Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention – Pressure suppression and relief
Patent
1998-03-30
1999-08-24
Wasil, Daniel D.
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
Pressure suppression and relief
376282, 376299, 376407, G21C 9004
Patent
active
059433841
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to a system for depressurizing pressurized steam operated plant.
The system is of the type in which cold water contained in a tank which is superelevated with respect to the pressurized plant, is injected under gravity.
As is known, this type of system is used to guarantee maximum safety in the event that pressurized plant suffer accidents which require the immediate depressurization of the plant.
A typical application is in the field of water-cooled nuclear reactors in which depressurization, in the event of a serious accident, consists in injecting directly into the container of the nuclear reactor or into the primary circuit, a large quantity of cold water which condenses the steam present and lowers the average temperature of the plant, with a consequent drop in the internal pressure.
Following this depressurization it will then be possible to bring in other accident mitigating systems.
An essential requirement in this sphere is that the depressurization system should come into action without any possibility of failure, which would have devastating effects because said other mitigating systems would be ineffective.
In this respect depressurization systems are known which employ injection, under gravity, of liquid coolant operating passively, i.e. able to fulfil their functions solely on the basis of physical laws, by virtue of suitable mechanical/functional and structural design.
In the systems mentioned above, the injection of liquid coolant is not triggered through the use of automatic logic enablers, by control systems, or manual ones, by operators. This therefore does not require the intervention of special actuation members such as, for example, valves, nor the presence of sources of external energy.
Patent Application No. WO 95/09425 describes a depressurization system in which the injection of water is triggered by means of a pressure reduction induced in the throat of an ejector traversed by steam from the plant to be depressurized condensing in a condenser forming part of the depressurization system.
This condenser, during normal operation of the plant, is flooded by water from the plant, whereas, should an accident occur, this condenser is gradually uncovered by the evaporation of the water, becoming operational and bringing about said circulation of steam.
The depressurization system described above has the drawback of triggering the injection of cold water at a speed proportional to the rate at which the plant is draining. In particular, in the case of accidents which involve ruptures in the plant of limited flow section, the triggering rate is too slow.
In addition to a delay in the triggering of the injection of cold water, the aforesaid system has the drawback of suffering from the presence of incondensibles in the steam, their presence further slowing down the condensation of the steam to the point where triggering is precluded.
The technical problem underlying the present invention is how to provide available a depressurization system for pressurized plant such as to overcome the drawbacks mentioned with reference to the prior art.
This problem is solved by a depressurization system for pressurized steam operated plant employing the injection, under gravity, of cold water contained in a tank which is superelevated with respect to said plant, said plant comprising a steam headspace defined by a liquid level during normal operation, said depressurization system comprising: around said plant; and an outlet collector; section and a throat; said ejector; closed loop caused by the condensation of steam from the plant in said condenser during the occurrence of an accident, characterised in that it comprises: to the inlet collector of said condenser; close to the pressurized steam operated plant; siphon-type hydraulic shutoff.
The principal advantage of the depressurization system according to the invention is its rapid triggering, which occurs independently of the magnitude of the damage from which the accident stems.
Further characteristics and adva
REFERENCES:
patent: 5661769 (1997-08-01), Mansani et al.
Alemberti Alessandro
Barucca Luciana
Mansani Luigi
Saiu Gianfranco
Finmeccanica S.p.A. - Azienda Ansaldo
Wasil Daniel D.
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