Patent Number: 048329045
Section: claims

1. In a pool type liquid metal cooled fast breeder reactor having a pressure vessel filled with liquid metal, a reactor core immersed in said liquid metal, a wall dividing said pressure vessel into an upper region or hot header receiving heated liquid metal which has passed through said reactor core, a lower region or cold header receiving cooled liquid metal from a heat exchanger, said wall having a portion or stepped wall extending in a radial direction of said pressure vessel, and an emergency core cooling system comprising at least one heat exchanger immersed in said hot header and having upper inlet and lower outlet openings for cooled liquid metal, the improvement wherein said emergency core cooling system further comprises (a) a substantially vertical tubular conduit passing through said stepped wall vertically below said exchanger and having a lower end opening into said cold header and an upper end opening into said hot header, below a lower part of said exchanger;  (b) a bell fixed to said heat exchanger in an extension of its lower part, open at the bottom and arranged so as to cap a top part of said conduit while providing a free space around said top part; and  (c) means for compressing inert gas and for relieving the pressure in an inner space of said bell, enabling complete separation of said liquid metal in said hot header from said liquid metal in said cold header, by means of compressed inert gas, or to bring cooled liquid lower metal outlet openings of said heat exchanger into communication with said cold header by means of said bell and of said conduit. 2. Emergency cooling system according to claim 1, further comprising a shell fixed to a casing of said heat exchanger above said outlet openings for cooled liquid metal surrounding said lower part of said heat exchanger and extended downwards so as to surround said bell over at least a part of its height and said top part of said tubular conduit. 3. Emergency cooling system according to claim 1 or 2, wherein said inner space of said bell is connected by a pipeline to a storage tank for compressed inert gas, arranged outside the reactor vessel. 4. Emergency cooling system according to claim 3, wherein said liquid metal is sodium, and said inert gas is argon. 5. Emergency cooling system according to claim 3, wherein a valve is arranged in said pipeline at an entry of said storage tank, and a vent pipe, in which a further valve is placed, is arranged as a branch on said pipeline. 6. Emergency cooling system according to claim 1, wherein said stepped wall is pierced with an opening vertically below said heat exchanger, a shell with a vertical axis is fixed on said stepped ramp along said opening, so as to project downwards inside said cold header, and said tubular conduit is fixed in a central opening of an annular bottom forming an integral part of the end of said shell opposite said opening in said stepped wall. 7. Emergency cooling system according to claim 6, wherein a shell forming an integral part of said lower part of said heat exchanger is extended downwards, inside a shell forming an integral part of said stepped wall, and has a diameter which is slightly smaller than a diameter of said shell forming an integral part of said stepped wall.