Patent Number: 039309398
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Having reference to FIG. 1, the outermost steel containment vessel 1 has a cylindrical side wall and a hemispherical top and the vessel totally encloses the reactor and its associated components. A concrete floor 2 supports the entire installation. The reactor pressure vessel 3, made of prestressed concrete, has an internal liner 5 which shields the concrete against radiation and within which the reactor core 7 is located, surrounded by a radial breeder jacket 8 and an axial breeder jacket 9. The core's components are supported by a mounting 10 on the outside of the pressure vessel. The pressure vessel 3 also encloses a steam generator 12 through which the gas coolant is circulated as indicated by the unnumbered arrows, the circulation being aided by a blower 13. In this instance the basin 14 is on the outside of the pressure vessel 3, it being located below the bottom 15 of the liner 5 and, of course, below the core 7. If the core is operated at excessively high temperatures, and melts and falls into the bottom 15, it potentially may burn through this bottom and the intervening concrete of the pressure vessel 3, to fall into the basin 14. The containment vessel 1 normally contains a gas and in the present embodiment this gas is used as a fluid coolant to effect the necessary dissipation of the heat of the melted core in the basin 14, the latter being of large horizontal transverse area permitting possible spreading of the core. The basin 14 is spaced below the bottom of the pressure vessel 3 and is enclosed by a vertical wall 3a which also functions to support the pressure vessel above the floor 2. To use the gas in the containment vessel 1 as a coolant for the basin's contents, a duct 16 extends through the wall 3a and upwardly, above the pressure vessel 3, and opens into the top of the containment vessel 1. The wall 3a has an inlet port 17, and so the heated gas can rise through the duct 16, flow along the inside of the containment vessel 1 for cooling by heat conduction through the latter's wall to the outside atmosphere, and when cooled, flow downwardly and in through the inlet port 17, the result being a constant circulation of the gas coolant. The top 18 of the containment vessel 1 has the hemispherical shape and the entire containment vessel is made of steel having good thermal conductivity. The duct 16 distributes the heated gas over a large area of the top 18, and water cooling sprays 19 are provided by nozzles (not shown) to shower down on the top 18. As shown by FIG. 1a, there are preferably a plurality of the ducts 16 and a plurality of the ports 17, this causing the circulating flow of gas coolant to be very widely distributed throughout the interior of the water cooled top 18 of the steel containment vessel. Although not shown, the ports 17 may have ducts which, like the ducts 16, extend upwardly so that the top 18 functions as the main cooling area for the gas-coolant. It follows that in the event of an accident, the melted core in the basin 14 is automatically and immediately subjected to very rapid cooling by large volumes of gas effectively cooled by the large area of the water-cooled hemispherical top 18 of the steel containment vessell. In FIG. 2 the basin 23 is located inside of the pressure vessel 3 directly beneath the core 7 and is provided beneath its bottom with a chamber 25 containing water. If the core 7 melts, and falls into the basin 23, the water is converted to steam and a pipe 26 carries this steam upwardly to the hemispherical top 18 for condensation, the condensate returning via a pipe 27 to the chamber 25, thus establishing circulation. In this case the hemispherical top 18 is a double-walled construction forming a hemispherical chamber 29 into the central portion of which the pipe 26 connects, the pipe 27 connecting with a lowermost portion of this chamber 29. A plurality of these pipes may be used in each instance. The water spraying means 19 are, of course, also used. The very large extent of the chamber 29 provides for very effective dissipation of large amounts of heat and provides an effective means for handling the steam incidental when the water in the chamber 25 is converted to steam by the heat of a melted core in the basin 23. The containment vessel's large top 18 functions as a large capacity heat exchanger. As shown, the pipe 26 connects with the upper portion of the chamber 25; the pipe 26 connects with the chamber's lower portion. As shown by FIG. 3, the basin 23 may be provided with downwardly extending ribs 20 projecting downwardly far enough to be within the solid water 31 in the chamber 25. If this is not done, the steam can separate the water from the bottom of the basin 23 with the result that the bottom could not transmit heat by direct conduction to the water. The basin 23 forms the primary intercept for an accidentally melted core and must withstand extreme temperatures. Therefore, it is preferably made of a refractory, such as graphite, inevitably having lower thermal conductivity than metal. Therefore, in FIG. 4 the efficiency provided by the ribs 30 is greatly increased by corresponding ribs 33 which extend upwardly into the basin 23 where the ribs 33 are embedded in metal 34 having a lower melting temperature. Metals such as mercury, tin, lead and the like may be used. If a component of the core melts and falls, it can cause extreme local overheating of the basin 23 in FIG. 3, but using this metal 34, as shown in FIG. 4, the metal forms a pool of metal of much higher thermal conductivity than graphite or other refractory, distributing the heat substantially uniformly throughout the basin 23. In FIG. 4 the distribution is throughout all of the upwardly projecting ribs 33. To further assist in the thermal conductivity efficiency, the ribs 30 and 33, which are in mutual registration, are provided with endless passages 35 arranged as loops extending from one registered rib to the other and filled with the metal of low melting temperature. When melted by heat occasioned by an accident, this metal establishes a circulating flow of molten metal from the molten metal 34 to the water 31 in the chamber 25, the intervening refractory portions being of small thickness. In FIG. 5 the ribs 30 are shown in direct contact with water pipes 36 which may be connected in circuit with the chamber 29 in the containment vessel's top 18, as by using pipes corresponding to 26 and 27 in FIG. 2, the details of this being easily understood and, therefore, not illustrated. The low melting temperature metal previously described may be used to surround the fins 30 and pipes 36, as shown at 37, and the chamber 31 may be extending upwardly around the side wall of the basin 23 by forming the chamber as shown at 38, the side wall of the basin being itself provided with the ribs 30 and water pipes 36. In this instance also the metal 37, when liquid, uniformly and widely distributes the heat while conducting it to the water which abstracts the heat by its conversion to steam, the latter being sent to the chamber 29 and returned as condensate. The construction shown by FIGS. 2 through 5 provides for a primary intercept of a melted core. If the core burns through the basin 23, the bottom 15 of the liner 5 and the intervening concrete portion 40 of the pressure vessel 3, it falls into the external basin 14 providing the ultimate intercept. Prior to this occurring the basin 14, in effect, is provided with a cover which is destructible by heat in the event a melted core goes through the various parts just mentioned. This concept may be applied to the basin 23 by providing it with a destructible cover (not shown for the basin 23) which closes its top against the flow of the gas-coolant during the normal operation of the reactor generating steam via the steam generator 12. As explained in connection with the FIG. 2 embodiment, the top 18 of the containment vessel 1 may be a double-walled construction forming the chamber 29 for the steam and condensate. Correspondingly, in the FIG. 1 construction the ducts 16 and 17 may be provided by passages formed by the double walls of the containment vessel, illustrated by FIG. 1a.