Showing papers by "Westinghouse Electric published in 2018"

Development of Cold Spray Coatings for Accident-Tolerant Fuel Cladding in Light Water Reactors

Abstract: The cold spray coating process has been developed at the University of Wisconsin-Madison for the deposition of oxidation-resistant coatings on zirconium alloy light water reactor fuel cladding with the goal of improving accident tolerance during loss of coolant scenarios. Coatings of metallic (Cr), alloy (FeCrAl), and ceramic (Ti2AlC) materials were successfully deposited on zirconium alloy flats and cladding tube sections by optimizing the powder size, gas preheat temperature, pressure and composition, and other process parameters. The coatings were dense and exhibited excellent adhesion to the substrate. Evaluation of the samples after high-temperature oxidation tests at temperatures up to 1300°C showed that the cold spray coatings significantly mitigate oxidation kinetics because of the formation of thin passive oxide layers on the surface. The results of the study indicate that the cold spray coating process is a viable near-term option for developing accident-tolerant zirconium alloy fuel cladding.

Nitride fuel for Gen IV nuclear power systems

Abstract: Nuclear energy has been a part of the energy mix in many countries for decades. Today in principle all power producing reactors use the same techniqe. Either PWR or BWR fuelled with oxide fuels. This choice of fuel is not self evident and today there are suggestions to change to fuels which may be safer and more economical and also used in e.g. Gen IV nuclear power systems. One such fuel type is the nitrides. The nitrides have a better thermal conductivity than the oxides and a similar melting point and are thus have larger safety margins to melting during operation. In addition they are between 30 and 40% more dense with respect to fissile material. Drawbacks include instability with respect to water and a sometimes complicated fabrication route. The former is not really an issue with Gen IV systems but for use in the present fleet. In this paper we discuss both production and recycling potential of nitride fuels.

Uranium nitride-silicide advanced nuclear fuel: Higher efficiency and greater safety

Abstract: As part of Accident Tolerant Fuel initiative for light water reactors, uranium silicide and silicide-nitride are being considered as fuels that can be combined with a more robust cladding such as a

Understanding corrosion and hydrogen pickup of zirconium fuel cladding alloys: the role of oxide microstructure, porosity, suboxides, and second-phase particles

Abstract: We have used a range of advanced microscopy techniques to study the microstructure, the nanoscale chemistry and the porosity in a range of zirconium alloys at different stages of oxidation. Samples from both autoclave and in-reactor conditions were available to compare, including ZIRLO, Zr-1.0Nb and Zr-2.5Nb samples with different heat-treatments. (Scanning) Transmission Electron Microscopy ((S)TEM), Transmission Kikuchi Diffraction (TKD) and automated crystal orientation mapping with TEM 2,3 were used to study the grain structure and phase distribution. Significant differences in grain morphology were observed between samples oxidised in the autoclave and in-reactor samples, with shorter, less well-aligned monoclinic grains and more tetragonal grains seen in the neutron irradiated samples. A combination of Energy Dispersion X-ray (EDX) mapping in STEM and Atom Probe Tomography (APT) analysis of SPPs can reveal the main and the minor element distributions respectively. Neutron irradiation seems to have little effect on promoting fast oxidation or dissolution of β-Nb precipitates, but encourages dissolution of Fe from Laves phase precipitates. Electron Energy Loss Spectroscopy (EELS) analysis of the oxidation state of Nb in β-Nb SPPs in the oxide reveal the fully oxidised Nb state in the SPPs deep into the oxide, but Nb in the crystalline SPPs near the metaloxide interface. EELS analysis and automated crystal orientation mapping with TEM have also revealed Widmanstatten-type suboxide layers in some samples with the hexagonal ZrO structure predicted by ab initio modelling. The combined thickness of the ZrO suboxide and oxygen-saturated layers at the metal-oxide interface correlates well to the estimated instantaneous oxidation rate, suggesting that the presence of this oxygen rich zone is part of the protective oxide that is rate limiting in the key in the transport processes involved in oxidation. Porosity in the oxide has a major influence on the overall rate of oxidation, and there is much more porosity in the rapidly oxidising annealed Zr-1.0Nb alloy than found in either the recrystallised alloy or the similar alloy exposed to neutron irradiation.

Consolidation of commercial-size UO 2 fuel pellets using spark plasma sintering and microstructure/microchemical analysis

Abstract: The development of advanced fuel fabrication technologies is important for developing accident-tolerant fuels and engineering fuels for safer and more effective nuclear energy systems. In this work, commercial-size uranium dioxide (UO2) fuel pellets with a theoretical density of 95% were consolidated by spark plasma sintering (SPS) at 1600°C for 5 min. Systematic investigations suggest uniform densification and stoichiometric UO2 with an ideal fluorite structure across the commercial-size fuel pellet, but with a distributed grain structure because of non-uniform distribution of temperature during sintering. This work demonstrates a great potential of using SPS for fabricating nuclear fuels at a cost-effective manner.

Density functional theory study of the magnetic moment of solute Mn in bcc Fe

Abstract: An unexplained discrepancy exists between the experimentally measured and theoretically calculated magnetic moments of Mn in \ensuremath{\alpha}-Fe. In this study, we use density functional theory to suggest that this discrepancy is likely due to the local strain environment of a Mn atom in the Fe structure. The ferromagnetic coupling, found by experiment, was shown to be metastable and could be stabilized by a 2% hydrostatic compressive strain. The effects of Mn concentration, vacancies, and interstitial defects on the magnetic moment of Mn are also discussed. It was found that the ground-state, antiferromagnetic (AFM) coupling of Mn to Fe requires long-range tensile relaxations of the neighboring atoms along $\ensuremath{\langle}111\ensuremath{\rangle}$ which is hindered in the presence of other Mn atoms. Vacancies and Fe interstitial defects stabilize the AFM coupling but are not expected to have a large effect on the average measured magnetic moment.

Investigating the Effect of Zirconium Oxide Microstructure on Corrosion Performance: A Comparison between Neutron, Proton, and Nonirradiated Oxides

Abstract: 18th International Symposium on Zirconium in the Nuclear Industry 1Materials Performance Centre, School of Materials, The University of Manchester, Manchester M13 9PL, UK 2Studsvik Nuclear AB, 611 82 Nykoping, Sweden 3Westinghouse Electric Company, Hopkins, SC 29061, USA 4Rolls Royce, Derby DE21 7XX, UK 5Amec Foster Wheeler, Walton House, Faraday Street, Birchwood Park, Risley, Warrington WA3 6GA, UK

Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses

Abstract: Laser - material interactions such as welding, heat treatment and thermal bending generate thermal gradients which give rise to thermal stresses and strains which often result in a permanent distortion of the heated object. This paper investigates the thermal distortion response which results from pulsed laser surface melting of a stainless steel sheet. Pulsed holography has been used to accurately monitor, in real time, the out-of-plane distortion of stainless steel samples melted on one face by with both single and multiple laser pulses. It has been shown that surface melting by additional laser pulses increases the out of plane distortion of the sample without significantly increasing the melt depth. The distortion differences between the primary pulse and subsequent pulses has also been analysed for fully and partially overlapping laser pulses.

Discovering Voices: College Students and Middle Schoolers Explore Identities, Differences, and Connections through the Structure of a Poem

Abstract: Co-authored by a college professor, a middle-school teacher, a college undergraduate, and a 7th grader, this article focuses on college and middle-school students’ experiences of discovering their own and others’ voices. The discovery unfolds through composing and reflecting on poems in the form of Jacqueline Woodson’s “it’ll be scary sometimes,” which focuses on the experience of being different. The students’ dis-covering of voices deepens their own and their teachers’ education and creates spaces, structures, and processes that affirm students’ diverse histories and identities. Honoring differences and finding connections in these ways contribute to greater equity and inclusiveness.