Patent Number: 047524391
Section: description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows a multiple part cylindrical steel pressure vessel 1, the individual parts of which are joined together at the flange 2. A nuclear reactor is installed in the steel pressure vessel 1. The reactor in FIG. 3 comprises a high temperature small reactor 33 located in the lower part of the vessel and having a capacity of 100 MWe, and a heat utilization system arranged in the upper part of the vessel. The heat utilization system comprises a plurality of heat exchange units or generators 34 and circulating blowers 3 following the generators in sequence. The heat exchanger units or generators are conventionally installed. The blowers 3 are mounted laterally on the upper part of the steel pressure vessel 1. The pressure vessel 1 rests on a cantilever ring 4 made of concrete. A safety enclosure 5 is arranged tightly around the steel pressure vessel 1. The enclosure 5 comprises two essentially cylindrical concrete shells, the inner concrete shell 6 and the outer concrete shell 7, together with a concrete cover 9 monolithically joined with the two concrete shells. The cantilever ring 4 is also integrated into the safety enclosure 5. The safety enclosure 5 rests on two support rings 10 and 11 made of concrete. It is again joined monolithically with the rings. Between the two concrete shells 6 and 7, there is an annular space 8, which is accessible to a limited extent and may be used as a work space. Several large passages are provided in the concrete cover 9 and in the center jacket area of the safety enclosures. These passages are closed off with removable pressure resistant and gas-tight covers 12. The passage 13 in the concrete cover 9 permits access to the steam generators in the heat utilization system and makes dismantling of these components also possible. The passages 14 provided in the jacket area of the safety enclosure 5 provide access to the inner concrete shell 6 to the blowers 3. The outer concrete shell 7 into which the covers 12 are set (in FIG. 1 one of the covers 12 has been removed) is reinforced in the area of the passage 14. The circulating blowers 3 may be removed through the passages 14 or maintenance and repair work may be performed on them. In the area of the center flange 2 of the steel pressure vessel 1, the inner concrete shell 6 has thickened part 15 projecting in the inward direction. A ring 16 rests on the part 15. It is set onto the steel pressure vessel 1. The ring 16 secures the steel pressure vessel 1 against earthquakes. In the cantilever ring 4, passages 17 are provided for a shutdown system 18, which comprises a plurality of absorber rods and their drive devices. A central passage 19 receiving a pebble removal tube 20 is also provided if the small HT reactor is operated with spherical fuel elements. The water supply lines 21 and the live steam lines 22 of the steam generators are installed at the bottom and outside the safety enclosure 5 in the reactor housing 23 surrounding the safety enclosure, passing horizontally through the support ring 11 to the outside. For a nuclear reactor installation with the abovementioned capacity, with four steam generators, the two concrete shells 6 and 7, together with the annular space 8, have a thickness of approximately 2.70 m. This includes a wall thickness of the inner concrete shell of 0.70 m and a width of 0.80 m of the annular space 8. To protect the inner concrete shell 6 against excessive thermal stresses, the safety enclosure 5 has a concrete cooling system 24. This system also has the simultaneous function of removing the secondary heat in case of a failure of the secondary heat removal devices on the primary side in the nuclear reactor installation. The concrete cooling system 24, operated with natural circulation is shown in FIG. 2. The concrete cooling system 24 includes an annular elevated reservoir 25 which is under atmospheric pressure. In addition, a plurality of ascending pipes 26 and downpipes 27 form a piping system wherein cooling water circulates in a closed loop. The closed loop is connected with the elevated reservoir 25. The elevated reservoir 25, which contains approximately 100 m.sup.3 water is set onto the inner concrete shell 6. It is connected with a second cooling system 28, wherein cooling water is again circulating. This second cooling water system transfers the heat generated in the elevated reservoir 25 to the outside. The ascending pipes 26 are installed within the inner concrete shell 6 on its side facing the steel pressure vessel 1. The downpipes 27 are on the side facing the outer concrete shell 7. The ascending pipes 26 may be equipped with azimuthal fins or a finned wall (not shown). A blow-off line 29 leading to the outside from the safety enclosure 5 is connected with the elevated reservoir 25. A pressure relief valve 30 is arranged in the blow-off line. By means of an inlet line 31 with a valve 32 for the supply of water, it is possible at any time to replenish the water in the elevated reservoir 25. When the cooling system operates for the removal of secondary heat from the primary cooling loop, the heat is transferred essentially by radiation to the inner concrete shell 6 of the safety enclosure 5. The heat is received by the water rising in the ascending pipes 26 by heat conduction. The heat is transported within the elevated reservoir 25 and thereby transferred to the second cooling water system 28. In case of a failure of the cooling water system 28, the water is heated in the elevated reservoir 25, but due to evaporation in reservoir 25 the removal of the secondary heat may be maintained for 2 to 3 days. If it is necessary to provide a longer period of time, the elevated reservoir 25 may also be refilled by means of the inlet line 31. The above description describes a preferred embodiment of the invention. It is to be understood however, that the invention is not limited to any single embodiment or feature, but should be construed to cover all modifications and alternative embodiments falling within the scope of the invention as defined by the claims which follow.