Los Alamos National Laboratory

Los Alamos National Laboratory

Delivering science and technology to protect our nation and promote world stability

The weapons will work

The Laboratory ensures U.S. nuclear weapons are safe, secure, and effective by continually assessing and updating them.
April 20, 2020
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Delivery systems.CREDIT: U.S. Air Force, U.S. Navy

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The Lab has replaced nuclear testing with a science-based approach—a combination of research, nonnuclear tests, computer simulation, and comparison with data from historical nuclear tests. This approach is called the Stockpile Stewardship Program.

By Whitney Spivey

Most nuclear weapons in the current U.S. stockpile were designed by Los Alamos and not intended to last indefinitely. These weapons are now more than 30 years old.

Before 1992, when the United States voluntarily ended nuclear testing, these aging nuclear weapons could be tested at the Nevada Test Site (today, the Nevada National Security Site). Now, the Lab has replaced nuclear testing with a science-based approach—a combination of research, nonnuclear tests, computer simulation, and comparison with data from historical nuclear tests. This approach is called the Stockpile Stewardship Program.

Through the Stockpile Stewardship Program, the Lab works in conjunction with other labs and plants in the NNSA complex to assess and ensure the safety, security, and effectiveness of each type of nuclear weapon in the stockpile. Each requires surveillance (a thorough examination of the weapon), routine maintenance, periodic repair, and replacement of limited-life components.

For weapons at the end of their original design life, Los Alamos may increase the weapon’s lifespan through a life extension program (LEP), which addresses aging and performance issues, enhances safety features, and improves security. Through an LEP, scientists and engineers comprehensively analyze all of a weapon’s components and, based on that analysis, reuse, refurbish, or replace certain components. An LEP helps the United States maintain a credible nuclear deterrent without producing new weapons or conducting underground nuclear tests.

Los Alamos may also conduct alterations (alts), which are changes to a weapon’s systems, sub-systems, or components. Not as extensive as an LEP, an alteration is a limited-scope change that affects the assembly, maintenance, and/or storage of a weapon.  The alteration may address identified defects and component obsolescence without changing a weapon’s operational capabilities.

Weapons may also undergo modifications (mods), which change a weapon’s operational capabilities. A modification may enhance the margin against failure, increase safety, improve security, replace limited-life components, or address identified defects and component obsolescence.

Here's a quick overview of the LEPs, alts, and mods that are complete or are currently underway at Los Alamos.

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Weapons updates. Photo: NNSA

B61-12 LEP

The B61 nuclear gravity bomb, deployed to U.S. Air Force and North Atlantic Treaty Organization (NATO) bases, has almost 50 years of service, making it the oldest and most versatile weapon in the enduring U.S. stockpile. Numerous modifications have been made to the B61 since it first entered service in 1968, and four B61 variants remain in the stockpile: the B61-3, -4, -7, and -11. However, the aging weapon system requires a life extension to continue deterring potential adversaries and reassuring our allies and partners of our security commitments to them.

The B61-12 LEP will refurbish, reuse, or replace all of the bomb’s nuclear and nonnuclear components, extending the bomb’s service life by at least 20 years. The LEP will address all of the bomb’s age-related issues and enhance its reliability, ease of field maintenance, safety, and use control. With these upgrades and the addition of a U.S. Air Force–supplied Boeing tail kit assembly, the B61‐12 LEP will consolidate and replace four B61 weapon designs (the B61-3, -4, -7, and -10). When fielded, the B61-12 will balance greater accuracy, provided by the modern tail kit, with a substantial reduction in yield, but there will be no overall change in military requirements or characteristics. The B61-12 LEP is critical to sustaining the nation’s strategic and nonstrategic air-delivered nuclear deterrent capability.

Los Alamos and Sandia National Laboratories are the design and engineering labs, respectively, for the B61-12 LEP, with Los Alamos also being responsible for producing detonators and other classified components. The B61-12 will be produced in fiscal year 2022. The bomb will be about 12 feet long and weigh about 825 pounds. If it is ever used, it will be ballistically air delivered in either gravity or guided drop modes. It is being certified for delivery by current strategic and dual-capable aircraft, as well as future aircraft platforms.

W88 alt 370

The W88 nuclear warhead entered the stockpile in late 1988 and is deployed on the Navy’s Trident II D5, a submarine-launched ballistic missile carried onboard Ohio-class submarines. Deployed now for almost 30 years, the warhead requires several updates to address aging issues and to maintain its current state of readiness.

The W88 Alt 370 program replaces the arming, fuzing, and firing subsystem, adds a lightning arrestor connector, and refreshes the weapon’s conventional high explosives to enhance nuclear safety and support future LEP options. The W88 Alt 370 program is scheduled to be completed concurrent with planned exchanges of limited-life, or routinely replaced, components, including the gas-transfer system and neutron generators. These will not change the warhead’s military requirements or capabilities.

The W88 Alt 370 program has been in development since 2012. Los Alamos and Sandia National Laboratories are the design and engineering labs for this alt, while multiple nuclear security facilities are responsible for other aspects. Los Alamos produces the detonator assemblies for this alt.

W76-2 mod

The W76-2 mod, a Los Alamos program, is a modification of the W76-1 warhead, which is used on the U.S. Navy’s Trident II D5 submarine-launched ballistic missile. The W76-1, which is still in use, produces a high yield; the W76-2 provides a low-yield, sea-launched ballistic missile warhead capability. The first W76-2 was produced on February 22, 2019, at the Pantex Plant in Amarillo, Texas. Completion of the W76-2 represents NNSA’s ability to achieve a significant program milestone in support of a national security initiative requested by the president in the 2018 Nuclear Posture Review.

W76-1 LEP

The W76-1 LEP was a refurbishment of the W76-0 warhead, the warhead for a submarine-launched ballistic missile system first introduced into the stockpile for the Navy in 1978. The LEP extended the warhead’s service life from 20 to 60 years. The W76-1 continues to meet all missions and capabilities of the original W76-0 warhead but does not provide new military capabilities. NNSA produced the first W76-1 at the Pantex Plant in December 2018.

Los Alamos and Sandia National Laboratories are the design agencies for the W76-1. The W76-1 LEP also required the capabilities of scientists, engineers, technicians, and support personnel from the Pantex Plant, the Y-12 National Security Complex, the Savannah River Site, the Kansas City National Security Campus, Lawrence Livermore National Laboratory, and the Nevada National Security Site.