Patent Number: 058728252
Section: summary

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of copending international application PCT/EP96/03844, filed Sep. 2, 1996, which designated the United States. BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to nuclear power generation, and more specifically it pertains to an apparatus for inerting and venting the atmosphere of a containment vessel in a nuclear power station, and to a method for operating an apparatus of this type. In the event of an emergency or an accident in a nuclear power station, where, for example upon the oxidation of zirconium when the core is heated, the formation and release of hydrogen gas within the safety vessel or containment surrounding the reactor core must be expected. Explosive gas mixtures may form as a result within the containment. In order to prevent explosive gas mixtures of this type from being formed in the containment of a nuclear power station, various devices or methods are envisioned. These include, for example, devices, such as catalytic recombinators, catalytically and electrically operated ignition devices, or the combination of the two systems, as well as methods for permanent or subsequent inerting of the containment. In order to inert the containment of a nuclear power station, a nonreactive gas, such as, for example, nitrogen (N.sub.2) or carbon dioxide (CO.sub.2), may be supplied as an inerting agent into the containment. In an alternative process, liquid gas may be fed in for inerting via branched nozzle systems or conventional gas feed systems with an integrated oil burner or gas burner evaporator plant. Other variants are based on a feed of liquid gas, a feed into a water sump within the containment also being provided on account of the absence of evaporation energy in the atmosphere of the latter. An apparatus for inerting the atmosphere in the containment of a nuclear power station is known, for example, from German patent specification DE 44 21 601 C1. Feeding an inerting agent into the containment may result in a pressure rise within the containment. Such a pressure rise may also occur in an already preinertized containment, in particular one with a high specific Zr mass and small containment volume. This in turn makes it necessary to relieve the containment pressure by venting the containment atmosphere. However, the containment atmosphere usually contains radioactive material, such as, for example, inert gases, iodine or aerosol, which could escape into the surroundings of the nuclear power station during venting. Accordingly, because of the radioactive material in the containment atmosphere, venting of the containment atmosphere in the event of an accident or fault does not come under consideration. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a device and method for inerting and venting the containment atmosphere in a nuclear power station, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which allows safe inerting and venting of the containment atmosphere of a nuclear power station and without harming the surroundings of the nuclear power station. With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for inerting and venting the containment atmosphere in a nuclear power station, comprising: a supply line for an inerting agent communicating with a containment vessel of a nuclear power station; PA1 a vent line for containment atmosphere communicating with the containment; and PA1 a joint reversible activity holdup device communicating with the vent line and with the supply line. In other words, the objects of the invention are satisfied by the reversible activity holdup device, through which a supply line for an inerting agent and a vent line for containment atmosphere are led jointly. Alternatively, the reversible activity holdup device is inserted into a line for supplying an inerting agent and for venting containment atmosphere, the line being connected to the containment. The use of an activity holdup in a nuclear power station is known, for example, from German published, non-prosecuted patent application DE 36 37 795 A1. However, there it is provided solely for relieving the pressure of the containment shell of the nuclear power station. In both alternatives, containment atmosphere vented from the containment flows through the activity holdup device. In this case, radioactive material, such as, for example, inert gases, iodine or aerosol, contained in the containment atmosphere is held up on adsorption material provided within the activity holdup device and is briefly stored. After the adsorption material has been charged in this way and before the radioactive material has broken through, that is to say before the material is released to the ambient air, the operating mode of the activity holdup device is changed in such a way that inerting agent now flows through the latter in the opposite direction. In this case, the held-up radioactive material is released from the adsorption material and is flushed back into the containment together with the inerting agent. It thus becomes possible to inert the containment atmosphere or maintain the inerting, while pressure relief is ensured for the containment at the same time. In this case, a release of radioactive material to the surroundings is reliably avoided at all times. Moreover, additional waste, for example in the form of clogged filter elements, is avoided due to the use of the reversible activity holdup device. In this case, the inerting agent may be, for example, nitrogen (N.sub.2), CO.sub.2, steam or else another gas having a nonoxidizing effect. In accordance with an added feature of the invention, the activity holdup device includes a filter element mounted rotatably about an axis. Such an activity holdup device, similar to a regenerating wheel, may be operated in continuous regeneration. In this case, the vent line and the supply line are led via spatially different regions of the activity holdup device, activity-resistant and noncombustible sealing materials expediently being selected for sealing off, relative to one another, the gas streams which are carried in the vent line and the supply line. Rotating the activity holdup device thus ensures that each part region of the activity holdup device is alternately laden with radioactive material by the vented containment atmosphere and is regenerated by inerting agent flowing through the part region in the opposite direction. In accordance with another feature of the invention, there is provided an apparatus for inerting and venting a containment atmosphere in a nuclear power station which comprising: a line for supplying an inerting agent to and for venting containment atmosphere from a containment of a nuclear power station, the line communicating with the containment; and a reversible activity holdup device inserted in the line. In accordance with an additional feature of the invention, the activity holdup device includes adsorption material which is activated charcoal, a molecular sieve, and/or zeolite. In accordance with a further feature of the invention, the adsorption material has an inner exchange surface of at least 1000 m.sup.2 /m.sup.3. In accordance with again an added feature of the invention, there is provided an aerosol separating device communicating with the activity holdup device for separating aerosols from the containment atmosphere. The activity holdup device is either preceded or followed by the separating device for aerosols and/or iodine sorbents in the direction of flow of the containment atmosphere. In accordance with again an additional feature of the invention, there is provided a superheater connected upstream from the activity holdup device in a flow of the inerting agent. Superheating the inerting agent assists particularly the regeneration of the adsorption material and thereby achieve a particularly long life for the activity holdup device. The superheater may, for example, be a water energy accumulator or else a high temperature dry accumulator. However, other heating devices or evacuating devices are also conceivable. Moreover, superheating of the inerting material which can be achieved in this way can ensure that only dry inerting agent flows through the activity holdup device. Dry inerting agent of this type has a particularly beneficial effect on regeneration of the activity holdup device. Advantageously furthermore, a control device is provided for setting the temperature of the inerting agent before the latter enters the activity holdup device. In order to avoid an excessive rise in pressure in the containment particularly effectively, the inerting agent expediently contains steam. Superheated steam supplied to the containment condenses within the latter. This condensation leads to a pressure reduction within the containment. Thus, particularly in conjunction with a suction extraction device advantageously provided in addition and connected to the vent line, it is possible to ensure that a vacuum is permanently maintained in the containment. This avoids a release of radioactive material into the surroundings in a particularly reliable way. A suction extraction device of this type can thus be used particularly effectively in the case of a nontight containment with leakage. In this case, the inerting agent may consist solely of steam or else contain other material, for example nitrogen (N.sub.2) or carbon dioxide (CO.sub.2) in addition to steam. It is possible with the invention to provide a stack which communicates with the vent line. In accordance with a concomitant feature of the invention, a selfclosing shutoff fitting is connected in the supply line. The self-closing fitting ensures that the containment is closed off relative to the environment and a release of radioactive material into the environment is thus reliably avoided. A selfclosing shutoff fitting of this type may be closed, for example, by spring force or by weight. When the inerting agent is being supplied, the fitting is opened by the pressure of the inerting agent, the pressure acting counter to the spring force or weight, so that it becomes possible for the inerting agent to flow into the containment. With the above and other objects in view there is also provided, in accordance with the invention, a method of inerting and venting a containment atmosphere in a containment of a nuclear power station. The method comprises at least the following steps: feeding inerting agent into a containment in a feed flow, venting a containment atmosphere from the containment in a vent flow, and alternatingly conducting the feed flow and the vent flow through a reversible activity holdup device. In accordance with again another mode of the invention, the method further comprises, in the activity holdup device, separating radioactive material out of the vent flow of the vented containment atmosphere and conveying the radioactive material back into the containment with the feed flow of the inerting agent through the activity holdup device. In an advantageous development, radioactive material contained in the vented containment atmosphere is separated in the activity holdup device and, when the inerting agent subsequently flows through the activity holdup device, is conveyed back into the containment. In this case, the activity holdup device may operate continuously, for example on the regenerating wheel principle, or else discontinuously, for example by changeover and countercurrent regeneration. In accordance with a concomitant feature of the invention, the temperature of the inerting agent is regulated before it enters the activity holdup device. Finally, the inerting agent may be superheated in order to be dried. The advantages achieved by means of the invention are, in particular, that, by virtue of the reversible activity holdup device, it is possible for the inerting agent to be supplied into the containment of a nuclear power station at any time, without an inadmissible pressure buildup taking place in the containment. Consequently, inerting the containment in this way does not entail the disadvantages normally associated with a pressure rise in the containment. Inerting of this kind may be used in a particularly flexible way and may also take place in a preemptive mode. The safety of the plant as a whole is therefore markedly increased not only in the event of emergency or accident situations, but also in the case of slight deviations of the state of the nuclear power station from a normal state. 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 an apparatus and method for inerting and venting the containment atmosphere in a nuclear power station, 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.