The EPR reactor, built by the French-led Areva-Siemens consortium on Finland's southwest coast, was started up in December for testing twelve years after its initial scheduled completion date of 2009.

The plant was supposed to be connected to Finland's national grid late last month, with regular energy production expected in June 2022.

But its operator said the start of electricity production had been postponed "due to modification needs observed during the test production phase".

"There is a need for modifications in the plant unit's automation related to control functions, as well as further testing related to the modifications," it said in a statement.

Under the revised schedule, "the OL3 EPR plant unit's electricity production starts at the end of February, and regular electricity production starts in July 2022".

At 1,650 megawatts, the plant is to become Europe's most powerful reactor, supplying 15 percent of the Nordic country's energy.

The French-developed EPR reactor model was designed to relaunch nuclear power after the Chernobyl catastrophe of 1986, and was touted as offering higher power and better safety.

But EPR builds in Finland, France and the UK have been plagued by delays and cost overruns.

cbw/ah/har

AREVA