Patent Number: 054147433
Section: summary

Cross-Reference to Related Application This application is a Continuation of International Application PCT/DE92/00665, filed Aug. 11, 1992. BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a secondary-side residual-heat removal system for a pressurized-water nuclear reactor, including a steam generator being connected into a primary loop of the nuclear reactor by the primary side of its heat-exchanging tubes, and a safety condenser having one side to which a secondary side of the steam generator is connected through circuit lines, with another (tertiary) side of the safety condenser allowing a throughflow of a tertiary medium for the cooling of its secondary side, and the safety condenser being situated at a higher level than the steam generator, defining a difference in level between the safety condenser and the steam generator being dimensioned for achieving a natural circulation in a secondary circuit leading through the secondary side of the steam generator and the safety condenser in a residual-heat removal operation. After shutting down nuclear reactors, so-called residual heat, which is also referred to as decay heat, occurs in all modes of operation and malfunction. In the case of pressurized-water nuclear reactors, the secondary side is used, at least in an initial phase, for the removal of the residual heat, in virtually all modes of operation and malfunction. That takes place by feeding the steam generators with feed-water and by discharging energy transferred in the heat generator from its primary side to its secondary side through its tube bundle, directly or indirectly into the atmosphere. In order to keep malfunctions under control, a previously known concept for secondary-side residual-heat removal in the installations of pressurized-water nuclear reactors provides an emergency feeding system on the secondary-side feeding side of the steam generators and a steam blow-off device with blow-control and a safety valve on the discharge side. Such a system is disclosed, for example, by German Published, Prosecuted Application DE-AS 24 59 150 (1) or by Published European Application No. 0 004 167 A3 (2). In publication (1) it is shown that the respective heat generator is connected by its secondary side not only to its operational feed-water and live-steam lines but also through emergency cooling circuit lines with a condensate recirculation pump to one side of a safety condenser. That safety condenser, which is referred to therein as a residual-heat removal heat exchanger and is equipped with additional condensate cooling means, may be replaced, if appropriate, by a water pool basin. Such a basin is shown in publication (2) and it serves for the blowing off of the secondary-side steam to be cooled, with the water pool being cooled by heat-exchanging tubes which are connected to a cooling circuit. The secondary-side steam is cooled and condensed by the blowing off into the water pool. The condensate is recirculated by means of a condensate recirculation pump to the secondary side of the steam generator, i.e. to its feed-water space. In the case of publication (1) and publication (2), residual-heat removal operation is initiated by the opening of conventional shut-off valves (reducing valves, shut-off valves). SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a secondary-side residual-heat removal system for pressurized-water nuclear reactors, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which provides for supplying a safety condenser (SACO) on its tertiary side and a secondary-side SACO circuit in such a way that switching on pumps and/or opening conventional shut-off valves is not required for putting the residual-heat removal by the safety condenser into operation, whereby the inherent safety of the residual-heat removal system can be increased. With the foregoing and other objects in view there is provided, in accordance with the invention, a secondary-side residual-heat removal system in a pressurized-water nuclear reactor having a primary loop, comprising a steam generator having a primary side, a secondary side, heat-exchanging tubes with a primary side being connected into the primary loop of the nuclear reactor, a feed-water connection on the secondary side, a main feed-water pump connected to the steam generator; a safety condenser, circuit lines having a cold leg leading from the safety condenser to the feed-water connection of the steam generator, the safety condenser having a secondary side connected to the secondary side of the steam generator by the circuit lines in a secondary circuit and having a tertiary side allowing a throughflow of a tertiary medium for cooling the secondary side of the safety condenser, the safety condenser being disposed at a higher level than the steam generator, defining a difference in level between the safety condenser and the steam generator being dimensioned for achieving a natural circulation in the secondary circuit leading through the secondary side of the steam generator and the safety condenser in a residual-heat removal operation; a vortex chamber valve having a supply connection, an outlet, a control connection and an internal flow path leading from the supply connection to the outlet and into the cold leg of the circuit lines, the control connection shutting off the internal flow path with a secondary-side control pressure to be picked or tapped off in normal operation of the steam generator, but releasing the control path in residual-heat removal operation, when the control pressure drops or disappears, for freely switching on the vortex chamber valve due to a reduced control pressure at the control connection and setting a circulating flow in motion in the secondary circuit through the vortex chamber valve, when the main feed-water pump is switched off; and a water reservoir being disposed at a geodetically higher level than the safety condenser for supplying the tertiary side of the safety condenser, with a minimum flow bypass line being connected to the water reservoir and the safety condenser having a tertiary-side intake being connected to the minimum flow bypass line, or with the safety condenser having a heat-exchanging tube bundle and the water reservoir having a water pool surrounding the heat-exchanging tube bundle of the safety condenser. The natural circulation may also be set in motion by switching off other pumps, for example start-up and shut-down pumps. In order to provide for the natural circulation, it is sufficient for the distance between the two water-column levels of the safety condenser (for example a condensate collector) and the steam generator to be on the order of magnitude of about 2 m. The tertiary medium evaporating in the safety condenser is expediently blown out over the roof through a blowing-off line. In accordance with another feature of the invention, the safety condenser has a tertiary-side intake, and there is provided a parallel connection connecting the water reservoir to the tertiary-side intake, the parallel connection having one branch with a minimum flow bypass line and a shut-off valve and another branch with a control valve. In accordance with a further feature of the invention, there is provided a pressure-side feed-water line part having a downgradient from the main feed-water pump and being connected to the control connection of the vortex chamber valve. In accordance with a concomitant feature of the invention, the water reservoir has a water pool, the safety condenser has a heat-exchanging tube bundle disposed in the water pool, forming a combined safety condenser/water reservoir, the steam generator has a secondary chamber, and including a control valve being open in normal operation of the steam generator, the outlet of the vortex chamber valve opening out into the secondary chamber through the control valve. It is also possible in principle for the control valve to be disposed between the safety condenser and the swirl chamber valve. Thus, in operation as intended (normal operation), the valve is open and does not have to be actuated until controlling the capacity of the safety condenser. The advantages which can be achieved with the invention are primarily to be regarded as that the passive characteristics of the residual-heat removal system are improved. The natural circulation is induced automatically/passively without active actuation of valves. The supply of the (tertiary) cooling medium to the safety condenser takes place without pumps. The actuation of a control valve is not required until controlling the cooling capacity or rate of flow when the natural circulation has established itself. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a secondary-side residual-heat removal system for pressurized-water nuclear reactors, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.