The power of Loviisa power plant's unit 1 will be temporarily reduced during 11 - 18 July, if necessary, so that the cooling system's discharge water temperature does not exceed the limits of the power plant’s local environmental water permit. According to the current estimate, the maximum power reduction is about 50 MW.
In Finland, every power plant, regardless of the form of production, has an environmental permit. The environmental permit also includes a local water permit, which specifies, among other things, the temperature limit for the discharged cooling water. The temperature of the seawater is important because the most significant environmental impact of a nuclear power plant is the heat load caused to the sea by the cooling water, as the cooling water heats up by about 10 degrees as it passes through the plant.
Seawater temperature is important for both environmental and nuclear safety. At the Loviisa power plant, we constantly monitor the temperature of both intaken and discharged seawater.
From the point of view of environmental safety (impact on marine vegetation and organisms), the temperature of the discharge water is important. If the temperature of the discharge water rises to 32 degrees, intensified monitoring and reporting to environmental authorities is initiated. The maximum temperature of the power plant's water permit for the discharge water is 34 degrees. Reducing the plant's power production ensures that the power plant remains within the limits set by the water permit.
From the point of view of nuclear safety, the temperature of the intaken seawater is important. If the temperature of the intaken seawater exceeds 20 degrees, intensified monitoring and testing of safety systems will begin. The test reveals the maximum permissible temperature of the seawater to be taken in. If it threatens to rise above the above-mentioned maximum permissible temperature, the plant will be run down proactively in order to maintain the plant's safety margins in accordance with the authority's requirements.
The temperature of the seawater coming to the Loviisa power plant is usually well below 20 degrees in summer because the cooling water is taken from a depth of about 6-8 meters. Due to long periods of warm weather, wind and sea currents, the temperature can rise above 20 degrees. The summer of 2021 has been exceptionally warm in Finland and the seawater temperature has been higher than typical. A similar situation was last experienced at the Loviisa power plant in July 2018 and before that in the summer of 2010.
In Finland, nuclear power plants are located on the coast and, due to the large body of water in the sea, changes in water temperature or the effects on production are usually not significant. Seawater temperature affects the efficiency and maximum capacity of electricity generation. Based on the Loviisa power plant’s production history, we can state that the variation of production in the summer and winter seasons is up to tens of megawatts due to the effect of seawater temperature.
Power reduction at the power plant is a controlled event and it does not endanger people, environment or the power plant.
Thomas Buddas, Deputy director, Loviisa power plant, +358 10 455 3710