Italy's Enel and the Romanian subsidiary of ArcelorMittal "have decided to sell their stakes of respectively 9.15 and 6.2 percent in EnergoNuclear," the project company, said Nuclearelectrica, a Romanian state-owned enterprise holding the remaining 84.65 percent.
Enel said "a change in the shareholder structure, with a company other than Nuclearelectrica set to become the majority stakeholder, is incompatible with its investment strategy," Nuclearelectrica added.
ArcelorMittal said it was no longer interested in the project, which is estimated to cost more than $5.4 billion.
The announcement came a month after Romanian Energy Minister Constantin Nita said China General Nuclear Power Corporation (CGN) plans to invest in the construction of two new reactors at the Cernavoda plant, in southeastern Romania, alongside Canada's SNC-Lavalin.
"A consortium has already been set up by Lavalin and the Chinese company," Nita said during a visit by Chinese Premier Li Keqiang in Bucharest.
Romania and China signed two nuclear cooperation agreements during Li's visit but their content was not made public.
Romania has been looking for private investors to finance the extension of Cernavoda since four shareholders of the project company, including CEZ (Czech Republic), RWE (Germany) and GDF Suez (France), pulled out in 2011, complaining of a lack of predictability in Romanian policy.
Two reactors, using the CANDU technology, are currently operating at Cernavoda, providing about 17 percent of the country's electricity.