Electricite de France SA said Wednesday it’s proposing to acquire 50% of U.S. wholesale power generator Constellation Energy (CEG) for $4.5 billion, challenging plans by a subsidiary of Warren Buffett’s Berkshire Hathaway (BRK.A) to take over the company.

After rejecting a full takeover bid for Constellation Energy in October, the France-based energy giant offered to gain a 50% ownership interest in Constellation’s nuclear operations through a joint venture.

EdF shares dropped after the proposal was made; they were down 6.2% at 10:00 am in Paris trading, but recovered to end the day down just 0.5% at EUR44.35.

According to EdF, which already owns 9.5% of Constellation, the offer totals about $52 per share, which represents a 96% premium to the existing $26.50-a-share takeover offer by Buffet’s MidAmerican Energy Holdings Co.

Constellation and MidAmerican declined to comment. EdF representatives were not available to comment.

EdF’s offer provides for an “upfront” cash investment of $1 billion and an option for Constellation to sell up to $2 billion in non-nuclear generation assets.

EdF expects that it could be approved for the acquisition within six to nine months.

Constellation, North America’s largest nuclear energy company, operates three nuclear power stations with five reactors based in Maryland and New York. A full 61% of energy generated by Constellation is nuclear. Coal, oil, and gas account for 35% of Constellation’s assets and renewable energies such as solar, geothermal, and hydro power make up four percent.

Maryland-based Constellation said Tuesday it would have probably filed for bankruptcy protection without an immediate $1 billion infusion from MidAmerican, which could give MidAmerican some leverage in any takeover battle.

In a U.S. regulatory filing, Constellation warned that unstable market conditions make the deal with MidAmerican necessary. MidAmerican announced its offer to buy Constellation for $26.50 per share in September, along with the $1 billion cash injection.

EdF proposed $35 per share in October, calling MidAmerican’s offer for Constellation insufficient.