What is subcritical testing?
Subcritical nuclear tests are a component of the U.S. Department of Energy's Science Based Stockpile Stewardship Management Program (SSMP) and are intended to show whether nuclear weapons components such as Plutonium and Uranium will develop problems as they age. The blasts will not produce a nuclear chain-reaction explosion. They are called "subcritical" because they never reach "critical mass." Anti-nuclear peace activists claim that subcritical tests violate the spirit of the Comprehensive Test Ban Treaty (CTBT) and could introduce a new round of the nuclear arms race.
As of October 1999 only two countries have acknowledged that they engaged in subcritical nuclear testing. These are the United States and Russia. France appears to have promised the United States to abstain from engaging in subcritical testing. On June 4, 1996, after two years of negotiations, France and the United States secretly enter into a pact to share nuclear weapons data from computer simulated nuclear explosions.