The governments said the first stage of work defined by a 2010 agreement on nuclear reactor conversion from highly enriched to lightly enriched uranium is complete.
"The conversion of Russian research reactors from highly enriched uranium to lightly enriched uranium directly supports the president's goal to reduce the dangers of nuclear material terrorism and weapons proliferation," Deputy U.S. Secretary of Energy Daniel Poneman said.
At least one reactor in Russia should be converted by 2014. The U.S. Department of Energy said nine of the 27 research reactors that used HEU in Russia were shut down already.
In terms of U.S. reactors, 20 of the 27 reactors were either converted for LEU or shut down.
"The U.S. will continue to make efforts to convert the remaining research reactors as promptly as possible," the Energy Department stated.
The 2010 agreement is between the Department of Energy and the Russian State Corporation for Atomic Energy.