Patent Number: 047132132
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The FIGURE shows a steel pressure vessel 1 with a cylindrical cross section, drawn-in in its center part 1a and expanding in its upper part 1b. In the principal part, the lower part, a small high temperature reactor 2 is installed, the core 3 whereof consists of a pile of spherical fuel elements. The pile is surrounded on all sides by a graphite reflector 4. The fuel elements are removed by means of four pebble extraction tubes 5 from the core 3. The fuel elements are added in from above (not shown). The cooling gas primary helix flows through the fuel element pile from bottom to the top. Over the roof part 4a of the graphite reflector 4 there is a hot gas collector chamber 6. A cold gas collector chamber 7 is provided under the core 3. Around the drawn-in part 1a of the steel pressure vessel 1 is a plurality of absorber rods 8 arranged on the pitch circle with a diameter smaller than that of the lower portion of the steel pressure vessel 1. The absorber rods are insertable into the graphite reflector 4 for the shutdown and control of the small high temperature reactor 2. Reservoirs 9 for small absorber pebbles are mounted in close proximity to the pressure vessel, outside said vessel. The absorber pebbles, which are introduced through conduits 10 into the core 3 and removed by means of the pebble extraction tubes 5, represent a second shutdown system for the small high temperature reactor. A heat utilization system is located in the center part 1a and the upper part 1b of the steel pressure vessel 1, which in the present case is a He/He heat exchanger 11. It comprises in this exemplary embodiment two separate annular coil bundles 12 and 13, arranged concentrically and connected in series. The two coil bundles 12 and 13 have different lengths, with the inner, longer coil bundle 12 extending to the hot gas collector chamber 6 and the shorter, outer coil bundle 13 being included in the pressure vessel 1b. The hot primary helium flows from the hot gas collector chamber 6 from below into the coil bundle 12 and is conducted on the outside along the bundle tubes upward, while transferring its heat to the secondary helium flowing through the bundle tubes. At the upper end of the inner coil bundle 12 the primary helium is reversed and enters from above the outer coil bundles 13, wherein it is cooled down further. By means of an annular conduit 14 located between the steel pressure vessel 1 and the jacket of the heat exchanger, and the annular gap 15 provided between the steel pressure vessel 1 and the graphite reflector 4, the cold primary helium is conducted to the bottom of the steel pressure vessel 1, on which on the outside two circulating blowers 16 connected in parallel, are mounted. The circulating blowers 16 move the cold helium back into the cold gas collector chamber 7. In the upper part 1b of the vessel, within the outer coil bundle 13 an annular decay heat exchanger 17 is installed; it follows in line on the primary side the outer coil bundle 13 and is therefore in normal operation located in the flow of cold gas. It is arranged concentrically on the inner coil bundle 12. The decay heat exchanger 17 may be divided in two systems, equipped with separate feed water lines 18a and 18b and the discharge lines 19a and 19b, respectively. To conduct the secondary side helium to the He/He heat exchanger 11, several connection fittings 20 are mounted laterally on the upper part 1b of the vessel, between the decay heat exchanger 17 and the outer coil bundle 13, and connected with a ring header 21. From the ring header 21, conduits lead to the heating surface tubes of the outer coil bundles 13. Above the outer coil bundle 13 a further ring header 23 is provided, wherein the secondary helium heated by the hot primary helium flowing in the opposite direction on the jacket side, is collected and then conducted--through the lines 24--to the heating surface tubes of the inner coil bundle. In these tubes the gas flows downward and enters an outlet header 25. The latter is connected with a tube 26 passing through the center of the inner coil bundle 12 and exiting on top from the steel pressure vessel 1. The secondary helium is removed by the tube 26 and conducted to its place of utilization.