Underground nuclear tests are not presently conducted in the United States, in accordance with the voluntary moratorium on nuclear testing beginning in 1992, but remnants from previous detonations continue to provide valuable insights for scientific and national security communities. While underground tests unfolded at a grand scale and displaced many thousands of tons of earth, some of the clearest records of these detonative processes are found in microscopic and atomic signatures that require dedicated laboratory facilities to access and interpret.
The Lasting Value of Drill-Backs
The blast from an underground nuclear detonation rips through the earth, irradiating and heating the ground so vigorously that rocks momentarily turn into plasma. As it cools, the plasma returns to a rocky state that can look similar to pumice or have a glassy surface, depending on the local geology of the test site. During the age of active nuclear testing, researchers conducted drill-backs, for which they ventured into the affected area well after the blast and used a technique called sidewall punching to bore a hole into rock with a slanted drill rig to extract samples for testing. The samples contain physical, chemical, and other radiological signatures that help scientists analytically reconstruct the split-second shockwave and understand the performance of the physics experiment. For today’s researchers, drill-back samples remain vital to validating the experimental data of historic tests and understanding the physics of detonations. In the absence of full-scale nuclear testing, Lawrence Livermore maintains a library of drill-back samples acquired before the moratorium, and these samples continue to benefit its programs. While these geologic samples retain only a small degree of their prior radioactivity, understanding their morphology and chemistry remain important for stockpile stewardship and modernization.
Processing drill-back samples for laboratory study requires highly sophisticated, dedicated facilities with strict access controls and safeguards against hazardous materials. Livermore is the only laboratory within the National Nuclear Security Administration (NNSA) boasting a dissolver facility specially equipped to handle nuclear debris. After an event, data from processed drill-back samples are interpreted and reported in a radiochemical assessment by scientists in the Nuclear Test Data Program (NTDP), which supports the Strategic Deterrence Principal Directorate’s design and modernization efforts. “The assessed data is used to estimate the performance of the test event. These conclusions are passed to design teams in Strategic Deterrence, who use the information to confer with their models,” explains William Kerlin, a Livermore radiochemist and NTDP group leader. The facility supports mission-focused programs in multiple Laboratory directorates and remains on standby for supporting nuclear testing if directed to do so by the President of the United States. “Livermore’s dissolver facility is an assured capability. In a sense, it is a facility-in-waiting, allowing us to quickly begin evaluating debris from new underground tests if given the directive,” says Kerlin.
Inside the Dissolver Train
Drill-back samples must be transformed into a liquid state to perform chemical analysis via multiple radiometric and mass spectrometric techniques. Once the drill-back samples arrive at the Laboratory, scientists place a sample into a shielded crusher box, which applies mechanical pressure to grind the rock into powder. This step increases the surface area of the sample several times over, making subsequent reaction steps more effective.
The pulverized sample is carefully placed into a metal crucible and transported via motorized transfer line to one of six dissolver gloveboxes built to safely manipulate radioactive and corrosive materials. Inside the glovebox, chemical treatment and intense heat provided by a hot plate further denature the sample. Scientists expose the sample to strong acid (such as hydrofluoric acid), which disintegrates the sample and causes some of it to volatilize. Through subsequent chemical steps involving similarly caustic substances, the sample is sufficiently dissolved and reduced to a liquid solution. Scientists repeatedly centrifuge the sample and decant the overlaying liquid until lingering solids are completely dissolved. Finally, the sample is removed from the dissolver box and taken to a holding location to await analysis.
Depending on the research needs of investigators, when scientists remove a small amount of the liquid, they can choose among several different chemical analysis techniques. To detect signatures of specific elements and isotopes, researchers often turn to mass spectrometry, which ionizes the sample and separates dislodged atoms according to their mass. Since periodic elements and their isotopes have unique, distinguishable masses, clues to the sample’s age and history of radioactivity exposure can be found by deciphering the relative abundance of isotopes present. Alternatively, scientists can use radiation-counting techniques to monitor the material’s fission products. When radioactive atoms undergo fission, they yield lower-mass daughter elements while also releasing energetic products including neutrons, gamma rays, or alpha particles, depending on the type of decay occurring. Gamma-ray spectrometry (gamma counting) detects radionuclides that emit characteristic gamma rays, while alpha counting detects alpha particle–emitting radioisotopes such as plutonium, uranium, and other actinides. Together, these analytical techniques provide insight into the makeup and physical history of a sample used to inform research programs ranging from weapons performance to nonproliferation.
High-Tech Renovation
Despite its uniqueness within the nuclear security enterprise, Livermore’s original dissolver facility was aging. “The last major revamp of this facility occurred in 1987,” says Kerlin. “At that time, Livermore technicians designed nearly every component from scratch—all of the scientific equipment down to the centrifuges, magnets, and heaters were custom-built onsite.” Although desire for customization gave the Laboratory full control over the facility’s setup and instrumentation, as an unintended consequence, it complicated the process for replacing aging parts following years of use. Some parts inevitably broke down after decades of frequent contact with harsh acids and bases—even those inside gloveboxes which are designed for chemical resistance. Until recently, just one of the facility’s 12 gloveboxes was operational. Acknowledging the need to update the dissolver facility and ensure mission continuity, NNSA funding for the necessary renovations was allocated through Infrastructure and Operations, a division of the Operations and Business Principal Directorate. The Laboratory celebrated the renovated facility with a ribbon-cutting ceremony in May 2026.
Planners involved with the latest renovation prioritized longevity, efficiency, and process automation in the reimagined facility. “This time, we opted to source as many components as we could from external vendors. The only fully custom part of the setup is the series of gloveboxes. That choice alone is an upgrade,” says Kerlin. If a component needs replacing in the future, the dissolver system does not need additional modification to slot in the new component. In short, minimizing the facility’s customization supports its longevity. “This system will still be ready for use in 30 years,” says Kerlin.
The upgraded facility was designed to ensure the safety of Laboratory personnel by updating hazardous materials safeguards and incorporating process automation. The dissolver train is a negative-pressure system, and its exhaust passes through a chemical scrubber before exiting the building. Hazardous materials are contained in gloveboxes covered in radiation shielding and coated with acid-resistant polyvinylidene fluoride. Workers in the dissolver facility are trained to understand the chemical and radiological hazards present, and dissolver train upgrades have reduced the hands-on time needed for experimental processes. “Now, the system can automatically dissolve materials to the point where we can manually handle them,” Kerlin says. After pulverizing the sample, technicians choose which chemical reaction sequence the equipment should perform, and the programmable system will distribute the necessary acids and heat the sample until it is ready to be centrifuged.
Beyond processing drill-back samples, the dissolver facility will continue to enable other nuclear forensics work performed by Livermore. For instance, the facility’s ability to safely process radioactive materials and hazardous substances bolsters the Laboratory’s emergency response capabilities maintained through the Technical Nuclear Forensics program, a joint mission between Lawrence Livermore, Pacific Northwest, and Los Alamos national laboratories. To ensure readiness of laboratory systems and research teams, scientists from one laboratory deliberately create chemical cocktails of materials that would be associated with a real-world postdetonation event. The Livermore facility is the ideal place to process these cocktails, which require high-energy reactors to generate fission products and strong acids to be dissolved. The materials are then transferred to research groups at partnering laboratories that perform chemical analyses to validate characterization capabilities remain standardized across the enterprise. By upgrading the dissolver train facility with a focus on safety, longevity, and efficiency, Lawrence Livermore is enabling ongoing, mission-relevant programs while ensuring the Laboratory can quickly follow through on future mission directives.
—Elliot Jaffe
For further information contact William Kerlin (925) 424-3105
(kerlin3 [at] llnl.gov (kerlin3[at]llnl[dot]gov)).
