The U1a Complex is an underground laboratory used for subcritical experiments and physics experiments to obtain technical information about the U.S. nuclear weapons stockpile. These experiments support the NNSA’s Stockpile Stewardship Program, created to maintain the safety and reliability of the U.S. nuclear weapons stockpile.
The U1a borehole was originally excavated in the 1960s for an underground nuclear test that was later cancelled. In 1988, the U1a shaft was constructed and the “Ledoux” nuclear test was conducted in 1990 in a horizontal tunnel mined south from its base, 963 feet below ground surface. The current U1a Complex is mined at the base of two vertical shafts: the original U1a shaft and the U1h shaft, which was constructed in 2004. The vertical shafts are equipped with mechanical hoists for personnel and equipment access. A third vertical shaft, U1g, is located between the two main shafts and provides cross ventilation, instrumentation and utility access, and an emergency exit. The underground facility is on one level, at the depth of the Ledoux test, and consists of horizontal tunnels and alcoves, which are approximately 1.4 miles collectively in length. The facility provides a high degree of safety for NNSS workers and the public, exceptional security for the experiments, and minimizes environmental impacts.