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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 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Elevation Change of the Greenland Ice Sheet: Reassessment

Elavation change measurements from satellite altimetry for the southern Greenland ice sheet (south 70 degrees north) are re-examined after incorporating technical advancements that significantly improve measurement accuracy.

Greenland Ice Sheet elevation change↗
DOE OSTI2019

Gamma Irradiation of Novel Optical Glasses at Elevated Temperature

Advanced Small Modular Reactors (AdvSMRs) are considered important future energy sources. However, in-vessel radiation fluxes are high and demands infrared (IR) optical fiberbased chemical sensing at temperatures that often exceed 400°C. This is a challenging environment for many current IR glasses, including covalently-bonded selenides and tellurides, such as As2Se3 and GeTe2, due their glass transition temperatures (Tg) being on the order of 200-350 °C. This work focuses on ?-irradiation affects at high temperatures on refractory ionic bonding based chalcogenide glasses in the BaS-La2S3-GeS2 system. Optical and selected physical properties were characterized before and after irradiation. It was found that both GeS2 and the 20BaS + 20La2S3 + 60GeS2 composition (in mole%) have minimal property changes when irradiated at 2.5 MGy cumulative dose at 300 °C. Sample density showed the largest characteristic change where densities initially decreased at 2 kGy dose, and then recovered at the highest dose of 2.5 MGy, resulting in an overall density change between 0.3 to 2%, depending on sample and composition. This work suggests the BaS-La2S3-GeS2 system as one for continued exploration as high temperature IR fiber sensors in radiation environments.

Gamma Irradiation, Novel Optical Glasses, Elevated↗
DOE OSTI2024

Elevated Temperature Graphite Mechanical Testing

High purity graphite will be used for core components within most High Temperature Reactor (HTR) designs. Several "high tech” industries currently utilize synthetic, high-purity, commercially available graphite components to fabricate photovoltaic cells, semi-conductors, optical fibers, and other high value electronic industry products. New advanced HTR designs are also interested in using these graphite grades for long-term, internal core component applications. Consequently, the US Department of Energy, Advanced Reactor Technologies (DOE-ART) program has spent several years testing different high purity graphite grades for potential use within these new nuclear reactor designs. A significant part of that effort has been in the development and improvement of American Society for Testing and Materials (ASTM) test standards specifically for nuclear graphite grades. Nearly all ASTM test standards have either been developed or improved by the DOE-ART program over the past 25 years. The ART program continues to assist in the development of new ASTM test standards in support of the future commercial HTR fleet currently being designed and built in the USA. The newest effort undertaken by ART is the development of high temperature mechanical testing practices that may be acceptable for a future ASTM test standard (or guide) for this critical material property measurement.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Summary of Alloy 617 and Alloy 709 Elevated Temperature Crack Growth Test Results from the Planned FY24 Crack Growth Test Activities

This report covers the results from crack growth rate testing performed at Idaho National Laboratory in the fiscal year 2024. It includes two creep crack growth rate tests and two creep-fatigue crack growth rate tests. Results are shown for each of these tests, included crack growth measured during the test using direct current potential drop, and measurements based off of the fracture surface. Load line displacement, as well as load, were also collected during the tests. Detailed analysis of the results will continue into the next fiscal year, however, a number of potential improvements to the equipment and testing procedures were identified that will increase testing reliability and throughput, as well as decrease complications with the analysis.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Anthropogenic pollution elevates the peak height of new particle formation from planetary boundary layer to lower free troposphere

New particle formation (NPF) and subsequent growth are primary sources of atmospheric aerosol particles and cloud condensation nuclei. Previous studies have been conducted in relatively clean environments; investigation of NPF events over highly polluted megacities is still lacking. Here in this paper we show, based on a recent yearlong aircraft campaign conducted over Beijing, China, from April 2011 to June 2012, that NPF occurrence peaks in the lower free troposphere (LT), instead of planetary boundary layer (PBL), as most previous studies have found and that the distance of NPF peak to PBL top increases with increasing aerosol loading. Further analysis reveals that increased aerosols suppress NPF in PBL, but enhance NPF in LT due to a complex chain of aerosol-radiation-photochemistry interactions that affect both NPF sources and sinks. These findings shed new light on our understanding of NPF occurrence, NPF vertical distribution, and thus their effects on atmospheric photochemistry, clouds, and climate.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Biocrust contribution to ecosystem carbon fluxes varies along an elevational gradient

Abstract Understanding how each component of an ecosystem contributes to carbon fluxes across a range of abiotic conditions enables accurate forecasts for future emission scenarios. In drylands, biological soil crust (biocrust) contribution to ecosystem carbon fluxes may vary at a regional scale but is rarely quantified due to the difficulty of parameterizing process‐based models or parsing biocrust (on the soil surface) from whole‐soil flux measurements. We measured excised biocrust carbon fluxes across current and future predicted warmer summertime temperatures from dryland sites (grassland, shrubland, savanna, and woodland) and compared those to the ecosystem and soil fluxes from eddy flux towers. Overall, biocrust fluxes showed net carbon loss during the warm growing season temperatures, suggesting that cool‐season photosynthesis is likely critical for maintaining positive biocrust carbon balance in these sites. Biocrust flux temperature responses differed by site: Grassland and shrubland biocrust gross photosynthesis was relatively invariant, while respiration increased with temperature; in the woodland and savanna, biocrust gross photosynthesis and respiration increased with temperature. Biocrust fluxes contributed <3% to the observed ecosystem gross primary productivity at 26°C and ecosystem respiration at 19°C in grassland, shrubland, and woodland, but contributed >10% of observed soil respiration in grassland and shrubland at 19°C, reinforcing the need to separate biocrust activity from root and subsurface heterotroph activity to understand drivers of fluxes at different sites. Regional resolution of biocrust type and cover will improve predictions of biocrust contribution to global carbon flux with changing temperatures.

54 ENVIRONMENTAL SCIENCES↗