Patent Number: 052290670
Section: description

Referring now in detail to FIGS. 1-4 of the drawing, there is seen a reactor tank 1 which is surrounded by a double tank 2 and stands in a reactor cavern 3, which has cooling surfaces 4 on the inner surface thereof. The double tank 2 includes a plurality of rings 2a and a base 2b. A supporting plate 7 is disposed on the double tank 2 and is connected at sides thereof to an outer conduit 8. A grid plate 9 is disposed on the supporting plate 7 and includes two perforated plates 9a and 9b which are connected by pipe nozzles 10. The pipe nozzles 10 transfer the weight of core assemblies 11 to the supporting plate 7. As is best seen in FIG. 4, a base 5 of the cavern 1 is constructed as a supporting platform 6 and bears the double tank 2, the reactor tank 1, the supporting plate 7, the grid plate 9 and the core assemblies 11, which are centered one on top of the other. Not shown in the drawings are sliding materials of a different metal which are disposed between planar bearing surfaces of the superposed parts, in order to permit different movements of neighboring parts at differing temperatures. A reactor core 12, which is only diagrammatically shown in FIG. 1 but is shown in more detail in FIG. 4, is surrounded all around by a multipart metal shield 13, which in turn is surrounded by an inner conduit 14 and is lockably connected to a shaft 15 above the core. The conduit 14 is extended in the upward direction by a stack 23, which is initially surrounded by a plurality of electromagnetic pumps including an active part 16 and a passive part 17, and above them by a heat exchanger 18 as part of a non-illustrated secondary circuit. This secondary circuit transports reactor heat to a steam circuit for supplying steam turbo-generators. The heat exchanger 18 may be made up of a single annular tube bundle or of a plurality of parallel connected partial tube bundles. Not shown, but likewise possible, is also the use of mechanical pumps, having pump shafts being led between the partial tube bundles of the heat exchanger 18 upward to a drive motor through a ring cover 21. In an upper region, the shaft 15, the stack 23 and an inner jacket of the heat exchanger 18 have small holes 19, which are initially evenly distributed over the circumference. Above that, the shaft 15 has larger slits 20. Hot sodium rising from the reactor core 12 can flow to the heat exchanger 18 through the larger slits 20 as well as through the holes 19. The heat exchanger 18 is fastened together with the active part 16 of the electromagnetic pumps to the ring cover 21, which can be installed independently of the instrumentation cover 22, because the latter is supported by the shaft 15. As is seen in FIG. 4, the shaft 15 connects a shield 25 to the instrumentation cover 22 and contains both a linkage 24 for the automatic control and shutdown and leads for the instrumentation of the reactor core 12. The instrumentation cover 22 is sealed off from the ring cover 21 by inflatable seals in such a way as to permit an axial movement of the components against one another. The seals are not shown herein but are usual in the case of liquid metal cooled nuclear reactors. Disposed above the inflatable seals is a lifting and turning apparatus for the cover 22. The lifting and turning apparatus, which is required when changing core assemblies, is likewise known in the field of nuclear reactors and is therefore not shown herein. FIG. 4 uses the same designations as in FIGS. 1 to 3 to show how the base 2b, the reactor tank 1, the supporting plate 7 and the grid plate 9 are superposed in a centered manner on the supporting platform 6 at the base 5 of the reactor cavern 3. In this case too, the sliding materials that were already mentioned above are not shown in detail. The reactor core 12, including the core assemblies 11, is first of all surrounded by the multipart metal shield 13, which in turn is surrounded by the conduit 14 that is also shielded. The shaft 15 and the additional axial shield 25 above the core assemblies 11 rest on the shield 13. This shield 25 has vertical clearances 26 for the passage of coolant, for receiving the linkage 24 and various core instrumentation means and for changing the core assemblies 11. FIG. 5 shows a reinforced point of contact between a ring 2a and the base 2b, which are held together by remotely operable bolts 30. Centering means 31 are provided on the inside. In the area of contact between the ring 2a and the base 2b there are two sealing rings 32, which may be metal O-rings, that are disposed in corresponding grooves. Between the sealing rings 32, a vertical test bore 33 leads to a horizontal bore 34 and then through an angle piece 35 to a test line 36, with which the seal can be monitored from the outside. As indicated in FIG. 6, a driver bit 37 for driving the bolt 30 is remotely advanced towards the bolt 30 by a remote control unit 38. In the case of normal operation, the hot sodium flows out of the reactor core 12 upward through the shaft 15 and through the holes 19 or slits 20 to the heat exchanger 18, while giving off its heat to the outside by means of the non-illustrated secondary coolant circuit. The cooled sodium which is in a delivery gap of the electromagnetic pumps formed by the active part 16 and the passive part 17, is thereupon forced downward, where it is actually between an inner wall surface of the conduit 8 and an outer wall surface of the conduit 14, to the grid plate 9, from where it is conducted in the usual manner through slits in the pipe nozzles 10 into the lower end of the core assemblies 11, in order to take up their heat. In the event of a failure of the pumps, the sodium flows in the same way by natural circulation, while it likewise gives off its heat to the outside by means of the secondary coolant circuit. If the latter should fail, the heat is given off through the tank 1 and the double tank 2 to the cooling surfaces 4 or to a circulating gas in the reactor cavern 3. For example, the double tank 2, including a plurality of the rings 2a and the base 2b, may have a diameter of 5 m, a wall thickness of 150 mm and be formed of a spheroidal cast iron GGG according to DIN 1693. Considerable amounts of heat can be accumulated in this wall and given off to the cooling surfaces 4 with a time delay. In comparison with the usual heat accumulation in concrete, much higher temperatures can be allowed. In order to change the core assemblies, a changing machine, which is known per se, is moved over the cover 22. The machine takes the spent core assemblies 11 directly out of the reactor core 12 and inserts fresh core assemblies. In order to do so, the already previously mentioned lifting and turning apparatus, which can be removed for the purposes of inspection or exchange, vertically raises the instrumentation cover 22 with shaft 15 and the shield 25 and turns it until an opening, which is not illustrated in the figures, is positioned over the core assembly to be changed. Subsequently, the desired core assembly is drawn into a flask and sealed off from the outside. If it becomes necessary to repair heat exchangers or pumps, a special component changing flask is moved over the ring cover 21. Through the use of the flask, the annular heat exchanger 18, with the active parts 16 of the electromagnetic pumps fastened thereto, can be exchanged, in a likewise inerted and sealed-off atmosphere. Changing flasks of this type are known and are usual for inspecting or exchanging heat exchangers and pumps in the case of liquid metal cooled nuclear power plants mentioned initially above. The dimensions of the modular reactor according to the invention, and in particular the relatively small diameter of about 5 m, allows the shaft 15 or the parts 7, 8, 9, 10, 13, 14, 17 and 23 surrounding the nuclear core, or even an entire reactor tank 1 and the individual rings 2a as well as the base 2b of the double tank, to also be exchanged in this way. According to the modular principle mentioned above, the other modular reactors of this same nuclear power plant are kept in operation during such repairs, as well as during the changing of core assemblies, so that a high availability of the nuclear power plant is ensured. According to the repair concept described above, quick and inexpensive disposal, with minimum possible radiation exposure for the environment and personnel, at the end of the service life of a reactor, is also ensured.