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Shao, Lin

Publications and source records attributed to Shao, Lin.

63 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

The influence of lattice defects, recombination, and clustering on thermal transport in single crystal thorium dioxide

Thermal transport is a key controlling property for thorium dioxide in many applications where defect-generating radiation fields are present. An understanding of the effect of nanoscale lattice defects on thermal transport in this material is currently unavailable due to a lack of high-quality, single crystal material from which unit processes may be investigated. In this work, a series of thorium dioxide single crystals are exposed to 2 MeV proton irradiation at room temperature and 600°C to create microscale regions with varying densities and types of point and extended defects. Defected regions are investigated using spatial domain thermoreflectance to quantify the change in thermal conductivity as a function of ion fluence as well as transmission electron microscopy and Raman spectroscopy to interrogate the structure of the generated defects. Together, this com- bination of methods provides important initial insight into defect formation, recombination, and clustering in thorium dioxide and the effect of those defects on thermal transport. These methods also provide a promising pathway for the quantification of the smallest-scale defects which cannot be captured using traditional microscopy techniques and play and outsized role in degrading thermal performance.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Formation of multicomponent alloy particles in doped ceria under I 2+ ion irradiation and thermal annealing

Multicomponent alloys resembling the e-phase particles in nuclear fuel have the potential to immobilize 99 Tc in a stable waste form. Formation of such multicomponent alloys under extreme conditions is studied in a non-activated model system: CeO 2 doped with 2 wt% Mo, 1.5 wt% Ru, 0.75 wt% Pd, 0.5 wt% Re and 0.25 wt% Rh. The doped CeO 2 films were irradiated with I 2+ ions (610°C, 10 16 and 5×10 16 I 2+ /cm 2 ). For selected samples post-irradiation heat treatment was conducted (900°C, 1100°C). Analytical TEM revealed the formation of 5-20 nm precipitates containing Pd, Mo, and Re sometimes associated with cavities. Iodine was found to segregate to grain boundaries and cracks. After heat treatment at 1100°C, the CeO 2 matrix had recrystallized. Precipitates containing Pd, Mo, Re, and Ru were observed near the interface with the polycrystalline YSZ substrate. It follows that Pd is the most mobile element, followed by Mo and Re. Finally, while irradiation promotes precipitation, high-temperature effects are more significant.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Irradiation-induced swelling of pure chromium with 5 MeV Fe ions in the temperature range 450–650 °C

A surface coating using pure chromium has been proposed to increase the accident tolerance of Zircaloy cladding in pressurized water reactors. However, there is not much irradiation experience with Cr alloys and especially pure Cr. In the present study, pure chromium was irradiated with 5 MeV Fe ions to 50 peak dpa (displacements per atom) at temperatures of 450, 500, 550, 600 and 650 °C. Then irradiation at the peak swelling temperature of 550 °C was conducted to 50, 100, 150 peak dpa. Swelling at 50 dpa was observed over the entire temperature range studied, 450–650 °C, but appeared to be decreasing strongly at the temperature boundaries of the experiment. After an initial transient of rapid swelling, chromium was observed to swell at a rate of ~0.03–0.04%/dpa (up to 120 local dpa), which is much lower than pure Fe at 0.2%/dpa. This low swelling rate was found to be relatively insensitive to dpa rate, which varied by a factor of ~2 over the depth of data collection. Here, swelling was observed to begin quickly with an incubation period less than 10 dpa. Self-organization in the form of void ordering was observed to be developing at 50 dpa, becoming better defined with increasing dose. The void alignment direction is determined to be the $\langle$111$\rangle$ axial direction.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Displacement of carbon atoms in few-layer graphene

Molecular dynamics simulations were performed to study the susceptibility of carbon atom displacement under electron irradiation. The mapping of threshold displacement energies at different recoiling directions showed that the energies are very sensitive to the layer configurations and positions of neighboring atoms. Carbon atoms on the top and the bottom layers of few-layer graphene are most vulnerable to irradiation damage due to lack of constraints from the neighboring graphene layers. As indirect experiment evidence, transmission electron microscopy was performed on the edge of folded few-layer graphene, which made it possible to reveal “the inside” and compare irradiation tolerance of atoms at different layers, by using an electron analysis beam for both displacement creation and in situ characterization.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Strain modulation using defects in two-dimensional MoS 2

We investigate the nature of strain in MoS 2 and correlate it to defect types and densities, while systematically assessing the tolerance of this low dimensional material to He and Au ion irradiations. Through a series of theoretical predictions and experimental observations, we establish the onset of the crystalline-to-amorphous transition in MoS 2 and identify sulfur vacancies as the most favorable defects introduced during irradiation. We note the presence of both tensile and compressive strains, which depend on the types of defects introduced into the lattice and vary with increasing fluence. In conclusion, the results show that defects can be used to tune strain in two-dimensional materials and provide an exciting pathway for using external stimuli to control properties of low dimensional materials.

2-dimensional systems↗
DOE OSTI2020

Radiation response of FeCrAl-coated Zircaloy-4

Coating the surface of Zircaloy-4 light water reactor fuel cladding tube is of considerable interest for enhancing its accident tolerance. In this study, thermal annealing of FeCrAl-coated Zircaloy-4 at 725 °C for 500 h, was used to induce interfacial reactions between Zircaloy-4 and FeCrAl. The interface zones were then irradiated by 3.5 MeV Zr ions at 400 °C, up to 50, 100, 150 peak dpa values. Transmission electron microscopy (TEM) and scanning TEM were used to characterize microstructural and composition changes before and after ion irradiation. Three interfacial phases were identified: FeZr 3 , (Fe,Cr) 2 Zr, and ZrC. The widest intermetallic layer, FeZr3, had large grains. The narrower phases, (Fe,Cr)2Zr and ZrC, contained small grains and were often mixed. The unexpected observation of the ZrC phase was attributed to the presence of very small impurity level concentrations of carbon in the powder material. No void swelling was observed in any of the phases, including the FeCrAl coating and Zircaloy-4 substrate. (Fe,Cr) 2 Zr, however, fully amorphized after irradiation, even at the lowest dpa.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ni coating on 316L stainless steel using cage plasma treatment: Feasibility and swelling studies

A modified cage plasma nitriding technique is used to coat a Ni film onto a 316L substrate as a protective layer for austenitic steels in molten fluoride salts. The coating is achieved by deposition of Ni atoms sputtered from a Ni cage with a 316L substrate floated at the same potential as the cage to reduce plasma sputtering on the substrate. The Ni coating is porosity-free and precipitation-free and forms a γ-(Fe, Ni) phase due to interdiffusion from the substrate. Beneath the interdiffusion layer exists a thick γ-phase layer mainly affected by long-range nitrogen diffusion along the grain boundary. This layer develops grain boundary Cr nitride precipitates. Ion irradiation on the polished cross-section of the plasma-treated sample shows no void swelling in the surface-deposited Ni layer, very limited void formation in N diffusion layer, and significant void swelling in bulk unaffected by nitrogen. The studies demonstrate the feasibility of the technique for Ni coating and show good swelling resistance of the coating layer and N diffusion-affected layer. Mechanisms are discussed in this paper.

36 MATERIALS SCIENCE↗