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Conference Article: Safety criteria and provisions for the evacuation of residual heat from graphite gas cooled reactors

Lheureux, R. (SPT, Division Calculus Nucleaires, Paris - La Defense (France)); Aguilera, A. (Centrale Nucleaire de Saint-Laurent A, La Ferte-Saint-Cyr (France))

Abstract

The power given off by GGCR reactors is evacuated by CO₂ that is displaced by four turbo-blowers driven by steam from the steam generator. In order to evacuate the residual power after a unit shutdown, the turbo-blowers are driven by steam from the auxiliary boilers (at SAINT-LAURENT A and BUGEY 1), or by electric motors placed at the shaft end as is done at CHINON A3. In the event of these cooling systems failing whilst the reactor remains pressurized, there are emergency systems. At SAINT-LAURENT A shutdown exchangers are placed in a high position thus creating natural convection. At CHINON A3 the steam generators are above the core which also creates natural convection. At BUGEY 1 a motordriven blower ensures that CO₂ circulates. The steam generator is kept in operation. At SAINT-LAURENT A and BUGEY 1 when the reactors are under slight air pressure four fans evacuate the residual power in an open circuit. At CHINON A3 the reactor is kept in a closed circuit and the turbo-blowers are driven by their electric motors. The steam generator remains supplied. These systems have proved efficient as after twenty years of operation there has only been one incident at CHINON A3, three days before definitive shutdown. This necessitated going over to natural convection which was done according to procedures without the slightest problem.

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key words: Gas Cooled Reactor, Nuclear Technology

Reference:: Specialists meeting on decay heat removal and heat transfer under normal and accident conditions in gas cooled reactors. Juelich (Germany). 6-8 Jul 1992; International Atomic Energy Agency, Vienna (Austria); IAEA-TECDOC--757, pp:29-41