14 @ The Containment of Underground Nuclear Explosions Photo crean Oawd waram '988 Sedan Crater atmospheric testing of nuclear weapons at the Johnston Atoll in the Pacific Ocean. LIMITS ON NUCLEAR TESTING The testing of nuclear weapons by the United States is currently restricted by three major treaties that were developed for both environmental and arms control reasons. The three treaties are: 1. the 1963 Limited Nuclear Test Ban Treaty, which bans nuclear explosions in the atmosphere, outer space, and underwater,andrestricts the release of radiation into the atmosphere, 2. the 1974 Threshold Test Ban Treaty, which restricts the testing of underground nuclear weapons by the United States and the Soviet Unionto yields no greater than 150 kilotons, and 3. the 1976 Peaceful Nuclear Explosions Treaty (PNET), which is a complement to the Threshold Test Ban Treaty (TTBT). It restricts individual peaceful nuclear explosions (PNEs) by the United States and the Soviet Union to yields no greater than 150 kilotons, and group explosions (consisting of a numberof individual explosions detonated simulatenously) to aggregate yields no greater than 1.500 kilotons. Although both the 1974 TTBT and the 1976 PNETremain unratified, both the United States and the Soviet Union have expressed their intent to abide by the yield limit. Because neither Country has indicated an intention notto ratify the treaties, both parties are obligated to refrain from anv acts that would defeat their objective and purpose * Consequently, all nuclear test explosions compliant with treaty obligations must be conducted underground, at specific test sites (unless a PNE), and with sields no greater than 150 kilotons. The test must also be contained to the extent that no radioactive debns ts detected outside the territorial limits of the country that conducted the test.'5 Provisions do exist, however,for one or twoslight, unintentional breaches per year of the 150 kiloton limit due to the technical uncertainties associated with predicting the exact yields of nuclear weaponstests.!° 14Art. 18, 1969 Vienna Convention on the Law of Treaties. 1SArt.I, 1(b), 1963 Limited Test Ban Treaty. 16Statement of understanding included with the transmittal documents accompanying the Threshold Test Ban Treaty and the Peacctul Nuciear Explosions Treaty when submited to the Senate for advice and consentto ratification on July 29, 1979.