Russia and the US have signed a key agreement on civilian nuclear power that will give Washington access to Moscow's nuclear technology and potentially hand Russia lucrative deals on storing spent nuclear fuel. The deal was signed by US Ambassador William Burns and Russia's top nuclear official, Sergei Kiriyenko, on Tuesday, the day before Dmitry Medvedev succeeds Vladimir Putin as president. Cooperation on nuclear issues between Russia and the US had cooled in recent years because of disagreements over how to handle Iran's perceived nuclear threat. The new agreement will formally allow nuclear deals between US and Russian companies. The US has similar agreements with other major economic powers, including China.