The paramount national security mission of the Laboratory is ensuring the safety and reliability of the nation’s nuclear weapons stockpile. Development of new nuclear weapons systems stopped nearly two decades ago, and today, the nation’s stockpile is maintained through the science-based Stockpile Stewardship Program. However, as weapon components age, ensuring the reliability of the stockpile has become an increasingly complicated and costly challenge.

The National Nuclear Security Administration (NNSA) is working to transform the U.S. nuclear weapons complex and the nation’s stockpile by shrinking the size of both and finding more cost-effective ways to maintain the remaining weapons. In short, procedures developed during the Cold War to ensure that the stockpile meets all performance requirements must be replaced with a more efficient approach, made possible by using modern technologies.

“The nuclear weapons complex is at a crossroads — maintaining the status quo is not an option we can afford,” NNSA Administrator Thomas D’Agostino said. “Delay and inaction will only increase the costs and elevate the risks associated with maintaining an aging stockpile.”

Livermore scientists and engineers are providing technical leadership to achieve this transformation. According to Livermore physicist Jim Trebes, “Weapons are hard to maintain; we want to do the job faster, better and cheaper.”

One of the most needed improvements is a cost-effective method to collect data about the state of nuclear weapons components, in particular, to detect corrosion, cracks and composition-changing properties without having to dismantle the weapons. Traditionally, a few randomly selected warheads and bombs are pulled from the field every year and transported to NNSA’s Pantex Plant in Texas, where they are disassembled for close inspection. While most are reassembled and returned to the stockpile, at least one warhead of each type is destroyed in the process. Some parts, for example, are cut open for inspection, and others are stressed to the failure point.

A promising Livermore effort is developing tiny, rugged sensors that could be embedded in every nuclear weapon. Embedded sensors, compatible with warhead materials, could provide information currently obtained from disassembly. Such devices could make possible for the first time “persistent surveillance” — continuous monitoring of the state of health for every weapon and practically instantaneous detection of anomalies.

Eliminating the costly and sometimes destructive testing of warheads is particularly important to comply with the Moscow Treaty on Strategic Offensive Reductions, which was signed in 2002. Under the terms of this treaty, the United States is reducing its total number of active nuclear weapons to between 1,700 and 2,200 warheads and bombs. As the number of U.S. weapons shrinks, fewer weapons are available for disassembly to provide statistical assurance about the stockpile’s health.

Sensors would most likely be embedded in existing weapons during a life-extension program — a rebuilding effort that significantly increases a warhead’s lifespan. Sensors also could be added to so-called shelf units stored at NNSA’s Y-12 Plant in Tennessee and at Pantex, where individual components are monitored closely for signs of aging and unexpected physical and chemical changes. In addition, if replacement warheads were developed, sensors could be integrated into the weapon assembly.

Once in place, an array of different sensors could signal the presence of unwanted gases, record stresses incurred as a warhead is moved and detect microscopic cracks and voids. Trebes, who is helping guide Livermore sensor designs, notes that an embedded sensor network also might reveal “unknown unknowns,” issues not previously encountered.

“If we could assess every weapon in real time, we would immediately know which warheads need to be pulled apart, and that would drive down costs,” said chemist Lou Terminello, who leads the Laboratory’s materials program.

Bruce Goodwin, principal associate director for Weapons and Complex Integration, adds, “Embedded sensors have the potential for a huge payoff in costs and manpower. They will give us stronger confidence in the stockpile. Instead of sending all 30 kids in a classroom to get a physical exam, one kid raises his hand and says, ‘I’m sick.’”