Patent Number: 058728252
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawing in detail, wherein like parts bear the same reference symbols in both figures, and first, particularly, to FIG. 1 thereof, there is seen an apparatus 1 for inerting and venting a containment atmosphere CA in a nuclear power station. The latter is not illustrated or described in more detail for purposes of brevity of this specification. The apparatus 1 comprises a line 2, into which an activity holdup device 4 is inserted. The line 2, capable of being shut off by means of a valve configuration 5, communicates, on the one hand, via a leadthrough 6 with the interior of a reactor safety vessel or containment 8 of the nuclear power station and, on the other hand, with a distributor 10 in the form of a threeway valve. In the distributor 10, the line 2 branches into a supply line 12 for an inerting agent I and into a vent line 14 for containment atmosphere CA. The supply line 12 has a heat exchanger 16 (superheater) provided with a control device 15 for temperature regulation inserted. The supply line 12 is connected to a storage tank 18 for the inerting agent I. The vent line 14 opens at its end 20, designed as a Venturi scrubber, into a tank 22 which is an iodine and/or aerosol separating device and which has a filter element 24 in its upper region. An exhaust-gas line 26 is connected to the tank 22 on the outlet side via the filter element 24. The exhaust-gas line 26 opens into a stack 27, advantageously via a non-illustrated gas suction extraction device. Moreover, the vent line 14 is shunted in parallel with the tank 22 to the exhaust-gas line 26 via a bypass line 29. The bypass line 29 can be shut off with a valve 28. The activity holdup device 4 has a number of filter inserts 30, two of which are shown in FIG. 1. In this case, each filter insert 30 has adsorption material A on its surface. When it becomes necessary to inert the containment atmosphere CA, first the inerting agent I, which is present in liquid form in the storage tank 18 up to a level 32, is partially evaporated by means of a heating device 34. In this case, the inerting agent I may, for example, be nitrogen (N.sub.2), carbon dioxide (CO.sub.2), water or a mixture of these. The evaporated inerting agent I flows to the distributor 10 via the supply line 12 and also passes through the heat exchanger 16. The inerting agent I is superheated in the heat exchanger 16. The heat exchanger 16 may be an actively heated heating element or else a permanently heated heat energy reservoir (high temperature dry accumulator). To supply inerting agent I' superheated in this way into the interior of the containment 8, the passage of the supply line 12 to the line 2 is opened via the distributor 10, so that the superheated inerting agent I' is supplied to the activity holdup device 4 via the line 2. In the activity holdup device 4, the superheated inerting agent I' flows through the filter inserts 30 and then passes via the line 2 and the leadthrough 6 into the interior of the containment 8, where it contributes to inerting the containment atmosphere CA. After a quantity of superheated inerting agent I'--so much as to require a pressure reduction --has been supplied to the interior of the containment 8, the connection between the supply line 12 and the line 2 is closed and the connection between the vent line 14 and the line 2 is opened via the distributor 10. With the distributor 10 in this position, it becomes possible to vent the containment atmosphere CA, i.e., to bleed the containment atmosphere CA. In this case, containment atmosphere CA vented from the containment 8 flows through the activity holdup device 4 and its filter inserts 30. Radioactive material, such as, for example, inert gases, contained in the containment atmosphere CA is held up by adsorption on the filter inserts 30. Then, as indicated by the arrow, the filtered containment atmosphere CA' flows to the iodine and aerosol separator tank 22. Due to the interaction of the end 20 of the line 14 and the filter element 24, wherein the end is designed as a Venturi washer, iodine and/or aerosols are removed from the containment atmosphere CA'. The containment atmosphere CA", which has thus been further cleaned, is then released into the surroundings via the stack 27. After the pressure in the interior of the containment 8 has thus been sufficiently equalized, additional inerting agent I is supplied to the containment once again in a further step. For this purpose, the distributor 10 closes the connection of the line 2 to the vent line 14 and simultaneously opens the connection of the line 2 to the supply line 12. Superheated inerting agent I' thus flows once again into the interior of the containment 8 and, in this case, once more passes the activity holdup device 4 and its filter inserts 30. When the inerting agent I' flows through the filter inserts 30, it releases the radioactive material absorbed on these and conveys it back into the interior of the containment 8. Operating the apparatus 1 alternatingly and therefore discontinuously in this way reliably avoids the release of radioactive material even when the containment 8 is being vented. Referring now to FIG. 2, in the alternative apparatus 1' for inerting and venting the containment atmosphere CA, the supply line 12 for the inerting agent I and the vent line 14 for containment atmosphere CA are connected to the interior of the containment 8 through the leadthroughs 40 and 41, respectively. In this embodiment too, the supply line 12, into which the superheater heat exchanger 16 is inserted, is connected to the storage tank 18 for the inerting agent I. The vent line 14 is connected to the stack 27 via the tank 22, which is an iodine and aerosol separating vessel. In this exemplary embodiment, the supply line 12 and the vent line 14 are led via a joint reversible activity holdup device 4'. Here, the activity holdup device 4' is designed as a regenerating wheel. It comprises a filter element 52 which is mounted rotatably about an axis 50 and which also is provided with an adsorption agent A. The activity holdup device 4' can be operated continuously. Containment atmosphere CA vented from the containment 8 flows through part of the filter element 52, the part being located in the region of the vent line 14. Only this part of the filter element 52 is laden with radioactive material contained in the containment atmosphere CA. Similarly to the exemplary embodiment according to FIG. 1, the filtered containment atmosphere CA' subsequently flows to the tank 22, which is an iodine and/or aerosol separating device. Due to the rotation of the filter element 52 about the axis 50, that portion of the filter element 52 which is laden with radioactive material is removed from the region of the vent line 14 and is replaced by a portion of the filter element 52 which is not laden with radioactive material. Partial areas of the filter element 52 are sealed off relative to one another with activity-resistant and noncombustible sealing material. Due to the rotation of the filter element 52 about the axis 50, that portion of the filter element 52 which is laden with radioactive material passes into the region of the supply line 12 for the inerting agent I. There, inerting agent I' (superheated in the heat exchanger 16 and to be supplied to the containment 8) flows through that filter portion which is laden with radioactive material. As a result, previously adsorbed radioactive material is released from the filter element 52 and flushed back into the containment 8. Each portion of the filter element 52 is thus continuously laden with radioactive material and subsequently regenerated. The operations of charging and regenerating the filter element 52 thus take place in parallel and simultaneously in the activity holdup device 4', so that the latter can be operated continuously. This rules out a buildup of excess pressure in the containment 8 at all times, so that inerting the containment 8 in this way is particularly flexible and may also take place as a preventive measure (prophylactic) at any time. The inerting agent I provided in the exemplary embodiment according to FIG. 2 and stored in the storage tank 18 is water. This water I is evaporated completely or partially by means of the heating device 34. Steam D flowing to the activity holdup device 4' via the supply line 12 is superheated in the heat exchanger 16, so that particularly effective regeneration of that part of the filter element 52 through which the steam flows becomes possible. The steam D supplied condenses within the containment 8. This condensation, illustrated by the shading K, results in a pressure reduction or vacuum within the containment 8. It thereby becomes possible, particularly in combination with the stack 27, to maintain a vacuum permanently in the interior of the containment 8. By maintaining a vacuum of this kind, a discharge of radioactive material into the environment is reliably avoided, even in the case of a nontight containment 8 or in the event of leakage, since, as indicated by the arrows L in FIG. 2, leakages flow solely into the containment 8. A further supply line 54 for supplying a further inerting agent I.sub.2 may be connected to the activity holdup device 4' in parallel with the supply line 12. In this case, the inerting agent I.sub.2 may be nitrogen (N.sub.2) or carbon dioxide (CO.sub.2). This arrangement of this type makes it possible to regenerate the filter element 52 by means of a mixture of steam D and inert gas I.sub.2. Each filter element 30, 52 of the activity holdup device 4 or 4' may advantageously have activated charcoal and/or a molecular sieve as adsorption material A. In this case, the finely distributed adsorption material has an inner exchange surface of at least 1000 m.sup.2 /m.sup.3. For particularly effective regeneration of the filter elements 30 or 52, the temperature of the inerting agent I', I.sub.2 supplied can be regulated. Temperature regulation of this type may be carried out, for example, by regulating the heat exchanger 16 by means of the control device 15 or else, in a way not illustrated in any more detail, by dividing the gas stream carried in the supply line 12 into part streams, only one of which is led via the heat exchanger 16 and is subsequently admixed again with the other part streams. According to the exemplary embodiments shown in FIGS. 1 and 2, the activity holdup device 4, 4' is arranged outside the containment 8, but it may alternatively also be arranged within the containment 8. In order to ensure that the containment 8 is closed off reliably and a discharge of radioactive material into the surroundings is thus safely avoided, the supply line 12, following the lead through 6 or 40 through the containment 8, is provided with a selfclosing shutoff fitting 60, 60'. This is opened, for example, by means of the feed pressure of the inerting agent I', I.sub.2, said feed pressure acting counter to a spring force or weight. Thus, in the event of a failure or termination of the supply of inerting agent I', I.sub.2, the containment 8 is closed off relative to the surroundings on a "failsafe" principle. By means of an apparatus 1 or 1' of this type, it becomes possible at any time to inert the containment atmosphere CA and simultaneously vent the latter. Since an excess pressure buildup within the containment 8 is avoided, inerting in this way is possible at all times. Inerting may therefore take place after a "blowdown" or according to other criteria, such as, for example, "H.sub.2 concentration too high", "core filling level too low", or else as a preventive measure, since under no circumstances is there any fear that radioactive material will be released into the environment. Moreover, it is possible for the containment atmosphere CA to be inerted for a short time and even in the event of a failure of important systems (station blackout).