Ensuring Material Survivability

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Two men working on a metal component in a laboratory.
Livermore researchers Eric Stern (left) and Kelton Grange (right) work on the fielding hardware commissioned for use in weapons survivability experiments. The steel case protects against the destructive force from significant amounts of x-rays and debris wind generated by megajoule-class inertial confinement fusion experiments.

The 2022 U.S. Department of Defense Nuclear Posture Review, which establishes U.S. nuclear policy, strategy, capabilities, and force posture for five- to ten-year periods, highlighted the importance of weapon survivability (the ability of materials and weapons components to survive a nuclear explosion) as a core attribute of the nation’s modern triad. Similar to car manufacturers’ use of crash test dummies in automobiles to ensure that humans would survive a car accident, scientists at Lawrence Livermore National Laboratory’s Weapons Survivability Program ensure survivability of nuclear and nonnuclear weapon components by testing them at the National Ignition Facility (NIF) and other facilities. 

NIF Support to Survivability

In the absence of underground testing following the Comprehensive Test Ban Treaty in 1996, survivability testing requires a radiation source, a platform to position samples near the source, and methods to diagnose and understand the test. NIF’s ability to simulate nuclear explosive environments supports survivability research. NIF is the only facility in the world that can generate intense radiation sources of 14-MeV neutrons. The neutrons are emitted during a fusion reaction between deuterium and tritium and effectively penetrate and almost uniformly heat material samples. NIF can also produce x-rays to rapidly vaporize the surface of a material and generate a shockwave that travels through test samples. The goal of these experiments is to understand how the material reacts and ensure the material’s performance is not compromised by the shockwaves and heating induced by exposure to radiation.  

Livermore’s Weapon Survivability Program develops modeling and simulation capabilities and experimental platforms to assess and certify the survivability of current and future weapons systems after encountering radiation, blast, and electromagnetic pulse environments. The program leverages NIF’s capabilities to conduct experiments exposing materials to neutrons and x-rays. Experiments test if different materials can survive and perform as expected under extreme environments. The results from these experiments will be applied to obtain data supporting future weapons systems’ certification.

Front and back of two disks with varying damage on black backgrounds.
Material samples used in National Ignition Facility (NIF) experiments assess the impact of hostile environmental conditions to different materials. The images depict the front (top) and back (bottom) of a titanium–molybdenum–zirconium sample following a NIF shot. NIF target debris fractures the front surface of the sample, and material melted by radiation output of the NIF target fill in the cracks of the fractures and resolidify. The significant strains to the front are relieved by cracking at the back of the target.

NIF shot yields—including the achievement of fusion ignition—have increased over the years, enabling materials and components to be tested for survivability at hotter and more intense conditions. “With high-yield inertial confinement fusion (ICF) designs, NIF can now deliver unprecedented data on how materials respond to high doses of radiation,” says Chad Noble, Weapon Survivability Program group lead. “These data are important to ensure that we design our stockpile to maintain its integrity in potential engagement scenarios. The high neutron fluence environment created by the igniting capsule also provides an excellent platform for studying nuclear physics, enabling radiochemistry experiments that can be used in the analysis of historical underground test data.” NIF’s material radiation effects platforms provide data through the National Security Applications Program. This U.S. government research initiative enables scientists to study the responses of nonnuclear weapon systems parts, such as electronics, to intense radiation, and to probe material properties at the same temperatures and pressures that can be found in nuclear environments.

Testing Platforms for Success

Exposing samples to radiation requires a carefully engineered experimental platform that can survive exposure to the radiation in the NIF experiment and measure the neutron or x-ray fluence at the sample. Prior to 2021, NIF neutron exposure experiments used room temperature Polar Direct Drive (PDD) capsules—gas-filled capsules without a cryogenic fuel layer (meaning the capsules could not achieve the 100-kilojoule yields necessary for ignition) directly irradiated by NIF lasers—to create neutron radiation fields for survivability testing. Hardness and Survivability snouts (HSurvs) held material samples, measuring responses to x-rays and neutrons. The PDD capsules provided initial neutron sources for designing and testing the HSurvs while also performing materials effects experiments. Engineers began testing candidate material for suitability in the harsh radiation testing environment. 

NIF pursued laser indirect drive (LID), which produced x-rays by shooting laser beams into a hohlraum, imploding a fuel (deuterium–tritium) capsule inside rather than directly irradiating gas-filled capsules. By 2021, LID had achieved significantly higher yields at NIF, leading the Survivability team to develop a new snout for experiments with LID neutron sources.

This cryogenic-compatible x-ray, neutron, and blast snout (CryoXNBS) can withstand significant amounts of neutrons, photons, and debris from megajoule-class ICF experiments without interfering with the NIF target and laser operation. In survivability experiments, researchers place the CryoXNBS in the main NIF target chamber at a distance of approximately 10 to 12 centimeters (cm) from the ignition source and expose the materials inside the snout to high fusion neutron fluences. The platform can be configured to accommodate a variety of samples, materials, and diagnostics supporting a diverse range of experiments. The team began testing the CryoXNBS in 2022, and it was successfully fielded on the December 5, 2022, shot that achieved ignition for the first time in a laboratory. 

Image of three small metal containers attached to a rectangular metal frame.
Pictured are Naiad containers to hold certain samples in survivability experiments. The samples typically consist of small materials or electronic samples securely sealed within robust containers, featuring feedthroughs for both electrical and optical diagnostic signals. These Naiads are installed within specialized snouts, which provide precise positioning and essential protection. Safeguarding the samples is crucial to prevent damage to NIF and to maintain the integrity of the experiment.

Livermore’s Weapons Survivability Program developed a secondary component of the platform, specially designed Naiad containers housed within the CryoXNBS. The Naiad’s multiple containment layers enable the fielding of fissile or otherwise hazardous material in harsh conditions while maintaining flexibility in experiment configuration and available in-situ diagnostics. Fissile materials such as uranium or plutonium can now be irradiated in these unique conditions while allowing unprecedented diagnostic capabilities in a well-controlled laboratory environment. Since the team began testing the CryoXNBS with the Naiad component on PDD and LID shots, it has become a core capability for neutron effects testing. 

Diagnosing Survivability

Diagnostics, the final element required for survivability testing, measure material response and refine the Laboratory’s predictive modeling and simulation capabilities with the experimental data. Unlike NIF’s ICF experimental diagnostics, which are well separated from the ignition source, survivability test diagnostics are in direct contact with the material sample inside the Naiad container. The diagnostic instruments measure the sample’s temperature, fluence, and surface displacement. Because samples heat quickly due to the rapid rate of neutron energy deposition during a test, temperature diagnostics require high temporal resolution to capture peak temperature rise. Non-contact diagnostics provide valuable information for survivability tests as well. 

With the support of the Weapons Survivability Program and the National Security Applications Program, NIF has expanded its capabilities with its Materials Radiation Effects Laboratory. This facility is dedicated to supporting experimentation, improving diagnostics, and fostering collaboration among Livermore scientists and other partners. In 2023, Livermore established the Survivability Laboratory to enable experimentation with complex assemblies, such as 3D objects, and develop advanced diagnostics to meet the program’s testing needs. An example is Photonic Doppler Interferometry, which determines how a material responds to radiation exposure during an experiment to validate model predictions of radiation-induced material displacement. Diagnostics developed for NIF experiments will also be fielded in experiments at the Annular Core Research Reactor facility at Sandia National Laboratories and the Transient Reactor Test facility at Idaho National Laboratory to ensure consistent data collection across platforms.

Two men and one woman stand in front of an open door and cut a ribbon.
Livermore physicist Paulius Grivickas, Strategic Deterrence Deputy Principal Associate Director Derek Wapman, and W87-1 Program Manager Juliana Hsu cut the ceremonial ribbon to officially open the Laser Induced Compression for Grain Scale with High Throughput Laboratory.

Livermore’s Laser Induced Compression for Grain Scale with High Throughput (LIGHT) Laboratory, part of the Direct Light Impulse (DLI) testing strategy, assesses a system’s response to mechanical impulses (shocks) generated by laser ablation. (See S&TR January/February 2024, Upgrading Facilities and Experiences.) The capabilities provided by NIF, NIF DLI, and the LIGHT Laboratory also allow the survivability community to test novel, advanced materials for future weapon systems at varying sizes. For example, tests on smaller samples can be performed at the LIGHT Laboratory more rapidly, slightly larger sample sizes at NIF (approximately a 1-cm radius), and larger samples around 30 cm in NIF DLI. In LIGHT experiments, the laser itself provides a radiation source to study material response in lower-stress environments than created in NIF experiments. However, the LIGHT Laboratory enables rapid testing so researchers can evaluate properties of materials used to assemble complex shapes. For the Survivability team, the LIGHT Laboratory offers a smaller-scale facility to obtain sample response data and evaluate diagnostic and sensor survivability to shocks from target debris similar to those the snout experiences in the NIF chamber. The facility has helped the team to ensure that sensors for the experiments can survive and record data in NIF experiments. For example, Resistive Temperature Diagnostics (RTDs) survived LIGHT experiments, providing a higher probability they would endure the extreme shocks of a costly NIF neutron shot. In the end, one of the RTDs survived the NIF shot. 

The Weapons Survivability Program aims to expand the types of materials used in experiments to integrate more sophisticated diagnostics and partner with universities to study x-ray matter interactions. Leveraging the achievements on NIF, Livermore, in collaboration with the National Nuclear Security Administration laboratories and the Department of Defense, is leading the charge to maintain the survivability of our nation’s nuclear deterrent now and into the future.

—Karen Leonard

For further information contact Chad Noble (925) 422-3057 (noble9 [at] llnl.gov (noble9[at]llnl[dot]gov)).