Do Subcritical Experiments Help?

In the absence of nuclear testing, subcritical tests are currently the only way to obtain some of the data needed to assess the health of the aging weapons in the U.S. nuclear stockpile—but how well do subcritical tests replace full-scale nuclear testing?

December 1, 2016

The Nevada National Security Site is the only place where subcritical experiments using plutonium and high explosives can be conducted. The U1a laboratory at the site, constructed nearly 1,000 feet underground, is where these experiments are typically conducted. Here, workers prepare to conduct a subcritical experiment in the U1a laboratory. (Photo: Los Alamos)

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Though valuable, subcrits don’t address all the issues required to maintain test readiness within a 24- to 36-month timeframe.

Although the United States halted full-scale nuclear weapons tests almost 25 years ago, the nation does conduct small-scale subcritical nuclear experiments using plutonium and high explosives.

These subcrits, as they’re called, are underground experiments at NNSS that are typically conducted inside steel confinement vessels. Subcrits are intended to help scientists study—without a full-scale nuclear weapon test—what, for example, are the negative effects aging plutonium pits have on the performance (the yield) of weapons in the U.S. nuclear stockpile.