Patent Number: 040574679
Section: description

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 the primary cooling water enters from the bottom into the reactor core 1, which consists of numerous, vertical, parallel fuel assemblies, not shown, and flows from there to an annular steam generator housing 2 concentrically arranged above the reactor core 1, flows through the housing 2 from the bottom to the top and is pushed by pumps 3, which are driven by electric motors 4, into the previously referred to hollow ring 5 of box-shaped cross section, which has at its underside, and more specifically, at its outer rim, numerous openings 6, through which the primary cooling water flows downwardly into a ring canal or passage 7 and from there into a space 8 to the side and below the reactor. Should the primary circulating pumps 3 fail, a natural thermal circulation system is set up, in which the hot primary water flows upward in the reactor core as in normal operation. As the steam generators 9 remain in operation, the primary cooling water is cooled down here. First, natural circulation is produced through the standing mechanism of the pumps 3. When the water level drops, an internal natural thermal circulation system is set up between the hot reactor core 1 and the cold steam generator 9, which can be utilized for the emergency removal of the core decay heat. FIG. 2 shows how the hollow ring 5 is clamped between a step or internal flange 10a of the pressure vessel 10 and the inner periphery 11a of the closure head 11. This clamping point is made in a manner not shown in detail of a ferritic metal which is coated with a thin austenitic metal, so that no appreciable thermal expansion can occur with respect to the ferritic metal pressure vessel. The hollow ring 5 carries, depending on the number of pumps, for instance, four inlet sections 12 (see FIG. 3), through which the primary water cooled down in the steam generator 9 flows from the steam generator housing 2 into the running mechanisms of the pumps 3. In each pump housing 13, the primary water is deflected and pushed into the hollow ring 5, which communicates with the ring canal or passage 7 via openings 6 which are distributed over the circumference of the parts. This ring canal 7 is formed on the one hand by the inner wall of the pressure vessel 10 and, on the other hand, by the outer wall of the steam generator housing 2. This steam generator housing 2, in turn, is bounded at its inside wall by a separate, closed ring canal 14, into which the cold feed water pipes 15 are led downward. The steam generator housing 2 is supported at several vertically sliding surfaces 17 against the inside wall of the pressure vessel 10 and is terminated at its lower end by a conical bottom 16 which supports, on the other hand, the core barrel 18, containing the core 1, which has at its lower end an inlet cage 19 which is provided with numerous holes and is centered at the pressure vessel bottom 21 in a vertically slidable manner via a central post 20. The core barrel 18 rests with a projection on the conical bottom 16 of the steam generator housing 2 and is secured there by the support structure 22, which can be bolted to the hollow ring 5 at its upper side. This support structure 22 serves at the same time for guiding and mounting the control rod drives 23. As shown by FIG. 2, this support structure 22 has a top periphery provided with an external flange 22a in engagement with the hollow ring 5. The steam nozzle 24 as well as the feed water nozzle 27 are connected via a welded lip seal with the pressure vessel 10 and carry on the inside short pipe stubs 25 which are brought through the ring canal 7 and are likewise connected by a welded lip seal. The lip seals permit the pipe stubs to be slid outwardly and free from the internals. FIG. 3 shows in a cross section through the pressure vessel a view from below onto the hollow ring 5 with the pump inlets 12 as well as the openings 6.