At Lawrence Livermore National Laboratory (LLNL), a multi-institutional team of researchers and collaborators successfully carried out an integrated vessel confinement system (VCS) experiment as part of an experimental campaign to study how nuclear materials react to high explosives without conducting a traditional nuclear test.
The Miramar experiment was a collaborative effort between LLNL, Los Alamos National Laboratory (LANL), the United Kingdom’s Atomic Weapons Establishment (AWE), and the Nevada National Security Site (NNSS). It is a significant milestone in the upcoming “Nimble” subcritical experiment series. The Nimble series is intended to remain below the nuclear criticality threshold in accordance with the United States’ commitment not to resume nuclear explosive testing. The Nimble series will be critical in assessing the safety, security, and effectiveness of the United States’ nuclear stockpile, as well as providing critical data for certifying that modernised warheads will perform as expected.
Miramar is the final dress rehearsal experiment before the Nimble series at NNSS’s Nevada underground U1a facility. The experiment will help to ensure that there are no vessel confinement or data-return surprises during the Nimble experiments in U1a. This was a fully integrated test, which meant that all vessel and confinement system components, as well as diagnostic and experimental components using relevant materials, were present.
“Miramar is a vessel mitigation experiment,” said Fady Najjar, an LLNL design physicist who helped spearhead the experiment. “The main goal was to demonstrate that the mitigation system design will protect the confinement vessel’s integrity from debris and damage, and that diagnostics will perform as expected.”
Miramar was made up of several experiments that were detonated within a fully enclosed steel vessel. The team also took advantage of this experimental opportunity to collect hydrodynamic physics data from novel diagnostics for upcoming subcritical experiments to measure detonation momentum.
“The demonstration of the recently implemented novel diagnostic to measure areal mass, developed collaboratively by NNSS and LLNL, was a major accomplishment and testament to the innovative and responsive nature of our scientific collaboration,” project experimental physicist Ed Daykin said. “Preliminary results show that all experimental packages within the vessel were successfully executed and returned high-quality data.”
Miramar operations and data collection included the design and assembly of a test area to simulate the U1a facility at LLNL’s remote experimental test site at Site 300, implementation of the intended VCS blast mitigation design, and assembly and demonstration of the timing and firing system. Extensive velocimetry and ranging, as well as temperature and vessel diagnostics, were all part of the experiment.
“Miramar provided valuable physics validation data that give us further confidence in our final designs for the Nimble subcritical experiment packages, in addition to being a final proof-test of a novel diagnostic developed under a very tight timeline,” said Garry Maskaly, design physicist. “The team’s dedication will help us obtain the highest quality data in future experiments, allowing us to best support future stockpile modernization programs.”
“The completion of this experiment provides the information and confidence required to move forward with upcoming Nimble series activities and experiments,” Najjar said. “Overall, Miramar was a very successful experiment with excellent data return, allowing the team to evaluate and verify procedures in preparation for fielding and executing subcritical experiments at U1a.”