Validating Weapon Simulations

NIF experimental data help inform and validate sophisticated, three-dimensional weapon simulations that are designed to improve understanding of important weapon physics. LLNL’s high-performance computing capabilities include the Sierra supercomputer (left), a 125 petaFLOPs (quadrillion operations per second) machine that is one of the fastest in the world. Data from NIF experiments (inset, right) and simulation (inset, left) are combined with deep learning methods to provide essential computational resources for nuclear weapon scientists. Credit: Tanya Quijalvo

Inertial confinement fusion and high energy density science experiments on NIF, coupled with the increasingly sophisticated simulations available from some of the world’s most powerful supercomputers here at the Laboratory, serve to increase our understanding of weapon physics, including the properties and survivability of weapons-relevant materials. The data from NIF experiments complement testing at other experimental facilities at Livermore and elsewhere.

Researchers no longer have to wait for a supernova event to gather data or attempt to parse information from an underground nuclear test with limited diagnostics.

NIF’s unique capabilities, including flexible and repeatable experimental configurations, precision target fabrication and metrology, and advanced diagnostics, have allowed the weapon programs of the national security laboratories to execute and deliver data in relevant regimes previously inaccessible to scientists.

NIF enables researchers to perform experiments in a controlled environment and at a much higher rate than could have been imagined with underground testing. A problem can be picked apart and individual physics pieces can be studied. Weapon researchers are now able to measure the phase, strength, and equation of state of plutonium and other weapon-relevant materials at extreme pressures, densities, and temperatures.

NIF experiments are uniquely capable of informing and validating three-dimensional weapons-simulation computer codes that support the W80-4 Life Extension Program (LEP) effort.

Maintaining the Nuclear Deterrent

The experiments are used to inform planned and proposed Stockpile Life Extension programs (LEPs), the regularly planned refurbishments of nuclear weapon systems to ensure long-term safety and reliability. Changes to weapon systems for safety and security can have unintended consequences if those changes cannot be fully validated. Full validation is achieved through the combination of experiments using facilities such as NIF and advanced computational modeling. The data acquired in NIF experiments are helping LLNL weapon designers assess replacement options for aged materials in the W80 warhead.

Radiation transport is also central to the operation of nuclear weapons; with NIF, researchers can perform detailed radiation-hydrodynamic experiments.

NIF studies will continue to pay dividends for certification of the annual assessments National Nuclear Security Administration (NNSA) laboratories conduct to evaluate if the U.S. stockpile is aging acceptably (see NIF and Stockpile Stewardship). They also will help the nation maintain the skills of nuclear weapon scientists, which is crucial in order to assess the age-related changes that could compromise weapon reliability .

In addition, researchers are using NIF to provide hostile x-ray and neutron environments for vulnerability and hardness testing. NIF radiation sources help researchers evaluate how well U.S. weapons will be able to survive—and function as expected—after traversing evolving adversary missile defenses. Without the ability to survive, these weapons would be unable to hold targets at risk, rendering the deterrent ineffective (see National Security Applications).

More Information

“NIF Experiments Support Warhead Life Extension,” NIF & Photon Science News, January 9, 2019

“Extending the Life of a Workhorse Warhead,” Science & Technology Review, October-November, 2018