Finland's OL2 nuclear reactor was shut down early on Friday and will remain off the electricity grid for an indefinite period due to problems caused by increased moisture in the facility's turbine, operator TVO said.
There was no impact on nuclear safety, TVO added.
The outage comes at a time of low wind power generation that has already lifted Finnish prices, according to Refinitiv analyst Petter Engblom Nordby.
Electricity prices for Friday soared up to 270 euros per megawatt hour (MWh) for hours where demand is typically highest, far exceeding prices in other parts of the Nordics and continental Europe, data from power exchange Nord Pool showed.
"We expect wind production to be 800-1,000 MWh lower per hour than normal in peak hours," Nordby said.
Wind production is also expected well below normal next week, with electricity prices forecast to stay high as well, he added. (Reporting by Nora Buli in Oslo and Louise Rasmussen in Copenhagen, editing by Terje Solsvik)