Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention – Recombiners
Reexamination Certificate
1999-11-29
2002-05-07
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
Recombiners
C376S301000, C361S253000
Reexamination Certificate
active
06385270
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a safety vessel of a nuclear facility having an ignition system with a plurality of spark igniters for the recombination of hydrogen in a gas mixture.
A safety vessel of this type is disclosed in Published, Non-Prosecuted German Patent Application DE 38 20 187 A.
In a nuclear facility, in particular in a nuclear power station, if there are situations in which an incident or accident occurs, in which oxidation of zirconium may occur, for example on account of the heating of the core, then the formation and release of hydrogen gas and carbon monoxide within the safety vessel or containment enclosing the reactor core must be expected. In particular after an incident involving a loss of coolant, large quantities of hydrogen may then be released. Explosive gas mixtures may consequently be generated within the containment enclosure. Unless counter measures are taken, the atmosphere in the containment enclosure may then become enriched with hydrogen to such an extent that, in the event of accidental ignition, the combustion of a relatively large quantity of hydrogen could compromise the integrity of the safety vessel.
Various devices or methods are under discussion for preventing the formation of explosive gas mixtures of this type in the containment enclosure of a nuclear power station. These include, for example, devices such as catalytic recombinators, catalytically and/or electrically operated ignition devices or the combination of the two devices mentioned above as well as methods for permanently inertizing the containment.
When an ignition system is used for eliminating hydrogen from the atmosphere of the containment enclosure, reliable recombination of hydrogen with oxygen by a controlled combustion should be achieved. In this case, a significant pressure build-up as a consequence of virulent hydrogen combustion should be reliably avoided. An ignition system of this type is then customarily configured in such a way as to ensure reliable ignition of hydrogen even at the upper ignition limit of a gas mixture, that is to say in a gas mixture that has a comparatively high hydrogen concentration.
European Patent 0 596 964 discloses a combined catalyst/ignition system for the recombination of hydrogen in a gas mixture. In this system, heat obtained during the catalytic recombination of hydrogen on a catalyst body is fed to an ignition device and used there to ignite hydrogen. However, in a combined catalyst/ignition system of this type, the hydrogen is not ignited until an ignition delay has elapsed after the release of the hydrogen. The reason for this is that, after the hydrogen is initially released, some time is needed until the catalyst body is heated enough to permit ignition of the hydrogen. The effect of this time delay is that, in the case of fast gas displacement processes inside the containment enclosure, the hydrogen does not ignite until comparatively high hydrogen concentrations have been produced.
An ignition system for controlled ignition of a hydrogen-containing gas mixture, disclosed by European Patent 0 289 907 contains a spark igniter which can be supplied via an integral energy store. The ignition system is in this case provided with a stand-alone energy store, so no supply lines are required. The energy store provided in this case is, in particular, a dry battery. However, because of the capacity of the integral energy store, this ignition system is suitable only for a limited operating time. In particular with early excitation of the spark igniter, there is only a restricted possibility of controlled ignition of the hydrogen in the course of an incident in which hydrogen is later released. In addition, this ignition system likewise does not react to the release of hydrogen until after an ignition delay has elapsed. The possibility of long-term operation of the ignition system, which would be needed to cover all conceivable incident scenarios, is also subject to restrictions. Furthermore, precautionary activation of the ignition system actually in advance of a developing incident from an external station, for example the control room of a power station facility, is not possible.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a safety vessel of a nuclear facility having an ignition system for the recombination of hydrogen in a gas mixture which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which is protected particularly well against the formation of an explosive gas mixture. In this regard, an ignition system with a plurality of spark igniters for the recombination of hydrogen in the gas mixture, in particular for the containment atmosphere of the nuclear facility, with which reliable ignition of the ignitable gas mixture is ensured even in the case of comparatively fast gas displacement processes is also to be provided.
With the foregoing and other objects in view there is provided, in accordance with the invention, a safety vessel of a nuclear facility, including a safety vessel body having an interior formed therein; and an ignition system having a plurality of spark igniters for a recombination of hydrogen in a gas mixture disposed in the interior of the safety vessel body, each of the plurality of spark igniters is a high-speed igniter with an operating frequency in excess of about 10 Hz.
For a safety vessel of the type mentioned above, the object is achieved according to the invention in that each spark igniter is configured as a high-speed igniter with an operating frequency in excess of about 10 Hz.
This being the case, the invention is based on the idea that, for reliable ignition of the gas mixture even in the case of fast gas displacement processes, direct ignition of the gas mixture flowing past the, or each, spark igniter should be ensured even in the case of a flow speed in excess of about 10 m/s. For reliable direct ignition of a gas mixture flowing with such a high flow speed, the spark igniters are configured as high-speed igniters with a correspondingly high operating frequency. By virtue of the high speed, the surrounding gas mixture is furthermore strongly pre-ionized, so that the ignition probability increases and reliable ignition is thereby ensured as soon as the lower ignition limit of the gas mixture has been exceeded. The loading due to combustion is in this case much less in comparison with later ignition.
In an advantageous configuration, the spark igniters are then configured as low-energy igniters with an operating power of less than 10 W, preferably less than 5 W. It is thereby possible to supply the spark igniters with power reliably using particularly simple devices. It is then possible, in particular, to provide power supply cables having a particularly small cable cross-section. The feed-throughs needed for the cables through the safety vessel of the power station facility can thereby be configured with correspondingly small dimensions.
In order to ensure reliable ignition of the ignitable gas mixture both in the event of a temporary failure of external units and when the operating time of the ignition system is particularly long, it is advantageous if the spark igniters are connected together in groups in order to supply them with energy. A group of spark igniters being connected to an intermediate energy store common to them, and the intermediate energy stores being connected to a central power supply unit. It is then possible, for example, for a group of about 10 to 20 spark igniters to be connected to each intermediate energy store. As an alternative, however, all the spark igniters may be connected to a single intermediate energy store.
In a two-stage power supply system of this type, independence of the power supply to the spark igniters with respect to external units is ensured for at least a transitional time through the intermediate energy stores. On the other hand, the ignition system is furthermore suitable for a particularly long working time of, for example, in
Eckardt Bernd
Hill Axel
Carone Michael J.
Greenberg Laurence A.
Locher Ralph E.
Matz Daniel
Siemens Aktiengellschaft
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