Patent Number: RE0298760
Section: description

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.