The Olkiluoto 3 nuclear reactor near Eurajoki in southwest Finland began regular electricity production in April and now produces power at a rate of around 1,600 MW without emitting greenhouse gasses.
However, climate groups have pointed to a number of adverse effects the largest reactor in the Nordic region will have on its surrounding environment, including the warming of the seawater used to cool the plant and its effects on marine life.
Olkiluoto 3 is by far the largest of the three reactors located at Eurajoki and its operations will almost double the amount of water required to cool the plants.
In total, the three reactors need around 120-130 cubic metres of cooling water per second. This is more than half the average flow of the nearby Kokemäenjoki river, and Olkiluoto 3 accounts for about 57 cubic metres of this volume.
Court orders investigation
The seawater used to cool the nuclear power plant will also inevitably contain fish and other marine organisms.
Finland's Administrative Court ordered an investigation to be carried out into the effects of Olkiluoto 3 on the local marine life when regular electricity production began in April.
The investigation will take place over the coming 12 months, and aims to clarify what effect — if any — the nuclear reactors are having on the local ecosystem. In practical terms, this means assessing the quantities and species of fish that are transported to the power plants by the cooling water.
The report will be divided into two parts, with smaller fish — less than a centimetre long — collected at one point of the cooling water intake canals, and bigger fish examined in filters that collect solids from the cooling water.
"In practice, all the fish that are transported with the cooling water die, thereby removing a small amount of nutrients from the sea," marine biologist Mika Sivil from the Southwest Finland Ely Centre explained.
One of the species that suffers most from the intake of cooling water is the perch, a freshwater fish popular with Finnish consumers.
Previous studies have found that a few hundred kilos of perch are destroyed every year by the cooling process.
"The number is not terribly large, but this new survey will provide more information. The effects on smaller fish have not been studied before, but now we are getting information on them too," Sivil said.
Water temperature will also be monitored
The seawater used to cool the Olkiluoto nuclear power plants returns to the sea about 10 degrees warmer after passing through the plants.
This is reflected in the warming of seawater some 3-5 kilometres from the cooling water discharge point.
Safety Director Veli-Pekka Nurmi of the plant's operator TVO told Yle he does not believe that the start-up of Olkiluoto 3 and the consequential increase in volumes of cooling water will significantly affect the surrounding environment.
"If it were to happen that we were heating the sea more than is allowed, we would limit the plant's capacity. We have not yet come close to such a situation," Nurmi said.
The plant's permit conditions dictate that the temperature of the sea water, measured as a moving weekly average, must not exceed 30 degrees Celsius at a distance of 500 metres from the discharge channel.
The permit conditions also limit the amount of seawater used for cooling and the heat load it can generate.
TVO has so far been well below the maximum levels set by the permit. Last year, about 3.3 million cubic metres of seawater were used for cooling, compared with the maximum volume of about 4.4 million cubic metres as per the permit.
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