Energy utility Teollisuuden Voima's Olkiluoto 3 nuclear reactor, which is still in the testing phase, has stopped producing electricity due to a newly discovered fault.
According to Nordpool, which administers the Nordic electricity market, the unit's power output fell to zero shortly before 9 pm Saturday.
According to plant owner TVO, the latest glitch is a turbine fault. Turbines are a key part of a nuclear plant's electricity production. Without them, the steam generated from the fuel rods cannot be converted into electricity.
The power plant had a similar steam turbine failure a month earlier, a day after restarting trial operations in late August. The turbines are separate from the core of the nuclear power plant itself, which is the pressure vessel.
On Saturday, before the new problem cropped up, the reactor's power output was raised to 90 percent. Before the power increase, the unit had been operating at 1200 megawatts (MW), as the power level is gradually increased towards the maximum power. The unit's maximum capacity is 1600 MW.
As of Sunday morning, the reactor was not producing any electricity. TVO said that the unit is to be gradually powered up on Sunday with the aim of generating just over 1200 MW of electricity by evening.
TVO said that the unit would begin feeding electricity into the national grid again around 6 pm, with the aim of reaching 1460 MW output, or just over 90 percent of capacity, early Monday morning.
According to the plan, full-power tests of the reactor should start in early October, with regular production due to begin in December. At that point, the OL3 reactor will be Finland’s biggest power generator, meeting roughly 14 percent of the country's electricity needs.
The unit, located about 50 km south of Pori, was originally to have begun producing electricity in 2009. Last year TVO predicted that it would start full commercial operations in February 2022.
13.58: Updated with restart information.