The claim was filed over payments, which Atomstroyexport owes to Bulgarian state-owned power utility NEK, the Bulgarian company said in a statement, without elaborating.
In July NEK said it would be taking Russia to court following an announcement made by Atomstroyexport, part of Russia's nuclear monopoly Rosatom, that it had filed a 58 million euro claim with the International Court of Arbitration against
NEK over the project's delays.
The Belene nuclear plant project, launched in the late 1980s, had been frozen for nearly two decades before Bulgaria hired Atomstroyexport in 2008 to build the 2,000-megawatt facility.
Last week, NEK and Atomstroyexport signed an annex to the agreement Sofia and Moscow concluded back in 2006 which extends the timeframe of the initial deal until March 31, 2012.
($ = 0.7493 euro)