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Nuclear fission is an important process with applications in astrophysics, nuclear reactors, and stockpile stewardship. Despite having been discovered over 80 years ago, fission is not fully described by a predictive model.
Precise knowledge of nuclear fission is a critical component for nuclear energy and stockpile stewardship research. Despite having been discovered over 80 years ago, fission is not fully described by a predictive theory, so thorough and accurate nuclear data libraries are necessary. These libraries provide information about the fission process in studied isotopes that is used in scientific and engineering models.
The Weapons Engineering Tritium Facility (WETF) is a Hazard Category 2 nonreactor nuclear facility located in Technical Area 16 (TA-16) of Los Alamos National Laboratory. Tritium related research, development, and processing in support of stockpile stewardship program activities is conducted at WETF. Within WETF, various devices can be used to contain tritium and certain devices are designated as Tritium Containment Vessels (TCVs). Several different device types are identified as TCVs within WETF such as LP-50s and AL-M1s. Historically, a threshold tritium mass value has been used as the mechanism for designating a device as a TCV. When the tritium content of the device was below the tritium mass threshold it was not considered to be a TCV in the formal context. When the tritium content was above the administrative threshold, the device was considered to be a TCV. An upper tritium mass limit was also established for TCVs.
LLNL’s Nuclear Data and Theory Group has created the 2011.5 revised release of the Evaluated Nuclear Data Library (ENDL2011.5). ENDL2011.5 is designed to support LLNL’s current and future nuclear data needs and will be employed in nuclear reactor, nuclear security and stockpile stewardship simulations with ASC codes. This database is currently the most complete nuclear database for Monte Carlo and deterministic transport of neutrons and charged particles. This library was assembled with strong support from the ASC PEM and Attribution programs, leveraged with support from Campaign 4 and the DOE/Office of Science’s US Nuclear Data Program. This document lists the revisions made in ENDL2011.5 compared with the data existing in the original ENDL2011.2 and ENDL2011.3 releases. These changes are made in parallel with some similar revisions for ENDL2009.5. We also describe ENDL2011.5-direct that directly uses ENDF sources wherever possible.
LLNL’s Nuclear Data and Theory Group have created a 2009.5 revised release of the Evaluated Nuclear Data Library (ENDL2009.5). This library is designed to support LLNL’s current and future nuclear data needs and will be employed in nuclear reactor, nuclear security and stockpile stewardship simulations with ASC codes. The ENDL2009 database was the most complete nuclear database for Monte Carlo and deterministic transport of neutrons and charged particles. It was assembled with strong support from the ASC PEM and Attribution programs, leveraged with support from Campaign 4 and the DOE/Office of Science’s US Nuclear Data Program. This document lists the revisions and fixes made in a new release called ENDL2009.5, by comparing with the existing data in the previous releases ENDL2009.3 and ENDL2009.4. In addition to the legacy library ENDL2009.5 from ENDL-format files generated by Fete, an ENDL2009.5-direct library is also released, in which ENDF6-formatted sources are used wherever possible to avoid possible translation errors from Fete.
The Chemistry and Metallurgy Research Building (CMR), located at TA-03-0029, was built in 1952 and was occupied by Los Alamos National Laboratory (LANL) employees in 1953. The facility was built to perform actinide analytical chemistry and material characterization in support of LANL and Department of Energy (DOE) mission of stockpile stewardship and research.
The experimental and calculated Raman spectrum of PuCl 3 has been reported for the first time. PuCl 3 is a primary species found in plutonium metal refinement, specifically in pyrochemical salt processes including multicycle direct oxide reduction, metal chlorination, and electrorefining. As such, Raman signatures of PuCl 3 could serve as potential forensic indicators of material process history. A novel technique for synthesizing PuCl 3 from the in-situ chlorination of plutonium metal with HCl was developed to establish these signatures. Cerium metal surrogates were utilized to ensure optimization of the plutonium experiments and to minimize personnel exposure, and all experiments were carried out in a Raman reaction chamber designed for air-tight, high vacuum environments. In-situ Raman spectroscopy was employed in conjunction with Density Functional Theory (DFT) to investigate the vibrational modes of PuCl 3 . Associated mixed oxy and hydroxyl phases are also reported. The combined Raman and DFT results have eliminated inconsistencies in Raman mode assignments for the MX 3 family of metal chlorides having P6 3 /m symmetry, and IR modes derived from the DFT calculations are additionally presented. The data observed in this study is of potential interest to nuclear forensic analyses, nuclear sample aging, nuclear energy, plutonium processing, and stockpile stewardship.
This milestone describes the development and fielding of EXAFS Phase II spectrometer designed to provide high quality (SNR>=5) EXAFS spectra for Plutonium measurements at the National Ignition facility (NIF). Benefits: the EXAFS data will be used by the High Energy Density (HED) Physics and more specifically the Focused Material Science program to measure the thermal state of compressed materials with good temperature sensitivity (~100-1000 Kelvin). Data with good signal to noise ratio (SNR>=5) and good spectral resolution allows the FMS program to fill a gap in diagnosing temperature to completely constrain material properties for weapon physics and Stockpile Stewardship applications.
The Z accelerator at Sandia National Laboratories conducts z-pinch experiments at 26 MA in support of DOE missions in stockpile stewardship, dynamic materials, fusion, and other basic sciences. Increasing the current delivered to the z-pinch would extend our reach in each of these disciplines. To achieve increases in current and accelerator efficiency, a fraction of Z’s shots are set aside for research into transmission-line power flow. These shots, with supporting simulations and theory, are incorporated into this Advanced Diagnostics milestone report. The efficiency of Z is reduced as some portion of the total current is shunted across the transmission-line gaps prior to the load. This is referred to as “current loss”. Electrode plasmas have long been implicated in this process, so the bulk of dedicated power-flow experiments are designed to measure the plasma environment. The experimental analyses are enhanced by simulations conducted using realistic hardware and Z voltage pulses. In the same way that diagnostics are continually being improved for sensitivity and resolution, the modeling capability is continually being improved to provide faster and more realistic simulations. The specifics of the experimental hardware, diagnostics, simulations, and algorithm developments are provided in this report. The combined analysis of simulation and data confirms that electrode plasmas have the most detrimental impact on current delivery. Experiments over the last three years have tested the theoretical current-loss mechanisms of enhanced ion current, plasma gap closure, and Hall-related current. These mechanisms are not mutually exclusive and may be coincident in the final feed as well as in upstream transmission lines. The final-feed geometries tested here, however, observe lower-density plasmas without dominant ion currents which is consistent with a Hall-related current. The picture of plasma formation and transport formed from experiment and simulation is informing hardware designs being fielded on Z now and being proposed for the Next-Generation Pulsed Power (NGPP) facility. In this picture, the strong magnetic fields that heat the electrodes above particle emission thresholds also confine the charged particles near the surface. Some portion of the plasmas thus formed is transported into the transmission-line gap under the force of the electric field, with aid from plasma instabilities. The gap plasmas are then transported towards the load by a cross-field drift, where they accumulate and contribute to a likely Hall-related cross-gap current. The achievements in experimental execution, model validation, and physical analysis presented in this report set the stage for continued progress in power flow and load diagnostics on Z. The planned shot schedule for Z and Mykonos will provide data for extrapolation to higher current to ensure the predicted performance and efficiency of a NGPP facility.
Our understanding on the distribution of fragment masses following fission, or fission yields is largely impacted by the quality of nuclear data. One of the most straightforward and reliable ways to determine the number of fissions that occurred in a chain reaction is done via detection of the characteristic γ-rays emitted during the β decay of the fission product. These γ rays are emitted in only a fraction of the decays, and this fraction (the γ-ray intensities) must be known accurately to determine the total number of fissions. Many long-lived fission products, such as 111 Ag, play an important role in science-based stockpile stewardship and nuclear forensics. The γ-ray intensities from the decay of 111 Ag are known to only 5%, leading to a 5% uncertainty in fission-chain yield. This work aims to improve the precision of these γ-ray intensities for the most intense emissions following the decay of 111 Ag, as seen in Figure 1.
Stockpile stewardship and nuclear waste remediation are inherently chemically complex, involving practically the full diversity of the periodic table, but existing methods are too expensive or not functional for a large diversity of atom types. Overall, the field of machine learning interatomic potentials (MLIPs) has advanced dramatically in 2024 with large high-accuracy datasets existing for bulk, surface, and organic chemical systems and new online leaderboards for diverse chemistry. To participate in, and bring LANL interests into this ecosystem, here, we have built upon existing technologies created by LANL to create a framework capable of creating machine learning interatomic potentials (MLIPs) for over 90 atom types. Our results have created a massively diverse coordination complex training dataset more than 3 times the size of existing datasets, parallelized MLIP training over multiple GPUs, enabling the training of an MLIP spanning the periodic table at 20 times the speed of prior training on 32 GPUs. These advances are substantial towards creation on foundational MLIPs for LANL-specific application areas.
Detailed knowledge of fission-product (FP) decay properties is needed for a variety of applications of nuclear science such as nuclear-energy production, nuclear-nonproliferation efforts, nuclear-forensics assessments, and stockpile stewardship, as well as for establishing a comprehensive understanding of the fission process, r-process nucleo-synthesis, and fundamental neutrino science. Although nearly a thousand radioactive isotopes are produced in fission, in many cases key pieces of nuclear data on only a handful of isotopes are needed to make a significant impact.
The Department of Energy Computational Science Graduate Fellowship (DOE CSGF) is necessary to meet the continual challenging national workforce needs that arise as computational science and engineering problems continue to grow in scope and complexity. Computational science and engineering (CSE) is a multidisciplinary approach that uses scientific computing to solve practical problems methods and to supply technical tools across the scientific discovery spectrum. In particular, the DOE CSGF emphasizes high-performance computing (HPC) that enables CSE that advances science and engineering in directions important to the DOE and the economy in general. Over the past half-century, HPC has been an essential tool for DOE’s success. During this period, important missions, such as nuclear stockpile stewardship, have turned to HPC as an essential technology. Entire science disciplines, such as biology and cosmology, have been transformed through the augmentation of scientific observation via HPC. At government laboratories and in industry, DOE CSGF alumni are helping push traditional HPC boundaries while contributing to discoveries in high-energy physics, renewable energy, fusion-reactor design, additive manufacturing, nanomaterials for next-generation batteries and transistors, and turbine and advanced nuclear reactor modeling. In addition, HPC is used to address national health needs that will eventually point to cures both by helping cancer researchers manage and analyze huge troves of data, by simulating biological mechanisms, and by accelerating drug development — including continuing to rise to the challenge of pandemic-related research. A 2023 report from the ASCAC Subcommittee on American Competitiveness and Innovation to the ASCR office, “Can the United States Maintain Its Leadership in High-Performance Computing?” says of the Program, “The CSGF program provides a barometer for disciplines that will be of interest to future DOE computing.” An explosion in scientific and technological data has driven the need for increasingly sophisticated HPC to transform those data into scientific understanding. With access to more and more data and the proliferation of HPC, Machine Learning and Artificial Intelligence are experiencing a renaissance, complementing the now well-established use of computational simulation. Indeed, in its September 2020 subcommittee report on “AI/ML, Data Intensive Science and High-Performance Computing”, the DOE Advanced Scientific Computing Advisory Committee (ASCAC) explicitly called for a fellowship program to train computational and data scientists to tackle exascale and data-intensive computing challenges. This collaboration of empirical and theory-based modeling will increasingly inform federal policymakers whose decisions affect American society and future generations, and it requires highly skilled and intellectually agile computational scientists who can support the fast-moving DOE National Laboratory research environment. In fact, the DOE CSGF program has explicitly and consistently addressed this need.
Based on planning and reviews conducted in 2020, it is clear today that the Z Facility must be sustained through 2040 or longer. This requires a well-developed and executed maintenance and sustainment effort. Z’s Sustainment Plan outlines the approach that Sandia’s Pulsed Power Sciences Center will pursue to assure that the Z Facility maintains its world class research and development program supporting the NNSA’s Science Based Stockpile Stewardship efforts. In FY24, the Pulsed Power Center at SNL planned and executed many substantial sustainment projects as well as maintenance-driven-sustainment aligned to the Sustainment Plan. These projects are listed in this section with brief descriptions of the work executed.
This document details the strategy proposed to meet the National Nuclear Security Administration (NNSA) requirement for the Dual-Axis Radiographic Hydrodynamic Test (DARHT) Facility Sustainment and Modernization projects identified in multiple NNSA Stockpile Stewardship and Management Plan (SSMP) reports to Congress [NNSA, 2020; 2021; 2022; 2023; 2024]. DARHT has become indispensable for the certification of the primaries of U.S. nuclear weapons since the current U.S. moratorium halted underground nuclear testing more than 30 years ago. However, aging facilities, evolving technology, and other issues are limiting or threatening the capability of DARHT to meet NNSA’s expanding mission needs now and into the future. This DARHT Capability eXpansion (DCX) strategy was developed to address NNSA needs by extending DARHT’s reliability and resilience, increasing the quality and quantity of DARHT data, and enabling hydrodynamic measurements in complex environments. The strategy can be implemented through integration of line-item projects, acquisition of major items of equipment, and other actions coordinated with the execution of the SSMP. This strategy document is intended for U.S. Government officials, particularly authorizers, appropriators, and program leaders. It may also be furnished to DARHT users, customers, collaborators, stakeholders, and visitors as needed
On December 5, 2022, Lawrence Livermore’s National Ignition Facility achieved the first-ever successful positive-gain ignition shot. This scientific advance, heralded worldwide, required a multidecadal effort to synthesize physics theory, laser technologies, computation and diagnostic capabilities, as well as engineering, materials development, and other inputs. The question, “Can ignition be achieved?” had been answered. Since then, the Laboratory has answered the question, “Can we do it again?” with additional ignition shots at increasing yield. Now Lawrence Livermore researchers ask, “Can we improve ignition outcomes?” for the benefit of the Stockpile Stewardship Program. Interrelated articles presenting the Laboratory’s ignition science, the role of supercomputing in achieving ignition, the evolution of diagnostic instruments to measure ignition data, and the ambitious steps required to realize a fusion energy future lead to one answer: “Yes, we can.”
The National Nuclear Security Administration (NNSA) is entrusted with ensuring the safety, security, and reliability of the nation’s nuclear weapons stockpile while advancing programs aimed at reducing global nuclear proliferation. These critical mission objectives are achieved through the expertise of a highly skilled team of professionals. The operations at the National Criticality Experiments Research Center (NCERC) play a vital role in developing and enhancing knowledge and expertise in advanced nuclear technologies. NCERC supports a wide range of mission areas, including nuclear criticality safety, nuclear emergency response, and nuclear nonproliferation, safeguards, and arms control. It also provides support to the Department of Homeland Security, advances stockpile stewardship science, and delivers scientific expertise to other government agencies, such as NASA and the Defense Threat Reduction Agency. NCERC conducts experiments utilizing diverse nuclear materials, from small neutron-emitting sources for testing radiation detection equipment to larger quantities of uranium and plutonium for criticality experiments. A cornerstone of NCERC's mission portfolio includes the operation of four critical mass assembly machines—Planet, Comet, Flattop, and Godiva-IV—which are instrumental in advancing nuclear science and ensuring the nation’s nuclear security objectives.
The goal of this one-year LDRD is to study novel experimental approaches to provide benchmark spectral opacity measurements at the most extreme conditions beyond existing measurements (i.e. 2x temperature, ~5x density). These conditions correspond to those at half the solar radius and would provide a unique and novel test for stellar physics. These conditions are also relevant to advance stockpile stewardship research. The basic idea is to embed a sample inside the z-pinch dynamic hohlraum on the Z facility and obtain its opacity from either 1) its self-emission or 2) its absorption from using a capsule backlighter. This study evaluates the feasibility, limitations to these two approaches from a design approach. We found that emission-based perspective gives, at best, an opacity accuracy of about 20% for the current studied pinch conditions due to the limit of LTE approximation and radiation transport effects. The capsule-backlighter-based approach overcomes this limitation although some specific design questions remain to be answered. Promising designs are proposed for follow-on Z experiments. Future designs would help maintain Z relevancy in relation to ignition-enabled platforms at NIF.