Patent Number: 044951370
Section: claims

1. A fast breeder reactor comprising: a reactor vessel;  a guard vessel enclosing said reactor vessel, spaced a predetermined distance from said reactor vessel; and  a liquid manometer structure, the space defined between said reactor vessel and said guard vessel communicating with the exterior of said guard vessel only through said liquid manometer structure, said manometer structure being filled with a liquid so as to liquid-seal said space between said reactor vessel and said guard vessel with respect to the exterior of said guard vessel said space between said reaction vessel and said guard vessel being charged with an inert gas so as to maintain said space at a pressure substantially greater than atmospheric pressure.  an annular flange extending horizontally from the outer periphery of said guard vessel at the upper end thereof, said annular flange having a radially outer portion having spaced apart vertical sidewalls and a substantially U-shaped cross section; and  an annular member extending horizontally from the outer periphery of said reactor vessel at a position above said flange and having an inverted L-shaped cross section;  said annular flange and said annular member being combined with each other in such a manner that the lower end of said annular member is inserted between said sidewalls, said space communicating with the exterior of said guard vessel between said annular flange and said annular member.  an annular flange extending horizontally from the outer periphery of said guard vessel at the upper end thereof, said annular flange having a radially outer portion having spaced apart vertical sidewalls and a substantially U-shaped cross section; and  an annular member extending horizontally from the outer periphery of said reactor vessel at a position above said flange and having a sideways turned T-shaped cross section;  said annular flange and said annular member being combined with each other in such a manner that the lower end of said annular member is inserted between said sidewalls, said space communicating with the exterior of said guard vessel between said annular flange and said annular member.  an annular flange fitted to the inner peripheral surface of said guard vessel at the upper end thereof, and having an inverted L-shaped cross section; and  an annular member fitted to the outer peripheral surface of said reactor vessel at the upper end thereof, and having an inverted L-shaped cross section;  said annular flange and said annular member being combined with each other in such a manner that said space communicates with the exterior of said guard vessel between the lower end of said annular member and said annular flange.  an annular flange fitted in the innner peripheral surface of said guard vesel at the upper end thereof, and having an inverted L-shaped cross section; and  an annular member fitted to the outer peripheral surface of said reactor vessel at the upper end thereof, and having a sideways turned T-shaped cross section;  said annular flange and said annular member being combined with each other in such a manner that said space communicates with the exterior of said guard vessel between the lower end of said annular member and said annular flange. 2. A fast breeder reactor according to claim 1, wherein said liquid manometer structure comprises a substantially U-shaped tube welded to a part of the outer circumferential surface of said guard vessel, said tube having an inner diameter sufficiently large enough to permit the passage of welders and welding tools therethrough. 3. The fast breeder reactor according to claim 1, wherein said liquid filling said liquid manometer structure is mercury. 4. The fast breeder reactor according to claim 1, wherein the pressure of said inert gas charged into said sealed space is about 1.5 to about 3 atms absoluted pressure. 5. A fast breeder reactor according to claim 1, wherein said liquid manometer structure comprises: 6. The fast breeder reactor according to claim 1, wherein said liquid manometer structure comprises: 7. The fast breeder according to claim 1, wherein said liquid manometer structure comprises: 8. The fast breeder reactor according to claim 1, wherein said liquid manometer structure comprises: 9. The fast breeder reactor according to claim 1, wherein said inert gas charged in said sealed space between said reactor vessel and said guard vessel comprises a tag gas, said reactor further including means for monitoring leakage of said tag gas from said sealed space. 10. The fast breeder reactor according to claim 9, wherein said means for monitoring leakage of said tag gas comprises means for detecting a pressure change inside said sealed space. 11. The fast breeder reactor according to claim 9, further comprising a cover gas space inside said reactor vessel, wherein said means for monitoring leakage of said tag gas comprises tag gas detection means, disposed in said cover gas space, for detecting leakage of said tag gas into said cover gas space. 12. The fast breeder reactor according to claim 9, wherein said means for monitoring leakage of said tag gas comprises tag gas detection means, disposed outside said guard vessel, for detecting leakage of said tag gas to ouside said guard vessel. 13. The fast breeder reactor according to claim 9, wherein said tag gas is helium. 14. The fast breeder reactor according to claim 9, wherein said tag gas is a gas containing therein a stable isotope of a rare gas. 15. The fast breeder reactor according to claim 11 or 12, wherein said tag gas detection means comprises a mass spectrometer and a gas sampling device cooperating therewith.