The articles included in this issue are derived from presentations given at the recent workshop “In-situ Sensing and Process Monitoring for NNSA Relevant Materials and Processes.”

By Bjørn Clausen | February 1, 2022

The articles included in this issue are derived from presentations given at the recent workshop “In-situ Sensing and Process Monitoring for NNSA Relevant Materials and Processes” held as a two-day virtual workshop at Los Alamos National Laboratory (LANL) in late August 2020. The workshop was co-sponsored by the State of Technology Awareness Initiative (STAI) and the Seaborg Institute at LANL, and organized by Bjørn Clausen and Donald Brown (LANL/MST-8), John Carpenter (LANL/SIGMA-2), and Brian Crone (LANL/INP-PUE). The Technical Director for STAI is Richard Sheffield (LANL/ASO: Accelerator Strategy Office) whose focus is advancing the science, technology, and engineering to enable the Dynamic Mesoscale Materials Science Capability (DMMS) at LANL.

The workshop had over 100 registered participants, which included 6 keynote talks and 10 invited talks, as well as 4 discussion sessions. Presenters were from LANL, Lawrence Livermore National Laboratory (LLNL), National Institute of Standards and Technology (NIST), Air Force Research Laboratory (AFRL), Colorado School of Mines (CSM), and Westinghouse Electric Company. In addition, the workshop also included participants from Pacific Northwest National Laboratory (PNNL), Kansas City National Security Campus (KCNSC), Y-12 National Security Complex (Y-12), and the Pantex Plant.

Our goals were to discuss and identify the most promising in-situ sensing and process monitoring techniques that provide a path towards rapid qualification of the material or certification of the component. We also aimed to identify techniques that best respond to current programmatic gaps or technology pulls. The workshop was focused on National Nuclear Security Administration (NNSA) programmatic needs and included both actinide and non-actinide materials. Processes discussed were very diverse, ranging from aqueous actinide processing, casting and heat treatment of actinides, to additive manufacturing of steels and nickel alloys. Many of these ideas followed Design for Manufacture (DfM) approaches, meaning that parts, components, or products are designed specifically for ease of manufacturing.

The discussion began with a wide range of sensor categories (including chemical, acoustic, thermal, force, and metrological) that can be employed in-situ on both existing and future production operations (e.g., casting, welding, additive manufacturing, hot pressing, heat-treatment, forming, and machining) to ensure processing conditions are within the specified envelope. By simulating these processes on advanced beamlines equipped with analogous sensors we can obtain in-situ microstructural characterization using diffraction, imaging, and small angle scattering. This feedback can be linked to sensor response during manufacture, or specifically during off-normal transients.

As a stretch goal, we aimed to identify methods that allow real-time sensor response to be correlated to specific microstructural features which control properties, thus enabling on-the-fly informed decisions during fabrication. Inherent in these discussions is the topic of advanced data reduction methods (e.g., machine learning and advanced physics-based materials and process modeling).

The talks and discussions all included pragmatic considerations of what can actually be measured and/or controlled on the factory floor and covered several traditional probes (e.g., thermocouples, pyrometry, off-gas analysis) and novel probes (e.g., LIBS: Laser Induced Breakdown Spectroscopy, RUS: Resonant Ultrasound Spectroscopy), in addition to imaging and scattering.

A promising method that was identified as having strong potential to be implemented on the factory floor is the use of LIBS for in-situ monitoring, which addresses both qualification and compliance needs. Moreover, it was shown that in-situ scattering probes coupled with additional instrumentation (e.g., thermocouples, RUS) can reveal the microstructural underpinnings of macroscopic events, providing the linkage between the process control “knobs” (the actual physical control input parameters that can be altered for the process) and properties of the product.

Among the challenges identified were issues such as how to relate control knobs to performance. In other words: What can we control or measure in the factory? What controls microstructure? And how does that influence properties? Another important challenge is to reduce the amount of the time from discovery to implementation, both for materials and processes. We can tackle this in part by increasing the dialogue between core mission (mission pull) and the science base (technological push). This may be effected by bringing together people from production and science, theorists/modelers, and experimentalists to enhance the cross-fertilization of ideas and knowledge between the disciplines. A practical example of this would be establishing mini-sabbaticals internally (e.g., between LANL science/technology and production divisions) or externally (e.g., between LANL and KCNSC). Another direct suggestion was to develop NNSA-sponsored beamlines at existing DOE/BES user facilities, enabling research on materials/processes that do not fit the typical BES mandates of cutting edge science leading to high visibility publications. Instead, this would enable experiments on mission-relevant materials and processes, including the ability to safely and securely handle sensitive, hazardous, and/or radioactive materials.

The following articles represent a good cross-section of the techniques discussed during the workshop: A new efficient and fast method for identifying actinides in aqueous waste streams based on rapid actinide identification via luminescence (RAIL) that also presents opportunities for in-situ sensing and improved process control (p3); A novel use of LIBS for in-situ determination of the chemical composition of nuclear materials that can be used in production lines as well as to determine processing needs for legacy materials (p9); A neutron diffraction based study of long term aging in Pu-Ga alloys from self-irradiation and cryogenic temperature exposure, which identified development of lattice strains that will impact the kinetics of defect evolution in the material (p17).