Patent Number: 046438700
Section: summary

2. Field of the Invention This invention relates to nuclear reactors, and particularly, to how nuclear reactor containment structures may dissipate heat following an extremely low probability meltdown and subsequent breach in the reactor vessel. 3. Background Discussion Because radioactive materials are contained in a nuclear reactor, great caution must be taken to prevent the escape of such materials to the environment. One type of nuclear reactor is the liquid metal fast-breeder reactor which employs a core immersed in liquid sodium coolant. If all heat removal capacity were lost and the temperature within the reactor should exceed the melting point of the core, the core would disintegrate and core materials could reach the bottom of the reactor, where the debris layer heat generation rate could be sufficiently high to melt the walls of the reactor vessel and guard vessel. If this would occur both sodium and fragmented, radioactive core debris would escape from the reactor vessel. The reactor containment must be designed to retain such radioactive materials which might penetrate the reactor vessel, and prevent their entry into the environment where they can endanger public health & safety. The present invetion provides a safe containment structure which has the advantages of a system for cooling the containment structure and retained core debris to provide protection in the extremely unlikely event of a breach of the reactor vessel, so that failure of the containment by the core debris interactions is avoided. BRIEF DESCRIPTION OF THE INVENTION The nuclear reactor of this invention includes a reactor vessel disposed in a thick-walled metal cavity. This cavity is preferably lodged partially or completely below the surface of the earth. Preferably it is tied to adjacent structural concrete. Preferably, the reactor vessel is seated in a guard vessel and both of these are seated within the surrounding metal cavity. There is a thick metal basemat beneath the reactor vessel at the bottom of the cavity. The cavity wall, at the bottom abutting the basemat, is welded or otherwise integral with the metal basemat. Disposed in the zone below the basemat and adjacent to it, are means for feeding water into this region. The zone immediately underneath the base plate is composed of porous media such as sand and gravel. If there is a core meltdown and subsequent breach in the reactor vessel, this zone below the basemat will eventually be heated above the boiling point of water. Water fed into the heated zone will be converted into steam. Its latent heat of vaporization provides cooling of both the basemat and contained core debris. Means are provided for venting the steam to the atmosphere as it is formed. The metal base plate preferably extends beyond the perimeter of the cavity wall and it is supported on metal pilings which preferably extend downwardly and outwardly into the earth. The metal pilings serve to conduct heat away from the reactor into water-saturated porous media and earth beneath. At the same time they support the reactor and prevent it from sinking into the earth.