The 1999 Blayais Nuclear Power Plant flood was a flood that took place on the evening of December 27, 1999. It was caused when a combination of the tide and high winds from the extratropical storm Martin led to the seawalls of the Blayais Nuclear Power Plant in France being overwhelmed. The event resulted in the loss of the plant's off-site power supply and knocked out several safety-related systems, resulting in a Level 2 event on the International Nuclear Event Scale. The incident illustrated the potential for flooding to damage multiple items of equipment throughout a plant, weaknesses in safety measures, systems and procedures, and resulted in fundamental changes to the evaluation of flood risk at nuclear power plants and in the precautions taken.
The Blayais plant, equipped with four pressurized water reactors, is located on the Gironde estuary near Blaye, South Western France, operated by Électricité de France. Due to records of over 200 floods along the estuary dating back to 585 AD, some 40 of which had been particularly extensive, the location of the plant was known to be susceptible to flooding, and reports of the 1875 floods mentioned that they were caused by a combination of a high tides and violent winds blowing along the axis of the estuary. The area had also experienced flooding during storms in the recent past, on December 13, 1981 and March 18, 1988. An official report on the 1981 floods, published in 1982, noted that it 'would be dangerous to underestimate' the combined effects of tide and storm, and also noted that the wind had led to 'the formation of real waves on the lower flooded floodplain'.
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