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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 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Transient testing of uranium silicide fuel in zircaloy and silicon carbide cladding

Using the newly restarted Transient Reactor Test (TREAT) facility at Idaho National Laboratories, fresh (unirradiated) U 3 Si 2 fuel pellets were tested under reactivity-initiated accident conditions in dry helium capsules. These tests were performed with total energy depositions sufficient to induce melting of the U 3 Si 2 fuel pellets based on available thermophysical property data. The instrumented experiments utilized in-pile thermocouples and infrared pyrometers to measure the cladding temperature during the transient, which are in reasonable agreement with predicted peak cladding temperatures using a simple BISON fuel performance model. This same model is then used to predict expected cladding stresses during the transients in areas where pellet cladding interaction is expected. It was shown that for transient energy depositions up to 528J/g rod like geometry of the test articles was maintained. While it is acknowledged that more confirmatory testing is required in more prototypic environments, these first of their kind experiments have demonstrated that unirradiated U 3 Si 2 fuel and unirradiated SiC-SiC claddings can likely retain a “rod like” geometry for transient energy depositions up to 528J/g.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Long-term sorption and desorption of uranium in saprolite subsoil with nanoporous goethite

Long-term (2–3 months) batch U(VI) sorption-desorption experiments were conducted to understand the long-term sorption-desorption behavior of U(VI) in saprolite subsoils from Oak Ridge Field Research Center (ORFRC), Tennessee, which contained naturally occurring nanoporous goethite. Three subsoil samples containing a range of dithionite-citrate-bicarbonate (DCB) extractable Fe oxide content (7138, 11,161, and 22,582 mg Fe/kg) were used for the experiments. Sorption of 50 μM U(VI) to the subsoils in the presence of Ca 2+ and HCO 3 - at circumneutral pH occurred rapidly during the first 2 days, after which slow U(VI) sorption continued over 3 months. U(VI) desorption from the soils by 10 mM NaHCO 3 solution exhibited an initial fast desorption step during the first 24 h, followed by slower desorption over a week. Sorption of 50 μM U(VI) for 1 day to 3 months in the presence or absence of Ca 2+ consistently resulted in higher U(VI) sorption to saprolite soil with higher amount of nanoporous goethite, while desorption of U(VI) for 1 week to 2 months was consistently lower in saprolite soil with higher amount of nanoporous goethite. Saprolite subsoils containing higher amounts of nanoporous goethite exhibited more resistant U(VI) desorption, and the proportions of irreversible U(VI) sorption increased with longer residence time with soils. These results indicates that more U(VI) became bound to the internal surfaces of nanoporous iron oxides during long-term sorption. This study suggests that naturally occurring nanoporous goethite may exert a significant role in controlling the mobility and transport of U(VI) in historically contaminated sites that have existed over decades.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Seasonal progression of uranium series isotopes in subglacial meltwater: Implications for subglacial storage time

The residence time of subglacial meltwater impacts aquifer recharge, nutrient production, and chemical signals that reflect underlying bedrock/substrate, but is inaccessible to direct observation. We report the seasonal evolution of subglacial meltwater chemistry from the 2011 melt season at the terminus of the Athabasca Glacier, Canada. We also measured major and trace analytes and U-series isotopes for twenty-nine bulk meltwater samples collected over the duration of the melt season. This dataset, which is the longest time-series record of ( 234 U/ 238 U) isotopes in a glacial meltwater system, provides insight into the hydrologic evolution of the subglacial system during active melting. Meltwater samples, measured from the outflow, were analyzed for ( 238 U), ( 222 Rn) and ( 234 U/ 238 U)activity, conductivity, alkalinity, pH and major cations. Subglacial meltwater varied in [238U] and (222Rn) from 23 to 832 ppt and 9 to 171 pCi/L, respectively. Activity ratios of ( 234 U/ 238 U) ranged from 1.003 to 1.040, with the highest ( 238 U), ( 222 Rn) and ( 234 U/ 238 U)activity values occurring in early May when delayed-flow basal meltwater composed a significant portion of the bulk melt. Furthemore, from the chemical evolution of the meltwater, we posit that the relative subglacial water residence times decrease over the course of the melt season. This decrease in qualitative residence time during active melt is consistent with prior field studies and model-predicted channel switching from a delayed, distributed network to a fast, channelized network flow. As such, our study provides support for linking U-series isotopes to storage lengths of meltwater beneath glacial systems as subglacial hydrologic networks evolve with increased melting and channel network efficiency.

58 GEOSCIENCES↗
DOE OSTI2025

Accelerated and heterogeneous corrosion of Cr-doped uranium nitride fuel pellets

The steam oxidation of Cr-doped UN fuel pellets is analyzed during sequential isothermal holds up to 720 °C. In situ neutron diffraction results show how Cr is accommodated in a secondary U 2 CrN 3 phase, leading to the formation of a duplex UN/U 2 CrN 3 microstructure. Under corrosion, the oxidation of the two phases begins at 400 °C for UN and 430 °C for U 2 CrN 3 , respectively. Because the UN phase is preferentially oxidized in the presence of U 2 CrN 3 , addition of Cr in UN based nuclear fuel is found to accelerate the corrosion rate. At 430 °C the oxidation of UN in the UN/U 2 CrN 3 microstructure is ~ 5 times faster than pure UN, increasing to ~19 times faster at 460 °C. The oxidation of U 2 CrN 3 produces UO 2 via the formation of two transient intermediate phases. In situ neutron diffraction enables oxidation processes of UN and U 2 CrN 3 components to be followed separately within the two-phase system.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Homoleptic 1,2-benzenedithiolate complexes of thorium and uranium

Reaction of 4 equiv. of [Li(TMEDA)] 2 [1,2-S 2 C 6 H 4 ] with [ThCl 4 (DME) 2 ] or [UCl 4 (THF) 3 ] in THF results in formation of [Li(THF) 2 ] 4 [An(1,2-S 2 C 6 H 4 ) 4 ] (An = Th, 1; An = U, 2), whereas reaction of 4 equiv. of [Li(TMEDA)] 2 [1,2-S 2 C 6 H 4 ] with UCl 4 in Et 2 O results in formation of [Li(TMEDA)] 4 [U(1,2-S 2 C 6 H 4 ) 4 ] (3). Complexes 1–3 represent the first reported benzenedithiolate complexes of the actinides. Here, they were characterized by NMR spectroscopy and X-ray crystallography. In the solid state, complexes 1–3 exhibit triangular dodecahedral geometries about their actinide centers. Additionally, their Li + cations are bound by two sulfur atoms of adjacent [1,2-S 2 C 6 H 4 ] 2− ligands, in addition to two solvent donor atoms. In solution, complexes 2 and 3 exhibit spectral data consistent with S 4 symmetry (and non-exchanging Li + sites), whereas complex 1 exhibits spectral properties consistent with labile Li + cations.

X-ray↗
DOE OSTI2017

Ca(BH 4 ) 2 as a simple tool for the preparation of thorium and uranium metallocene borohydride complexes: First synthesis and crystal structure of (C 5 Me 5 ) 2 Th(η 3 -H 3 BH) 2

Here, calcium borohydride allows for the high-yielding synthesis of (C 5 Me 5 )2An(η 3 -H 3 BH) 2 (An = Th, U) by reaction with (C 5 Me 5 ) 2 AnCl 2 (An = Th, U). While a preparative synthesis of (C 5 Me 5 ) 2 U(η 3 -H 3 BH) 2 has been previously reported in the literature using K(C 5 Me 5 ) and U(BH 4 ) 4 , the use of Ca(BH 4 ) 2 is higher yielding and mild. Full characterization of the novel compound (C 5 Me 5 ) 2 Th(η 3 -H 3 BH) 2 is presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

A comparison of carbon impurities in pre- and post-melt uranium Part 2: Scanning/Transmission electron microscopy analysis

We report the speciation and morphology of U carbide inclusions in pre- and post-melt U metal have been explored using high-resolution analytical electron microscopy (AEM). This report presents Part 2 of our study, in which aberration (C s ) corrected transmission and scanning transmission electron microscopy (S)TEM was used to elementally and crystallographically characterize C-containing impurities and defect features in U samples for comparison with results obtained by scanning electron microscopy (SEM) in Part 1, previously published by this journal. Elemental mapping and unit cell matching of inclusions by (S)TEM are consistent with phases observed by SEM, and new dislocations can be observed associating with some inclusion morphologies and not others.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A comparison of carbon impurities in pre- and post-melt uranium Part 1: Scanning electron microscopy analysis

Although C impurities in U have been studied for decades, fundamental questions regarding their incorporation, migration, and overall transformation during metal processing still exist. In two written Parts, we compare the chemical speciation, distribution, crystallography, and morphologies (size, shape, etc.) of carbon-containing impurities in U metal both before and after melting using high resolution analytical electron microscopy (AEM). This first Part demonstrates the variability of carbide inclusions in depleted U (DU) metal with respect to their chemical phases and morphologies as observed by scanning electron microscopy (SEM). Here, a variety of inclusion types, such as the pill-shaped U monocarbide (UC), previously only hypothesized, are summarized. Additionally, delineation between hopper-shaped U carbonitride U(C,N) and dendritic UC inclusions is discussed in relationship to archived literature.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Diffusion and phase formation in the γ-uranium-technetium system

Phase formation in the U-Tc binary system at 800 °C was investigated using a diffusion couple experiment. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) identified four novel potential intermetallic phases - U 7 Tc 3 , U 13 Tc 12 , U 3 Tc 5 , and UTc 4 . Diffusion coefficients were calculated for the intermetallic phases using the Boltzmann-Matano method and were respectively found to be – 120, 38.2, 15.6, and 1.51 × 10 −18 m 2 /s. Tc also exhibits a solid-solution phase with high penetration into the U with a diffusion coefficient of ∼ 10 −14 m 2 /s. Furthermore, these findings expand the number of known U-Tc phases and provide the first diffusion coefficients for the U-Tc system, and contribute valuable data to the broader field of actinide metallurgy.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

Uncertainty analysis of multi-rate kinetics of uranium desorption from sediments

A multi-rate expression for uranyl [U(VI)] surface complexation reactions has been proposed to describe diffusion-limited U(VI) sorption/desorption in heterogeneous subsurface sediments. An important assumption in the rate expression is that its rate constants follow a certain type probability distribution. In this paper, a Bayes-based, Differential Evolution Markov Chain method was used to assess the distribution assumption and to analyze parameter and model structure uncertainties. U(VI) desorption from a contaminated sediment at the US Hanford 300 Area, Washington was used as an example for detail analysis. The results indicated that: 1) the rate constants in the multi-rate expression contain uneven uncertainties with slower rate constants having relative larger uncertainties; 2) the lognormal distribution is an effective assumption for the rate constants in the multi-rate model to simualte U(VI) desorption; 3) however, long-term prediction and its uncertainty may be significantly biased by the lognormal assumption for the smaller rate constants; and 4) both parameter and model structure uncertainties can affect the extrapolation of the multi-rate model with a larger uncertainty from the model structure. The results provide important insights into the factors contributing to the uncertainties of the multi-rate expression commonly used to describe the diffusion or mixing-limited sorption/desorption of both organic and inorganic contaminants in subsurface sediments.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2014

Influence of calcite on uranium(VI) reactive transport in the groundwater–river mixing zone

Calcite is an important mineral that can affect uranyl reactive transport in subsurface sediments. This study investigated the distribution of calcite and its influence on uranyl adsorption and reactive transport in the groundwater-river mixing zone at US Hanford 300A, Washington State. Simulations using a 2D reactive transport model under field-relevant hydrogeochemical conditions revealed a complex distribution of calcite concentration as a result of dynamic groundwater-river interactions. The calcite concentration distribution in turn affected the spatial and temporal changes in aqueous carbonate, calcium, and pH, which subsequently influenced U(VI) mobility and discharge rates into the river. The results implied that calcite distribution and its concentration dynamics is an important consideration for field characterization, monitoring, and reactive transport prediction.

calcite, surface complexation, uranium, reactive t↗
DOE OSTI2017

Mechanical properties examined by nanoindentation for selected phases relevant to the development of monolithic uranium-molybdenum metallic fuels

Nanomechanical properties, specifically the reduced modulus and hardness of several intermetallic and solid solution phases are reported here to assist the development of the U-10 wt% Mo (U-10Mo) monolithic fuel system for research and test reactors. Findings from this study and reported values of mechanical properties provide data critical for understanding and predicting the structural behavior of the fuel system during fabrication and irradiation. The phases examined are products of interdiffusion and reaction between (1) the AA6061 cladding and the Zr diffusion barrier, namely (Al,Si) 3 Zr and Al 3 Zr, (2) the U-10Mo fuel and the Zr diffusion barrier, namely UZr 2 , Mo 2 Zr, and a-U, and (3) the U (or U-10Mo) and Mo, namely a mixture gradient of α- and γ-phases. The UC inclusions observed within the fuel alloy were also examined. Only phases present in thick or continuous microstructure on cross-sectioned fuel plates and diffusion couples were investigated for reduced modulus and hardness. Concentration-dependence of room-temperature reduced modulus in U solid solution with 0–10 wt% Mo was semi-quantitatively modeled based on mixture of α- and γ-phases and solid solutioning within the γ-phase.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗