Patent Number: 
Section: description

In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown an ignition system 1 intended for the recombination of hydrogen in a gas mixture, specifically in the containment atmosphere of a safety vessel 2, excerpts of which are represented in FIG. 1, of a nuclear facility. For this purpose, the ignition system 1 contains a plurality of spark igniters 4 which are disposed inside the safety vessel 2 on an internal wall 3, and each of which is configured for on-demand production of ignition sparks for a controlled combustion of hydrogen released in the interior of the safety vessel 2. In order to be supplied with ignition energy, the spark igniters 4 are connected to a two-stage power supply system 6. The power supply system 6 contains a plurality of intermediate energy stores 8 connected to a central power supply unit 7. In the illustrative embodiment, low-voltage accumulators are provided as the intermediate energy stores 8. As an alternative, the intermediate energy stores 8 may also be configured as dry batteries. The intermediate energy stores 8 are suspended inside the safety vessel 2, from a further internal wall 9. A group of about 15 spark igniters 4 is connected to each of the intermediate energy stores 8. In other words, the spark igniters 4 are connected together in groups in order to supply them with energy, each group of spark igniters 4 being connected to the intermediate energy store 8 common to them. The grouped connection of the spark igniters 4 is symbolized in FIG. 1 by the bundled representation of power transmission lines 10. The power transmission lines 10 are in this case, in an embodiment suitable for high temperatures, configured as metal-clad cables with mineral insulation. On an input side, the intermediate energy stores 8 are connected to the central power supply units 7 via supply lines 12 fed through the safety vessel 2. Each of the intermediate energy stores 8 is configured for an autonomy time of about 24 hours and can be recharged via the central power supply unit 7. In the illustrative embodiment, a back-up diesel generation network is provided as the central power supply unit 7. As an alternative, it is also possible for a separate battery or a different power generator to be provided. However, each of the intermediate energy stores 8, which are respectively connected via the line 12 to the central power supply unit 7, contains an automatic switch 14 which is intended to trigger an ignition process and has a catalytically coated temperature sensor 16 and an integral pressure switch 18. The ignition system 1 is therefore equipped for redundant automatic ignition activation as a function of the pressure and/or the temperature in the interior of the safety vessel 2. In addition, each of the intermediate energy stores 8 is connected via a signal line 22 to a manual trigger system 24. The trigger system 24 may in this case for example form part of the control room of a nuclear power station on an input side, the trigger system 24 is connected via a signal line 26 to a hydrogen sensor 28. The power supply to the spark igniters 4 via the intermediate energy stores 8 respectively connected upstream of them may in this case alternatively be triggered via the automatic trigger 14 respectively integrated in the intermediate energy stores 8, or via the manual trigger system 24. Furthermore, each of the intermediate energy stores 8 is equipped with an integral cooling unit 29 in the form of a heat sink. The cooling unit 29 is in this case configured in such a way that a temperature of 100xc2x0 C. in the interior of the intermediate energy store 8 is not exceeded even in the case of an incident in which a large amount of heat is released. The intermediate energy stores 8 can therefore be operated reliably in a wide variety of incident scenarios, even in the embodiment as low-voltage accumulators. The spark igniter 4 of the ignition system 1 is schematically represented in FIG. 2. The spark igniter 4 is configured as a high-speed igniter with an operating frequency of about 100 Hz and as a low-energy igniter with an operating power of about 5 W, and for this purpose contains ignition electronics 30 whose essential components are a clock generator, a high-voltage transistor, a charging capacitor and an ignition transformer. The ignition electronics 30 are connected on the input side to the power supply line 10 which is connected to the intermediate energy store 8 allocated to the spark igniter 4. On an output side the ignition electronics 30 are connected to a spark gap 32 whose end 34 projects in a region of the interior of the safety vessel where an incident with increased release of hydrogen is to be expected. The spark igniter 4 contains a multi-layer housing 36 whose outer casing 38 consists of a material which is stable at high temperature, for example VA steel or titanium. An insulating casing 40 which, in the illustrative embodiment, is configured in a double-casing fashion as an air gap between the outer casing 38 and an inner casing 42, is disposed inside the outer casing 38. As an alternative, an insulant that is resistant to high temperatures and radiation and is disposed between the outer casing 38 and the inner casing 42 may also be provided for the insulating casing 40. Inside the housing 36, the ignition electronics 30 are disposed in an inner housing 44 configured as a radiation screen. An intermediate space 46 between the inner housing 44 and the inner casing 42 is filled in the manner of a water bath up to a level 48 with water W which serves as a heat sink integral to the spark igniter 4 The inner housing 44 is fastened to the housing 36 via a fastening element 50 made of an insulating material. At its end that faces the spark gap 32 and is closed off with a cover 52, the housing 36 is provided with a ceramic heat shield 54. The interior 46 communicates with the external space of the housing 36 via a discharge line 58 which can be closed off by a safety valve 56. The housing 36 is suspended via a fastening element 60 from the internal wall 3. The housing 36 suspended via the fastening element 60 from the internal wall 3 is in this case surrounded by a further insulating casing 62 disposed directly on the internal wall. In the event of an incident inside the safety vessel 2, the fact whether hydrogen has been released is ascertained by the hydrogen sensor 28 or by the temperature sensors 16 and/or the pressure switches 18 provided as sensors. If hydrogen has been released, then the spark igniters 4 are activated manually using the trigger unit 24 or automatically using the automatic triggers 14 integrated in the intermediate energy stores 8. An ignition spark which leads to controlled combustion or recombination of the hydrogen is in this case produced by the spark gap 32 of each spark igniter 4 at its end 34. By virtue of the spark igniter 4 configured as a high-speed igniter with an operating frequency of about 100 Hz, reliable ignition of the hydrogen is in this case ensured even in the case of comparatively fast gas displacement processes with flow speeds in excess of 10 m/s. In addition, by virtue of the high operating frequency of the spark igniters 4, particularly strong pre-ionization of the gas mixture is ensured, so that early ignition directly after the ignition group has been passed is ensured, even in the case of a slow-moving gas atmosphere. The levels of loading due to combustion which follow ignition are therefore particularly low. The ignition system 1 is configured for particularly high operating safety, even for a wide variety of incident situations. By virtue of the two-stage configuration of the power supply system 6 for the spark igniters 4, the ignition system 1 is suitable both for medium-term autonomous operation and for long-term continuous operation. In medium-term autonomous operation, the power supply for the spark igniters 4 takes place exclusively via the intermediate energy stores 8, which provide for an operating time of at least 24 hours without any extra supply. Reliable operation of the ignition system 1 is therefore ensured even if external devices fail. Reliable long-term operation of the ignition system 1 is in addition ensured by the central power supply unit 7. On account of their structure, the spark igniters 4 are configured for a high degree of operating safety even in the event of a wide variety of accident scenarios. The functional safety of the relevant ignition electronics 30 is in this case ensured even at high external temperatures due to the respective incident. This is contributed to, further to the insulating casing 40 provided in the housing 36 of each spark igniter 4, in particular by the integral heat sink in the form of the water W surrounding the internal housing 44 as well. This is because the water W vaporizes as a result of elevated temperature and thereby contributes through its heat of evaporation to cooling the ignition electronics 30. A particularly long working period is in this case ensured by the safety valve 56. This is because the rate at which the vaporized water W is discharged from the housing 36 can be adjusted using the safety valve 56. Even if the supply of water is limited, the integral heat sink is therefore available for a particularly long working period.