Management confirmed to the Financial Times "that the final price would be closer to 4.5 billion euros instead of the initial three billion euro estimate".
Disputes between Areva and the Finnish utility TVO, which ordered the reactor, are now to be settled through arbitration. Areva made the announcement on Friday when it issued second quarter results in Paris.
TVO Vice President Jouni Silvennoinen, who takes over as OL3 Project Director on Monday, told YLE the arbitration proceedings are related to "technical and insignificant" cost overruns.
The Olkiluoto project, which is two years behind schedule, last week faced a special inspection after reports of shoddy workmanship as well as a strike threat due to irregularities concerning pay and benefits for Polish labourers at the site.
Inspection Finds Faults - But No Cause for Concern
The Radiation Safety Centre's (STUK) inspection of the site found that the site's welding work was up to par.
Inspectors did criticise the builders for failing to adhere to the highest standards on less-crucial welding work. STUK, however, says the uncovered welding faults do not weaken the soundness of standing structures.
A recent YLE television programme claimed that employees have done welding without proper instruction and been gagged from speaking with anyone about the issue.
Dissatisfied with the scope of STUK's findings, Greenpeace Finland is demanding further inspection by an independent, international body.