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Having no technical expertise in the industry, i wondered what's happened there, discovering a Level 2 Incident at the Blayais plant on the Atlantic coast.
With some eerie similarities to Fukushima.
Prior to the flooding, units 1, 2 and 4 were at full power, while unit 3 was shut down for refuelling. Starting from 7:30 pm all four units lost their 225 kV power supplies, while units 2 and 4 also lost their 400 kV power supplies. The isolator circuits that should have allowed units 2 and 4 to supply themselves with electricity also failed, causing these two reactors to automatically shut down, and diesel backup generators started up, maintaining power to plants 2 and 4 until the 400 kV supply was restored at around 10:20 pm. In the pumping room for unit 1, one set of the two pairs of pumps in the Essential Service Water System failed due to flooding; had both sets failed then the safety of plant would have been endangered. In both units 1 and 2, flooding in the fuel rooms put the low-head safety injection pumps and the containment spray pumps, part of the Emergency Core Cooling System (a back-up system in case of coolant loss) out of use. Over the following days, an estimated 90,000 m3 (3,200,000 cu ft) of water would be pumped out of the flooded buildings.
Around two and a half hours after the flooding began, a high-tide alarm for the estuary was triggered in the observation room of plant 4, although those in the other plants failed to activate. This should have caused the control room operators to launch a 'Level 2 Internal Emergency Plan', however this was not done as the requirement had been omitted from the operation room manual; instead they continued to follow the procedure for the loss of the off-site power supply, so failing to shut down the operating reactors at the earliest opportunity to allow the residual heat to start to dissipate.
During the morning of December 28, the Institute for Nuclear Protection and Safety estimated that, if the emergency cooling water supply failed, there would have been over 10 hours in which to act before core meltdown started.
The emergency response seems to have been highly competent and effective. Further to their credit, there was "no quantifiable effect on radiation." After a few years of procrastination, the sea walls were raised and sealed.
So the incident confirms there was enough redundancy in the design to cope with this particular event. Still, makes one wonder. How much higher is the extreme event probability in a climate warmed world?
The adequacy of the sea walls has, however, been disputed by Professor Jean-Noël Salomon, head of the Laboratory of Applied Physical Geography at Michel de Montaigne University Bordeaux 3, who believes that, due to the potential harm and economic cost that would result from a future flood-related disaster, the sea walls should be designed to withstand simultaneous extreme events, rather than simultaneous major events.
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