Patent Number: 
Section: description

Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is seen a catalytic recombination device. The gas to be recombined emerges out of the paper plane from below, as indicated by the vector heads 4. An electrical heating device 6, that is to say a permanently heated catalytically active zone, is located in the front region between two central catalyst bodies 2. The heating device 6 may be a small heating body, such as a heating bar, a filament or another heating element. The electrical heater 6 is supplied by an energy source 8, for example by a local energy store, such as a battery. The heating device 6 is arranged in such a way that it transfers heat energy to the two adjacent catalyst bodies 2 (in the middle of the drawing figure). The further heat transfer is indicated with the arrows w. The volume and heating capacity are dimensioned such that only a small part of the entire available catalytic surface, preferably less than 5% of the surface, is maintained permanently at a temperature level above ambient temperature by the introduction of heat energy. The permanent heating of the central surface part is carried out in such a way that temperatures of more than 50xc2x0 C., advantageously of more than 80xc2x0 C., are maintained within this zone. The decrease, known as aging, in catalytic activity which, at increased temperatures, is decisively reduced over time, for example due to the sorption of pollutants from the containment atmosphere during the continuous operation of the nuclear power plant, is decisively minimized. According to FIG. 1, the recombination device comprises a multiplicity of mutually parallel catalyst plates or catalyst bodies 2. Each of the catalyst bodies 2, as described in the European patent EP 0 527 968 C1, comprises a baseplate made from sheet steel and of catalytic material, such as platinum and palladium, applied on both sides. The individual catalyst bodies 2, which, as a whole, possess a predetermined catalytic surface, are braced in form-lock (positive) and friction lock (non-positive) in a metallic carrier 10. They have a plate spacing of less than 2 cm, preferably of about 1 cm. It is desirable for the spacing between the catalyst plates to be maintained within the framework of these values, since, on account of the laminar flow states between the plate-shaped catalyst bodies 2, there is only insufficient heat transfer by convection and the heat is transferred primarily by radiation. Due to the non-positive friction lock of more than 0.1 kp between each individual catalyst body 2 (thickness about 0.05 mm) and the carrier 10, direct further heat transfer into the adjacent catalyst body 2 occurs after the starting of the catalyst. The further heat transfer in the metallic carrier 10 is identified by the horizontal arrows w. Cooling influences caused by the surroundings is kept at a low level by an insulating air gap 14, through which the flow does not pass. The air gap 14 is provided between the housing wall 12 and the metallic carrier 10. The air gap may have a width of more than 5 mm. Instead of an air gap 14, a solid insulating layer may also be provided. The recombinator outer temperatures are reduced by means of the air gap 14, so that, if ignition is not desired and if there are relatively high hydrogen concentrations of, for example, 8 to 10% by volume, it becomes possible for the device to operate without ignition. With reference to FIG. 2, an electrically heatable heating body 6 is arranged once more between two catalyst bodies 2 of a catalytic recombination device. The heating body 6 consists essentially of a heating coil 16, which is supplied by the energy source 8, and of a wire mesh 18 which lies around it and which is a good heat conductor and transfers the heat generated permanently by the heating coil 16 on to the two catalyst bodies 2. For this purpose, the wire mesh 18 rests firmly on the surface of the two plate-shaped catalyst bodies 2. Instead, here too, a catalytically heatable element 16 or 18 may again be used. The heating body 6 is surrounded on both sides by filter bodies 20. The filter bodies 20 consist of a metallic filter fleece and/or sorption medium, such as, for example, activated charcoal or zeolite. The filter bodies 20 ensure that the incidents of aerosol-like and/or gaseous pollutants in this sensitive zone can be kept low. Referring now to FIG. 3, the heat is transferred on to further catalyst bodies 2 from the zone of the two adjacent catalyst bodies 2 heated by the heating device 6. This purpose is served by heat transport elements 22 which, in particular, are rod-shaped or plate-shaped and consist of metal. They may extend over a plurality of catalyst bodies 2. Here too, heat conduction is identified by the arrows w. Referring now to FIG. 4, there is shown a recombination device 24 within a reactor safety vessel 26 (containment 26). The containment wall of the latter in designated by 28. The recombination device 24 is designed, in particular, as shown and described in the European patent EP 0 527 968 C. Here, however, mutually parallel plates 2 are employed. The inlet orifice is marked by 30 and the outlet orifice arranged perpendicularly thereto is marked by 32. The plate-shaped catalyst bodies 2 aligned parallel to one another are located in the lower region 34. The heating body 6 is also accommodated here. The latter is supplied, via a change-over switch, trip switch, or switching element 36, either by an internal electricity supply unit 38 in the event of an incident or, by way of a lead-through 40 in the wall 28, by an external electricity supply unit 42 for normal operation. The change-over switch 36 can be actuated in such a way that only in the event of a failure of the external electricity supply unit 42 is a change-over made from this to the internal electricity supply unit 38. As shown in FIG. 5, the heating element 6 in the recombination device 24 may be supplied permanently by a radiation-resistant battery 44 which is arranged in or directly next to the device 24. This is, therefore, a decentral incident-proof energy supply, and the battery 44 may be referred to as a local energy store. The following should be appreciated with regard to FIGS. 4 and 5: The partial heating minimizes the necessary energy requirement, in particular in incident situations, to such an extent, for example to less than 100 W, preferably to less than 10 W, that it is possible for energy to be introduced from the energy store 38, 44 over a period of several hours. In the embodiment of FIG. 5, the energy store arranged within the reactor safety vessel 26 consists of one or more separate electrical batteries 44 which, in the event of a failure of the current supply over a specific period of more than 2 hours, preferably of more than 24 hours, come into operation automatically and maintain the heating and temperature control of the active catalyst zone. Referring now to FIG. 6, the recombination device 24 may be provided with a storage device 50 for heat, also referred to herein as a heat store 50. The heat store 50 contains a liquid or solid heat storage material. The storage device 50 is maintained permanently at an increased temperature of more than 200xc2x0 C., preferably more than 400xc2x0 C., by means of electric resistance heating. The necessary energy injection is effected from an external electricity supply device 42. In order to keep the heat losses low, the store 50 is surrounded by an incident-proof insulation 52, in particular a vacuum insulation or solid insulation. Heat is transported from the heat store 50 to the heating element 6 in the unit 24 by direct heat conduction, specifically via an insulated heat transport element 54, for example a metal rod. If the supply line between the resistance heating in the heat store 50 and the external supply 42 is interrupted, the stored heat is sufficient to keep a predetermined small area of the catalytic surface at an increased temperature, specifically for a period of hours. Here too, the-passive initial-igniter catalyst part is arranged, counter to the direction of flow, in the lower part or region 34 of the device 24. Referring now to FIG. 7, there is shown a heatable heating element 6 which comprises a heating coil 56 or a catalytically coated filament and a wire mesh 58 or a catalytically coated filter fleece. The latter rests on a fastening or retaining means 60 or directly on the plane catalyst body 2. Referring, finally, to FIG. 8, the electrically heated heating element 6 may be integrated to a greater or lesser extent into the catalyst body 2 or it may rest directly on the catalyst body. The latter instance is shown here. A plate-shaped carrier body 62, for instance an austenitic metal foil, is covered by an electrical insulating layer 64. A zigzag-shaped conductor track 66 for electrical heating is accommodated in the insulating layer 64. The plate-shaped catalyst body 2, only a portion of which is shown for the sake of greater clarity, rests on the insulating layer 64. Here again, the catalyst body 2 is a thin precious metal plate which is covered on top with a catalyst layer based on Pd/Pt. Due to the relatively low energy requirement of the device illustrated in FIGS. 1 to 8, a combination with the supply of other measuring devices in the reactor safety vessel which are supplied with emergency current, such as, for example, with the supply for the purpose H2 measurement, is possible. This signifies a comparatively low outlay. To restore catalytic activity, a brief high-temperature phase of more than 200xc2x0 C. (cyclic or else to be triggered by hand, for example within the framework of repeat tests) may additionally be triggered, for example by means of a trip switch 36 in FIG. 4. This achieves a highly effective reactivation of the heated catalytic part in the region of the heating element 6, so that, during continuous operation, heating at a markedly lower level is sufficient, since reversible catalyst poisons are qualitatively adsorbed.