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Conference Article: The roles of water addition and gas composition in AGR accident management

Abstract

Severe Accident Guidelines (SAGs) are being produced in line with best international practice for managing a severe accident in an AGR. Such an accident would be extremely unlikely due to the long timescales for recovery prior to core damage. A number of actions proposed in the SAGs are concerned with the prevention of air ingress and the deliberate injection of water into the core. Air ingress is minimized by sealing breaches and by the controlled injection of inert gases into the vessel, although at high temperatures the change in reactor gas from CO₂ to CO provides a more inert atmosphere and reduces any ingressing oxygen. Consideration would be given to the injection of water into the core if the installed cooling systems could not be recovered sufficiently in a direct or improvised manner. In such cases sufficient cooling should be possible by injecting water uniformly across the core into a few tens of channels. Ideally the water would be injected before significant fission product release had occurred and before the graphite had become hot enough to oxidise in steam. This advice is reinforced by experiments with a simulated fuel pin in the presence of reactor graphite which showed that fission products released from the pin could be transported on fine (0.1 mum) graphite aerosols.

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Reference:

Technical committee meeting on response of fuel, fuel elements and gas cooled reactor cores under accidental air or water ingress conditions. Beijing (China). 25-27 Oct 1993

International Atomic Energy Agency, Vienna (Austria)

IAEA-TECDOC--784, pp:110-115