Nevada National Security Site (NNSS)
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Subcritical experiments at the U1a Complex 
Subcritical experiments at the U1a Complex 
 
Cygnus Dual Beam Radiographic Facility 
Cygnus Dual Beam Radiographic machine 

Stockpile Stewardship Program


A primary mission of the NNSS is to help ensure the Nation’s nuclear weapons stockpile remains safe, reliable, and secure from our enemies. To accomplish this, Stockpile Stewardship deploys a wide range of science and technologies, focused on experiments in weapons science and the potential for weapons dismantlement.


Since the United States no longer conducts full-scale nuclear tests – the U.S. voluntarily ended underground nuclear testing in 1992 – Stockpile scientists and engineers now obtain data from breakthrough scientific experiments, engineering audits and analysis, high-tech computer simulations, and world-class diagnostic measurement systems. To keep existing warheads reliable, secure, and safe, every aspect of a weapon’s performance is meticulously studied so the national laboratories can predict not only what will happen during an explosion (i.e., measurements within billionths of a second), but also measure what will happen to a device as it changes and ages over time, as the nuclear arsenal is now more than 50 years old.


The NNSS has a number of unique facilities and capabilities directly contributing to the continued certification of the nuclear deterrent.


The Birth of the Stockpile Stewardship Program
The Stockpile Stewardship Program was established in response to the 1994 National Defense Authorization Act (Public Law 103-160) which requires, in the absence of nuclear testing, a program to:

  • support a focused, multifaceted program to increase the understanding of the enduring stockpile;
  • predict, detect, and evaluate potential problems of the aging stockpile;
  • refurbish and re-manufacture weapons and components, as required; and
  • maintain the science and engineering institutions needed to support the nation's nuclear deterrent, now and in the future.

As the civilian steward of the nation's nuclear weapons complex, the NNSA is responsible for the safety and reliability of the nation's nuclear arsenal. The DoD partners with the DOE in setting requirements and establishing production goals. A key challenge to the Stockpile Stewardship Program is to balance military weapon performance goals against civilian and military surety and safety concerns.

Assessment and Certification
In the absence of nuclear testing, different experiments and tools are relied on to obtain data relevant to nuclear warhead performance as components within a warhead potentially change properties with age. The Stockpile Stewardship Program utilizes several approaches to assess and certify the nuclear weapons stockpile. Test data from new experiments and improved computer modeling help address the reliability of the nuclear weapons stockpile by allowing scientists to improve understanding of the dynamic properties of aging nuclear materials.


A suite of enhanced capabilities and facilities across the Nuclear Security Enterprise (NSE), which includes weapons laboratories, production plants, and the NNSS, have been developed to fill in the knowledge gaps and to provide data relevant to identified stockpile concerns. Capabilities specific to the NNSS include the following:

  • Subcritical Experiments obtain technical information about the U.S. nuclear weapons stockpile in the absence of nuclear testing. In subcritical experiments, chemical high explosives generate high pressures that are applied to nuclear weapon materials, such as plutonium. The configuration and quantities of explosives and nuclear materials are such that no nuclear explosion will occur. Thus, the experiments are consistent with the existing U.S. nuclear testing moratorium. They are called "subcritical" because there will be no critical mass formed (i.e., no self-sustaining nuclear fission chain reaction will occur). Scientific data is obtained on the behavior of nuclear weapon materials by the use of a wide variety of sophisticated, high-speed diagnostic instruments.

  • The Joint Actinide Shock Physics Experimental Research (JASPER) two-stage gas gun experiments generate high shock pressures, temperatures, and strain rates to simulate those of a nuclear weapon. The gas gun forces a high-velocity projectile to a target containing special nuclear material. When the projectile hits the target it produces a high-pressure shock wave. Diagnostic equipment, triggered by the initial wave, measures the properties of the shocked material inside the target.

  • The Big Explosives Experimental Facility (BEEF) is a hydrodynamic testing facility at the NNSS. BEEF provides data, through conventional high-explosive experiments, to support the Stockpile Stewardship Program, along with a variety of new experimental programs to expand the Nation's non-nuclear experiment capabilities.