The agreement does not require approval of the Congress and will enter into force after 90 days of "continuous session" of Congress, unless Congress passes a law that would explicitly rejecting the agreement (see CRS analysis of the requirements).
U.S.-Russian 123 agreement on nuclear cooperation resubmitted to Congress
On May 10, 2010, President Obama transmitted to the Congress the Agreement Between the Government of the United States of America and the Government of the Russian Federation for Cooperation in the Field of Peaceful Uses of Nuclear Energy. This agreement was signed on May 6, 2008 and submitted to the Congress by the Bush administration on May 13, 2008 (follwo the link for the text of the agreement and accompanying documents). The administration withdrew the agreement in September 2008.