Patent Number: 059303190
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a reactor building 1 formed of concrete and containing a non-illustrated reactor pressure vessel having a reactor core in a central reactor pit 2 seen in FIG. 2. A non-illustrated collecting conduit extending at an inclination to the horizontal leads from the reactor pit 2 into a propagation space 4 in a lower part of the reactor building 1. As is shown in FIG. 2, the propagation space 4 has an elongate hexagonal cross-section with plane vertical walls 5. A ring conduit 6, which is constructed as a spray conduit with spray nozzles 7, extends around the entire cross-section. The spray nozzles 7, which in the simplest instance are produced as cylindrical holes in the ring conduit 6, are directed horizontally into the interior of the propagation space 4, so that its cross-section can be sprayed over a large area. A spray mist is indicated by jets 8. In order to feed the ring conduit 6, a reservoir 3 is disposed so high in an upper part of the reactor building 1 that a pressure of, for example, 1 bar, that is suitable for reliable supply, prevails at the ring conduit 6. The feed takes place through the use of coolant pipes 3' and two feed conduits 10 which are mounted on virtually opposite sides of the ring conduit 6. The feed conduits 10 are angled pipe connections with a lower leg 11 seated on a bottom 12 of an intercepting trough 13. The ring conduit 6 rests on an upper edge 14 of the intercepting trough 13. The low position of the leg 11 ensures that a temperature-sensitive device 16 puts a feed of coolant into operation as soon as a diagrammatically indicated core melt 17 spreads out on the bottom 12, as is seen in FIG. 3. It then immediately destroys a melting body 18 made of plastic or of a low-melting metal, through the use of which a sealing disc 19 of the device 16 is pressed onto a sealing seat 20 counter to the pressure of the coolant. The coolant then passes through the feed conduits 10 into the ring conduit 6 and from there it becomes the jets or spray mist 8 which ensures the desired rapid cooling and formation of a crust 15 on the core melt 17. At the same time, due to the fine distribution of the water, a steam atmosphere shielding the structures of the reactor building 1 is generated without steam explosions. The coolant flows over a large area through a housing of the device 16 and thereby ensures that it remains intact, even when the melt 17 rises higher. It is also possible, however, to lengthen a shank 21 leading to the sealing disc 20, in such a way that the device 16 is located above the highest expected level of the melt 17, without impairing the rapid opening of the device 16 through the use of the melting body 18 located on the bottom 12. FIG. 4 shows a longitudinal section through an embodiment of the device 16, which is disposed so far above the bottom 12 of the propagation space 4 that the diagrammatically represented core melt remains clearly below the device 16. The device 16 is located on a flanged connection 26, at which the feed conduit 10, that extends along a main axis 9, is connected to the ring conduit 6. In the device 16, the cross-section of the feed conduit 10 is blocked at the flanged connection 26 through the use of a bursting disc 23. A coolant 22 bears on the bursting disc 23 within the feed conduit 10, for example with a pressure of about 1 bar. A piezoelectric element 24 which is mounted fixedly in the ring conduit 6 on the bursting disc 23, is connected to a thermocouple 25 lying on the bottom 12 of the propagation space 4. When the core melt 17 spreads out within the propagation space 4, a signal is generated within the thermocouple 25 by the core melt through direct contact or as a result of heat radiation and is transmitted to the piezoelectric element 24. As a consequence of the signal applied to the piezoelectric element 24, the latter undergoes expansion which leads to destruction of the bursting disc 23 and consequently to an inflow of the coolant 22 into the ring conduit 6. The initiation of the spraying operation and consequently the cooling of the core melt by spraying are thereby put into operation. FIG. 5 shows a longitudinal section through an embodiment of the device 16 which is similar to the device of FIG. 3. The device 16 extends symmetrically along a main axis 9. In a genetically upper region, a wall 28 of the device 16 extends at an inclination to the main axis 9, so that this region has the form of a cone extending towards the main axis 9. The feed conduit 10 opens into one side of this conical wall and the ring conduit 6 leads away from another side of the wall 28. Disposed inside the device 16 is a likewise conical sealing body 27 which extends along the main axis 9 and blocks both the feed conduit 10 and the ring conduit 6 in a sealing position. The sealing body 27 is held in this sealing position by the melting body 18 which projects out of the device 16 along the main axis 9 and rests on the bottom 12 of the propagation space 4. The melting body 18 is fixed in its position by a screw 30 which likewise extends along the main axis 9. The melting body 18 is formed of plastic and the sealing body 27 is formed of a metal, such as steel, or a ceramic or plastic. When the diagrammatically represented core melt 17 comes in contact with the melting body 18, the latter melts open, with the result that the pressure acting on the sealing body 27 displaces it along the main axis, out of its sealing position, due to the coolant bearing on it in the feed conduit 10. This allows the coolant 22 to flow through the device 16 into the ring conduit 6, as is represented by flow arrows 29. FIG. 6 shows a section through a device 16 which extends along a main axis 9. The feed conduit 10 likewise extends along the main axis 9 and leads into the device 16 and the ring conduit 6 likewise extends along the main axis 9 and leads out of the device 16. The device 16 has a sealing disc 19 which rests on a sealing seat 20 and thereby closes the cross-section of the feed conduit 10. The sealing disc 19 is held in a position closing the feed conduit 10 by a plate 31 extending perpendicularly to the main axis 9. This is accomplished by two screws 30 extending along the main axis 9 and being surrounded in each case by a melting sleeve 18 which prevents the screws 30 and therefore the plate 31 from moving along the main axis 9. When a core melt 17 enters the propagation space 4, the melting sleeves 18 melt down, so that the sealing disc 19 is displaced along the main axis 9 as a result of the pressure exerted on it by the coolant 22. The coolant 22 thereby passes into the device 16 and flows through the ring conduit 6 to the non-illustrated spray nozzles. The devices 16 of FIGS. 3-6 may be referred to as fittings or valves. The invention is distinguished by a passively released spray system in a propagation space for a core melt. Through the use of the spray system, early cooling of the spreading core melt over a large area is carried out with a small quantity of cooling water, so that the risk of steam explosions is clearly reduced. The spraying of the core melt preferably takes place through a ring conduit which extends along the circumference of the propagation space and is connected to a coolant reservoir that is disposed geodetically so high above the ring conduit that a pressure necessary for large-area spraying is generated. Coolant is constantly present in corresponding feed conduits and is held back from the ring conduit by a device. The device opens passively in a temperature-dependent manner, as a result of which direct cooling of the core melt takes place in a reliable way without operating personnel being involved, when the core melt enters the propagation space. Furthermore, there are provided at least two flooding conduits which are connected to a large coolant reservoir and through which coolant can be supplied for long-term cooling of the core melt.