The Olkiluoto nuclear power plant, located at Eurajoki on Finland's southwest coast, uses large volumes of seawater in its cooling system.
The water management licence granted to the plant obliges its operator, Teollisuuden Voima, to investigate the impact of the plant units on the fish population in the area.
A study was carried out last year and at the beginning of this year collected samples of fish from the flushing channels of the seawater pumping plants of all three units.
These channels accumulate all the organic matter that comes in with the cooling water. In addition to fish, this consists of algae, mussels, aquatic plants and polyps.
According to the company's report, the total number of fish sucked in by the Olkiluoto units during the monitoring period of just over a year was estimated to be around 27.6 million. The estimated total weight of the fish was about 42.4 tonnes.
"The number of individual fish is, of course, huge, but in total it is however made up of very small ones," Ilkka Tammela, TVO's fisheries economist, pointed out in a company release.
No impact on commercial fisheries
According to the survey results, 95 percent of the fish that caught up in the cooling water weighed three grammes or less. Of these, 87 percent were non-economically important fish species.
The three most common fish species at the Olkiluoto 1 unit were three-spined stickleback, ten-spined stickleback and small members of the genus Pomatoschistus. At Olkiluoto 2, the corresponding species were three-spined stickleback, ten-spined stickleback, as well as smelt and Baltic herring fry. At Olkiluoto 3, the most common species were three-spined stickleback, ten-spined stickleback and Baltic herring.
A new intrusive species to the Baltic Sea, the bryozoa, or moss animal, Conopeum chesapeakensis, was found at Olkiluoto in samples for the study.
A similar survey was last carried out in 2010. The new survey became necessary following the completion of the Olkiluoto 3 unit and was more detailed than the previous one.
Teollisuuden Voima has turned over the results of the study to the Centre for Economic Development, Transport and the Environment.
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