* Cost overruns stand at 3.6 bln eur -Les Echos
* Areva, Siemens urge cooperation from Finland partner
PARIS, Oct 12 (Reuters) - French nuclear plant builder Areva's total bill for its oft-delayed next-generation Finnish reactor is seen swelling to 6.6 billion euros ($9.1 billion) from an initial budget of 3 billion, according to a report in daily Les Echos citing lawmaker Marc Goua.
The construction of the 1,600 megawatt European Pressurized Reactor (EPR) is three years behind schedule, a delay Areva blames largely on Finnish power operator TVO's "inertia" in validating technical documents before passing them to the Finnish nuclear safety authority.
"Areva's management is talking about a total overrun of 3.6 billion euros. We are going from an initial budget of 3 billion to 6.6 billion," Marc Goua said in an extract of an article to be published in Les Echos' Thursday edition.
Areva was unavailable for comment.
Areva and industrial partner Siemens earlier on Wednesday appealed to Finnish utility firm Teollisuuden Voima (TVO) for "intense cooperation and mutual commitment" during the testing phase for an oft-delayed nuclear reactor now under construction.
Areva said in a statement that commissioning the reactor would require "significant efforts from all parties" after TVO earlier on Wednesday blamed Areva for further delays to the construction of the Olkiluoto 3 nuclear plant. ($1 = 0.725 Euros)