Attack of the jellyfish

I've just read this story in the Edinburgh Evening News about the nuclear power station at Torness being shut down because jellyfish had clogged the intake for the cooling system.

On its own, this incident would not be too serious. Both reactors were shut down safely on Tuesday afternoon, although this does raise questions about why it has only just been reported. However it is not all that easy to start the reactors up again after a shutdown. As yet EDF Energy have not given any dates, but the National Grid don't expect them to be back on line until the 5th or 6th July ... which means both reactors will not have been producing energy for more than a week.

     

My reason for highlighting this story is simply that it provides an example of the sort of minor, unexpected things that can shut down a nuclear reactor without any warning. Things like this can happen to any power station, but only nuclear power stations take so long to start producing electricity again after the event which caused the shutdown has been fixed.

But how often do these things happen? Are events like these so rare as to not have any significant effect on overall electricity generation when evened-out over the years?

Well, no. Events like this are in fact quite frequent. This report in the Guardian in March of this year details a whole list of unplanned shutdowns at Torness in the last quarter of 2010, including one where the cooling intake had been blocked ... but on that occasion by seaweed rather than jellyfish. However there were also some more serious events which could be called safety blunders.

The revelations have reignited concerns about the safety of Britain's nuclear stations. French-owned EDF Energy admitted that it had not followed the correct procedures, but insisted that there had been no danger to the public.

A report posted online by the UK government's Nuclear Installations Inspectorate (NII) discloses that there were two significant safety "events" at Torness in September last year. "Correct operational procedures appear not have been observed," says the report.

In one incident, an equipment malfunction cut off the electricity supplied to a gas circulator. Gas circulators are critical components because they ensure that air is kept moving to cool reactor fuel and prevent it from overheating.

The second incident also involved problems with electricity supply, though this time to a radioactive fuel dismantling facility at Torness. According to EDF Energy, the two events were "entirely unconnected".

The NII report says: "The events included contributions from operators not complying in full with the instructions provided to ensure safe limits and conditions are observed during plant operations."

Guardian, 22 March 2011

One of the most frequent criticisms of renewable power from sources such as wind is that it requires backup. That's true, of course. But so does every form of generation; including gas, coal ... and nuclear.

Over the last five years the load factor of nuclear power stations in the UK has varied between a high of 72.4% in 2005 and a low of 49.4% in 2008 (Table 5.10). This shows that nuclear is by no means as reliable a source of power as some people would have us think.