Plant operator Teollisuuden Voima (TVO) on Thursday restricted electricity production at Olkiluoto 1 due to a turbine malfunction.
On Friday, TVO said damage to a pipe leading to the condenser was the cause of the fault.
The reactor had been ramping up output early Thursday morning following a scheduled annual maintenance outage. It was at this point that the fault was discovered in the turbine facility.
TVO said it expects electricity production to resume during the night. The operator previously said that the incident poses no risk to nuclear safety.
In total, Olkiluoto generates about 28 percent of the electricity used in Finland, so service outages can have significant impacts on the supply and price of electricity in the country.
In total, nuclear power accounted for 39 percent of Finland's electricity consumption last year, according to the Ministry of Economic Affairs.
