HELSINKI (Reuters) - Finland's Teollisuuden Voima (TVO) said on Thursday it had received a favourable partial decision from the International Chamber of Commerce (ICC) in its long-running dispute with French nuclear power engineering company Areva (>> Areva).

The two companies are claiming billions of euros from each other at the ICC's arbitration court due to delays and cost overruns on the Olkiluoto 3 reactor project.

Originally expected to start operations in 2009, the Olkiluoto 3 plant is now expected to open in 2018.

TVO said the partial award did not take a position on monetary claims but said it resolved many issues in its favour.

"Partial award has finally resolved the great majority of these facts and matters in favour of TVO, and conversely has rejected the great majority of the supplier's contentions," it said in a statement.

But Areva said the ICC decision was just one of several partial decisions the court makes before giving its final ruling.

"We're at the very beginning of the process. The court has not established responsibilities, nor the compensation yet. The hearings are ongoing and Areva is waiting for a final decision around the end of 2017 or early 2018,” a company spokesman said.

TVO has claimed 2.6 billion euros (£2.29 billion) from Areva in the arbitration court, while Areva has made a counter claim for 3.5 billion euros.

The cost of Olkiluoto 3 was initially estimated at 3.2 billion euros (£2.81 billion), but Areva has since estimated the overall cost at closer to 8.5 billion euros.

The European Pressurised Reactor is set to become Finland's fifth and largest, and to provide about 10 percent of the country's power.

In September TVO began a new legal action against Areva to seek assurances that the French company's restructuring would not cause further delays.

In the restructuring of the French nuclear power industry, Areva is due to sell its nuclear reactor engineering unit to state-controlled utility EDF (>> E.D.F.), but the Olkiluoto 3 is planned to be handed to another legal entity.

That has made TVO concerned that the French would prioritise other nuclear projects, such as Flamaville in France and Hinkley Point in Britain.

(Reporting by Tuomas Forsell, additional reporting by Benjamin Mallet; Editing by Jason Neely, Greg Mahlich)