neutron emitting radioactive material, the beta-gamma
shielding being able to absorb some neutrons and slow some other
neutrons. The outer wall 6 has a smooth exterior surface made of a
material which also is corrosion resistant to decontaminating
solutions, such as nitric acid.
Heat is dissipated through detachable fin plates 10, having the
fins 12 permanently affixed to a base plate 14. The fin plates 10
are mounted against the smooth outer surface of wall 6 by bolts 16
or otherwise held in close heat conducting contact with the
container surface, such as by springs or other conventional holding
means. These fin plates 10 and heat dissipation fins 14 are removed
during loading and unloading and, therefore, they need not be
constructed of a material resistant to corrosion by decontaminating
solutions. They may, preferably, be constructed of aluminum which
has a thermal conductivity approximately 4 times that of steel and
approximately 14 times that of stainless steel and a density about
one-third that of steel or stainless steel. The resulting weight of
the heat dissipation system may be approximately one-twelfth that
of previously used stainless steel to obatin equal heat dissipation
capability and a corresponding lower weight of stainless steel. A
typical road trailer mounted container used to ship spent power
reactor fuel elements, for example, might require 12,000 pounds of
heat dissipating fins if they were composed of stainless steel. The
same heat can be dissipated with approximately 1,000 pounds of
aluminum fins or less.
It is to be understood, of course, that where the container of the
present invention is to transport radioactive materials which do
not necessitate neutron attenuation, the additional jacket 5 and
outer wall 6 are an unnecessary part of the container. Under such
circumstances, the jacket 5 and wall 6 are eliminated from the
package, and the detachable fin plate 10 is mounted directly on
outer wall 4 in the same manner as described for mounting the plate
on wall 6.
Turning now to FIG. 3, it will be noted that a conventional
tractor-trailer 20 has a trailer frame 22 on which are pivotally
mounted at each side fin plates 24. Plates 24 include fins 26
permanently affixed to base plates 28 in the same manner as
described for fin plates 10. Fin plates 24 are also transversely
hinged at a point to allow these plates to surround a smooth
exterior wall container 30 similar to that illustrated in FIG. 1.
Accordingly, it can be seen that the detachable fin system of the
present invention may be pivotally mounted on a conveyance and
after placing the smooth wall container holding the radioactive
material in position on the body, the detachable fins are then
assembled around the container, as shown in dotted lines in FIG. 3,
in heat conducting relation thereto.
It will be apparent to those skilled in the art that numerous
modifications of the invention herein described and shown are
possible without departing from the invention, which is to be
interpreted in accordance with the appended claims.
* * * * *