UPDATE: Raised radiation levels at Finland's Olkiluoto Unit 2, reactor shut down: IAEA

London — Unit 2 of Finland's Olkiluoto nuclear power plant was shut Dec. 10 following an event at the site that is possibly related to a failure of the reactor's water-purification system, the Finnish Radiation & Nuclear Safety Authority said in statements.

STUK said that "there is no indication of fuel leakage and there are no more abnormal radiation levels at the unit."

Elevated radiation levels were measured inside the plant and the reactor was shut down, the International Atomic Energy Agency said in a statement early in the day. STUK informed the IAEA of the incident at 1156 GMT, the agency said.

Both STUK and TVO said in their statements that there were no radioactive releases to the atmosphere and plant workers had not been exposed to higher-than-normal radiation levels.

The Olkiluoto nuclear power station, located on Olkiluoto Island about 220 km northwest of Helsinki, is owned by TVO. Unit-2 has a capacity of 890 MW.

TVO said that shortly after 6 pm Finnish time the unit was in cold shutdown, the safest and most stable state of reactor operations. As a result, TVO said reactor pressure had been lowered and its temperature was below 100 degrees Celsius.

The scram, or automatic shutdown of the fission reaction, was triggered by elevated radiation levels in the unit's containment structure, which surrounds the reactor vessel, TVO said. The scram caused the containment to be sealed off.

STUK, in one of its statements, called the situation "an exceptional event." The unit began commercial operation in1980 and has never automatically scrammed before.

In an early-day statement, owner TVO said there had been "a disturbance at Olkiluoto 2 (OL2) nuclear power plant at 1222 [1022 GMT], where the main steam line's isolation has been triggered and the containment has been isolated. An automatic reactor scram has occurred at the plant."

During the reactor scram, the plant operated as planned, TVO said. "The situation is currently being investigated," it said.

In a follow-up statement Dec. 10, TVO said an ion-exchanging mass from the water purification system had "probably started to move into the [purification system] pipelines." Such ion-exchange materials are used to filter radionuclides from the cooling system.

Nord Pool's REMIT page showed a reactor trip in the morning had caused an unplanned outage at the unit.

At 1516 CET, the REMIT message was updated to say the outage was expected to last until Dec. 12.

STUK said in a tweet it would continue to monitor the situation.

(Updating with company, regulator statements)