Retrofittable nuclear reactor core catcher

Claim 1

A passive system for the prevention of the escape of radioactive material to the biosphere from a nuclear reactor plant suffering a major core-destructive accident with melt-down of the reactor, said nuclear reactor plant having a main above-ground structural containment shell, said system comprising: an isolation conduit or tube extending downward from the floor of the nuclear reactor plant immediately below the reactor core, said isolation conduit or tube including an outer reinforced concrete shell, refractory lining material within the concrete shell and an inner layer of a high strength, high temperature resistant metal; said isolation tube having a diameter which is the same order of magnitude as said core, and a depth at least two times greater than its diameter; a relatively thin sealing layer extending over the upper end of said isolation tube; means mounted within said isolation tube for delaying the descent of said core through said isolation tube following melt-down; a core-catcher heat exchanger having a relatively large surface area mounted below said isolation tube to receive melted core material flowing through said isolation tube; said isolation conduit and said core-catcher heat exchanger being formed as a single long sustantially vertically extending channel, said heat exchanger including an inner structural liner of good heat transfer material forming an inner metal wall surrounding said channel and a thin enclosing water jacket having upper and lower conduits and said core-catcher heat exchanger having a sufficiently small cross-section for containing the core material to preclude a critical assembly for the particular core material employed in the reactor, said core-catcher heat exchanger being of a size and shape for sufficiently cooling the molten core material to provide a solid liner formed from said molten core material on the inner wall of said core-catcher heat exchanger, wherein an outer reinforced concrete shell extends the length of said core-catcher heat exchanger and the cross-section of said channel at its lower end being sufficiently small so as to preclude said critical assembly, said water jacket having an outer wall spaced a short distance from said inner metal wall to provide said thin water jacket, supporting means in said space for maintaining said inner and outer walls in said spaced relation, means mounted within said core-catcher heat exchanger for delaying the descent of said molten core material through said core-catcher heat exchanger; a passive body of cooling water positioned adjacent the main nuclear reactor plant, said body of cooling water being open to the atmosphere to permit the boiling off of water; means for coupling said upper and lower conduits to said body of cooling water, to facilitate the flow of heat between said core-catcher heat exchanger and said body of cooling water; and additional passive heat exchanger means coupled between the space within said reactor plant containment shell and said body of cooling water.