The United States was to conduct a subcritical nuclear test Wednesday at an underground test site in Nevada, the Energy Department said Monday.
The test, the 17th of its kind and the fourth under the administration of President George W. Bush, is part of the so-called Oboe series of relatively small-scale subcritical nuclear experiments, the department said.
The department earlier said it had completed the Oboe series of experiments with last December's test. But a department official said it has become necessary to conduct at least one more test to collect new data.
The U.S. argues the tests, which do not involve nuclear explosions, yield essential scientific data and technical information needed to maintain the safety and reliability of the U.S. nuclear weapons stockpiles.
Antinuclear groups say the tests run counter the spirit of the Comprehensive Test Ban Treaty on nuclear weapons.
But the department says they do not violate the treaty because no critical mass is formed and therefore no self-sustaining nuclear chain reaction occurs.