Patent Number: 046684670
Section: description

DETAILED DESCRIPTION OF THE INVENTION The safety installation constructed in accordance with the present invention and illustrated by the single appended figure incorporates a reservoir 1 for storing a cooling liquid 2 such as water, a pump 3, a conduit 4 which connects the reservoir 1 to the pump 3 and a conduit 5 which leaves the pump 3 and terminates in the water reactor circuit (not shown) of a power station. The pump 3 makes it possible, in particular, to aspirate the cooling liquid 2 from the reservoir 1 and to discharge the said liquid, or part of it, via the conduits 4 and 5, into the circuit of the reactor. As is the case with the pump 3, the reservoir 1 is located outside the sealed containment 6 which encloses the reactor circuit. A spraying manifold 7 is located in the upper part of the containment 6. It consists of one or more distributing tubes 16 equipped with regularly spaced spray nozzles 17. The said manifold is designed to project part of the cooling liquid 2 of reservoir 1 into the interior of the containment over at least a large part of the volume occupied by the latter, the said manifold being supplied with cooling liquid by the pump 3, a pipe-line 8 connecting conduit 5 to the manifold, downstream of the said pump 3. Not only does this double injection of water make it possible efficiently to cool the circuit of the reactor and thus prevent the latter from melting, but it also serves to reduce the pressure in the containment by reducing the temperature in the latter when a break occurs in the reactor's circuit. In order to pass from the injection phase to the recirculation phase of the cooling liquid, the installation is provided with an ejector 9, the said ejector making it possible to recover the cooling liquid falling into the sump 10 of the containment 6, the cooling liquid being mixed with water from the reactor in the event of a break or rupture in the circuit of the latter, and conduct this liquid mixture by non gravitational flow towards the pump 3 after the liquid 2 has passed into the circuit of the reactor. To this end, a pipe-line 11 connects the ejector 9 to the conduit 4 upstream of pump 3, and a pipe-line 12 connects the conduit 5, downstream of pump 3, to the ejector 9. A valve 13, which is incorporated in the pipe-line 12, and two valves 14 and 15 which are incorporated in the pipe-line 11, are arranged to permit or block the flow of cooling liquid and of the water coming from the circuit of the reactor. In order to reactivate the ejector 9 and/or in order to raise the pressure of the liquid circulating in the pipe-lines 11, 12 associated with the ejector, to separate gases from the liquid the installation is provided with a hermetically sealed tank 18 whose axis is vertical. This tank 18, which is inserted in the pipe-line 11 between the valves 14 and 15, has, let into its upper part, an opening 19 to which is connected the part of the pipe-line 11 coming from the ejector 9, the lower part of the tank also being provided with an opening 20 to which is connected the part of the pipe-line 11 connected to the conduit 4. A vent pipe 21 leading to the containment 6 is set up to allow the gas or contaminated vapors, which accumulate in the top part of the tank when the ejector's pipe-lines are filled with cooling liquid and water, to escape to the interior of the containment. This tank 18 could, of course, be replaced by a normal pipe-line, that is, a pipe-line 11 could be provided without the tank 18. In this case, restarting of the ejector is effected via the principal reservoir 1. Means 22, inserted in the conduit 5 downstream of the pump 3, are provided to contain a cooling fluid and to permit an exchange of heat between this cooling fluid and the cooling liquid and reactor water to be cooled, after the liquid, and, if such be the case, the reactor water, have passed through the reactor circuit. The installation is provided with a non-return valve 23 incorporated in the conduit 4, the valve allowing cooling liquid and water to pass towards the pump 3 and prevents them from passing in the reverse direction, that is, it prevents them from discharging into the reservoir 1. In order, in particular, to verify that the pump 3 is functioning or to refill the reservoir 1 when the latter is empty, there is provided a conduit 24 which connects the conduit 5, downstream of the pump 2, to the reservoir 1, and also a valve 25 which is inserted in the said conduit 24 and which is normally closed when the installation is functioning. In addition to the above-mentioned advantages, the safety cooling installation of the invention has the following advantages when compared with conventional installations: (1) The ejector has no problem in pumping water loaded with debris such as pieces of concrete, heat-insulating rock wool, etc., with no risk of destruction. (2) The ejector can function at a very low inlet pressure and withstands cavitation which could either result in a partial blockage of the inlet or in too low a water level in the sump. (3) The ejector can easily be designed to withstand an earthquake. (4) The ejector may be installed at the location most appropriate as far as operation and protection against possible missiles are concerned. (5) In the event of the aspiration being blocked, unblocking may be effected by water pressure, by reversing the direction of flow. (6) Since the size of the safeguarding pumps are conditioed by the injection phase, the said pumps having a large margin during the recirculation phase, and a fraction of their flow can be used for driving the injectors. Some installations are not equipped with a spray circuit within the containment and, on the other hand, where such a circuit exists, it is preferable to stop the spraying as soon as possible by closing the valve 26 in such a way as to limit the dispersion of contaminated water over the equipment and the structures. Consequently, in the most probable case of a small rupture in the primary circuit, the recirculation flow-rate is very small when the spraying function is absent, which greatly reduces the rate at which the heat stored in the sump water is removed. In addition, if so desired, the installation of the invention makes it possible to maintain a high rate of recirculation, thus ensuring rapid cooling of the sump water. This has a direct effect on the temperature of the containment and, consequently, on the pressure reigning within it. The way in which the safety cooling installation of the invention functions may be easily understood by referring to the appended figure. Subsequent to a break which leads to a depressurization of the reactor circuit and, as a result, to an increase of pressure in the containment 6, the one or more pumps 3 are put into service automatically and inject water under adequate pressure into the circuit of the reactor and, if such be the case, into the interior of the containment via the conduits 4, 5 and 8, the water being drawn from the storage reservoir 1. When the water level in the reservoir 1 reaches a predetermined lower limit, the ejector circuit is put manually or automatically into operation by progressively opening the valves 13 and 14. The ejector 9 takes back the sump water, that is, the injection water coming from the storage reservoir 1 and the functional water coming from the so-called reactor circuit. After a certain time, the ejector circuit is completely filled with water, the air containing the contaminating radioactive products having been expelled to the interior of the containment via the evacuation vent-pipe 21 belonging to the tank 18. The ejector 9 also has the effect of raising the pressure of the water circulating in the conduits, the pressure of the water leaving the tank 18 via the section of tube 11 being appreciably higher than that reigning in the conduit 4 on the reservoir side. The valve 15 is then opened, the pump 3 then being supplied with water coming from the sump 10 and the ejector 9. This water, which is radioactive, is not discharged into the reservoir 1 because the non-return valve 23 blocks the flow of water in this direction. The heat exchanger 22, which is cooled by a different water circuit, makes it possible rapidly to reduce the temperature of the water put back into circulation. The water is next re-injected into the reactor circuit via the conduit 5 and eventually to the interior of the containment via the conduit 8. Part of the sump water likewise passes through the pipe-line 12 and is conveyed towards the ejector 9. For better understanding the circuit associated with the ejector 9 is shown by the slightly thicker lines. The return conduit 24 to the reservoir 1 is normally closed by the valve 25 and is only used to verify that the one or more pumps 3 are functioning, for filling the reservoir 1 or, if need be, for other purposes. In addition, in the event of a momentary stoppage of the circuit as, for example, during an interruption of the electric power supply, the ejector may be re-energized either by closing the valves 13, 14 and 15 and causing the injection to restart from the reservoir 1 and recommencing the above-defined sequence, or by using the reserve of water contained in the priming tank 18 insofar as the latter is filled. It will be noted that the water coming from the so-called reactor circuit, which generally contains a certain amount of boric acid, and the cooling liquid coming from the storage reservoir, which likewise normally consists of water, and more particularly borated water, flow in the installation in a closed circuit. This prevents any possible contamination from occurring outside the containment and the above-mentioned installation. It should be understood that the present invention is in no way limited to the embodiments described above, and modifications may be made without departing from the scope of the present patent.