The No. 1 nuclear reactor at Olkiluoto on Finland's west coast remains offline due to an electrical problem. The fault was detected on Friday when technicians were re-starting the plant after annual maintenance work.
The TVO utility is trying to find out what caused the problem, and says that it is impossible to say when the reactor can be re-started.
Because of a malfunction of a generator automatic voltage regulator, several recirculation pumps stopped working.
The second reactor at Olkiluoto, known as OL2, has the same kind of pumps. Its output has been cut by 20 percent while the problem with its twin is being analysed.
OL2 was reconnected to the national grid three weeks ago after its annual maintenance outage.
Problems with 3rd Reactor, Too
TVO is building a third reactor at Olkiluoto, a project which is far behind schedule and over budget. The reactor plant is being delivered by a consortium led by the French company Areva.
France and Finland are two of the EU states most favourable to nuclear power. On a visit to Helsinki on Friday, French Prime Minister Francois Fillon called for the EU to use more nuclear power to help cut greenhouse emissions.
The Olkiluoto power station is in the coastal municipality of Eurajoki, between Pori and Rauma. Eurajoki will also be the site of a disposal site of spent nuclear fuel, to be located 400 to 700 metres inside the bedrock. The facility is to begin operations in 2020.
Finland's other atomic power plant is in Loviisa, east of Helsinki and Porvoo.