Polls indicate that Bulgarians will on Sunday vote "yes" to a second nuclear power plant in a referendum, in a closely watched contest between the government and the opposition ahead of elections in July.

Even if stopping short of explicitly mentioning it, Bulgaria's first plebiscite since the fall of communism in 1989 concerns the revival of a long-delayed project at the northern site of Belene.

Price haggling and an inability to find a strategic investor prompted Prime Minister Boyko Borissov in March to scrap a deal with state-owned Russian firm Atomstroyexport to build the 2,000-megawatt plant.

Atomstroyexport filed a one-billion-euro ($1.3 billion) compensation claim at the Paris-based International Court of Arbitration. The opposition Socialists, who want to revive the project, then pressed for a referendum.

Low voter turnout is largely expected to invalidate the plebiscite but this has not stopped the contest becoming a hard-fought popularity test between the ruling GERB party and the Socialists before July.

Surveys on the eve of the ballot showed that 60-62 percent of an expected 1.6 to 2.1 million people who turn up to vote Sunday will back Belene compared with 38-40 percent against.

Analysts explained the low turnout by people's doubts that they can make an informed choice on such a complicated issue and the number of uncertainties still plaguing the project.

A key one among them is its cost -- 4.0 to 5.1 billion euros according to the Socialists, 6.3 billion euros according to Atomstroyexport and as much as 11.0 billion euros according to the government.

Questions about site safety, reactor technology, funding and potential electricity markets also remain unanswered, puzzling voters even further.

If 20 percent of all eligible voters participate in the referendum and over half of them say "yes", Bulgaria's parliament will have to review the issue within three months.

"A referendum can resolve political issues, not engineering or economic," Alpha Research analyst Boryana Dimitrova commented.

"You cannot ask people to give an expert opinion on a business project," political analyst Ivan Krastev said, slamming the referendum as "absurd."

The initial reasoning behind Belene was to compensate for lost capacity and keep Bulgaria's position as a top electricity exporter on the Balkans after shutting down part of its sole Soviet-built nuclear power plant at Kozloduy, further east on the Danube river.

But even after mothballing four out of Kozloduy's six reactors ahead of joining the European Union in 2007, Sofia did not experience shortages and kept providing record amounts of electricity to Greece, Macedonia and Serbia.

The government also envisages extending the operational life of Kozloduy's two 1,000-megawatt units beyond their 2017 and 2021 deadlines and is also considering a new reactor at Kozloduy.