"A comprehensive test ban treaty, or CTBT, is the oldest item on the nuclear arms control agenda. Three treaties currently limit testing to underground only, with a maximum force equal to 150,000 tons of TNT. According to the Natural Resources Defense Council, the United States conducted 1,030 nuclear tests, the Soviet Union 715, the United Kingdom 45, France 210, and China 45. The last U.S. test was held in 1992; Russia claims it has not conducted nuclear tests since 1991. Since 1997, the United States has held 22 'subcritical experiments' at the Nevada Test Site, most recently on February 23, 2006, to study how plutonium behaves under pressures generated by explosives. It asserts these experiments do not violate the CTBT because they cannot produce a self-sustaining chain reaction. Russia has reportedly held some since 1998, including several in 2000. The U.N. General Assembly adopted the CTBT in 1996. As of August 16, 2006, 176 states had signed it; 135, including Russia, had ratified; 41 of the 44 that must ratify the treaty for it to enter into force had signed; and 34 of the 44 had ratified. Four conferences have been held to facilitate entry into force, most recently in 2005. […] In current practice, Congress addresses nuclear weapon issues in the annual National Defense Authorization Act and the Energy and Water Development Appropriations Act. Congress considers the Stockpile Stewardship Program, which seeks to maintain nuclear weapons without testing."
CRS Report for Congress, RL33548