The long-simmering tensions between Areva and Bouygues erupted in a row over new problems with the French nuclear group’s reactor project in Finland, the flagship for French president Nicolas Sarkozy’s campaign to make his country the world’s leading nuclear technology provider.

The Finnish nuclear safety authority, STUK, has this week launched an inquiry into welding work on non-load bearing parts of the reactor – which is already running two years late and at least €1bn ($1.5bn) over budget – after a Greenpeace report raised questions over quality control.