Swarming jellyfish force shutdown of French nuclear power plants for second time in a month

Two French nuclear power stations have had to partially shut down operations in the past month due to swarms of jellyfish infiltrating the pumping station filters.

In an example of how the effects of climate change can have wildly unlooked-for consequences, France’s government-owned electric utility company EDF has had to twice shut down operations of nuclear power reactors at two separate nuclear power plants in the past month because of the jellyfish swarms.

The 5.5-gigawatt (GW) Gravelines nuclear power plant was forced to shut down production at four of its six nuclear reactors on August 10 and 11 due to what EDF described as “the sudden and massive arrival of jellyfish” at the filters of the power plant’s pumping station.

Staff at the power plant were able to maintain and clean the filters of the seaborne invaders, although several smaller swarms apparently arrived in the following days, including a ‘notable’ swarm on August 23 which forced one of the reactors to again be shut down as a precautionary measure.

Less than a month later, on September 6, the 5.2 GW Paluel nuclear power plant was also forced to shut down one of its four nuclear reactors “following the arrival of jellyfish at the filters”.

EDF also chose to reduce production at another of its reactors “as a precaution”, which left only one reactor operational, with a third already down for scheduled maintenance.

Three of the four reactors were all operational by Saturday, September 6, with the No. 2 reactor still shut down for scheduled maintenance.

EDF explained in August that the “arrival of sticky, gelatinous jellyfish” in the pumping station ‘exceeded expectations’ and created a “sudden increase in blockages”.

Both power stations are situated on the north-west coast of France and use seawater pumped directly from the North Sea or English Channel for their cooling systems. This obviously opens the door for potential foreign objects to enter the pumping station, which is why they use pre-screens and filter drums.

However, the arrival of so many jellyfish was to much for the filtering systems, necessitating the shut down of the reactors which could have potentially received less water than was necessary to maintain safe operations.

According to EDF, the culprit was the Rhizostoma Octopus, also known as the barrel jellyfish, dustbin-lid jellyfish, or frilly-mouthed jellyfish.

Jellyfish like the Rhizostoma Octopus follow warm water currents for their yearly reproduction cycle. In the past, the seasonal shift in water temperatures would eventually cause conditions to become unfavourable for the jellyfish to remain.

However, according to a report in The Guardian in early August, record-high sea surface temperatures in Spring, which have been exacerbated by global heating, have proven particularly enjoyable for jellyfish this year, resulting in what experts describe as a population bloom and prolonged stay in UK waters.

Of the common jellyfish species benefiting from the warmer waters is the barrel jellyfish, which can grow to a metre in diameter and has long frilly arms with only a relatively mild sting.

EDF promised an “in-depth local, national, and international analysis” of the events which caused it to shut down its nuclear reactors, to be completed in conjunction with the World Association of Nuclear Operators (WANO).

The analysis will reportedly take several months but is expected to “allow seaside sites to adjust current procedures and find new effective solutions”.

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