Patent Number: 
Section: claims

1. A containment cask for storage or transport of a radioactive material comprising:a metallic inner shell;a metallic intermediate shell disposed on an outer side of the inner shell;an outer shell disposed so as to cover an outer side of the intermediate shell;lead solidified from a molten lead poured between the inner shell and the intermediate shell to serve as a gamma ray shielding material; anda low melting point metal filled in either one or both of (i) a first void layer formed at a boundary between the inner shell and the solidified lead or (ii) a second void layer formed at a boundary between the intermediate shell and the solidified lead. 2. A containment cask according to claim 1, wherein the low melting point metal has a melting point lower than the melting point of lead. 3. A containment cask according to claim 1, wherein the low melting point metal has a melting point lower than an allowable temperature of the containment cask for the radioactive material. 4. A containment cask according to claim 1, wherein the low melting point metal is a metal or an alloy in a liquid state at a normal temperature. 5. A containment cask for storage or transport of a radioactive material comprising:a metallic inner shell;a metallic intermediate shell disposed on an outer side of the inner shell wherein a homogenization treatment is performed on only one of either an outer surface of the inner shell or on an inner surface of the intermediate shell;an outer shell disposed so as to cover an outer side of the intermediate shell;lead solidified from a molten lead poured between the inner shell and the intermediate shell to serve as a gamma ray shielding material; anda low melting point metal filled in a void layer formed at a boundary between the solidified lead and either the outer surface of the inner shell or the inner surface of the intermediate shell, whichever surface was not homogenization treated. 6. A containment cask according to claim 5, wherein the low melting point metal has a melting point lower than the melting point of lead. 7. A containment cask according to claim 5, wherein the low melting point metal has a melting point lower than an allowable temperature of the containment cask for the radioactive material. 8. A containment cask according to claim 5, wherein the low melting point metal is a metal or an alloy in a liquid state at a normal temperature. 9. A containment cask for storage or transport of a radioactive material comprising:a metallic inner shell;a metallic intermediate shell disposed on an outer side of the inner shell;an outer shell disposed so as to cover an outer side of the intermediate shell;a plurality of lead bodies, formed beforehand into any desired shape and size and inserted into a space between the inner shell and the intermediate shell to serve as a gamma ray shielding material; anda low melting point metal filled in a void layer formed among the lead bodies. 10. A containment cask according to claim 9, wherein the low melting point metal has a melting point lower than the melting point of lead. 11. A containment cask according to claim 9, wherein the low melting point metal has a melting point lower than an allowable temperature of the containment cask for the radioactive material. 12. A containment cask according to claim 9, wherein the low melting point metal is a metal or an alloy in a liquid state at a normal temperature. 13. A containment cask according to claim 9, wherein the void layer formed among the lead bodies is filled with a good thermal conductivity oil, instead of using the low melting point metal.