Bulgaria said Wednesday it had agreed to pay Russia over 600 million euros ($655 million) in compensation after cancelling plans to build a nuclear plant on the Danube.

Bulgaria's national electricity company, NEK, will make "full payment" to the Russian nuclear giant Atomstroyexport by December 25, the energy ministry said in a statement.

The Geneva-based International Court of Arbitration ruled in June that NEK should pay Atomstroyexport 601 million euros plus interest for equipment ordered for a planned 2,000-megawatt twin-reactor plant at Belene on the Danube.

Bulgaria and Russia also agreed on Wednesday that Atomstroyexport will waive part of the interest of 130,000 euros per day if NEK repays it ahead of the December 25 deadline, the ministry added.

The Belene scheme was scrapped in 2012, with Bulgaria blaming ever-rising costs.

However, the government is mulling whether to revive it using a private investor, and is in early talks with Atomstroyexport about a possible procurement deal that would reduce the compensation payout.

After joining the EU in 2007, the country -- a former top electricity exporter on the Balkans -- was left with only two operational 1,000-megawatt nuclear reactors at its sole nuclear power plant in Kozloduy, also on the Danube.

On Tuesday, the energy ministry announced that a consortium of the Russian Rosenergoatom and French EDF will study options for extending the operational life of one of the Kozloduy reactors by as much as 30 years -- until 2047. The plant's other reactor has a lifetime that is scheduled to expire in 2021.