A public debate on whether to build a mammoth underground nuclear waste facility in northeastern France began this week amid praise and skepticism.

France's National Commission for Public Debate launched the proceedings Wednesday as French Minister of Ecology, Sustainable Development and Energy Delphine Batho visited the proposed site at the Meuse/Haute Marne Underground Research Laboratory in Bure, France.

Opponents contend the debate is rigged in favor of the building the $20 billion-$45 billion facility and, in any event, is premature because the country is debating whether France should transition from its dependence on nuclear power.

French President Francoise Hollande has pledged to reduce nuclear power's 75 percent share of the energy mix to 50 percent by 2025.

But Batho said the safe disposal of the country's nuclear waste is necessary no matter how that issue is decided.

"We must ensure its safe storage conditions, regardless of the evolution of our energy mix and the nuclear share that is now the subject of the national debate on energy transition," she told the daily L'est Republicain.

The deep burial of nuclear waste was decided by a 2006 law after an earlier debate and during the past eight years research has been conducted at the underground lab to determine if it could be expanded to serve as a repository.

The debate launched Wednesday is a legally binding procedure expected to last four months, after which the agency charged with waste disposal is to begin the long process of securing planning permissions to construct the repository, known by the French acronym Cigeo.

The government hopes to break ground on the effort by 2019, with a commissioning in 2025.

The facility would be built in a 160 million-year-old layer of clay about 1,650 feet beneath the surface and designed to accept long-lived, high- and intermediate-level nuclear waste, whose lethality to human health extends over tens of thousands of years.

Batho said the facility would be constructed with "reversibility" for its first 100 years, meaning future generations would be able to remove the waste if a more satisfactory way to store highly radioactive materials is found.

The Cigeo effort is opposed by the French Green Party -- part of Hollande's governing center-left coalition -- and other nuclear power opponents, led by the Collective Against the Burial of Nuclear Waste, CEDRA.

CEDRA leader Michel Gueritte participated in a Wednesday session of a high-level policy committee including Batho, French nuclear power company EDF, local officials and other stakeholders in the process, and afterwards said he remained unconvinced Cigeo is a good idea.

"We are told that it is better to trust in geology than in man," he told the daily L'est-Eclair. "In fact, there are only geologists, and some of them are opposed to the landfill."

He dismissed the national debate on Cigeo as nothing more than public relations exercise to lend legitimacy to a decision that's already been made, the newspaper reported.

Batho, however, defended the process and said it should be held this year despite the concurrent debate on transitioning away from nuclear energy.

"The National Commission for Public Debate is independent," she said. "This is a guarantee that everyone can give their opinion and to express his point of view."