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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Process Design and Economics for the Conversion of Lignocellulosic Biomass to Hydrocarbon Fuels and Coproducts: 2018 Biochemical Design Case Update; Biochemical Deconstruction and Conversion of Biomass to Fuels and Products via Integrated Biorefinery Pathways

Over the past decade, NREL conducted a campaign to quantify the economic implications associated with observed and future targeted performance for the biochemical conversion of corn stover to ethanol through techno-economic modeling. This report serves as an update to the biological sugar conversion approach, reflecting modifications to underlying conversion operational strategies, as well as refinements to the techno-economic model details. In addition, the report includes a more quantitative focus on envisioned processing requirements for achieving final fuel cost goals moving further into the future, via inclusion of value-added coproducts.

09 BIOMASS FUELS↗
DOE OSTI2019

High Performance Anion Exchange Membrane Fuel Cells Enabled by Fluoropoly(olefin) Membranes

Abstract Although the peak power density of anion exchange membrane fuel cells (AEMFCs) has been raised from ≈0.1 to ≈1.4 W cm −2 over the last decade, a majority of AEMFCs reported in the literature have not been demonstrated to achieve consistently high performance and steady‐state operation. Poly(olefin)‐based AEMs with fluorine substitution on the aromatic comonomer show considerably higher dimensional stability compared to samples that do not contain fluorine. More importantly, fluorinated poly(olefin)‐based AEMs exhibit high hydroxide conductivity without excessive hydration due to a new proposed mechanism where the fluorinated dipolar monomer facilitates increased hydroxide dissociation and transport. Using this new generation of AEMs, a stable, high‐performance AEMFC is operated for 120 h. When the fuel cell configuration is subjected to a constant current density of 600 mA cm −2 under H 2 /O 2 flow, the cell voltage declines only 11% (from 0.75 to 0.67 V) for the first 20 h during break‐in and the cell voltage loss is low (0.2 mV h −1 ) over the subsequent 100 h of cell testing. The ease of synthesis, potential for low‐cost commercialization, and remarkable ex situ properties and in situ performance of fluoropoly(olefin)‐based AEM renders this material a benchmark membrane for practical AEMFC applications.

Zhu, Liang↗
DOE OSTI2019

Carbon-Based Metal-Free ORR Electrocatalysts for Fuel Cells: Past, Present, and Future

Replacing precious platinum with earth-abundant materials in fuel cells for oxygen reduction reaction (ORR) has been the objective worldwide for several decades. In last ten years, the carbon-based metal-free ORR electrocatalysts is the fastest-growing branch in this area. Great progresses have been made in promoting the performance and understanding the underlying ORR process. This article presents a comprehensive review of this filed by emphasizing on the emerging issues such as the design and controllable construction of porous structures and doping configurations, mechanistic understanding from the model catalysts and the combined experimental and theoretical studies, and more importantly, the performance evaluation in a full cell. Centering these topics, the most up-to-date results are presented, along with the remarks and perspectives for the future development of carbon-based metal-free ORR electrocatalysts.

Yang, Lijun↗
DOE OSTI2019

PGM-free Cathode Catalysts for PEM Fuel Cells: a Mini-Review on Stability Challenges

In recent years, significant progress has been achieved in the development of platinum group metal-free (PGM-free) oxygen reduction reaction (ORR) catalysts for proton exchange membrane (PEM) fuel cells. At the same time the limited durability of these catalysts remains a great challenge that needs to be addressed. In this mini-review, we summarize the recent progress in understanding the main causes of instability of PGM-free ORR catalysts in acidic environments, focusing on transition metal/nitrogen co-doped systems (M-N-C catalysts, M: Fe, Co, Mn). Of several possible degradation mechanisms, demetalation and carbon oxidation are found to be the most likely reasons for M-N-C catalysts/cathodes degradation.

Shao, Yuyan↗
DOE OSTI2017

Production of jet fuel precursor monoterpenoids from engineered Escherichia coli : Production of Jet Fuel Precursor Monoterpenoids

Monoterpenes (C 10 isoprenoids) are the main components of essential oils and are possible precursors for many commodity chemicals and high energy density fuels. Monoterpenes are synthesized from geranyl diphosphate (GPP), which is also the precursor for the biosynthesis of farnesyl diphosphate (FPP). FPP biosynthesis diverts the carbon flux from monoterpene production to C 15 products and quinone biosynthesis. In this study, we tested a chromosomal mutation of Escherichia coli's native FPP synthase (IspA) to improve GPP availability for the production of monoterpenes using a heterologous mevalonate pathway. Monoterpene production at high levels required not only optimization of GPP production but also a basal level of FPP to maintain growth. The optimized strains produced two jet fuel precursor monoterpenoids 1,8-cineole and linalool at the titer of 653 mg/L and 505 mg/L, respectively, in batch cultures with 1% glucose. The engineered strains developed in this work provide useful resources for the production of high-value monoterpenes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Hydrothermal Corrosion of SiC Materials for Accident Tolerant Fuel Cladding with and Without Mitigation Coatings

As a candidate material for accident-tolerant fuel cladding for light water reactors (LWR), SiCf–SiC composite materials possess many attractive properties. However, prior work has shown that SiC is susceptible to aqueous dissolution in LWR coolant environments. To address this issue, candidate coatings have been developed to inhibit dissolution. For this study, CVD SiC samples were prepared with Cr, CrN, TiN, ZrN, NiCr, and Ni coatings. Uncoated SiC and SiCf–SiC samples were also prepared. The samples were exposed for 400 h in 288 °C water with 2 wppm DO in a constantly-refreshing autoclave to simulate BWR–NWC. Cr and Ni coated samples lost less mass than the uncoated SiC sample, indicating an improvement in performance. The CrN coating resisted oxidation, but some of the coating was lost due to poor adhesion. The TiN coated sample gained significant mass due to oxidation of the coating. ZrN and NiCr coatings showed significant corrosion attack. SiCf–SiC ceramic matrix composite materials dissolved much faster than the CVD SiC sample, demonstrating the need for mitigation coatings if CMCs are to be used in LWRs. This work demonstrates the promise of Cr, Ni and CrN coatings for corrosion mitigation in LWRs, and shows that NiCr and ZrN are not promising coating materials.

Raiman, Stephen S.↗
DOE OSTI2021

Fuel Cycle Considerations for Uranium, Plutonium and Minor Actinide Partitioning and Transmutation

This paper is written in memorial of the authors' past collaborations with Max Salvatores in the area of advanced nuclear fuel cycle evaluation. In this regard, a summary is provided of the results from two international studies led by Max Salvatores in which the authors participated: (1) the expert group on Homogeneous versus Heterogeneous Recycling of Transuranics in Fast Nuclear Reactors, and (2) the expert group on Potential Benefits and Impacts of Advanced Nuclear Fuel Cycles with Actinide Partitioning and Transmutation. Both of these studies presented the authors with the opportunity to contribute the results of past and ongoing research in the U.S., facilitating engagement and discussion on these subjects with researchers from other countries and organizations, resulting in the creation of broad international views on the relative benefits and challenges of transuranic recycle (NEA, 2012a; NEA, 2012b), a testament to the leadership and capabilities of Max Salvatores. Published by Elsevier Ltd.

Taiwo, Temitope↗
DOE OSTI2020

Epsilon Metal: A Waste Form for Noble Metals from Used Nuclear Fuel

Epsilon metal (e-metal) is the metallic phase that forms as inclusions at the grain boundaries in the UO2 fuel during reactor operation. This metal is composed of Pd, Mo, Rh, Ru, and Tc. These metallic inclusions are insoluble in strong acid and remnants of these metallic inclusions have been found in the UO2 matrix that remains from the natural reactors in Gabon that were active 1.8 billion years ago, therefore e-metal should be an excellent waste form for the immobilization of the long-lived isotopes 107Pd (6.5 ? 106 a) and 99Tc (2.13 ? 105 a), with 99Tc being the isotope of interest for repository performance. Therefore, the chemical durability of this potential waste form is assessed in this study. Typically, corrosion rates for metallic materials are measured electrochemically because they are quick, inexpensive, and can reveal the mechanism by which a metal corrodes, at least initially. However, in a repository the waste form would be subjected to slowly flowing water without an applied electrical potential over long time periods. Therefore, the corrosion rates of e-metal specimens were measured with both electrochemical tests and the single-pass flow-through test (SPFT). Potentiodynamic and potentiostatic polarization results suggest that a thin passive film exists on the alloy surface, which seems to be responsible for its high corrosion resistance. Additionally, X-Ray photoelectron spectroscopic results suggest that Pd oxides are significantly enriched in the passive film Results from the SPFT show that the dissolution rates were weakly dependent on pH. Only Mo and Re were found in solution and were used for the calculation of the dissolution rates. In general, the electrochemically determined corrosion rates agree reasonably well with the initial dissolution rate measured with the SPFT test, but they are about one or two orders of magnitude higher than the steady state rates. The causes for this discrepancy are discussed.

epsilon-metal, nuclear waste form, corrosion, sing↗
DOE OSTI2020

Defect cluster and nonequilibrium gas bubble associated growth in irradiated UMo fuels – a cluster dynamics and phase field model

Irradiation examination shows that gas bubble swelling kinetics is much faster after irradiation-induced recrystallization than that prior recrystallization in UMo fuels. It implies that gas bubbles in coarse grains and small recrystallized grains have different growth behavior. In this work, a phase-field model of gas bubble evolution integrating microstructure dependent cluster dynamics has been developed, for the first time, to study the gas bubble swelling behavior in the recrystallization zone of UMo fuels. Generation, diffusion, reaction, sink, emission and clustering of vacancies and interstitials are described by the cluster dynamics model while a phase-field model is used to describe the evolution of non-equilibrium gas bubbles including nucleation and growth. With the coupled model, the effect of defect generation rate, clustering rate, interstitial emission and sink rates on grain boundaries on the gas bubble evolution are systematically simulated. A set of model parameters (defect generation rate, clustering rate, interstitial emission and sink rates) is determined by comparing measured and simulated gas bubble swelling kinetics. The results demonstrate that interstitial clustering is one of the important physical mechanisms which results in a fast gas bubble swelling kinetics in the recrystallization zone. The developed model can also be extended to study the associated growth of defect and second phase precipitates often observed in irradiated materials.

Hu, Shenyang↗
DOE OSTI2020

Nondestructive measurements of residual 235 U mass of Israeli Research Reactor-1 fuel using the Advanced Experimental Fuel Counter

In 2018, a measurement campaign took place with participants from Los Alamos National Laboratory (LANL), the Nuclear Research Centre-Negev (NRCN) and Soreq Nuclear Research Center (SNRC) at the Israeli Research Reactor-1 (IRR-1) in which 14 of the reactor’s used fuel assemblies (FAs) with varied amount of depletion were measured with the nondestructive assay instrument Advanced Experimental Fuel Counter (AEFC). Designed for safeguards purposes, the AEFC measures both neutrons emitted from the FA (passive neutrons) and fission neutrons induced by an external neutron source (in this experiment, 252 Cf). Signals recorded with the AEFC include total neutron count rates (Singles), time-correlated neutron count rates (Doubles), and total gamma-ray count rates. The 235 U content of the FAs was previously assessed by two independent methods: (1) measurement of the transparency of the FA to low-energy gamma rays from an activated rhenium source (rhenium gamma transmission, or the RGT method) and (2) calculation of the 30-year burnup history of the core using detailed three-dimensional Monte-Carlo core depletion calculations. The results from the FAs that had been measured via the RGT method were used to construct the calibration curves, which translate the AEFC count rates to 235 U mass. Then, the calibration was evaluated using AEFC measurements of six additional FAs that were not measured via the RGT method. From the results, it was determined the Doubles calibration curve was more reliable than that of the Singles and follows a simple second-order polynomial fit for the whole range of residual 235 U mass content, albeit with larger statistical uncertainty. Detailed uncertainties quantification was conducted for both the AEFC Singles and Doubles. This includes the analysis of statistical uncertainties, calibration uncertainty, and random uncertainties due to the sensitivity of the AEFC to several sources of uncertainty, namely the FA position, FA orientation, interrogation source position, and ambient pool temperature. Finally, an overall total uncertainty of 6 g of 235 U is estimated for the Singles and Doubles, which is mainly due to calibration uncertainty (for the Singles) and statistical uncertainty (for the Doubles), and which constitutes 3%–6% of the 235 U total mass in the FAs, depending on their level of depletion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Laser ablation spectrometry for studies of uranium plasmas, reactor monitoring, and spent fuel safety

Nuclear security is one of the defining challenges of our time. Nuclear threats range from deliberate dispersal of radioactive material to contaminate the vital infrastructure to diversion and smuggling of special nuclear material for clandestine nuclear programs and nuclear terrorism, respectively. There is an associated need to develop and sustain the nuclear forensics capabilities, which requires the understanding of complex processes that occur in plasmas of nuclear materials. The area of nuclear safety has seen a resurgence of public interest, and there is a concomitant need to safely store used nuclear fuel and detect structural material failure in nuclear power systems, especially in innovative reactor designs envisioned for future adoption. Laser-produced plasmas are complicated extreme environments that can generate intense and rich, highly specific signatures of nuclear and radiological materials, which can then be explored in a wide range of applications. They include interdiction and rapid detection of nuclear materials, including their isotopic composition, detection over long distances, laboratory simulation of weapons effects, monitoring the condition of structural materials in dry cask storage containers, and novel instrumentation for nuclear power systems. We present a compilation of recent representative examples of the application of laser spectroscopy, and laser-induced breakdown spectroscopy in particular, to nuclear safety and security problems. A case is made that spectroscopic techniques based on laser-produced plasmas offer complementary, and sometimes unique, capabilities that motivate the continued exploration of their efficient production and understanding of the signatures they produce

(020.3260) Isotope shifts, (140.3440) Laser-induce↗