Olkiluoto nuclear power plant in Eurajoki. Photograph: Greenpeace Finland

The emergency standby resulting from a disturbance at the Olkiluoto 2 (OL2) nuclear power plant unit has ended, and the repair work is being continued during the cold shutdown state.

The immediate repair work has progressed as planned. The plant unit is not producing electricity for the time being and information about the plant rejoining the grid will be given separately at a later time.

During a disturbance, the need for starting emergency preparedness actions at a nuclear power plant is assessed, and these were also initiated in this situation. Emergency preparedness actions started immediately when the plant failure occurred, and ended on Friday, December 11 2020 at 16:50 when the reason for the failure became clear and the plant unit’s risk level went back to normal.

The failure occurred when warmer water than usual entered the cleaning system of the reactor water as a result of a failure. 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 OL 2 plant unit is currently being prepared for a cold shutdown state, which means that the plant unit’s reactor will be driven down and cooled off. In this case, there is no pressure in the reactor and the temperature is below 100 degrees.

No harm has been caused to people or the environment.