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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Phosphor thermometry device for synchronized acquisition of luminescence lifetime decay and intensity on thermal barrier coatings

A phosphor thermometry device includes a laser that generates a laser pulse onto a thermal barrier coating (TBC) applied onto a substrate. A metallic bond coat layer is on the substrate. A ceramic top coat layer is on the bond coat layer and includes an undoped layer and a doped sensing layer having co-doped first and second rare-earth luminescent dopants that emit respective first and second different emission wavelengths upon excitation by the laser pulse. A detector receives reflected, convoluted luminescence signals from the TBC. First and second photomultiplier devices detect respective first and second different emission wavelengths of the convoluted luminescence signals. A controller receives and processes signals generated from respective first and second photomultiplier devices and determines luminescence lifetime decay and intensity variations for each of the respective first and second rare-earth luminescent dopants for temperature monitoring of the TBC.

Fouliard, Quentin↗
DOE OSTI2018

Life-Cycle Assessment of Alternative Pyrolysis-Based Transport Fuels: Implications of Upgrading Technology, Scale, and Hydrogen Requirement

In an effort to diversify liquid fuel supply and address climate change, there are ongoing studies on the use of biomass as a renewable source of energy. Bio-oil produced from fast pyrolysis of biomass is a promising substitute for fossil fuels that can meet climate change mitigation goals, spur rural economies, and diversify liquid fuel supply. However, for bio-oil to be used as a transportation fuel, it requires upgrading to remove oxygen present in the oil. Hydrodeoxygenation (HDO) is one means of upgrading fast pyrolysis oil, however, one of its main limitations is a large hydrogen requirement. We evaluate an alternative electrochemical deoxygenation (EDOx) method that uses catalytic electrode membranes on a ceramic, oxygen permeable support, to generate hydrogen in-situ for deoxygenation at the cathode and remove oxygen at the anode. We analyze the life cycle greenhouse gas (GHG) emissions and scale effects of gas-phase upgrading pyrolysis oil (300 metric tons per day (MTPD)) using EDOx, which reduces energy needs for condensing the pyrolysis gas to bio-oil prior to deoxygenation. The dispersed woody biomass can be accessed and thus more efficiently used if a small scale process is used to densify and stabilize the bio-oil product. We evaluate two configurations of the small-scale deoxygenation, full electrochemical deoxygenation (EDOx), which removes 100% of oxygen present in the bio-oil and partial EDOx, which removes 96% of oxygen present in the bio-oil and compare them to the large scale (2000 MTPD) deoxygenation (HDO). The partial EDOx process has the lowest total GHG emissions of 4.95 gCO2 eq. and 7.43 gCO2 eq. per MJ of a vehicle operated with diesel and gasoline respectively compared to full EDOx (8.36 g CO2 eq. diesel, 10.86 g CO2 eq. gasoline) and HDO (39 gCO2 eq. per MJ for diesel and gasoline). In addition, with the EDOx processes, we can site 10 times more small-scale pyrolysis upgrading sites compared to HDO, suggesting that small-scale on-site partial or full deoxygenation can reach more inaccessible forest biomass resources.

bio-oil hydrotreating, Biomass, deoxygenation, sol↗
DOE OSTI2014

Enhancement in the transport critical current density J{sub c} in YBa{sub 2}Cu{sub 3}O{sub 7−δ} added with an insulating nano crystalline YBa{sub 2}HfO{sub 5.5} perovskite

When a magnetic field is applied to type II superconductors, such as YBa{sub 2}Cu{sub 3}0{sub 7−δ} (YBCO), the flux quanta penetrate the material as a regular array of vortices. However when transport currents are applied, they act to move these vortices, thus lowers the critical current density (J{sub c}) as well as destroying superconductivity. The development of microstructures made of YBCO materials has enabled engineers to increase the critical current density, within Type II materials by introducing flux pinning centres into the material. The microstructure and flux pinning properties of YBa{sub 2}Cu{sub 3}O{sub 7−δ} system with varying levels (0-5 wt. %) of a nano perovskite ceramic insulator; YBa{sub 2}HfO{sub 5.5} addition was studied in detail. Orthorhombic YBa{sub 2}Cu{sub 3}O{sub 7−δ} powder was prepared through conventional solid state route and a modified combustion method was used for synthesizing nanocrystalline YBa{sub 2}HfO{sub 5.5}. The structure and microstructure of the samples examined by X-ray diffraction and scanning electron microscopy showed that YBa{sub 2}HfO{sub 5.5} and YBCO remained unreacted even at higher processing temperature without deteriorating the superconducting properties. The scanning electron microscope image shows that YBa{sub 2}HfO{sub 5.5} forms an electrical-network between grains. These observations suggest that the YBa{sub 2}HfO{sub 5.5} addition to the Y-123-compounds improve the electrical connection between superconducting grains and substantial improvements in the relative electrical transport properties of the composites. The variation of sintering temperature, density, critical transition temperature (T{sub c}) and magnetic field dependence of critical current density (J{sub c}) of YBa{sub 2}Cu{sub 3}O{sub 7−δ} having different proportions of YBa{sub 2}HfO{sub 5.5} in the matrix were also studied in detail. It is found that the addition of these elements considerably enhances the flux pinning strength of the system, and there is also an increase of critical temperature (T{sub c}) and critical current density (J{sub c}) up to an optimum value of 8.76 × 10{sup 4} A/cm{sup 2} for a concentration of 2 wt % addition of nano YBa{sub 2}HfO{sub 5.5}. The enhancement of the critical current density in the YBa{sub 2}Cu{sub 3}O{sub 7−δ} - YBa{sub 2}HfO{sub 5.5} samples is attributed to the sustained formation of the insulating and non-reacting YBa{sub 2}HfO{sub 5.5} phase acting as pinning center. The addition of YBa{sub 2}HfO{sub 5.5} in YBa{sub 2}Cu{sub 3}O{sub 7−δ} bulk superconductor also enhances the pinning force density from 3 ×10{sup 6} N/m{sup 3} to 69.6 × 10{sup 6}N/m{sup 3} at 77 K.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Examination of Hybrid Metal Coatings for Mitigation of Fission Product Release and Corrosion Protection of LWR SiC/SiC

There is a need to increase the safety margins of current and future light water reactors (LWRs) due to the unfortunate events at Fukushima Daiichi Nuclear Plant. Safety is crucial to restore public confidence in nuclear energy, acknowledged as an economical, high-­density energy solution to climate change. The development of accident-­tolerant fuel (ATF) concepts is crucial to this endeavor. The objective of ATF is to delay the consequences of accident progression, being inset in high temperature steam and maintaining high thermomechanical strength for radionuclide retention. The use of advanced SiCf-­SiC composite as a substitute for zircaloy-­based cladding is being considered. However, at normal operations, SiC is vulnerable to the reactor coolant and may corrode at an unacceptable rate. As a ceramic-­matrix composite material, it is likely to undergo microcracking operation, which may compromise the ability to contain gaseous fission products. A proposed solution to both issues is the application of mitigation coatings for use in normal operations. At Oak Ridge National Laboratory (ORNL), three coating technologies have been investigated with industry collaborators and vendors. These are electrochemical deposition, cathodic arc physical vapor deposition (PVD hereafter) and vacuum plasma spray (VPS). The objective of this document is to summarize these processing technologies, the resultant as-­processed microstructures and properties of the coatings. In all processes, substrate constraint resulted in substantial tensile stresses within the coating layer. Each technology must mitigate this tensile stress. Electrochemical coatings use chromium as the coolant facing material, and are deposited on a nickel or carbon “bond coat”. This is economical but suffers microcracking in the chromium layer. PVD-­based coatings use chromium and titanium in both metallic form and nitrides, and can be deposited defense-­in-­depth as multilayers. This vapor method eliminated tensile stress during processing and coatings were up to ~30 μm thick without microcracking. VPS produced coatings based on Zircaloy-2, which has a proven reactor-­compatibility. The tensile stresses appearred to be partially mitigated by annealing. Analysis showed that VPS coatings required further optimizations to prevent adverse reactions with the substrate and need a minimum thickness of ~50 μm. In addition, development of coatings are constrained by neutronic depletion analysis, which clearly indicated enrichment as an issue if the coating is too thick. Based on the present work, the cathodic arc PVD technology was considered ready for the extensive testing and evaluation on cladding materials due to their ability to mitigate the excessive tensile stresses and the reasonable coating quality achieved. The VPS Zircaloy-­2 coating technology required additional development toward mitigation of issues related to the substrate reaction and porosity. In the future, PVD and VPS will have be scaled upon successful development and demonstration. Electrochemical coatings, which are proven scalability, currently require development to mitigate issues related to the tensile stress after deposition.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2024

Modularization of Ceramic Hollow Fiber Membrane Technology for Air Separation

This proposed project is aimed at studying high performance and economically competitive ceramic membrane technology for air separation and high-purity oxygen production using hollow fiber ceramic membrane stack and module technology. The design of the single permeate membrane is a hollow fiber substrate-supported thin tri-layer structure. Radially well-aligned micro-channels are embedded in the thick substrate and open at the inner surface of the substrate, enabling facile air/gas diffusion. The tri-layer structure of thin dense membrane layer (~ 10 µm) sandwiched by porous surface layer on either side is then built on the substrate using advanced fabrication process. The tri-layer structure design allows different materials to be used in different layers, where the materials of surface layers have high surface exchange coefficients while the material of dense layer has high bulk diffusivity. Such a synergetic combination leads to high permeation performance. The focus of the proposed project will be on membrane stack/module development using the developed single hollow fiber membranes, including: 1) fabrication and characterization of novel single hollow fiber membranes; 2) membrane stack design and assembly using fabricated single membranes; 3) stack modeling and analysis to guide membrane stack designs; 4) permeation performance testing and characterization of membrane stacks. The hollow fiber feature and simple sealing requirement enable very compact design of membrane stacks, which have excellent flexibility for further modularizations at different scales. The operations of such membrane stack and module may employ the exhaust heat from other components of Integrated Gasification Combined Cycle and oxy-combustion systems. Therefore, modularization of such an air separation membrane technology can be incorporated into the DOE’s REMS (radically engineered modular systems)-gasification skid and support the oxidant feed of an oxygen-blown REMS gasifier scaled to different ranges.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2018

Vitrification Process for Idaho HLW Calcine - 18433

The majority of the liquid wastes produced from reprocessing of several types of spent nuclear fuel at the Department of energy's (DOE) Idaho site have been volume reduced by calcination. The resulting ∼155,600 ft{sup 3} of calcined waste is stored in 43 shielded stainless steel bins, which have a 500-year design life. The calcined material is both a high-level waste and a RCRA hazardous waste, which complicates treatment and disposal options. In addition to a potential direct disposal option, treatment options that have been considered include steam reforming, hot isostatic pressing (HIP), and vitrification. This paper describes testing and evaluation of a vitrification option for the calcine. Vitrification to produce a borosilicate glass has the advantage that it is the only treatment that provides a waste form that meets the current HLW repository waste acceptance criteria. It is therefore the lowest risk option in terms of regulatory and legislative concerns. The present work addressed several key questions: (i) Calcine waste loadings in glass, which determine the number of HLW canisters produced and the required glass production rate (throughput) for the system design; (ii) Melt rate per unit glass pool surface area of the melter, which determines the sizing of the vitrification system; and (iii) The ability to meet waste form acceptance requirements (PCT and TCLP) while achieving reasonable waste loadings. These are issues of fundamental importance to the sizing estimates for the unit operations and overall flow-sheet and they, therefore, directly impact the cost and schedule estimates. Fully compliant, high-waste-loading glasses were developed for two of the four Idaho calcine wastes. The results demonstrate that waste loadings of 35 wt% waste oxides are achievable for the two alumina calcines and about 30 wt% is achievable for the two zirconia calcines. Testing of these formulations in a joule-heated ceramic melter showed glass production rates of over 5000 kg/(m2/d) for the Alumina calcine and over 8500 kg/(m{sup 2}/d) for the Zirconium-Na Blend calcine. These extremely high production rates translate directly into smaller system size and shorter mission duration and, therefore, reduced costs. Based on these results, a preliminary design for the full-scale vitrification system was developed. The system consists of waste receipt, vitrification, off-gas treatment, and canister sealing and decontamination equipment. The calcine is blended with the appropriate glass forming chemicals (or glass frit) and fed to the melter as a solid stream. The melter has a glass pool surface area of about 2.5 m{sup 2} and is equipped with a bubbling system to increase processing rates. Glass production rates of about 6 metric tons per day are projected. The vitrification system would be installed into the existing Idaho Waste Treatment Unit Facility (IWTU) so that no new facilities are required to house the treatment system, thus greatly reducing overall cost, duration, and risk. The system would be designed to treat all of the calcine waste within a period of 12 years at an operating efficiency of 80%, producing a total of about 8500 canisters each weighing two metric tons. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

On the confluence of ultrafast high-temperature sintering and flash sintering phenomena

Ultrafast high-temperature sintering (UHS) and flash sintering are novel methods for rapid sintering of ceramics, often completed in just a few seconds. Here, we show that both also share two additional features: an abrupt rise in electrical conductivity, which is electronic, and electroluminescence. More fundamentally, both are related to phonon physics where MD calculations have shown that proliferation of phonons at the edge of the Brillouin zone can induce Frenkel pairs without the application of electrical fields. Here, we show that, indeed, heating without the application of electric field, can also induce flash: Rapid heating processes of thin films of an oxide-salt deposited on silk fibers, with a propane torch, are shown to induce electronic conductivity, electroluminescence, and rapid sintering of the oxide. Further, the discussion in this article harkens back to two inventions, more than a century ago, which can now be related to flash and UHS: (i) the Nernst glow lamp circa 1900, made from zirconia, and (ii) the Welsbach mantle, constituted from ceria doped thorium oxide, in the late nineteenth century. Thus, the confluence between high heating rate and electric field induced flash phenomena links the past to the new. The emerging question is how injection of phonons that has been shown to create Frenkels can further induce high electronic conductivity and electroluminescence in oxides. Both electronic conductivity and luminescence are likely related to the generation of electron–hole pairs.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Process and apparatus for continuous production of porous structures

An apparatus and process are presented for continuous production of metal-based micro-porous structures of pore sizes from 0.3 nm to 5.0 μm from a green part of characteristic diffusion mass transfer dimension less than 1 mm through chemical reactions in a continuous flow of gas substantially free of oxygen. The produced micro-porous structures include i) thin porous metal sheets of thickness less than 200 μm and pore sizes in the range of 0.1 to 5.0 μm, ii) porous ceramic coating of thickness less than 40 μm and ceramic particle sizes of 200 nm or less on a porous metal-based support structures of pore sizes in the range of 0.1 to 5 μm.

Liu, Wei↗
DOE OSTI2024

Glass-bonded ceramic waste forms for immobilization of radioiodine from caustic scrubber wastes

Glass-bonded sodalite composite waste forms have been developed for the immobilization of liquid radioactive wastes resulting from off-gas treatment during aqueous reprocessing of used nuclear fuel, with a particular focus on 129I. The proposed composite waste form is comprised of aluminosilicate ceramic phases containing volatile radionuclides bonded with a glassy matrix. In this work, a suite of ten candidate low-temperature glass binders (ZnO-Bi2O3-based glasses and a Na2O-B2O3-SiO2 glass) were examined. Six glasses were mixed with caustic scrubber waste simulant previously converted into a sodalite-rich material (to provide glass fractions of 10 and 20 wt.%), uniaxially pressed into pellets, and sintered at 350 °C or 550 °C for 8 h in air. Iodine retention after heat treatment was assessed by neutron activation analysis, showing retention of 67-100 % of expected iodine. The aqueous durabilities of the resulting materials were then determined, following the ASTM C1308 standard test, showing iodine releases of 1 to 23 g m-2 after 4 d. The cumulative iodine release for the best performing system (a zinc-bismuth-borate glass binder) was <1 g m-2, and its iodine retention from processing was 67 %. The iodine releases compared favorably with other waste forms. In parallel, this best-performing composition was also consolidated via hot isostatic pressing (HIP) in a stainless-steel canister at 550 °C for 2 h under 100 MPa pressure. The HIPed sample was produced at the ~20 g scale and showed improved densification and minimal reaction with the canister.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Tailoring the Toughening Effects in Two-Dimensional Nanomaterial-Reinforced Ceramic Matrix Composites

Abstract Ceramic matrix composites (CMCs) reinforced by two-dimensional (2D) nanomaterials have shown extraordinary load-carrying capacities, even in the harsh environments required by emerging applications. Their exceptional mechanical performance, especially fracture toughness, primarily arises from their heterogeneous microstructures. The deliberate dispersion of 2D reinforcements enables toughening mechanisms that are extrinsic to the matrix and thus endows the composites with substantial resistance to catastrophic failure. However, the incomplete understanding of the fracture behavior of such nanocomposites, especially the complex energy dissipation process of the matrix/reinforcement interface, limits the development of stronger and tougher CMCs. To overcome these limitations, we investigate crack deflection and energy dissipation in nanocomposites using an extended cohesive shear-lag model. This new model accounts for interfacial debonding and friction, which critically control the toughening of nanocomposites. Our analysis provides mechanistic insights for optimizing the toughening effects of CMCs.

Mechanics↗
DOE OSTI2019

Effects of Co{sub 3}O{sub 4} Addition on Friction and Dry Sliding Wear Characteristics of 8 mol% Yttria-Stabilized Cubic Zirconia

The aim of the present study was to investigate the influence of Co{sub 3}O{sub 4} additive on the microstructure, wear, and tribological properties of 8 mol% yttria-stabilized cubic zirconia (8YSZ) using a pin-on-disk tribometer, surface profilometer, hardness tester, and a scanning electron microscopy system. Specimens were produced by doping 1-15 wt.% Co{sub 3}O{sub 4} in 8YSZ using a colloidal process, sintering at 1500 °C for 1 h, and subsequent annealing at 1500 °C for 10 and 50 h. Microstructural analysis showed that Co{sub 3}O{sub 4} dissolved partially in 8YSZ, with the undissolved Co{sub 3}O{sub 4} precipitating as a secondary phase at the grain boundaries. Further, the addition of Co{sub 3}O{sub 4} enhanced the grain size. Wear tests were carried out using an Al{sub 2}O{sub 3} ball as the counterface against ceramic disk under dry sliding friction conditions at room temperature (24 °C). The wear volume of 8YSZ decreased from 0.30 to 0.11 mm{sup 3} as a result of the addition of 15 wt.% Co{sub 3}O{sub 4}. Additionally, friction coefficient of the 8YSZ significantly reduced from 0.55 to 0.17 at the beginning stage of the sliding after the addition of 15 wt.% Co{sub 3}O{sub 4}. This was because Co{sub 3}O{sub 4} creates a thin lubricating layer on the friction surface. In addition, the undoped and Co{sub 3}O{sub 4}-doped 8YSZ specimens exhibited abrasive wear under the dry sliding friction conditions, owing to the formation and propagation of microcracks, which resulted in the removal of material from the surface. The specific wear rate of 8YSZ decreased with increasing the Co{sub 3}O{sub 4} content. Thus, the addition of Co{sub 3}O{sub 4} to 8YSZ improves its wear resistance and surface topography.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microwave induced plasma discharge in multi-cell superconducting radio-frequency cavity

A R&D effort for in situ cleaning of 1.5 GHz Superconducting Radio Frequency (SRF) cavities at room temperature using the plasma processing technique has been initiated at Jefferson Lab. This is a step toward the cleaning of cryomodules installed in the Continuous Electron Beam Accelerator Facility (CEBAF). For this purpose, we have developed an understanding of plasma discharge in a 5-cell CEBAF-type SRF cavity having configurations similar to those in the main accelerator. The focus of this study involves the detailed investigations of developing a plasma discharge inside the cavity volume and avoids the breakdown condition in the vicinity of the ceramic RF window. A plasma discharge of the gas mixture Ar–O{sub 2} (90%:10%) can be established inside the cavity volume by the excitation of a resonant 4π/5 TM{sub 010}-mode driven by a klystron. The absence of any external magnetic field for generating the plasma is suitable for cleaning cavities installed in a complex cryomodule assembly. The procedures developed in these experimental investigations can be applied to any complex cavity structure. Details of these experimental measurements and the observations are discussed in the paper.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Influence of Osmotic Drying with an Aqueous Poly(ethylene Glycol) Liquid Desiccant on Alumina Objects Gelcast with Gelatin

Gelcasting and liquid desiccant drying are novel forming and drying methods used to mitigate common issues associated with the fabrication of complex advanced ceramic objects. Here, the molecular weight and osmotic pressure of aqueous poly(ethylene glycol) (PEG) desiccant solutions were simultaneously varied to understand their influence on the net mass loss rates of gelcast alumina samples prepared using gelatin as a gelling agent. Additionally, the amount of PEG diffusion and water diffusion to and from the ceramic samples after 150 min of immersion in the liquid desiccant was correlated to the solution properties as was the final bulk density of the sintered samples. Furthermore, solutions with high molecular weight and low osmotic pressure resulted in low PEG gain and low water loss, while solutions with low molecular weight and high osmotic pressure resulted in high PEG gain and high water loss. In some cases, more than 40 wt% of the total water per sample was removed through the liquid desiccant drying process.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Surface restructuring of a perovskite-type air electrode for reversible protonic ceramic electrochemical cells

Reversible protonic ceramic electrochemical cells (R-PCECs) are ideally suited for efficient energy storage and conversion; however, one of the limiting factors to high performance is the poor stability and insufficient electrocatalytic activity for oxygen reduction and evolution of the air electrode exposed to the high concentration of steam. Here we report our findings in enhancing the electrochemical activity and durability of a perovskite-type air electrode, Ba 0.9 Co 0.7 Fe 0.2 Nb 0.1 O 3-δ (BCFN), via a water-promoted surface restructuring process. Under properly-controlled operating conditions, the BCFN electrode is naturally restructured to an Nb-rich BCFN electrode covered with Nb-deficient BCFN nanoparticles. When used as the air electrode for a fuel-electrode-supported R-PCEC, good performances are demonstrated at 650 °C, achieving a peak power density of 1.70 W cm –2 in the fuel cell mode and a current density of 2.8 A cm –2 at 1.3 V in the electrolysis mode while maintaining reasonable Faradaic efficiencies and promising durability.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Composite Cathode Architectures Made By Freeze-Casting for All Solid State Lithium Batteries (CRADA Final Report)

As part of a Battery 500 seedling project, MBRDNA partnered with LBNL and Montana State University (MSU) to develop solid-state batteries based on an Al-substituted LLZO (Li 7 La 3 Zr 2 O 12 ) ceramic ion-conductor. All solid-state lithium batteries are attractive contenders for use as power sources for electric vehicles because of their potential for better safety and higher energy density than state-of-the-art lithium-ion batteries, although they are still at early stages of development. Al-substituted LLZO is one of the most promising solid electrolytes for battery applications based on high ionic conductivity, a wide operating voltage window, and apparent stability vs. reduction by lithium. However, difficulties with processing thin (< 20 $\textit{um}$ and dense LLZO membranes have hampered development of devices based on this material. It is non-compressible and must be sintered at high temperatures to densify components. It is also difficult to maintain contact between the active cathode material and LLZO in the composite cathodes, which is critical for successful operation. This research project aimed to use novel processing methods to overcome these issues. The end result was the first ever-reported truly all solid-state battery based on LLZO operating at room temperature without application of exogenous pressure. During the course of the project, we also identified a number of issues that need to be addressed to improve the technology readiness level of this battery.

25 ENERGY STORAGE↗
DOE OSTI2019

Reactor physics analysis of a new Accident Tolerant Fuel called Fuel-in-Fibers

Fuel-in-Fibers (F-in-F) is an Accident Tolerant Fuel (ATF) concept aimed at significantly increasing the fission product retention capability of nuclear fuel at high temperatures, similar to another ATF concept, Fully Ceramic Microencapsulated Fuel (FCM). FCM, however, when implemented in a conventional Pressurized Water Reactor (PWR) fuel geometry, is not able to maintain an 18-month fuel cycle length and remain below the proliferation enrichment limit of 20 w/o 235 U using the standard cycle reload strategy. The F-in-F enrichment is decreased by putting the fuel in a cylindrical fiber instead of a spherical particle in order to increase the volume fraction of fuel in the pellet. The fibers are created with a direct manufacturing process that allows for the minimization of the volume occupied by the SiC matrix and the maximization of uranium loading via direct deposition of high density fuels like uranium nitride (UN). The full core reactor physics simulation showed that when the F-in-F design used UN as a fuel, it only required enrichments of 6% to maintain an 18-month fuel cycle length. Based on a full core analysis when compared to the current reference fuel for a standard 4-loop Westinghouse PWR, F-in-F has a similar steady state thermal hydraulic and neutronic performance.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Effects of Dopant Ionic Radius on Cerium Reduction in Epitaxial Cerium Oxide Thin Films

The role of trivalent rare-earth dopants in ceria epitaxial films on surface ion exchange reactivity and ion conductivity has been systematically studied. Single-crystal epitaxial films with unique crystal orientation and micro-structure nature have allowed us to rule out the influence of structural defects on both transport and surface ion exchange properties. The films conductivities were larger than those reported in literature for both polycrystalline ceramic pellets and crystalline films. An increase in oxygen vacancies and Ce 3+ concentration while decreasing the dopant ionic radius from La 3+ to Yb 3+ was observed, thus explaining the measured increased activation energy and enhanced surface reactivity. The more significant ability of smaller dopant ionic radius in releasing the stress strength induced by the larger Ce 3+ ionic radius allows promoting the formation of oxygen vacancies and Ce 3+ , which are two precious species in determining the efficiency of ion transport and surface ion exchange processes. This can open new perspectives in designing ceria-based materials in tailoring functional properties, either ion migration or surface reactivity, by rational cation substitutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗