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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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7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Mobility assessment of the BCC and carbide phases in the C-Nb, C-U and Nb-U systems

Uranium carbides with refractory metal additions are considered for Gen IV nuclear reactors and nuclear thermal propulsion as fuels for their high-temperature and corrosion resistant properties. Understanding kinetic effects that dictate microstructural evolution during fabrication and operating conditions is essential to advance technological development of these fuels. This work presents the development of an atomic mobility database for C-Nb-U systems based off available experimental data supported with ab-initio methods. The mobility assessments and uncertainty quantification (using Markov chain Monte Carlo) were conducted in the Kawin software. Carbon diffusion is considered dominant, as metal diffusion is much slower, with niobium diffusion being even slower and rate limiting than uranium metal. We provide a comprehensive and self-consistent thermo-kinetic database that is validated by diffusion couple simulations through Kawin. In conclusion, this enables prediction of microstructural and phase evolution critical for the development and lifetime assessment of next generation nuclear fuels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Structural basis for cloverleaf RNA-initiated viral genome replication

The genomes of positive-strand RNA viruses serve as a template for both protein translation and genome replication. In enteroviruses, a cloverleaf RNA structure at the 5' end of the genome functions as a switch to transition from viral translation to replication by interacting with host poly(C)-binding protein 2 (PCBP2) and the viral 3CD pro protein. We determined the structures of cloverleaf RNA from coxsackievirus and poliovirus. Cloverleaf RNA folds into an H-type four-way junction and is stabilized by a unique adenosine-cytidine-uridine (A•C-U) base triple involving the conserved pyrimidine mismatch region. The two PCBP2 binding sites are spatially proximal and are located on the opposite end from the 3CD pro binding site on cloverleaf. We determined that the A•C-U base triple restricts the flexibility of the cloverleaf stem–loops resulting in partial occlusion of the PCBP2 binding site, and elimination of the A•C-U base triple increases the binding affinity of PCBP2 to the cloverleaf RNA. Based on the cloverleaf structures and biophysical assays, we propose a new mechanistic model by which enteroviruses use the cloverleaf structure as a molecular switch to transition from viral protein translation to genome replication.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1993

Interband optical transitions between confined and unconfined states in quantum wells

The interband optical absorption in single quantum wells (SQWs) due to transitions between confined states and unconfined continuum states (C-U transitions) were measured, calculated, and compared to absorption due to transitions involving pairs of confined states (C-C transiitons). An In(0.25)Ga(0.75)As/GaAs SQW with a 61-A well width was used in the experiment. A simple model describes how the slow-turnon absorption line shapes characterisic of SQWs evolve into sharp steplike features as more wells are added.

Ksendzov, A.↗
DOE OSTI2020

Materials Data on UC2 by Materials Project

UC2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. U6+ is bonded in a 10-coordinate geometry to ten equivalent C3- atoms. There are two shorter (2.29 Å) and eight longer (2.58 Å) U–C bond lengths. C3- is bonded in a 2-coordinate geometry to five equivalent U6+ and one C3- atom. The C–C bond length is 1.38 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U2C3 by Materials Project

U2C3 is Plutonium carbide structured and crystallizes in the cubic I-43d space group. The structure is three-dimensional. U6+ is bonded in a 6-coordinate geometry to six equivalent C4- atoms. There are three shorter (2.44 Å) and three longer (2.53 Å) U–C bond lengths. C4- is bonded to four equivalent U6+ and one C4- atom to form a mixture of distorted edge and corner-sharing CU4C trigonal bipyramids. The C–C bond length is 1.44 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U3C by Materials Project

U3C is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. U is bonded in a distorted square co-planar geometry to four equivalent C atoms. All U–C bond lengths are 2.86 Å. C is bonded to twelve equivalent U atoms to form a mixture of face and corner-sharing CU12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on UC2 by Materials Project

UC2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. U6+ is bonded in a body-centered cubic geometry to eight equivalent C3- atoms. All U–C bond lengths are 2.33 Å. C3- is bonded to four equivalent U6+ atoms to form a mixture of edge and corner-sharing CU4 tetrahedra.

36 MATERIALS SCIENCE↗