A nuclear cooperation agreement which will see Australia sell uranium to Russia has been ratified by the countries' two leaders at the G20 summit in South Korea.

At a meeting before the opening of the G20 summit, Prime Minister Julia Gillard and Russian president Dmitry Medvedev exchanged notes ratifying the nuclear cooperation agreement.

The agreement, which allows Australian uranium to be enriched in Russia and used in the country's nuclear reactors, was signed in Sydney three years ago.

But it was opposed by a parliamentary committee which had called for the deal to be blocked unless Russia met a series of conditions, including separating its civilian and military nuclear plants.

Greens Leader Bob Brown has condemned the deal.

"This is greed over common sense," he said.

"We are all aware that if you provide uranium for Russia to put into peaceful purposes, it releases other uranium for them to put into building nuclear warheads."