NNSSsmall.pngThe Nevada National Security Site helps ensure the security of the United States and its allies by supporting the stewardship of the nuclear deterrent, providing emergency response capability and training, and contributing to key nonproliferation and arms control initiatives. We execute unique national-level experiments, support national security customers through work for others, manage the legacy of the Cold War nuclear deterrent, and provide long-term environmental stewardship for site missions.

A Premier National Security Resource
A large, geographically diverse outdoor testing, training, and evaluation complex, the Nevada National Security Site (NNSS) is a preferred location for the National Nuclear Security Administration's defense programs, as well as many other research and development efforts.
The area of the NNSS (1,360 square miles) is larger than the state of Rhode Island.
Access to the site is controlled.
The site is surrounded by federally owned land.
Free from Encroachment
It is located 65 miles from the nearest major population center.
In the Beginning
After the first nuclear test at the Trinity Site in New Mexico, the United States moved its nuclear weapons experimentation program to the Pacific. Security and logistical issues quickly illustrated the need for a continental test site. After consideration of many possible sites, an Atomic Energy Commission meeting on December 12, 1950, concluded that the Las Vegas Bombing and Gunnery Range in Nevada satisfied nearly all of the established criteria for a continental proving ground. As a result, President Harry Truman authorized a 680-square mile section of the Nellis Air Force Gunnery and Bombing Range in Southern Nevada (65 miles northwest of Las Vegas) as the Nevada Proving Grounds on December 18, 1950. In 1955, the name was changed to the Nevada  Test Site (NTS).  
 Atmospheric and underground testing

On January 27, 1951, the first atmospheric nuclear test was detonated at the NTS, code-named Able. A total of 100 atmospheric tests were conducted at the NTS until July 1962. All atmospheric testing was banned on August 5, 1963, when the Limited Test Ban treaty was signed in Moscow; this gave birth to the age of underground testing. The United States conducted 828 underground tests at the NTS. The last underground test, Divider, was conducted on September 23, 1992.

The end of nuclear testing and the start of subcritical experiments
After conducting 928 nuclear tests, full-scale nuclear testing came to an end in 1992 when the U.S. entered into the Comprehensive Nuclear Test Ban with Russia and France. In order for the U.S. to maintain the safety and reliability of its nuclear stockpile without conducting full-scale tests, subcritical experiments were initiated at the NTS. An experiment is considered subcritical if no critical mass is formed and no self-sustaining nuclear reaction occurs. Subcritical experiments occur more than 900 feet below ground at the U1a tunnel complex. In 2010, the name of the Site was changed to the Nevada National Security Site (NNSS).
For more than 65 years, the NNSS has played a vital role in the security of our nation. Today, the Site provides a unique and indispensable extension of the national laboratories' experimental capabilities in support of the Stockpile Stewardship Program. The Site also has become the nation's leader in Homeland Security with respect to nuclear/radiological testing, training, and emergency response. In addition to ongoing environmental cleanup of historic nuclear research and testing areas on the NNSS, non-defense research, development and training activities are conducted in cooperation with universities, industries, and other federal agencies. 


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