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DOE OSTI2022

Hand Calculations for Nuclear Criticality Safety — Primer Revision [Abstract]

The document “ Hand Calculation Methods for Criticality Safety –A Primer, ” was published by the authors (Los Alamos National Laboratory report LA-14244-M) in December 2006 to provide an overview of the most common hand calculation methods used for criticality safety analysis. Hand calculation methods can be used as a starting point for more advanced calculations, and in many circumstances, they can provide sensitivity and perturbation information quicker than using a criticality code, such as KENO or MCNP. This report has been revised to augment existing basis information and example problems for each of the methods discussed: 1-group and modified 1-group diffusion theory, core-density conversions, buckling conversions, limiting surface density method, density analog method, surface density method, and solid angle method. This primer discusses the applicability of the various methods, illustrates how they are used, and provides an interpretation of the example problem results. The example problems provided are simple, practical problems, and the reference data to solve each example problem is provided. This paper will provide an overview of the Primer revision and how it can be useful for new Nuclear Criticality Safety practitioners.

96 KNOWLEDGE MANAGEMENT AND PRESERVATION↗
DOE OSTI2016

MO-DE-BRA-05: EUTEMPE-RX: Combining E-Learning and Face-To-Face Training to Build Expert Knowledge, Skills and Competences for Medical Physicists in Diagnostic and Interventional Radiology

Purpose: In 2013, the EURATOM authorities of the European Commission decided to support the Horizon2020 project submission ‘EUTEMPE-RX’ that aimed for a new set of course modules to train medical physicists in diagnostic and interventional radiology to expert level with small group deep learning. Each module would consist of 2 phases: an e-learning and a face-to-face phase, each phase requiring typically 40h of participant time. Methods: The European Federation (EFOMP) and 13 European partners, all of them selected for their excellent scientific and/or educational skills, led the 12 course modules. A quality manual ensured the quality of course content and organization. Educational workshops familiarized the teachers with e-learning techniques and methods for assessment. Content was set in accordance with the EC document RP174 that lists learning outcomes in terms of knowledge, skills and competences (KSCs) for different specialties and levels of medical physics. Surveys for stake holder satisfaction were prepared. Results: Today the course modules are being realized. The modules cover most of the KSCs in RP174 document. Teachers have challenged the participants with unique tasks: case studies in medical physics leadership, Monte Carlo simulation of a complete x-ray imaging chain, development of a task specific QA protocol, compilation of optimization plans, simulation tasks with anthropomorphic breast models, etc. Participants undertook practical sessions in modern hospitals and visited a synchrotron facility, a calibration lab, screening organizations, etc. Feedback form quality surveys was very positive and constructive. A sustainability plan has been worked out. Conclusion: The modules have enabled the participants to develop their KSCs and cope with challenges in medical physics. The sustainability plan will be implemented to continue the unique combined e-learning and face to face training at high level training in diagnostic and interventional radiology also beyond Europe. The EUTEMPE-RX project is funded by the Horizon2020 - EURATOM program of the European Commission.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Development and Testing of Techniques for In-Ground Stabilization, Size Reduction and Safe Removal of Radioactive Wastes Stored in Large Containments in Burial Grounds - 13591

Radioactive waste materials, including Transuranic (TRU) wastes from laboratories have been stored below ground in large containments at a number of sites in the US DOE Complex, and at nuclear sites in Europe. These containments are generally referred to as caissons or shafts. The containments are in a range of sizes and depths below grade. The caissons at the DOE's Hanford site are cylindrical, of the order of 2,500 mm in diameter, 3,050 mm in height and are buried about 6,000 mm below grade. One type of caisson is made out of corrugated pipe, whereas others are made of concrete with standard re-bar. However, the larger shafts in the UK are of the order of 4,600 mm in diameter, 53,500 mm deep, and 12,000 below grade. This paper describes the R and D work and testing activities performed to date to evaluate the concept of in-ground size reduction and stabilization of the contents of large containments similar to those at Hanford. In practice, the height of the Test Facility provided for a test cell that was approximately 22' deep. That prevented a 'full scale mockup' test in the sense that the Hanford Caisson configuration would be an identical replication. Therefore, the project was conducted in two phases. The first phase tested a simulated Caisson with surrogate contents, and part of a Chute section, and the second phase tested a full chute section. These tests were performed at VJ Technologies Test Facility located in East Haven, CT, as part of the Proof of Design Concept program for studying the feasibility of an in-situ grout/grind/mix/stabilize technology for the remediation of four caissons at the 618-11 Burial Ground at US Department of Energy Hanford Site. The test site was constructed such that multiple testing areas were provided for the evaluation of various tools, equipment and procedures under conditions that simulated the Hanford site, with representative soils and layout dimensions. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

The SRNL technical assistance program: transferring lessons learned from two decades of remedial successes to the DOE complex - 15438

The Savannah River Site has an established history of developing implementable risk reduction strategies, developing and deploying innovative technological solutions, and collaboratively achieving realistic and protective environmental end states for complex environmental problems. Part of this success results from the strong historical collaboration between site environmental restoration groups and the Savannah River National Laboratory which results in the promulgation of innovative technical approaches and technologies from the laboratory to ongoing remediation campaigns. Much of the underlying research and development effort was funded by DOE's Office on Environmental Management through a series of applied technology demonstration projects (Integrated Demonstration Project, Integrated Programs and the Applied Field Research Site). Concomitant with the research efforts, SRNL has managed a dynamic and efficient national program that provides teams of technical experts with a broad experience base to recommend strategies that reduce risk and/or technical uncertainty for challenging environmental problems at other DOE facilities. At many of these sites, standard remedial approaches (e.g., excavation, pump and treat, soil vapor extraction) have either failed or proved to be too costly, inadequate, or ineffective. Alternatively, other sites struggle with implementation of innovative but less well understood approaches. The technical assistance teams use a structured process that based on several basic concepts, specifically, development of site specific technical frameworks, and careful matching of remedies to site-specific chemical, geological and physical conditions. Development of technical frameworks is a key strategy to apply basic science to an applied field problem. When directed toward understanding complex real-world environmental remediation challenges, frameworks are tools that support practical identification and incorporation of the key-controlling scientific processes and principles. Frameworks can also be used to minimize technical risks, encourage efficiency and effectiveness, and provide the basis for innovative and creative solutions. Efficient and effective environmental cleanup also requires matching the character of remediation and stabilization methods to the nature of the target zone of contamination as the nature of the target zone evolves through the life of the remedial project. A contaminant plume can be divided into the following zones: the source zone, the impact zone, and the transitional zone that then can be used to identify classes of technologies that are appropriate to that zone. For example, physical and chemical methods (e.g., trapping, immobilization, destruction, or isolation) that directly address the source contaminants are often appropriate for the disturbed zone during the remedial process. A variety of methods that include both active treatments (e.g., pump and treat or active bioremediation) and enhanced attenuation technologies (e.g., geochemical manipulation or reactive barriers) are often suitable for the primary contamination zone or impact zone. Various strategies based on natural attenuation processes may be applicable to the primary contamination zone and these methods are typically applied for the transition or baseline portions of the plume. Careful matching of remedies to site-specific conditions is critical to long-term success in environmental cleanup and restoration. The matching process facilitates selection of technologies with particular strengths that align with real-world needs and constraints, encourages strategic use of multiple or combined technologies to address major plume sub-domains, and supports transitioning technologies in space and time as remediation progresses. Since 2006, the SRNL Technical Assistance program has focused on providing support across the DOE complex. During this time, over 25 teams have visited eleven DOE sites and made recommendations that yielded an estimated cost savings of $100 M. Examples will be provided that illustrate key aspects and significant successes of the technical assistance program. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

OpenACC Unified Programming Environment for Multi-hybrid Acceleration with GPU and FPGA

Accelerated computing in HPC such as with GPU, plays a central role in HPC nowadays. However, in some complicated applications with partially different performance behavior is hard to solve with a single type of accelerator where GPU is not the perfect solution in these cases. We are developing a framework and transpiler allowing the users to program the codes with a single notation of OpenACC to be compiled for multi-hybrid accelerators, named MHOAT (Multi-Hybrid OpenACC Translator) for HPC applications. MHOAT parses the original code with directives to identify the target accelerating devices, currently supporting NVIDIA GPU and Intel FPGA, dispatching these specific partial codes to background compilers such as NVIDIA HPC SDK for GPU and OpenARC research compiler for FPGA, then assembles binaries for the final object with FPGA bitstream file. In this paper, we present the concept, design, implementation, and performance evaluation of a practical astrophysics simulation code where we successfully enhanced the performance up to 10 times faster than the GPU-only solution.

Boku, Taisuke↗
DOE OSTI2017

Nonlinear Methods for Current Limit Constraint Satisfaction in Tokamak Plasma Shape Control

The DIII-D tokamak is capable of supporting a wide variety of plasma equilibria because of its relatively large number of coils and their proximity to the plasma. To support its advanced tokamak mission, the DIII–D experimental program continues to push the envelope of this capability, frequently encountering limits imposed by allowable currents in poloidal shaping coils. Violation of current constraints is presently dealt with by operator adjustment of control targets and gains between plasma discharges. At the same time, demands for more precise and stable control have motivated efforts to develop and install advanced multivariable algorithms for control of plasma shape in DIII-D and other devices. Further, there is currently no way to ensure respect of nonlinear current constraints in a multivariable linear controller design and no practical way to manually tune these fully coupled controllers between discharges after installation. Various linear minimization schemes can be implemented to encourage currents to remain within limits, but adherence to these limits cannot be guaranteed by linear methods alone. In this paper, we describe ongoing efforts to provide methods that guarantee currents will not exceed preset limits, and that simultaneously achieve the best obtainable quality of control subject to current limit constraints.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Scoping Study Using Randomized Controlled Trials to Optimize Small Buildings' and Small Portfolios' (SBSP) Energy Efficiency Programs

This report is an initial step in determining whether randomized controlled trials (RCTs) should be used by the U.S. Department of Energy (DOE), utilities, and others to optimize energy efficiency programs targeting the small buildings and small portfolios (SBSPs) community. This scoping study reviews the use of RCTs to evaluate consumer purchasing and decision-making behaviors and to inform energy-efficient decision making. The scoping study discusses the relevant work, gaps in existing work, and potential value in pursuing further RCTs as related to energy-efficiency decision making in the SBSPs community. Our findings show that the factors that drive consumer behavior toward the purchasing of green products or energy efficiency programs remain complex, requiring further study of the underlying behavior mechanisms leading to environmental concern and action. Although small- and medium-sized businesses may share some purchasing behaviors with individual consumers and large commercial portfolios, important differences should be considered. Factors that are relevant to businesses include firm size to determine economies of scale, regulation, age, and turnover of capital equipment. Marketing approaches to promote green services such as energy efficiency need to go beyond a conventional cost-benefit analysis to include the highlighting of the psychological benefits and delivery of practical benefits, such as energy efficiency.

Guzowski, Leah↗
DOE OSTI2013

Development of a Training Program for Commercial Building Technicians

This project focused on developing and deploying a comprehensive program of 22 training modules, including certification requirements, and accreditation standards for commercial building technicians, to help achieve the full savings potential of energy efficient buildings, equipment, and systems. This curriculum extended the currently available commercial building technician programs -- training a labor force in a growing market area focused on energy efficiency. The program helps to remove a major market impediment to low energy/zero energy commercial building system acceptance, namely a lack of operating personnel capable of handling more complex high efficiency systems. The project developed a training curriculum for commercial building technicians, with particular focus on high-efficiency building technology, and systems. In Phase 1, the project team worked collaboratively in developing a draft training syllabus to address project objectives. The team identified energy efficiency knowledge gaps in existing programs and plans and plans to address the gaps with either modified or new curricula. In Phase 2, appropriate training materials were developed to meet project objectives. This material was developed for alternative modes of delivery, including classroom lecture materials, e-learning elements, video segments, exercises, and hands-on training elements. A Certification and Accreditation Plan and a Commercialization and Sustainability Plan were also investigated and developed. The Project Management Plan was updated quarterly and provided direction on the management approaches used to accomplish the expected project objectives. GTI project management practices tightly coordinate project activities using management controls to deliver optimal customer value. The project management practices include clear scope definition, schedule/budget tracking, risk/issue resolution and team coordination.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2017

ROS-DOE: Leveraging Open-Source Robotics Software for the DOE-EM Mission? - 17181

In order to establish a common software framework for its robotic systems, the United States Department of Energy - Environmental Management (DOE-EM) is considering the possibility of extending the Robot Operating System (ROS) open source robotics software to address the varied, complex challenges facing DOE-EM. The effort, preliminarily called ROS-DOE, would enhance the reliability, robustness, security, and user friendliness of ROS to meet the requirements of the nuclear waste remediation mission, and those of DOE as a whole. As envisioned, the ROS DOE program would also support rapid progress to mature cross-cutting capabilities including supervised autonomy, inter-operability with off-the-shelf industrial equipment, and physics-based robot simulation (i.e., Gazebo). This paper provides background context about the current state of ROS software and its supporting community, surveys DOE-EM needs and requirements for robotic solutions, and analyzes the gaps between the current state of ROS and those needed for DOE-EM robotics. It then identifies new capabilities that are recommended for ROS-DOE and outlines software development practices that could be leveraged to blend the best of the open-source world with high-reliability software development practices. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

White Paper: Research & Development for the Time at Temperature Approach

Recent advancements in nuclear power research are greatly improving reactor safety and performance through the development of Accident Tolerant Fuel (ATF) and Low-Enriched Uranium Plus (LEU+). These innovations can address Departure from Nucleate Boiling (DNB) margins, which are vital for reactor safety. DNB happens when the coolant switches to film boiling, significantly decreasing heat transfer and posing a risk of fuel cladding failure. The U.S. Nuclear Regulatory Commission (NRC) employs conservative DNB criteria, which can potentially restrict the operational flexibility and efficiency of reactors. The Time at Temperature (TaT) approach could provide a more detailed and adaptable operational guideline by establishing acceptable time-temperature limits, accounting for the duration a material can withstand elevated temperatures without losing its integrity. This method allows reactors to operate more efficiently and safely, offering additional operational margins, faster power adjustments, and improved fuel cycle economics. TaT criteria allow for higher power levels and more flexible responses to operational transients, particularly applicable for anticipated operational occurrences (AOOs) that result in short durations of post-DNB conditions. It enhances plant operational flexibility, allows faster startup times, and enables quicker power level adjustments, optimizing fuel loading patterns and improving fuel cycle economics. Implementing TaT limits reduces core design constraints, lowers fuel usage, and reduces costs, essential for the long-term sustainability of Light Water Reactors (LWRs). TaT maximizes the use of advanced fuel technologies like ATF and LEU+, further enhancing their economic and environmental benefits. To apply the TaT approach in existing LWRs, collaborative research activities among various DOE-sponsored programs are essential. These efforts should incorporate fuel experiments, physics-based high-fidelity modeling, ML-based surrogate modeling, and optimization techniques. This whitepaper proposes four research and development areas: 1) Investigation of the feasibility of new operations of LWR with updated safety limits; 2) Assessment of reactor operation limits through uncertainty reduction; 3) Evaluation of power uprate in virtual environment; and 4) Lattice and reactor core design for power uprate. Each area includes why this research is in need and a suggested scope of work. These comprehensive research areas ensure practical and beneficial advancements for existing reactors, translating innovations in nuclear fuel and cladding technology into improved reactor performance and safety.

42 - ENGINEERING↗
DOE OSTI2020

Inner Engineering Practices and Advanced 4-day Isha Yoga Retreat Are Associated with Cannabimimetic Effects with Increased Endocannabinoids and Short-Term and Sustained Improvement in Mental Health: A Prospective Observational Study of Meditators

Anxiety and depression are common in the modern world, and there is growing demand for alternative therapies such as meditation. Meditation can decrease perceived stress and increase general well-being, although the physiological mechanism is not well-characterized. Endocannabinoids (eCBs), lipid mediators associated with enhanced mood and reduced anxiety/depression, have not been previously studied as biomarkers of meditation effects. Our aim was to assess biomarkers (eCBs and brain-derived neurotrophic factor [BDNF]) and psychological parameters after a meditation retreat. Methods. This was an observational pilot study of adults before and after the 4-day Isha Yoga Bhava Spandana Program retreat. Participants completed online surveys (before and after retreat, and 1 month later) to assess anxiety, depression, focus, well-being, and happiness through validated psychological scales. Voluntary blood sampling for biomarker studies was done before and within a day after the retreat. The biomarkers anandamide, 2-arachidonoylglycerol (2-AG), 1-arachidonoylglycerol (1-AG), docosatetraenoylethanolamide (DEA), oleoylethanolamide (OLA), and BDNF were evaluated. Primary outcomes were changes in psychological scales, as well as changes in eCBs and BDNF. Results. Depression and anxiety scores decreased while focus, happiness, and positive well-being scores increased immediately after retreat from their baseline values (P < 0.001). All improvements were sustained 1 month after BSP. All major eCBs including anandamide, 2-AG, 1-AG, DEA, and BDNF increased after meditation by > 70% (P < 0.001). Increases of ≥20% in anandamide, 2-AG, 1-AG, and total AG levels after meditation from the baseline had weak correlations with changes in happiness and well-being. Conclusions. A short meditation experience improved focus, happiness, and positive well-being and reduced depression and anxiety in participants for at least 1 month. Participants had increased blood eCBs and BDNF, suggesting a role for these biomarkers in the underlying mechanism of meditation. Meditation is a simple, organic, and effective way to improve well-being and reduce depression and anxiety.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Progress in Monitoring Strategies for Risk Reduction in Geologic CO2 Storage

Abstract: This geophysical monitoring review is intended to lay the ground work for an approach to integrating monitoring strategies with risk assessment and risk reduction and to summarize work conducted by U.S. Department of Energy's National Risk Assessment Partnership (NRAP) participants that addresses key questions related to monitoring strategies. Commercial, demonstration and pilot geologic CO2 storage (GCS) projects have provided a wealth of practical experience in monitoring technologies. In this manuscript we review a few key projects, specific geophysical methods, well-based methods, geophysical workflows and some suggested best practices. These practices are often driven and governed by regulatory requirements (e.g. U.S. Environmental Protection Agency [US-EPA] Class VI underground injection regulation) and the need for effective reservoir management of pressures and volumes as well as the site-specific risks to containment, plume migration, and underground sources of drinking water. Reducing uncertainty in monitoring is likely to lead to reducing uncertainty in risk. One of our conclusions is the need for field experiment testing that is risk-driven. It is notable that GCS pilot projects have been designed for safe storage, and to date they have been successful. Technical challenges at all geologic CO2 storage sites include assuring injectivity and capacity predictions are reliable, the fate and subsurface topology of the CO2 plume is acceptable, regulatory permitting and compliance are accomplished in a timely manner, needed business assurances are supported by quantitative technical data, and the storage operation is acceptable to stakeholders. There is risk associated with all of these challenges necessitating a monitoring program utilizing both direct and indirect monitoring methods. Because of the direct association of risk and monitoring in GCS, geophysical monitoring is viewed as a key component in approaching risk assessment. To address monitoring in the context of risk assessment the U.S. Department of Energy's National Risk Assessment Partnership (NRAP) has undertaken a review of work related to monitoring storage sites. In this review we provide a framework for monitoring and then present some specific monitoring tools that may be useful for regulatory compliance, as well as technologies that are applicable to leakage detection.

Harbert, William↗
DOE OSTI2022

How deep to dig: effects of web-scraping search depth on hyperlink network analysis of environmental stewardship organizations

Abstract Social network analysis (SNA) tools and concepts are essential for addressing many environmental management and sustainability issues. One method to gather SNA data is to scrape them from environmental organizations’ websites. Web-based research can provide important opportunities to understand environmental governance and policy networks while potentially reducing costs and time when compared to traditional survey and interview methods. A key parameter is ‘search depth,’ i.e., how many connected pages within a website to search for information. Existing research uses a variety of depths and no best practices exist, undermining research quality and case study comparability. We therefore analyze how search depth affects SNA data collection among environmental organizations, if results vary when organizations have different objectives, and how search depth affects social network structure. We find that scraping to a depth of three captures the majority of relevant network data regardless of an organization’s focus. Stakeholder identification (i.e., who is in the network) may require less scraping, but this might under-represent network structure (i.e., who is connected). We also discuss how scraping web-pages of local programs of larger organizations may lead to uncertain results and how our work can combine with mixed methods approaches.

Sayles, Jesse S. (ORCID:0000000218378920)↗
DOE OSTI2014

On the spin separation of algebraic two-component relativistic Hamiltonians: Molecular properties

The idea for separating the algebraic exact two-component (X2C) relativistic Hamiltonians into spin-free (sf) and spin-dependent terms [Z. Li, Y. Xiao, and W. Liu, J. Chem. Phys. 137, 154114 (2012)] is extended to both electric and magnetic molecular properties. Taking the spin-free terms (which are correct to infinite order in α ≈ 1/137) as zeroth order, the spin-dependent terms can be treated to any desired order via analytic derivative technique. This is further facilitated by unified Sylvester equations for the response of the decoupling and renormalization matrices to single or multiple perturbations. For practical purposes, explicit expressions of order α{sup 2} in spin are also given for electric and magnetic properties, as well as two-electron spin-orbit couplings. At this order, the response of the decoupling and renormalization matrices is not required, such that the expressions are very compact and completely parallel to those based on the Breit-Pauli (BP) Hamiltonian. However, the former employ sf-X2C wave functions, whereas the latter can only use nonrelativistic wave functions. As the sf-X2C terms can readily be interfaced with any nonrelativistic program, the implementation of the O(α{sup 2}) spin-orbit corrections to sf-X2C properties requires only marginal revisions of the routines for evaluating the BP type of corrections.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Performance House: A Cold Climate Challenge Home, Old Greenwich, Connecticut (Fact Sheet)

By working with builder partners on test homes, researchers from the U.S. Department of Energy's Building America program can vet whole-house building strategies and avoid potential unintended consequences of implementing untested solution packages on a production scale. To support this research, Building America team Consortium for Advanced Residential Buildings (CARB) partnered with Preferred Builders Inc. on a high-performance test home in Old Greenwich, Connecticut. The philosophy and science behind the 2,700 ft2 "Performance House" was based on the premise that homes should be safe, healthy, comfortable, durable, efficient, and adaptable to the needs of homeowners. The technologies and strategies used in the "Performance House" were best practices rather than cutting edge, with a focus on simplicity in construction, maintenance, and operation. Achieving 30% source energy savings compared with a home built to the 2009 International Energy Conservation Code in the cold climate zone requires that nearly all components and systems be optimized. Careful planning and design are critical. The end result was a DOE Challenge Home that achieved a Home Energy Rating System (HERS) Index Score of 20 (43 without photovoltaics [PV]).

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

PIPER: Performance Insights for Programmers and Exascale Runtimes

During the lifetime of the project, the PIPER at the University of Utah worked in collaboration with the team from the partner institutions to establish a set of software tools for analyzing and improving the performance parallel computing tools. These activities complement and complete the work performed by the other X-Stack 2 projects with the definition of a common data models and computing infrastructures, which have been a central element in the targeted performance analysis pipeline and new programming models. The University of Utah team have focused mainly on developing data analysis and visualization systems to facilitate exploration, comparison and evaluation of the behavior and performance of complex algorithms in modern HPC infrastructures. This is involved several demonstrations of the performance achieved and presentation of the results in a way that facilitates the users understand bottlenecks and ways to overcome them. One major focus of the University of Utah activities has been the analysis of the performance characteristics of Fat-Tree and Dragonfly topology networks. The work involved the development of practical visualization systems especially in collaboration with the team at LLNL, and published several papers and gave invited talks at prestigious venues such as the Salishan Conference on High-Speed Computing or the International Conference on High Performance Computing, Data, and Analytics. In addition, the university of Utah team has advanced the core activities on analyzing the performance characteristics of I/O and other data movement systems and their practical use for scaling Uintah and other simulation codes poised for use in the exascale computing environments of the future.

42 ENGINEERING↗
DOE OSTI2025

Wafer-Free Crystalline Silicon Solar Cells (CRADA Final Report)

This CRADA project, based on the DOE Solar Energy Technologies Office (SETO) Solar Prize Voucher program, helped Leap Photovoltaics to develop methodologies to immobilize Si particles by permanently attaching them to an Al-coated substrate and thereby forming carrier-selective electrical contacts to the Si particles. The bigger goal was to help Leap Photovoltaics develop these immobilized and contacted particle arrays into relatively efficient, inexpensive, and industrially relevant solar cells. By using Si particles instead of wafers in a solar cell absorber layer, one can avoid costs associated with growing monocrystalline Si ingots, then diamond-sawing them into wafers, then processing wafers into cells – a mainstream practice in today's high-efficiency Si cell and module technology. Monocrystalline or polycrystalline Si particles can be obtained in various ways: for example, Si kerf from wafer sawing is monocrystalline; recycled Si cell wafers can be ball-milled into particles; particles can be grown using various gas-phase techniques (mostly from SiH4). These Si particles can be assembled onto a substrate and serve as an absorber layer for the solar cell, absorbing photons to generate photocarriers. The challenge with this technique is to collect photocarriers from individual Si particles, with separation of photogenerated electrons to the negative cell’s electrode and positive photogenerated holes to the positive electrode. Therefore, each particle must have two isolated, carrier-selective contacts: one for electrons and one for holes. Plus, particles need to be immobilized onto a solid substrate. The goal of this work was focused on the immobilization of Si particles and creating hole-selective contact to them at the same time, using industrially relevant Si photovoltaic (PV) cell technology: screen printing of Al back-surface field electrodes. This is used in the mainstream Propane Education and Research Council (PERC) technology for hole-collecting contacts at the back of the cell. The work performed at NREL consisted of screen printing of Al metal paste on substrates, spreading Si particles onto it, and thermally processing the structures to form hole-collecting contacts. The final structures were investigated by scanning electron microscopy (SEM) after focused ion beam (FIB) cross-sectioning and polishing. The work was done jointly by NREL staff and Leap Photovoltaics (Leap PV) employees stationed at NREL. The samples were then taken to Leap PV for further processing. Training the Leap PV employee on various NREL techniques (laser cutting, screen printing, thermal processing, characterization) was part of the scope.

14 SOLAR ENERGY↗