One of NNSA’s core missions is to ensure the United States maintains a safe, secure, and reliable nuclear stockpile through the application of unparalleled science, technology, engineering, and manufacturing. The Office of Defense Programs carries out NNSA’s mission to maintain and modernize the nuclear stockpile through the Stockpile Stewardship and Management Program. Details about nuclear weapons, deterrence, and NNSA’s management of the stockpile can be found in the Nuclear Matters Handbook and the current Stockpile Stewardship and Management Plan.
Most nuclear weapons in the U.S. stockpile were produced during the 1950s and 1960s. At the time of their original production, nuclear weapons were not designed or intended to last indefinitely.
Because the United States also voluntarily ended underground nuclear explosive testing, NNSA uses a science-based assessment of the reliability of nuclear weapons to assess and certify the stockpile without nuclear explosive testing, called the Stockpile Stewardship Program.
NNSA’s nuclear security enterprise is composed of a nationwide network of government-owned, contractor-operated national security laboratories and nuclear weapons production facilities. These facilities provide the necessary research, development, testing, and production capabilities needed to carry out stockpile stewardship.
Part of keeping the U.S. nuclear weapons stockpile safe and effective includes working with the Department of Defense, through the Nuclear Weapons Council, to maintain the quantity and quality of weapons necessary for U.S. national security needs.
The New Strategic Arms Reduction Treaty (START) caps the strategic deployed nuclear arsenals of each country at 1,550 warheads. Today’s stockpile is the smallest it has been since 1960, and it is certified by the Nuclear Weapons Council as effective in meeting the national security needs of the United States.
NNSA continually assesses and evaluates each nuclear weapon to determine its reliability and to detect and anticipate any potential issues that may result from aging, from concept to production to retirement. These activities allow NNSA to meet today’s military and national security requirements. Each different weapon type in the U.S. nuclear stockpile requires routine maintenance, periodic repair, replacement of limited life components, and surveillance (a thorough examination of a weapon) in order to ensure continued safety, security, and effectiveness and other support activities as necessary.
Joint Test Assembly Flight tests performed jointly by the applicable Department of Defense military service and NNSA are one of the most important data sources used to support assessment of the nuclear weapon stockpile.
Stockpile Stewardship and Management includes the role to safely dismantle and dispose of components from warheads that have been retired. Some limited number of components from the dismantled warheads are preserved for potential reuse in Life Extension Programs, but most are disposed of in compliance with current directives.
Over the next 20 years, the U.S. nuclear stockpile will be sustained and modernized through vigorous surveillance, assessment, life extension, and dismantlement efforts. The stockpile will continue to be assessed to ensure it remains safe, secure, and effective.
Life Extension Programs & Alterations
The Stockpile Stewardship Program enables NNSA to extend the lifespan and ensure the continued safety, reliability, and effectiveness of weapons that have reached the end of their original design life through life extension programs. These life extensions address aging and performance issues, enhance safety features, and improve security.
As with any complex mechanical system, components in nuclear weapons degrade over time, even when kept in storage. A life extension program comprehensively analyzes all of a weapon’s components and determines whether to reuse, refurbish or replace them to extend the service life of the weapon.
When planning life extension programs, NNSA must develop specific solutions to extend the lifetime of each weapon type because each is unique. Life extension programs also require NNSA to certify the weapon’s protected period, its new lifetime, for 20 to 30 years. By extending the time that a weapon can safely and reliably remain in the stockpile, NNSA is able to maintain a credible nuclear deterrent without producing new weapons or conducting underground nuclear explosive tests.
NNSA also conducts alterations of weapons at the system, sub-system, or component level to make sure the weapons is safe, secure, and effective. An alteration is a limited scope change that affects assembly, tests, maintenance, and/or storage of weapons. An alteration may address identified defects and component obsolescence, however it does not change a weapon’s operational capabilities.
Each facility in NNSA's nuclear security enterprise contributes to these programs. See Our Locations for information about what kind of work is conducted at each of the nuclear security enterprise facilities.
There are several major programs underway today. Click the links for facts about each program, and read the current Stockpile Stewardship and Management Plan for more information.
Research, Development, Test, and Evaluation
NNSA scientists are able to accurately model nuclear weapons performance and physics without nuclear explosive testing. To accomplish this, NNSA conducts new scientific research and combines it with existing data from past nuclear tests, the nation’s long history in nuclear science, and computer simulations. NNSA’s nuclear weapons research and development supports stockpile stewardship through advanced development of science-based capabilities to assess a broad range of weapons-related concerns.
To make sure all the components of a nuclear weapon will perform as needed, NNSA scientists study materials to describe and predict the behaviors of weapons materials in the extreme conditions of nuclear weapon operation, including high-pressure, high-temperature, and high-strain.
NNSA must assess the effects of aging and manufacturing processes on the nuclear stockpile, without nuclear explosive testing. In hydrodynamic testing, non-fissile isotopes (which can’t sustain a neutron chain reaction), such as uranium-238 and plutonium-242, are subjected to enough pressure and shock that they start to behave like liquids – becoming hydrodynamic. While these experiments don’t create nuclear yield, they provide data that, combined with theory, modeling, simulation tools, and other focused experiments, underwrite the confidence in the Nation’s nuclear deterrent.
Hydrodynamic testing gives scientists vital data about what happens during a nuclear detonation. To capture what happens during these experiments, NNSA has made many advancements in radiographic sources and other advanced diagnostic techniques. These facilities can produce high-speed radiographic images that contribute to understanding and simulation of weapon physics:
High energy density science—the study of properties and behavior of matter and radiation at conditions of extreme temperature, pressure, or density—must be understood in order to probe fundamental weapons physics issues and validate the codes and models used to certify the stockpile. Scientific understanding and experimental capabilities in high energy density physics contribute to national capabilities in this area, including:
NNSA delivers leading-edge computer platforms, sophisticated physics and engineering codes, and uniquely qualified staff to support addressing a wide variety of stockpile issues for design, physics certification, engineering qualification, and production. Advanced technology systems are delivered to weapon physicists and engineers as tri-laboratory resources, to take on the most challenging simulation problems of the day:
Read more about high-performance computing at this link.
In a joint collaboration, NNSA is working to accelerate delivery of a capable exascale computing ecosystem for breakthroughs in scientific discovery, energy assurance, economic competitiveness, and national security through the Exascale Computing Project: