Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention – Recombiners
Patent
1990-12-14
1993-07-27
Wasil, Daniel D.
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
Recombiners
376300, 423580, G21C 900
Patent
active
052308596
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for removing flammable gas mixtures in a gas space. The invention also relates to devices for carrying out such processes. In some processes, for example of a chemical nature, the formation of flammable gas mixtures is unavoidable. Explosions of flammable gas mixtures can cause considerable damage to the plants containing these gas mixtures.
The removal of a hydrogen/air mixture after a core-melting accident in a nuclear power station (NPS) serves as an application example for describing the invention.
In the event of core-melting, large quantities of hydrogen are released within a short time in the containment vessel (CV) of the NPS due to metal/water reactions, which hydrogen must be removed immediately from the gas space of the CV, so that no uncontrolled reactions of the hydrogen (H.sub.2) with the oxygen (O.sub.2) of the CV air are ignited; otherwise, it would not be possible to exclude premature CV failure in such a case in the event of an H.sub.2 /O.sub.2 deflagration or detonation.
It has been proposed to use open ignition sources for removing such a flammable hydrogen/air mixture. Battery-operated spark gaps of catalytic ignition devices are on offer //Siemens: Hydrogen ignition device, Order No. A 19100-U822-A107 May 1988// which initiate a deflagration or detonation in an ignitable hydrogen/air mixture in the containment vessel of a nuclear power station, for example in the event of a core-melting accident.
Further processes for the recombination of H.sub.2 and O.sub.2 have been known for a long time, for example: into a reaction chamber and recombined therein, for example thermally or catalytically. With a free volume of about 70,000 m.sup.3 of the CV of a German light-water reactor, the continuous flow process proves to be unsuitable because of the extremely long time required; this includes Swiss Patent Specification 514,217 which describes the formation of a combustion chamber in a line carrying an exit gas flow by means of porous isolation devices. recombinators (contact catalysts) have been proposed. Catalytic processes react very sensitively to traces of catalyst poisons. If catalytic surfaces act as recombinators, they heat up in the case of sufficient H.sub.2 /O.sub.2 availability to temperatures>ignition temperature of the explosive H.sub.2 /O.sub.2 mixture //loc. cit. Siemens, May 1988// and initiate a deflagration or detonation in the CV.
It is also known that flammable gas mixtures present in a container deflagrate below the detonation limit if the ignition occurs at one place in the container. It is also known, however, that, as a result of almost simultaneous ignition of a flammable gas mixture likewise below the detonation limit at various points in a container, detonation-like effects, which do not occur in the case of local ignition at only one point in the container under otherwise the same overall conditions, are already reached as a result of a kind of explosion jet. Even without detonation-like effects, a hydrogen deflagration in the CV of an NPS can lead, as a result of the associated release of heat energy, to the build-up of a pressure of>10 bar, which exceeds the failure pressure of the CV of 9.5 bar.
The question whether detonations--even if they may be locally limited--in the case of serious nuclear power station accidents, such as e.g. core-melting accidents, should be accepted in the CV, if the CV represents the last intact barrier towards the environment, has not yet been checked by large-space experiments in a sensible volume ratio to the CV, but only by means of computer calculations for simulated accident sequences. All such computer codes require the fixing of defined overall conditions which must completely cover and describe the serious accidents, for which the nuclear power stations are not designed. This leaves open the question whether and to what extent potential core-melting accidents may perhaps deviate from the preconceived ideas of the users of such simulation codes with respect to the sequence of events.
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