Patent Number: 047770139
Section: description

The high-temperature reactor 1 is enclosed by a reactor protecting building 2. Within the reactor protecting building 2, a reactor pressure container 5 made of prestressed concrete is mounted on columns 3, 4. The inside of the reactor pressure container 5 is fully lined in pressure-resistant manner with a steel plate liner 6. The reactor pressure container 5 contains a graphite reflector 7 enclosing the reactor core 8 which consists of a heap of spherical fuel elements 9. At the bottom, the reactor core 8 joins a removal pipe 10 through which the fuel elements 9 can be withdrawn downwardly from the reactor core 8. The reactor core 8 is crossed by the coolant helium passing through conduits shown only diagrammatically herein, the helium in the process rising in temperature from about 250.degree. C. to 750.degree. C. Cooling ducts, illustratively denoted by 11, are mounted to the outside of the liner 6. The cooling ducts are connected in alternating sequence to one of two liner cooling equipment 12, 13. The arrows A and B indicate the direction of flow in the intakes 14, 15 of the liner cooling equipment 12, 13, while the letters C and D denote the direction of flow in the discharge conduits 16, 17 toward a pump not shown in further detail herein. Two branch-pipes 18, 19 and 20, 21 extend from the intakes 14, 15 to the cooling ducts 11. In each case another branch pipe 22, 23 passes upwardly into a heat insulating housing 24 and arrives at a cooling apparatus 25 therein. Then they return downwardly to the discharge conduits 16, 17 which also receive the exhaust pipes 26, 27 and 28, 29 resp. from the cooling ducts 11. A safety valve 30, 31 starts at each of the discharge conduits 16 and 17, each valve being adjusted to a pressure somewhat above the operational pressure of the liner cooling equipment 12, 13. A motor-driven valve 32, 33 is provided in parallel and is remote-controlled and capable of totally pressure-relieving the discharge conduits 16, 17. The venting lines 34, 35, connected to the safety valves 30, 31,--that is to the motor-driven valves 32, 33--issue into a perforated manifold 36 within a water seal 37. A safety valve 38 is mounted in the heat insulating housing 24 and is connected to a relief conduit 39 issuing from the inner chamber of the reactor pressure container. 5. A normally-open, motor-driven valve 40 also is located within this relief conduit 39. FIG. 2 schematically shows in greater detail the design of the safety valve 38. Its intake stub 41 is covered by a valve cone 42. This cone is connected by an actuation rod 43 having a helical spring 44, the lower end of the helical spring 44 resting on a pressure plate fixed to the actuation rod 43 and the upper end resting against a disk 47 connected to the spring case 46. The intake stub 41 is enclosed by the discharge stub 48 at right angle to it. A cooling apparatus 25, in the form of welded-on cooling coils 49, is mounted on the outside of the spring case 46. The cooling coils 49 are supplied from both liner cooling equipment 12, 13 through the branch pipes 22, 23, the arrows A, B, C and D already shown in FIG. 1 indicating the particular directions of flow. The arrows E and F show the direction of flow when the safety valve 38 is open. The above described system functions as follows when there is overheating of the nuclear reactor: If, for instance the reactor gas cooling fails, the temperature within the reactor pressure container 5 rises and simultaneously therewith the pressure. Thereupon, the safety valve 38 triggers; that is, upon reaching a given design pressure, for instance 55 bars, the helical spring 44 no longer can keep the valve cone 42 out of the intake stub 41, whereby the valve cone 42 lifts off. The gas from the reactor pressure container 5 passing through the relief conduit 39 and flowing into the safety valve 38 is then vented through the discharge stub 48 into the reactor protecting building 2. The dimensions of the safety valve 38 are such that the excess pressure decays only in one to two hours. The gas flowing in from the reactor pressure container 5 substantially raises the temperature of the lower part of the safety valve 38 because the gas itself is at a high temperature. However, heating of the helical spring 44 is essentially prevented by the cooling apparatus 25 as long as the liner cooling equipment 12, 13 operates properly, whereby the cooling apparatus 25 is provided through the branch pipes 22, 23 with cooling water. Accordingly, the helical spring 44 retains its design closing force, so that the safety valve 38 will at once close again the moment the pressure in the reactor pressure container has dropped to the normal operating pressure of 50 bars. In this malfunction, therefore, there is no pressure relief. If one of the liner cooling equipment 12, 13 fails, then the other liner cooling equipment will maintain the cooling of the helical spring 44 adequately enough that this spring retains its closing force in such a malfunction. Only when both liner cooling equipment 12, 13 fail will the cooling apparatus 25 no longer be supplied and then fail itself. The gas flowing into the safety valve 38 then also heats the space enclosed by the spring case 46, and hence the spring 44 itself to such an extent that its closing force drops appreciably. Thereby any heat radiation through the heat insulating housing 24 will be prevented. The remaining closing force of the spring valve 44 no longer is adequate to close the safety valve 38, even when the pressure drops back to normal operating pressure. This takes place only after a further drop in pressure matching the still present closing force of the helical spring 44. However, in that state the safety valve 38 still ensures there is overpressure, which even if below the operational pressure illustratively may be 16 bars. If following failure of the liner cooling there takes place in the late stages of overheating of the nuclear reactor the melting of the liner 6, then a connection will be made between the reactor pressure container 5 and both liner cooling equipment 12, 13. If thereupon by evaporation of the concrete water there should be a new rise in pressure in the reactor pressure container, then this new pressure will be dropped by the safety valves 30, 31 which are set for the pressure level of the properly operating liner cooling equipment 12, 13, for instance at 16 bars. The gas mixture flowing away through the safety valves 30, 31 into the discharge conduits 34, 35 thereupon passes through the perforated manifold 36 into the water seal 37, where the steam condenses and where the solid and volatile fission products contained in the gas are washed out. If full pressure relief of the reactor pressure container 5 is desired, the motor-driven valves 32, 33 are opened by remote control, whereby the gas still contained in the reactor pressure container 5 flows into the water seal 37 where it is washed out or condensed.