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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Comparative Critical Mass Calculations for NNL and ENDF/B-VIII.0 Zirconium Hydride Thermal Neutron Scattering Laws

Zirconium hydride (ZrH x ) is a moderator material for TRIGA reactors and historical space reactor systems, such as SNAP-10A. Thermal neutron scattering laws (TSL) for two phases of this material, δ and ε, have been previously evaluated by Naval Nuclear Laboratory (NNL) and submitted to the National Nuclear Data Center (NNDC) for inclusion in the US national ENDF/B-VIII.1 nuclear data library. In contrast to the current ENDF/B-VIII.0 TSL evaluations, which consider only a single phase, the new evaluations are derived from separate ab initio calculations for both phases and include coherent elastic effects of the zirconium sublattice. To estimate the impact of these changes to the TSL evaluation of this material, comparative critical mass calculations were performed with MC21 for homogenous mixtures of high- enriched uranium (HEU) and ZrH x in bare and water reflected sphere configurations. These calculations yield an impact on the estimated critical mass as a function of 235 U loading density with maximum differences as large as 1% - 5% for over-moderated thermal spectrum systems. Consequently, the NNL TSL evaluations are anticipated to have a small impact on criticality calculations of thermal reactor systems regardless of the material phase. Nevertheless, characteristic differences exist in the predicted thermal spectra as function of energy for the two sets of TSL evaluations, which are attributed to difference in the underlying phonon density of states of hydrogen bound in ZrH x .

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Equivalent radiation damage in zirconium irradiated in various reactors - 2016-0101

The physical properties and in-reactor performance of core components made from zirconium alloys are a function of the radiation-induced atomic displacements that occur during service. The vacancy and interstitial point defects and their clusters created by the atomic displacements modify the microstructure, and therefore physical properties such as strength and ductility, by forming dislocation loops. The rate of production of point defects also affects time-dependent properties such as creep and diffusion (mass transport). To simulate the effect of irradiation on core components, researchers have used materials test reactors for many years to irradiate and test materials. Such reactor tests can target an accumulated displacement damage dose to simulate the state of a material at a given stage in reactor life but at an accelerated rate. Each nuclear reactor has a specific neutron energy spectrum that also depends on the in-reactor location. Therefore, to use test reactor data to determine the effect of radiation damage on power reactor materials, one must convert the accumulated dose into a unit that is common in its effect on the material properties. For many property changes in nuclear reactor cores, this unit is displacements per atom. This paper compares the damage production for zirconium irradiated under differing neutron energy spectra in various power and test reactors. The damage rates as a function of different measures of neutron flux were used to relate atomic displacements in various materials test reactors to CANDU and light-water reactor conditions. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2013

Modeling of Some Physical Properties of Zirconium Alloys for Nuclear Applications in Support of UFD Campaign

Zirconium-based alloys Zircaloy-2 and Zircaloy-4 are widely used in the nuclear industry as cladding materials for light water reactor (LWR) fuels. These materials display a very good combination of properties such as low neutron absorption, creep behavior, stress-corrosion cracking resistance, reduced hydrogen uptake, corrosion and/or oxidation, especially in the case of Zircaloy-4. However, over the last couple of years, in the post-Fukushima Daiichi world, energetic efforts have been undertaken to improve fuel clad oxidation resistance during off-normal temperature excursions. Efforts have also been made to improve upon the already achieved levels of mechanical behavior and reduce hydrogen uptake. In order to facilitate the development of such novel materials, it is very important to achieve not only engineering control, but also a scientific understanding of the underlying material degradation mechanisms, both in working conditions and in storage of used nuclear fuel. This report strives to contribute to these efforts by constructing the thermodynamic models of both alloys; constructing of the respective phase diagrams, and oxidation mechanisms. A special emphasis was placed upon the role of zirconium suboxides in hydrogen uptake reduction and the atomic mechanisms of oxidation. To that end, computational thermodynamics calculations were conducted concurrently with first-principles atomistic modeling.

42 ENGINEERING↗
DOE OSTI2020

Comparison of Hafnium Dioxide and Zirconium Dioxide Grown by Plasma-Enhanced Atomic Layer Deposition for the Application of Electronic Materials

We report the growth of nanoscale hafnium dioxide (HfO 2 ) and zirconium dioxide (ZrO 2 ) thin films using remote plasma-enhanced atomic layer deposition (PE-ALD), and the fabrication of complementary metal-oxide semiconductor (CMOS) integrated circuits using the HfO 2 and ZrO 2 thin films as the gate oxide. Tetrakis (dimethylamino) hafnium (Hf[N(CH 3 ) 2 ] 4 ) and tetrakis (dimethylamino) zirconium (IV) (Zr[N(CH 3 ) 2 ] 4 ) were used as the precursors, while O 2 gas was used as the reactive gas. The PE-ALD-grown HfO 2 and ZrO 2 thin films were analyzed using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The XPS measurements show that the ZrO 2 film has the atomic concentrations of 34% Zr, 2% C, and 64% O while the HfO 2 film has the atomic concentrations of 29% Hf, 11% C, and 60% O. The HRTEM and XRD measurements show both HfO 2 and ZrO 2 films have polycrystalline structures. n-channel and p-channel metal-oxide semiconductor field-effect transistors (nFETs and pFETs), CMOS inverters, and CMOS ring oscillators were fabricated to test the quality of the HfO 2 and ZrO 2 thin films as the gate oxide. Current-voltage (IV) curves, transfer characteristics, and oscillation waveforms were measured from the fabricated transistors, inverters, and oscillators, respectively. The experimental results measured from the HfO 2 and ZrO 2 thin films were compared.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Study of Anharmonicity in Zirconium Hydrides Using Inelastic Neutron Scattering and Ab-Initio Computer Modeling

The anharmonic phonon behavior in zirconium hydrides and deuterides, including ϵ-ZrH 2 , γ-ZrH, and γ-ZrD, has been investigated from aspects of inelastic neutron scattering (INS) and lattice dynamics calculations within the framework of density functional theory (DFT). The harmonic model failed to reproduce the spectral features observed in the experimental data, indicating the existence of anharmonicity in those materials and the necessity of further explanations. Here, we present a detailed study on the anharmonicity in zirconium hydrides/deuterides by exploring the 2D potential energy surface of hydrogen/deuterium atoms and solving the corresponding 2D single-particle Schrödinger equation to obtain the eigenfrequencies, which are then convoluted with the instrument resolution. The convoluted INS spectra qualitatively describe the anharmonic peaks in the experimental INS spectra and demonstrate that the anharmonicity originates from the deviations of hydrogen potentials from quadratic behavior in certain directions; the effects are apparent for the higher-order excited vibrational states, but small for the ground and first excited states.

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

Comparative critical mass calculations for NNL and ENDF/B-VIII.0 - Zirconium hydride thermal neutron scattering laws

Zirconium hydride (ZrH{sub x}) is a moderator material for TRIGA reactors and historical space reactor systems, such as SNAP-10A. Thermal neutron scattering laws (TSL) for two phases of this material, δ and ε, have been previously evaluated by Naval Nuclear Laboratory (NNL) and submitted to the National Nuclear Data Center (NNDC) for inclusion in the US national ENDF/B-VIII.1 nuclear data library. In contrast to the current ENDF/B-VIII.0 TSL evaluations, which consider only a single phase, the new evaluations are derived from separate ab initio calculations for both phases and include coherent elastic effects of the zirconium sublattice. To estimate the impact of these changes to the TSL evaluation of this material, comparative critical mass calculations were performed with MC21 for homogenous mixtures of high-enriched uranium (HEU) and ZrH{sub x} in bare and water reflected sphere configurations. These calculations yield an impact on the estimated critical mass as a function of {sup 235}U loading density with maximum differences as large as 1% - 5% for over-moderated thermal spectrum systems. Consequently, the NNL TSL evaluations are anticipated to have a small impact on criticality calculations of thermal reactor systems regardless of the material phase. Nevertheless, characteristic differences exist in the predicted thermal spectra as function of energy for the two sets of TSL evaluations, which are attributed to difference in the underlying phonon density of states of hydrogen bound in ZrH{sub x}. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

Excitation Function Calculations of Neutron-Induced Reactions of Some Zirconium Target Isotopes

Nuclear structures with high performance materials will be critical for the success of future fusion energy. Zirconium alloys are extensively used for nuclear reactor core materials as fuel cladding and guide tubes due to excellent radiation and corrosion resistant properties. In this paper, the excitation functions of {sup 90}Zr(n,2n){sup 89}Zr, {sup 90}Zr(n,α){sup 87}Sr, {sup 91}Zr(n,p){sup 91}Y and {sup 92}Zr(n,p){sup 92}Y nuclear reactions were calculated for energies up to 25 MeV. Besides, ALICE/ASH and TALYS 1.6 codes were used for the cross section calculations. The obtained calculations were compared with the experimental data in the literature.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Phase Transformations Driving Biaxial Stress Reduction During Wake-Up of Ferroelectric Hafnium Zirconium Oxide Thin Films

Biaxial stress is identified to play an important role in the polar orthorhombic phase stability in hafnium oxide-based ferroelectric thin films. However, the stress state during various stages of wake-up has not yet been quantified. In this work, the stress evolution with field cycling in hafnium zirconium oxide capacitors is evaluated. The remanent polarization of a 20 nm thick hafnium zirconium oxide thin film increases from 9.80 to 15.0 µC cm –2 following 10 6 field cycles. This increase in remanent polarization is accompanied by a decrease in relative permittivity that indicates that a phase transformation has occurred. The presence of a phase transformation is supported by nano-Fourier transform infrared spectroscopy measurements and scanning transmission electron microscopy that show an increase in ferroelectric phase content following wake-up. The stress of individual devices field cycled between pristine and 10 6 cycles is quantified using the sin 2 (ψ) technique, and the biaxial stress is observed to decrease from 4.3 ± 0.2 to 3.2 ± 0.3 GPa. The decrease in stress is attributed, in part, to a phase transformation from the antipolar Pbca phase to the ferroelectric Pca2 1 phase. This work provides new insight into the mechanisms controlling and/or accompanying polarization wake-up in hafnium oxide-based ferroelectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Isolating the Electrocatalytic Activity of a Confined NiFe Motif within Zirconium Phosphate

Unique classes of active-site motifs are needed for improved electrocatalysis. Herein, the activity of a new catalyst motif is engineered and isolated for the oxygen evolution reaction (OER) created by nickel–iron transition metal electrocatalysts confined within a layered zirconium phosphate matrix. It is found that with optimal intercalation, confined NiFe catalysts have an order of magnitude improved mass activity compared to more conventional surface-adsorbed systems in 0.1 m KOH. Interestingly, the confined environments within the layered structure also stabilize Fe-rich compositions (90%) with exceptional mass activity compared to known Fe-rich OER catalysts. Through controls and by grafting inert molecules to the outer surface, it is evidenced that the intercalated Ni/Fe species stay within the interlayer during catalysis and serve as the active site. After determining a possible structure (wycherproofite), density functional theory is shown to correlate with the observed experimental compositional trends. It is further demonstrated that the improved activity of this motif is correlated to the Fe and water content/composition within the confined space. This work highlights the catalytic enhancement possibilities available through zirconium phosphate and isolates the activity from the intercalated species versus surface/edge ones, thus opening new avenues to develop and understand catalysts within unique nanoscale chemical environments.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The Central Role of Oxo Clusters in Zirconium‐Based Esterification Catalysis

Oxo clusters are a unique link between oxide nanocrystals and Metal‐Organic Frameworks (MOFs), representing the limit of downscaling each of the respective crystals. Herein, the superior catalytic activity of clusters, compared to zirconium MOF UiO‐66 and nanocrystals is shown. Focus is on esterification reactions given their general importance in consumer products and the challenge of converting large substrates. Oxo clusters have a higher surface‐to‐volume ratio than nanocrystals, rendering them more active. For large substrates, for example, oleic acid, MOF UiO‐66 has negligible catalytic activity while clusters provide almost quantitative conversion, a fact we ascribe to limited diffusion of large substrates through the MOF pores. Clusters do not suffer from limited mass transfer and we also obtain high conversion in solvent‐free reactions with sterically hindered alcohols (hexanol, 2‐ethyl hexanol, benzyl alcohol, and neopentyl alcohol). The cluster catalyst can be recovered and shows identical activity when reused. The structural integrity of the cluster is confirmed using X‐ray total scattering and pair distribution function analysis. Moreover, when homogeneous zirconium alkoxides are used as catalysts, the same oxo cluster is retrieved, showing that oxo clusters are the active catalytic species, even in previously assumed homogeneously catalyzed reactions.

Pulparayil Mathew, Jikson↗
DOE OSTI2019

Zirconium chloride molecular species: combining electron impact mass spectrometry and first principles calculations

Zirconium tetrachloride was synthesized from the reaction between zirconium metal and chlorine gas at 300 °C and was analyzed by electron impact mass spectrometry (EI-MS). Substantial fragmentation products of ZrCl 4 were observed in the mass spectra, with ZrCl 3 being the most abundant species, followed by ZrCl 2 , ZrCl, and Zr. The predicted geometry and kinetic stability of the fragments previously mentioned were investigated by density functional theory (DFT) calculations. Here, energetics of the dissociation processes support the most stable fragment to be ZrCl 3 while the least abundant are ZrCl and ZrCl 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Determination of the five parameter grain boundary character distribution of nanocrystalline alpha-zirconium thin films using transmission electron microscopy

Grain boundary engineering and other fundamental materials science problems (e.g., phase transformations and physical properties) require an improvement in the understanding of the type and population of grain boundaries in a given system – yet, databases are limited in number and spare in detail, including for hcp crystals such as zirconium. One way to rapidly obtain databases to analyze is to use small-grained materials and high spatial resolution orientation microscopy techniques, such as ASTAR™/precession electron diffraction. To demonstrate this, a study of grain boundary character distributions was conducted for α-zirconium deposited at room temperature on fused silica substrates using physical vapor deposition. The orientation maps of the nanocrystalline thin films were acquired by the ASTARα/precession electron diffraction technique, a new transmission electron microscope based orientation microscopy method. The reconstructed grain boundaries were classified as pure tilt, pure twist, 180°-twist and 180°-tilt grain boundaries based on the distribution of grain boundary planes with respect to the angle/axis of misorientation associated with grain boundaries. The results of the current study were compared to the results of a similar study on α-titanium and the molecular dynamics results of grain boundary energy for α-titanium.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Photocatalytic degradation of orange II dye via high pore volume polymorph zirconium-doped titania under visible light irradiation

A series of mixed-phase Zr-doped TiO 2 was utilized for the photocatalytic degradation of orange II dye. These materials were synthesized through a sol–gel technique by varying the amounts of zirconium in the photocatalysts. These materials were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray fluorescence (XRF), Raman spectroscopy, thermogravimetry analysis (TGA), and X-ray photoelectron spectroscopy (XPS) among others. XRF and XPS data showed that the elemental composition of the photocatalysts consists of zirconium, titanium, and oxygen. In addition, XRD and Raman spectroscopy confirmed the existence of anatase and rutile phases of TiO 2 . The TGA analyses showed that the undoped TiO 2 was the most stable, with no significant weight loss during the heating range. Furthermore, the materials can effectively degrade orange II dye solution up to 7 cycles through asymmetric cleavage of the azo bond.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Oxidation and Hydrogen Uptake in Zirconium, Zircaloy-2 and Zircaloy-4: Computational Thermodynamics and Ab Initio Calculations

Zirconium-based alloys Zircaloy-2 and Zircaloy-4 are widely used in nuclear industry as cladding materials for BWRs and PWRs, respectively. Over more than 60 years these materials displayed a very good combination of properties such as low neutron absorption, creep behavior, stress-corrosion cracking resistance, reduced hydrogen uptake, corrosion, and/or oxidation, especially in the case of Zircaloy-4. However, over the last couple of years energetic efforts were undertaken to improve their oxidation resistance during off-normal temperature excursions, as well as to further improve upon the already achieved levels of mechanical behavior and reduced hydrogen uptake. In order to facilitate the development of such novel materials, it is very important to achieve not only engineering control, but also scientific understanding of the underlying material degradation mechanisms, both in working conditions and in storage of spent nuclear fuel. This paper strives to contribute to these efforts by constructing the thermodynamic models of both alloys, constructing of the respective phase diagrams, and oxidation mechanisms. A special emphasis was placed upon the role of zirconium suboxides in hydrogen uptake reduction and the atomic mechanisms of oxidation. To that end, computational thermodynamics calculations were conducted concurrently with first-principles atomistic modeling.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Generation of electric-field stabilized zirconium monoxide secondary phase within cubic zirconia

Flash sintering of cubic yttria-stabilized zirconia has been studied via in situ energy dispersive diffraction. A secondary rocksalt-phase zirconium monoxide was observed emerging from the primary fluorite-phase zirconium dioxide, previously only observed as a thin interlayer at metal-oxide interfaces, upon application of a direct current electric field. The average secondary phase intensity rose over extended flow of direct current through the ceramic, faded upon removal of the field and disappeared entirely upon application of an alternating current electric field. The results indicate that the sustained application of a direct current electric field can result in significant electrochemical reduction of zirconia under high current density conditions. Poor sinterability and cracking under direct current is apparent and potential mechanisms discussed therein.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Engineering Electrical Conductivity in Stable Zirconium-Based PCN-222 MOFs with Permanent Mesoporosity

Electrically conductive metal–organic frameworks (MOFs) featuring zirconium-based nodes are of great interest for electrochemical and optoelectronic applications due to their exceptional thermal and chemical stability, although the number of such MOFs remains limited. Here in this paper, we demonstrate that electron deficient molecules such as transition metal(IV) bis(dicarbollide) (TM IV (C 2 B 9 H 11 ) 2 ; TM IV CB for short, where TM = Ni, Pd, and Pt) or C 60 , spatially infiltrated in the microporous channels of the zirconium-based porphyrinic MOFs PCN-222 and PCN-222-Zn, generate highly stable and electrically conductive frameworks in which the mesopores remain accessible to other guests. Solid-state density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations indicate incorporation of Ni IV CB and C 60 in the MOF micropores is energetically and structurally feasible. Interestingly, in contrast to the free species, strong donor–acceptor interactions between the MOF and Ni IV CB restrain it to a single conformation. Calculated electronic structures and charge-hopping conduction probabilities illustrate that efficient charge-transfer (CT) from photoexcited linkers to the guest molecules facilitates charge hopping in the framework, making the MOFs electrically conductive. The donor–acceptor conjugates also enhance exciton dissociation at their heterojunctions, fostering the formation of long-lived electron-trapped states with potential utility for photo- and electrochemical devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Ultrastable Zirconium-Based Cationic Metal–Organic Frameworks for Perrhenate Removal from Wastewater

The effective removal of radioactive 99 TcO 4 – anion from nuclear wastewater remains a very difficult unsolved problem. Functional adsorbent materials with high stability, anion-exchange capacity, excellent selectivity, and recyclability are much needed to solve this problem. In this work, we designed two stable cationic metal–organic frameworks (MOFs)—Zr-tcbp-Me and Zr-tcpp-Me—for possible use as adsorbent materials to remove 99 TcO 4 – . Both compounds were synthesized by solvothermal reactions of the tetracarboxylate ligand with zirconium salt, followed by postsynthetic modification (N-methylation). Here, the crystallinity of both zirconium-based MOFs can be well retained under harsh conditions, and they exhibit high adsorption capacity and selectivity toward ReO 4 – anion, a nonradioactive analogue of 99 TcO 4 – . Zr-tcbp-Me and Zr-tcpp-Me demonstrate the highest framework stability toward acidity among all previously reported cationic MOFs that have been tested for perrhenate removal from wastewater.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Pyroelectric response in crystalline hafnium zirconium oxide (Hf 1- x Zr x O 2 ) thin films

Pyroelectric coefficients were measured for 20 nm thick crystalline hafnium zirconium oxide (Hf 1-x Zr x O 2 ) thin films across a composition range of 0 ≤ x ≤ 1. Pyroelectric currents were collected near room temperature under zero applied bias and a sinusoidal oscillating temperature profile to separate the influence of non-pyroelectric currents. The pyroelectric coefficient was observed to correlate with zirconium content, increased orthorhombic/tetragonal phase content, and maximum polarization response. The largest measured absolute value was 48 μCm -2 K -1 for a composition with x = 0.64, while no pyroelectric response was measured for compositions which displayed no remanent polarization (x = 0, 0.91, 1).

36 MATERIALS SCIENCE↗