Patent Number: 059490845
Section: summary

CROSS-REFERENCE TO RELATED APPLICATIONS Not Applicable STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not Applicable REFERENCE TO A MICROFICHE APPENDIX Not Applicable BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains generally to shielding for radioactive materials and more particularly to a lightweight storage container for radioactive materials. 2. Description of the Background Art At the present time, there are approximately 560,000 tons of depleted uranium hexaflouride under storage in 50,000 cylinders which cost about $10,000,000 annually to maintain. Putting the depleted uranium to practical use would cut the maintenance costs significantly. One such use of depleted uranium is as shielding material for radioactive materials. Using the depleted uranium in such a manner is not only useful, but also serves to eliminate the depleted uranium from the environment. The storage and/or transportation of radioactive materials require effective shielding to protect the operating personnel and the surrounding environment. The storage and/or transportation of radioactive materials have been accomplished using canisters, containers, receptacles or vessels that possess photon and neutron absorption capability and sufficient structural strength. The radiation absorption capability shields the environment and operating personnel from radiation emitted by the radioactive materials, while structural strength allows the vessel to withstand normal handling and storage stresses and even some accidental impacts upon the vessel. One such known storage vessel utilizes a hollow body having lateral walls and a base formed unitarily with one another and open at an upper end. The walls of the body have an outer layer, an intermediate layer and an inner layer. The outer and intermediate layers are cast unitarily from a carbon containing ferrous metal of copper alloy while the intermediate layer consists of a cast matrix phase within which heavy metal particles, such as depleted uranium, are embedded to absorb radiation. A plurality of separate channels disposed longitudinally within the outer layer is filled with neutron absorptive material, and a removable cover is fitted over the upper end after the radioactive has been placed therein. The multi-layer configuration of such storage vessels result in a shielding system that is large dimensionally and in mass, thus limiting the quantity of radioactive material that can be stored, especially when storage area is limited. Without the separate longitudinal channels containing the neutron absorptive material, the vessel would be ineffective, as depleted uranium is useless by itself for neutron absorption. Such a large multi-layer configuration also requires ancillary cooling systems to dissipate heat generated by the enclosed radioactive material. Accordingly, there is a need for a radiation storage vessel that combines the functions of attenuating photon radiation, neutron absorption and shock mitigation from impact, while minimizing the thickness of the vessel's walls and weight such that the vessel can be more readily transported and a larger quantity of radioactive material can be stored in a given area. The foregoing reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicant's acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these teach or render obvious, singly or when considered in combination, applicant's claimed invention. BRIEF SUMMARY OF THE INVENTION The present invention is a vessel for the storage and transportation of radioactive materials. The vessel generally comprises a mixture of small metal particles, preferably but not necessarily spherical, embedded in a matrix that contains neutron moderating and absorbing material. The use of spherical particles, however, assures maximum density of packing so that the thickness of the vessel's wall is minimized while allowing sufficient space in the interstices between the particles for the neutron absorber/moderator. The composite mixture of metal particles and neutron absorbing matrix is poured into an annular space between an inner vessel that is used to contain the radioactive material and an outer casing that serves both as a form for the shielding system and a protective covering. The metal particles are composed of depleted uranium, lead or other like material. The inclusion of neutron absorbing material within the matrix eliminates the need for a separate layer of neutron absorptive materials thus reducing the weight and amount of space occupied by the vessel. An object of the invention is to provide a radioactive material storage vessel which attenuates photon radiation, absorbs neutron emissions and mitigates shock from impacts. Another object of the invention is to provide a radioactive material storage vessel which minimizes thickness and weight so that a larger quantity of radioactive material can be stored in a minimum amount of space therein, thereby maximizing the efficiency of the storage system. Another object of the invention is to provide a radioactive material storage vessel which minimizes thickness and weight so that the vessel is more readily transportable. Another object of the invention is to provide a radioactive material storage vessel in which heat generated by the radioactive contents can be more easily dissipated by thermal conduction. Still another object of the invention is to provide a radioactive material storage vessel which allows retrieval of the metal components of the storage vessel using conventional techniques. Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.