The cause of the automatic emergency shutdown of the Olkiluoto 2 (OL2) reactor in southwest Finland on Thursday has become clear.
The owner of the plant, nuclear power utility TVO, said in a Friday morning press release that the failure occurred when warmer-than-usual water entered the cleaning system of the reactor.
"This released filter material into the reactor pressure vessel, in which it was activated. The radiation level in the steam line increased, which caused a momentary peak in the steam line's radiation measurement. This launched safety systems as planned, and led to a reactor trip," the statement said.
The company added that the emergency standby resulting from the disturbance has now ended and repair work will continue during the cold shutdown state. The plant unit is not currently producing electricity and information about the plant’s reconnection to the grid will be given separately at a later date.
TVO's Senior Vice President Sami Jakonen said he believes that the reactor could generate electricity as early as Sunday.
The Olkiluoto plant, located between Rauma and Pori on Finland's west coast, has two reactors and a long-delayed third one still under construction.