Patent Number: 040574644
Section: summary

BACKGROUND OF THE INVENTION The invention concerns a nuclear reactor installation with a reactor building which contains equipment and operating rooms and is closed during the operation of the reactor. Equipment rooms are called here those parts of the nuclear reactor installation which contain heavily radiating components and can therefore be entered only with special protective measures, e.g., protective clothing. Operating rooms, on the other hand, are such rooms, in which accessibility is assured operationally, i.e., also in the absence of special occurrences, as testing or maintenance work is to be performed there. In connection with pressurized water reactors, reactor buildings are known which are partly accessible during the operation of the reactor. Here, a relatively expensive ventilation system takes care that sufficiently clean i.e., radiation-free, atmosphere is available in these accessible parts. The air is here drawn-in from the outside and pushed into the accessible rooms. From there, it flows through leaks, and optionally, through intentional passage openings, into the rooms in which a higher radiation level is permissible and underpressure relative to the accessible rooms is maintained. The air leaves the reactor building finally via filters and optionally, purification equipment with delay sections, decay tanks, etc. For this purpose, an exhaust gas chimney can be used, which serves to ensure sufficiently wide distribution and therefore, dilution of the gases. Other pressurized water reactors, which are common particularly in the U.S.A, have a reactor building which is completely closed during the operation of the reactor. Here, one therefore gives up quite intentionally the accessibility during operation. The ventilating system can thereby be simplified, of course, as ventilation takes place only outside the operating time of the reactor, when the reactor building is to be opened. SUMMARY OF THE INVENTION It is an object of the invention to create a nuclear reactor installation, in which the discharge of radioactivity to the outside is reduced as far as possible, while at the same time the accessibility is improved over installations with a completely closed reactor building. According to the invention, the reactor building is subdivided in a manner known per se into two ventilation-wise separate zones and in the one zone, which comprises at least parts of the operating space, overpressure is present relative to the second zone, which comprises the entire equipment space, by transporting filtered air from the second zone into the first zone. In this new nuclear reactor installation, continuous supply of fresh air for the ventilation of accessible rooms is dispensed with. It is therefore also unnecessary to have an outlet continuously open in normal operation, through which air can escape that may be radioactively contaminated. The activity-free ventilation necessary for accessibility is instead obtained by internal circulation between the two zones. In the one zone, which is part of the operation space, as low a radioactivity level can be maintained by filtering as is required for the desired accessibility. For this purpose, a filter that adsorbs primarily iodine can be provided between the first and the second zone. Although not all the radiating components of the air can be captured thereby, filters for all components are substantially more expensive than those that are required for the relatively simple adsorption of iodine. On the other hand, iodine is the most dangerous radiating component, while the rare gases which are otherwise contained normally in air during the operation of the reactor, can usually be kept out by simple precautionary measures. For instance, .beta.-radiation of rare gases, which is dangerous primarily for the conjunctive of the eye, can be screened out by means of goggles, which do not seriously limit the mobility and ability of workmen to work. In another embodiment of the invention, a space is divided off in a gas-tight manner from the first zone, i.e., the ventilation-wise "clean" zone, and is connected ventilation-wise via a rare gas filter. In this space provision is thus made for complete purification of the air, which permits working entirely without protective devices. However, as the room is smaller than the first zone overall, considerably smaller rare gas filters are sufficient. Only a partial stream of about one-twentieth of the total quantity of the air circulated between the zones need pass through the rare gas filters. For better separation, the room can further be equipped with double doors. A drying section can be placed in series with the filters for subdividing the interior of the reactor in accordance with the invention, whereby improved air conditioning can be obtained. A line, which can be shut off by means of a valve and connects the first and second zones, can furthermore be provided parallel to the filter. The valve may be openable, for instance, as a function of pressure. It is avoided thereby that in the case of accidents or special operating conditions, undesirably large pressures become effective between the individual zones, which stress the filters and possibly also the walls between the zones, excessively. One can further achieve by means of valves that, independently of the internal circulation provided by the invention, purging from the outside is possible. Such purging can take place, for instance, when the reactor is taken out of operation for refueling. The subdivision according to the invention into two zones ventilated by internal circulation can be implemented in such a manner that spaces which are exposed to possible radiation danger because of leaks but are to belong, on the other hand, to the accessible first zone, such as rooms with leak-prone valves or measuring instruments that have to be read or serviced, are arranged in the flow path of the air through the first zone immediately ahead of the passage into the second zone. The air is thereby conducted intentionally in such a manner that the maximum radiation dose rate occurs practically shortly before the air leaves the accessible zone. According to the further invention, one can make access to rooms exposed to radiation danger due to leaks, more difficult, for instance, by special interlocks, air locks or the like. In the case that the reactor building comprises a containment, particularly of steel, which contains the equipment and operating rooms and is enclosed by a protective structure or secondary shield made of concrete, so that a ring or annular space is created, the ring space may have exhaust air filters leading to the outside and contain all activity-carrying auxiliary systems which are not located in the containment. Here, the ring space is therefore not counted as one of the two zones which, according to the invention, are ventilation-wise placed in series.