Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention – Recombiners
Reexamination Certificate
1999-08-09
2002-03-12
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
Recombiners
C376S300000, C422S211000, C423S580100, C423S645000, C431S328000, C431S346000
Reexamination Certificate
active
06356613
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an apparatus for the recombination of hydrogen in a gas mixture, in particular for a nuclear power station.
In a nuclear power station, if there are situations in which an incident or accident occurs, however unlikely these may be, oxidation of zirconium could occur, for example, due to the heating of the core. In this case, the formation and release of hydrogen gas and carbon monoxide within the safety vessel or containment enclosing the reactor core must be expected. Explosive gas mixtures may consequently be generated within the containment.
Various devices or methods are under discussion for preventing the formation of explosive gas mixtures of this kind in the containment of a nuclear power station. These include, for example, devices, such as catalytic recombinators, catalytically and electrically operated ignition devices or the combination of the two devices mentioned above as well as methods for permanently or subsequently inertizing the containment.
When a catalytic recombinator is used for eliminating hydrogen from the atmosphere of the containment, early flameless recombination of hydrogen with oxygen is to be achieved in particular. In this case, a significant pressure build-up as a consequence of virulent hydrogen combustion is to be reliably avoided. An early-starting recombination device suitable for this purpose, which, even when dwelling for a relatively long time in the containment atmosphere, does not lose activity to any appreciable extent and starts passively at low ambient temperatures, is proposed in earlier, commonly assigned German Patent Application 196 36 557.0. By use of a recombination device of this type, “smooth” recombination of hydrogen in a, for example, steam-inertized phase of the containment atmosphere, without ignition, is possible. A catalyst system for the recombination of hydrogen with oxygen is also known from U.S. Pat. No. 5,167,908.
Published, European Patent Application EP 0 436 942 A1 discloses a recombinator system with a housing protection device which opens automatically as a function of an external temperature.
By contrast, in a state of readiness of the recombination system, the housing protection device is closed, so as to avoid the catalytically active surface of the recombinator being contaminated.
By contrast, in a recombinator device known from Published, European Patent Application EP 0 416 140 A1, filter media are provided, which retain the pollutants from the ambient atmosphere, such as, for example, aerosols, and thus protect the catalyst of the recombinator device against contamination.
Published, European Patent Application EP 0 388 955 A1 discloses a recombinator device, in which an ignition device is additionally provided for triggering controlled hydrogen combustion.
Every known recombinator system is configured for a particularly high recombinator capacity, along with particularly small component dimensions, and for high resistance to contamination. However, to use an apparatus for the recombination of hydrogen in a gas mixture in a nuclear power station, it is also necessary, furthermore, to ensure that no effects adversely influencing the safety of the nuclear power station can occur. It must be remembered that a catalyst configuration used for the recombination of hydrogen normally heats up as a result of recombination and, on account of its increased temperature, could contribute unintentionally to ignition of the gas mixture within the containment atmosphere of the nuclear power station.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an apparatus for the recombination of hydrogen in a gas mixture that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which apparatus unintentional ignition of the gas mixture is avoided in a particularly reliable way.
With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for a recombination of hydrogen in a gas mixture, including a housing; a catalyst configuration disposed in the housing and through which a gas mixture can flow by free convection in an operating situation; and a flame retention device associated with the catalyst configuration and having a number of inflow orifices formed therein for an inflow of the gas mixture and the inflow orifices having an average size of at least 0.2 mm and of at most 3 mm.
For an apparatus of the above-mentioned type, the object is achieved, according to the invention, in that the associated catalyst configuration, which is disposed in the housing through which the gas mixture can flow by free convection in the operating situation, is assigned the flame retention device. The flame retention device has a number of inflow orifices provided for the inflow of the gas mixture and have an average size of more than 0.2 mm and at most 3 mm.
The terminology “free convection”, in particular, means that a local increase in temperature of the gas mixture, the increase resulting from the recombination of hydrogen in the vicinity of the catalyst configuration, results in a lift which overcompensates the pressure loss in the recombination apparatus in such a way, that the flow of the gas mixture through the recombination apparatus is ensured without external drive devices. In this case, the housing is configured in the manner of an approximately vertically disposed well, so that, in the operating situation, a chimney effect occurs so as to assist the flow of the gas mixture.
The dimensioning of the inflow orifices ensures the functioning of the flame retention device, and that particles of smaller sizes, such as, for example, aerosols, are capable of penetrating freely. The risk of clogging by small particles, such as, for example, aerosols, is thus reliably avoided. The pressure loss relevant for the flow behavior of the gas mixture through the recombination apparatus therefore remains particularly low, even after a lengthy period of operation. Moreover, with dimensioning of this kind, in combination with a suitably selected onflow surface, it is possible to configure the recombination apparatus for a particularly favorable flow velocity of the inflowing gas mixture with a view to the hydrogen recombination rate.
The invention proceeds from the knowledge that unintentional ignition of the gas mixture in the vicinity of the recombination apparatus could be triggered by a flame generated during recombination and emerging from the latter. In order to avoid this in a reliable way, the interior of the recombination apparatus, the interior being enclosed by the housing, should be uncoupled in terms of explosion from the space outside the recombination apparatus. A flame retention device is provided for this purpose. In this case, the flame retention device should be disposed in such a way that, in particular, flame propagation opposite to the direction of flow of the gas mixture is reliably prevented.
The flame retention device may be configured as a perforated plate or grid surrounding the housing completely or partially. The flame retention device preferably precedes the catalyst configuration.
In order to avoid unintentional ignition of the gas mixture surrounding the recombination apparatus in a particularly reliable way, the catalyst configuration is advantageously preceded by a sediment trap.
As emerged surprisingly in this regard, even so-called “stray” hot catalyst particles may contribute to ignition of the gas mixture surrounding the recombinator apparatus. When the recombination apparatus is in operation or even shut down, particles may be detached from the catalyst configuration. These detached catalyst particles may have a high temperature due to the heat released during the recombination of the hydrogen and may thus cause ignition when they enter an ignitable gas mixture, for example in the vicinity of the recombination apparatus. In order to avoid ignition of this kind caused by stray catalyst particles discharged from the recomb
Eckardt Bernd
Hill Axel
Carone Michael J.
Greenberg Laurence A.
Lerner Herbert L.
Richardson John
Siemens Aktiengesellschaft
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