Patent Number: 043604960
Section: description

Referring now particularly to the single FIGURE of the drawing, it is seen that the auxiliary systems of a nuclear installation have liquid or gas loops into which, on the primary side, heat exchangers 1,2 are inserted for heat removal, the heat exchangers 1,2 having secondary connections 1a, 1b on the one hand; and 2a, 2b on the other hand, which are connected to cooling-liquid lines. By inserting the heat exchangers 1 and 2 into the liquid or gas loops of the auxiliary systems of a nuclear installation, an additional safety barrier is provided against the escape from the area of the nuclear installation which is secured by partitions and monitoring devices of radioactive liquid or gases that might be contained in the liquid or gas loops of the auxiliary systems. The heat absorbed in the heat exchangers 1 and 2 from the coolant is given off to the ambient air in the dry cooling tower 8 through the cooling elements 7 by means of a closed loop. For this purpose, cooling systems which require earthquake-proof water supplies are customarily provided so that safe heat removal from the secondary apparatus can be ensured even in the event of a failure of a supplemental water supply. In the illustrated embodiment example, this purpose is served by the dry cooling tower 8 in conjunction with a supplemental heat exchanger 11 cooled on the secondary side through a refrigeration machine and a bypass line 4. In detail, the construction of the circuit is as follows: In the heat exchangers 1 and 2, the liquid flows from the connections 1b, 2b to the connections 1a, 2a, from where it is transported into an outgoing line 3 for the cooling liquid. The bypass line 4 is branched off from the outgoing line 3, and at the boundary 5 of the secured area, a fast-acting shut-off valve 6 is inserted into the outgoing line 3. Behind the fast-acting shut-off valve 6, the outgoing line 3 leaves the secured area and opens into the cooling elements 7 of the dry cooling tower 8. This dry cooling tower 8 is erected outdoors and can be supplied with cooling air through a blower 9 or, with appropriate construction, as a natural-draft cooling tower. The liquid leaving the cooling elements 7 of the dry cooling tower 8 then flows into the return line 10, into which the supplemental heat exchanger 11 is inserted, on the primary side thereof. The return line 10 then goes back into the secured area. In the interior of the secured area, a fast-acting shut-off valve 12 is inserted in series with a control valve 13, and the bypass line 4 which is equipped with a control valve 14, also leads into the return line 10. In the interior of the secured area, an expansion tank 16 is connected to the return line 10 over a rising line 15. Furthermore, two pumps 17 and 18 are inserted, parallel to each other and in series with check valves 19 and 20 in the return line 10 which is connected behind these check valves to the connections 1b and 2b of the heat exchangers 1 and 2. The supplemental heat exchanger 11 is constructed as an evaporator of a refrigeration loop, into which a compressor 21, a condenser 22 and a choke or throttle point 23 are inserted. Thus, the secondary side of the supplemental heat exchanger 11 constitutes a refrigeration loop which is known per se and is capable of ensuring that the required temperature for the cooling medium in the return line is maintained in operation if the air temperatures are too high. Should the power supply for the compressor 21 fail in case of an accident, the cooling loop through the outgoing line 3 and the return line 11 will continue to remain operative. The reliable heat removal which is necessary for safety considerations is also maintained, therefore, at a higher temperature level even in the event of an accident, and even if the additional cooling of the cooling liquid through the supplemental heat exchanger fails. In order to ensure cooling of the secondary apparatus in all cases, the hereinafore-described cooling system must be provided redundantly. To reliably prevent the coolant in the dry coolant tower as well as in the outgoing and return line from freezing in the event of low temperatures, a mixture of water and glysantine, for instance, is provided as a cooling liquid. (Glysantin is a registered Trademark by BASF Aktiengesellschaft which is a German Corporation for Antifreeze Composition for Water Heating and Water Cooling). The bypass line 4 makes it possible, in connection with an appropriate action of the control valves 13 and 14, to prevent the temperature in the return line 10 at the entrance of the pumps 17 and 18 from dropping below a desired value. The compressor 21, and therefore additional cooling in the supplemental heat exchanger 11 is switched-on only when required at high air temperatures. The fast-acting shut-off valves 6 and 12 are closed if, for instance, a leak in the cooling system inside the secured area occurs, in order to limit flooding by escaping coolant. This hereinafore-described construction thus makes it possible to ensure that cooling liquid with a constant temperature is available in operation. Excessively high temperatures of the cooling liquid are prevented in operation by a refrigeration machine; in the event of a failure of the refrigeration machine in an accident, the cooling system remains operative so as to safely remove the heat from the secondary apparatus.