Russia and the United States signed on Tuesday a long awaited civilian nuclear cooperation pact that will allow firms from the world’s two biggest atomic powers to expand bilateral nuclear trade.The deal will open up the booming U.S. nuclear market and Russia’s vast uranium fields to firms from both countries.Without a deal, cooperation potentially worth billions of dollars was severely limited and required official consent.Russia’s state nuclear corporation Rosatom said in a statement the deal signed by its head Sergei Kiriyenko and US ambassador to Russia William Burns, would create the legal basis for such cooperation.“The signing of the document . will provide for the normal development of atomic energy and the nuclear fuel cycle while reducing the risk of the proliferation of atomic weapons,” the Rosatom statement said.At the 2006 Group of Eight summit in St Petersburg, US President George W Bush and Russian President Vladimir Putin blessed the deal but it has faced opposition from some US congressmen because of Russia’s cooperation with Iran.On Wednesday, Putin will formally hand over powers to his successor, ally Dmitry Medvedev, who was elected in March.