PARIS (Reuters) - France’s CEA nuclear agency has dropped plans to build a prototype sodium-cooled nuclear reactor, it said on Friday, after decades of research and hundreds of millions of euros in development costs.

Confirming a report in daily newspaper Le Monde, the state agency said it would finalize research in so-called “fourth generation” reactors in the ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration) project this year and is no longer planning to build a prototype in the short or medium term.

“In the current energy market situation, the perspective of industrial development of fourth-generation reactors is not planned before the second half of this century,” the CEA said.

In November last year the CEA had already said it was considering reducing ASTRID’s capacity to a 100-200 megawatt (MW) research model from the commercial-size 600 MW originally planned.

Le Monde quoted a CEA source as saying that the project is dead and that the agency is spending no more time or money on it.

Sodium-cooled fast-breeder reactors are one of several new designs that could succeed the pressurized water reactors (PWR) that drive most of the world's nuclear plants. [tinyurl.com/y84d2hvc]

In theory, breeders could turn nuclear waste into fuel and make France self-sufficient in energy for decades, but uranium prices have been on a downward slope for a decade, undermining the economic rationale for fast-breeder technology.

There are also serious safety concerns about using sodium instead of water as a reactor coolant.

Since sodium remains liquid at high temperatures - instead of turning into steam - sodium reactors do not need the heavy pressurized hulls of PWRs. But sodium burns on contact with air and explodes when plunged into water.

An earlier French model was scrapped in the 1980s after encountering major technical problems.

The ASTRID project was granted a 652 million euro ($723 million) budget in 2010. By the end of 2017 investment in the project had reached 738 million euros, according to public auditor data quoted by Le Monde.

The CEA said a revised program would be proposed by the end of the year for research into fourth-generation reactors beyond 2020, in line with the government’s long-term energy strategy.