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Home  /  RESPONSIBILITY  /  Environment and climate  /  Environmental impacts  /  Cooling water

COOLING WATER

Cooling water is the most significant environmental aspect of the Olkiluoto nuclear power plant. The total amount of seawater used for the cooling of the OL1 and OL2 plant units is approximately 76 m3/s.

In 2017, 2,109 million cubic meters of seawater was used for cooling, and the resulting thermal load on the sea was 24.7 TWh. In fact, the cooling water’s thermal load on the environment is the most significant environmental aspect of TVO’s operations. Seawater temperatures are monitored as required by the environmental permit. One of the environmental permit regulations is that the seawater temperature does not exceed the target value of 30°C when measured as a weekly average at a distance of 500 meters from the cooling water discharge channel. Limit values have also been specified for the amount of cooling water (max. 3,800 million m3) and the thermal load (max. 56.9 TWh) in the environmental permit. None of the permit limits were exceeded in 2017.

As the cooling water passes through a plant unit, its temperature increases by approximately 10°C, after which it mixes with seawater. The cooling water does not come into direct contact with the power plant’s circulating water. Throughout the operation of the power plant, TVO has monitored the impacts of cooling water and conducted related surveys. The cooling water accumulates in an extensive sea area in the surface layer from where part of the heat transfers into the air. Depending on the weather conditions, an increase in temperature can be observed at an approximate distance of 3–5 kilometres from the cooling water discharge location. The cooling water also causes changes in the ice conditions, as the cooling water discharge area remains unfrozen throughout the winter. The size of the unfrozen and weak ice area varies depending on the winter weather, being at a maximum of around 7 km2. TVO issues warnings about the unfrozen area to the local residents in newspapers and on ice warning boards. The warm cooling water extends the growth period in the unfrozen sea area and increases its overall biological production. Other biological effects caused by the cooling water are minor.


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Cooling water (million m3)
20172016201520142013
OL1
1,1341,114
1,164
1,140
1,170
OL2
9761,147
1,075
1,172
1,118
Total
2,1092,261
2,238
2,312
2,288

Thermal load on the sea (GWh)
20172016201520142013
OL1
13,26313,098
13,721
13,481
13,872 
OL2
11,42313,474
12,677
13,871 
13,208
Total
24,68626,572
26,398   27,352 
27,080