A man adjusts equipment to support the U1a Complex.

Stockpile Stewardship

A man adjusts equipment to support the U1a Complex.


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, the NNSA Stockpile Stewardship Program 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.

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 view of Cygnus X-ray Diagnostic Machines used at the U1a Complex.
Cygnus X-ray Diagnostic Machines.

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.

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 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.

Interested in Joining Our Team?

NNSS hires a wide variety of science, technical, and engineering professionals in support of Stockpile Stewardship and our vital mission.

A man makes adjustments to equipment at the NNSS' JASPER facility.