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Agence France-Presse
Washington, December 07, 2012
The United States said on Thursday it has conducted a "subcritical" nuclear test at an underground site to study the behavior of nuclear materials without triggering an atomic explosion. The test, conducted on Wednesday in Nevada, aims to gather scientific data that will "provide crucial information to maintain the safety and effectiveness of the nation's nuclear weapons," the Energy Department said in a statement.

"Challenging subcritical experiments maintain our capabilities to ensure that we can support a safe, secure and effective stockpile without having to conduct underground testing," said National Nuclear Security Administration head Thomas D'Agostino.

Staff from the Nevada National Security Site, Los Alamos National Laboratory and Sandia National Laboratories conducted the experiment, known as Pollux.
   
It marked the 27th subcritical experiment to date. The last one, known as Barolo B, took place in February 2011.
   
Subcritical nuclear tests, which do not trigger a self-sustaining chain reaction that would create a nuclear explosion, examine how plutonium behaves when it is shocked by forces produced by chemical high explosives.
   
The United States halted underground nuclear tests in 1992. By then, it had conducted 1,032 tests since 1945, according to UN figures.