Patent Number: 042382904
Section: summary

BACKGROUND OF THE INVENTION The invention concerns a nuclear reactor installation with a containment and a live-steam line which leads from the inside of the containment to the outside and contains a fast-acting valve with an aperture cross section corresponding to the cross section of the live-steam line and with a valve disk which is closed in case of a leak in the live-steam line, under the action of a pressure medium. The fast-acting valve permits to shut off the live-steam line quickly, particularly if in the case of a leak the danger exists of steam, which might possibly be radioactively contaminated due to an accident, getting to the outside. However, the closing means of necessity also that the cooling of the reaction installation, i.e., the transport of energy in the form of the steam flow, is interrupted. This gives rise to problems, as it is not always possible, even with a fast shutdown of the nuclear reactor, to lower the production of energy fast enough to keep particularly the pressure within permissible limits in the generation of steam. For these problems, the invention attempts to find a solution in the form of a valve combination which is to serve at the same time as a shut-off valve and a safety valve. SUMMARY OF THE INVENTION According to the invention, an opening mechanism with pressure-dependent action, which opens at a pressure higher than the operating pressure of the live-steam line but releases no more than half the aperture cross section, is associated with the valve disk. This makes possible a pressure limitation which prevents the live-steam line and the steam generating plant feeding the former from being overloaded. A differentiation, which is important for the invention, is made here between the normal operation of the valve, when the aperture cross section corresponding to the full cross section of the line is released so that there is practically no pressure drop in the valve, and the case of an accident, when the valve acts as a safety valve. In the latter case it is prevented by the limitation of the aperture cross section in accordance with the invention that the steam, which can escape unimpeded in the event of a break of the live-steam line, has too high an outflow rate and thereby loads or stresses the steam generating system excessively, or damages the nuclear reactor by too fast a cooling rate. In one embodiment of the invention, the opening mechanism includes a stop which prevents, at least for a short time, the aperture cross section from being opened more than 30%. This stop can be provided as an additional element in a valve which can be opened fully in the normal case. After shutting off in accordance with the meaning of a fast-acting valve, however, the stop becomes effective and limits the aperture. The limitation to 30% of the aperture cross section need not be adhered to rigidly in all operational cases. The stop may advantageously also comprise an adjustable slide, at which the valve disk stops when opening. A slide is to denote here any device which is adjustable in the direction of the opening stroke of the valve disk and limits the travel of the valve disk. However, the slide need not engage the valve disk directly. It is also conceivable that the stop is associated with the actuating mechanism of the valve disk, e.g., with a shaft which leads to a piston of the drive mechanism. Such a slide can be adjustable by a motor by means of a screw thread, particularly a spindle. However, it is also conceivable that the movement of the slide or another limitation of the opening stroke of the valve disk is accomplished through the action of a pressure medium. Besides the above-mentioned embodiment of the stop as a slide, which allows continuous adjustment of the opening stroke, the valve can be simplified by associating two open positions having a cross section smaller than the aperture cross section, with a pressure medium actuator and/or the opening mechanism in a pressure or time relationship. Thus, two different open positions, which are different from each other but are fixed in themselves, are provided for reopening the valve after a fast shut-off. The choice of the opening cross section used here depends advantageously on the preceding power production, in order to make possible a power removal matched to the load by the fast-acting valve acting as a safety valve. A limitation of the closing movement, which gives a residual aperture cross section of the valve of between 5 and 20% during the closing process, may also be associated with the valve disk. It is hereby accomplished also for the case of an accident and the closing of the fast-acting valve caused thereby, that the removal of live steam and thereby, continued cooling of the nuclear reactor is possible. As the valve was not closed completely, the stress on the valve disk and the valve seat is substantially reduced as the shock-like landing of the valve disk by the fast shut-off is eliminated or at least does not occur so often. Also the limitation of the closing movement, which determines the smallest cross section still immediately obtainable in the case of a fast shut-off, may be adjustable. The limitation of the closing movement is advantageously reduced to zero in a time span of 10 to 60 seconds, i.e., the steam removal is throttled down for the time interval mentioned, more-and-more, until the complete closing is finally accomplished. It is advantageous for all embodiments of the invention if the valve disk with its valve seat forms the shape of an annular Venturi tube in the vicinity of the closed position. One can thereby attain the velocity of sound in the vicinity of the nozzle, i.e., at the valve disk, such that a uniform limitation of the outflow rate is achieved over a wider range of pressures. This purpose is achieved in a simple manner by making the valve disk conical at the rim with a smaller angle than that of the likewise conical valve seat.