A civilian nuclear cooperation deal between Russia and the United States came into force on Tuesday, dpa reported.
The accord, which was signed in 2008 when US president George W Bush was in office, was put on ice for three years by the US after Russia's invasion of Georgia that year.
"The agreement is very important for Moscow because the United States is a key part of the global market for nuclear technology," said Sergei Kiriyenko, head of Russia's state-run nuclear holding company Rosatom.
Among other aspects, the deal allows Russia to reprocess US spent nuclear fuel rods.
It came into force after an exchange of diplomatic notes in Moscow between US Ambassador John Beyrle and and Russian Deputy Foreign Minister Sergei Ryabkov.