Isabella van Rooyen

Profile Information
Name
Isabella van Rooyen
Institution
Idaho National Laboratory
Position
Distinguished Staff Scientist
Affiliation
University of Florida,
h-Index
ORCID
0000-0001-8524-938X
Expertise
Additive Manufacturing, Ceramics, Characterization, Cladding, Composites, Fission Products, Grain Boundary, Silicon Carbide (SiC), TRISO, uranium compounds, Zirconium
Publications:
"Associations of Pd, U and Ag in the SiC layer of neutron-irradiated TRISO fuel" Thomas Lillo, Isabella van Rooyen, Journal of Nuclear Materials Vol. 460 2015 97-106 Link
Knowledge of the associations and composition of fission products in the neutron irradiated SiC layer of high-temperature gas reactor TRISO fuel is important to the understanding of various aspects of fuel performance that presently are not well understood. Recently, advanced characterization techniques have been used to examine fuel particles from the Idaho National Laboratory’s AGR-1 experiment. Nano-sized Ag and Pd precipitates were previously identified in grain boundaries and triple points in the SiC layer of irradiated TRISO nuclear fuel. Continuation of this initial research is reported in this paper and consists of the characterization of a relatively large number of nano-sized precipitates in three areas of the SiC layer of a single irradiated TRISO nuclear fuel particle using standardless EDS analysis on focused ion beam-prepared transmission electron microscopy samples. Composition and distribution analyses of these precipitates, which were located on grain boundaries, triple junctions and intragranular precipitates, revealed low levels, generally <10 atomic %, of palladium, silver and/or uranium with palladium being the most common element found. Palladium by itself, or associated with either silver or uranium, was found throughout the SiC layer. A small number of precipitates on grain boundaries and triple junctions were found to contain only silver or silver in association with palladium while uranium was always associated with palladium but never found by itself or in association with silver. Intergranular precipitates containing uranium were found to have migrated ~23 µm along a radial direction through the 35 µm thick SiC coating during the AGR-1 experiment while silver-containing intergranular precipitates were found at depths up to ~24 µm in the SiC layer. Also, Pd-rich, nano-precipitates (~10 nm in diameter), without evidence for the presence of either Ag or U, were revealed in intragranular regions throughout the SiC layer. Because not all grain boundaries and triple junctions contained precipitates with fission products and/or uranium, along with the differences in migration behavior between Pd, Ag and U, it was concluded that crystallographic grain boundary and triple junction parameters likely influence migration behavior.
"Effect of Neutron Irradiation Damage on Fission Product Transport in the SiC Layer of TRISO Fuel Particles" Isabella van Rooyen, Subhashish Meher, OSTI.gov, Conf. Proceedings Vol. 2018 Link
"Effect of Sample Preparation Techniques on Grain Boundary Characterization of Annealed TRISO-Coated Particles" Mary Lou Dunzik-Gougar, Isabella van Rooyen, C.M. Hill, T. Trowbridge, J. Madden, J. Burns, Nuclear Technology Vol. 196(1) 2016 111-120
"Influence of SiC grain boundary character on fission product transport in irradiated TRISO fuel" Thomas Lillo, Isabella van Rooyen, Journal of Nuclear Materials Vol. 473 2016 83-92 Link
In this study, the fission product precipitates at silicon carbide grain boundaries from an irradiated TRISO particle were identified and correlated with the associated grain boundary characteristics. Precession electron diffraction in the transmission electron microscope provided the crystallographic information needed to identify grain boundary misorientation and boundary type (i.e., low angle, random high angle or coincident site lattice (CSL)-related). The silicon carbide layer was found to be composed mainly of twin boundaries and small fractions of random high angle and low angle grain boundaries. Most fission products were found at random, high-angle grain boundaries, with small fractions at low-angle and CSL-related grain boundaries. Palladium (Pd) was found at all types of grain boundaries while Pd-uranium and Pd-silver precipitates were only associated with CSL-related and random, high-angle grain boundaries. Precipitates containing only Ag were found only at random, high-angle grain boundaries, but not at low angle or CSL-related grain boundaries.
"Microstructure and Fission Product Distribution Examination in the UCO kernel of TRISO Fuel Particles" Isabella van Rooyen, Yong Yang, Terry Holesinger, Mukesh Bachhav, OSTI.gov, Conf Proceedings Vol. 2018 Link
"Precession electron diffraction for SiC grain boundary characterization in unirradiated TRISO fuel" Thomas Lillo, Isabella van Rooyen, Yaqiao Wu, Nuclear Engineering and Design Vol. 305 2016 277-283 Link
Precession electron diffraction (PED), a transmission electron microscopy-based technique, has been evaluated for the suitability for evaluating grain boundary character in the SiC layer of tristructural isotropic (TRISO) fuel. This work reports the effect of transmission electron microscope (TEM) lamella thickness on the quality of data and establishes a baseline comparison to SiC grain boundary characteristics, in an unirradiated TRISO particle, determined previously using a conventional electron backscatter diffraction (EBSD) scanning electron microscope (SEM)-based technique. In general, it was determined that the lamella thickness produced using the standard focused ion beam (FIB) fabrication process (∼80 nm), is sufficient to provide reliable PED measurements, although thicker lamellae (∼120 nm) were found to produce higher quality orientation data. Also, analysis of SiC grain boundary character from the TEM-based PED data showed a much lower fraction of low-angle grain boundaries compared to SEM-based EBSD data from the SiC layer of a TRISO-coated particle made using the same fabrication parameters and a SiC layer deposited at a slightly lower temperature from a surrogate TRISO particle. However, the fractions of high-angle and coincident site lattice (CSL)-related grain boundaries determined by PED are similar to those found using SEM-based EBSD. Since the grain size of the SiC layer of TRSIO fuel can be as small as 250 nm (Kirchhofer et al., 2013), depending on the fabrication parameters, and since grain boundary fission product precipitates in irradiated TRISO fuel can be nano-sized, the TEM-based PED orientation data collection method is preferred to determine an accurate representation of the relative fractions of low-angle, high-angle, and CSL-related grain boundaries. It was concluded that although the resolution of the PED data is better by more than an order of magnitude, data acquisition times may be significantly longer or the number of areas analyzed needs to be significantly greater than the SEM-based method to obtain a statistically relevant distribution. Also, grain size could be accurately determined but significantly larger analysis areas would be required than those used in this study.
"Sample Preparation Techniques for Grain Boundary Characterization of Annealed TRISOCoated Particles" Mary Lou Dunzik-Gougar, Isabella van Rooyen, C. M. Hill, James Madden, Jatuporn Burns, Tammy Trowbridge, Nuclear Technology Vol. 196 2017 111-120 Link
Crystallographic information about layers of silicon carbide (SiC) deposited by chemical vapor deposition is essential to understanding layer performance, especially when the the layers are in nonplanar geometries (e.g., spherical). Electron backscatter diffraction (EBSD) was used to analyze spherical SiC layers using a different sampling approach that applied focused ion beam (FIB) milling to avoid the negative impacts of traditional sample polishing and address the need for very small samples of irradiated materials for analysis. The mechanical and chemical grinding and polishing of sample surfaces can introduce lattice strain and result in the unequal removal of SiC and the surrounding layers of different materials due to the hardness differences among these materials. The nature of layer interfaces is thought to play a key role in the performance of SiC; therefore, the analysis of representative samples at these interfacial areas is crucial. In the work reported herein, a FIB was employed in a novel manner to prepare a more representative sample for EBSD analysis from tristructural-isotropic layers that are free of effects introduced by mechanical and chemical preparation methods. In addition, the difficulty of handling neutron-irradiated microscopic samples (such as those analyzed in this work) has been simplified using pretilted mounting stages. The results showed that while the average grain sizes of samples may be similar, the grain boundary characteristics can differ significantly. Furthermore, low-angle grain boundaries comprised 25% of all boundaries in the FIB-prepared sample compared to only 1% to 2% in the polished sample from the same particle. This study demonstrated that the characterization results from FIB-prepared samples provide more repeatable results due to the elimination of the effects of sample preparation.
"SiC Grain Boundary Character and Fission Product Transport in Irradiated TRISO Fuel Particles" Isabella van Rooyen, Thomas Lillo, Nuclear Fuels & Material Spotlight Vol. 5 2016 31-38 Link
"Silicon carbide grain boundary distributions, irradiation conditions, and silver retention in irradiated AGR-1 TRISO fuel particles" Jeffery Aguiar, Thomas Lillo, Isabella van Rooyen, Nuclear Engineering and Design Vol. 329 2018 46-52 Link
Distributions of silicon carbide grain boundary types (random high angle, low angle, and coincident site lattice-related boundaries), were compared in irradiated tristructural isotropic-coated fuel particles from the Advanced Gas Reactor-1 experiment exhibiting high (>80%) and low (<19%) Ag-110m retention. Grain orientation from transmission electron microscope-based precession electron diffraction data, and, ultimately, grain boundary distributions, indicate irradiated particles with high Ag-110m retention correlate with lower relative fractions of random, high-angle grain boundaries. An inverse relationship between the random, high-angle grain boundary fraction and Ag-110m retention was found and is consistent with grain boundary percolation theory. Also, the SiC grain boundary distribution in an irradiated, low Ag-110m retention, Variant 1 particle was virtually identical to that of a previously reported as-fabricated (unirradiated) Variant 1 TRISO particle. Thus, SiC layers with grain boundary distributions associated with low Ag-110m retention may have developed during fabrication and were present prior to irradiation, assuming significant microstructural evolution did not occur during irradiation. Finally, irradiation levels up to 3.6 × 1025 n/m2 and 16.7% fissions per initial metal atom were found to have little effect on association of fission product precipitates with specific grain boundary types in particles exhibiting between 19% and 80% Ag-110m retention.
"STEM-EDS Analysis of Fission Products in Neutron-Irradated TRISO Fuel Particles from AGR-1 Experiment" bin leng, Kumar Sridharan, Izabela Szlufarska, Yaqiao Wu, Isabella van Rooyen, Journal of Nuclear Materials Vol. 475 2016 62-70 Link
Historic and recent post-irradiation-examination from the German AVR and Advanced Gas Reactor Fuel Development and Qualification Project have shown that 110 m Ag is released from intact tristructural isotropic (TRISO) fuel. Although TRISO fuel particle research has been performed over the last few decades, little is known about how metallic fission products are transported through the SiC layer, and it was not until March 2013 that Ag was first identified in the SiC layer of a neutron-irradiated TRISO fuel particle. The existence of Pd- and Ag-rich grain boundary precipitates, triple junction precipitates, and Pd nano-sized intragranular precipitates in neutron-irradiated TRISO particle coatings was investigated using Scanning Transmission Electron Microscopy and Energy Dispersive Spectroscopy analysis to obtain more information on the chemical composition of the fission product precipitates. A U-rich fission product honeycomb shape precipitate network was found near a micron-sized precipitate in a SiC grain about ∼5 μm from the SiC-inner pyrolytic carbon interlayer, indicating a possible intragranular transport path for uranium. A single Ag-Pd nano-sized precipitate was found inside a SiC grain, and this is the first research showing such finding in irradiated SiC. This finding may possibly suggest a possible Pd-assisted intragranular transport mechanism for Ag and may be related to void or dislocation networks inside SiC grains. Preliminary semi-quantitative analysis indicated the micron-sized precipitates to be Pd2Si2U with carbon existing inside these precipitates. However, the results of such analysis for nano-sized precipitates may be influenced by the SiC matrix. The results reported in this paper confirm the co-existence of Cd with Ag in triple points reported previously.
"The Effect of High-Temperature Annealing on the Grain Characteristics of a Thin Chemical Vapor Deposition Silicon Carbide Layer" Isabella van Rooyen, Philippus van Rooyen, Mary Lou Dunzik-Gougar, Microscopy and Microanalysis, 19 (Supplement 2) Vol. 19 2013 1948-1949 Link
Presentations:
"Advanced Electron Microscopic Examination Aided in the Identification of Silver and Palladium in Irradiated TRISO Coted Particles" Isabella van Rooyen, TMS 2014 February 16-20, (2014)
"Effect of Neutron Irradiation Damage on Fission Product Transport in the SiC Layer of TRISO Fuel Particles" Isabella van Rooyen, Subhashish Meher, HTR 2018 October 8-10, (2018)
"Microstructure and Fission Product Distribution Examination in the UCO Kernel of TRISO Fuel Particles" Isabella van Rooyen, Yong Yang, Terry Holesinger, , HTR 2018 October 8-10, (2018)
NSUF Research Collaborations

APT Study of Fission Product Transport in Unirradiated/Neutron Irradiated TRISO Fuel Particles - FY 2015 RTE 1st Call, #541

Characterization and correlation of SiC layer grain size/grain boundary orientation with strength/layer growth conditions - Lite - FY 2013 RTE Solicitation, #410

Characterize the Irradiated Microstructure and Understand the Fission Product Behavior in an Irradiated and Safety Tested AGR-1 TRISO Fuel Particle New Proposal - FY 2017 RTE 3rd Call, #1091

Electron Tomography for Three-Dimensional Characterization of Intragranular Fission Product Transport in Neutron-Irradiated Silicon Carbide in TRISO Fuel - FY 2018 RTE 1st Call, #1151

Enhancing irradiation tolerance of steels via nanostructuring by innovative manufacturing techniques - FY 2016 CINR, #3038

Fission Product Distribution Comparison in Irradiated and Safety Tested AGR-1 and AGR-2 TRISO Fuel Particles - FY 2018 RTE 1st Call, #1256

Investigation of Ag, Pd, I, Ru, and Sr fission products in bulk and grain boundaries of neutron irradiated SiC - FY 2018 RTE 3rd Call, #1600

Microstructural characterization of in-situ ion irradiated SiC layer of TRISO fuel - FY 2019 RTE 2nd Call, #1810

Performance and Structural Damage Analysis of Chalcogenide Glass Phase Change Temperature Sensors Under Ion Irradiation - FY 2019 RTE 3rd Call, #2832

STEM/EELS Study of Fission Product Transport in Neutron Irradiated TRISO Fuel Particles - FY 2015 RTE 3rd Call, #581

STEM/LEAP Study of Fission Product Transportation in Neutron Irradiated TRISO Fuel Particles - FY 2013 RTE Solicitation, #412

Understand the atomic positions of the metallic fission product in UCO Fuel Kernels and Determine the exact stoichiometry of UC, UO phase of Irradiated TRISO Fuel Particles by Using Titan Themis 200 with EELS characterization Capability - FY 2019 RTE 2nd Call, #1779

Understand the Fission Products Behavior and Irradiation Effects in UCO Fuel Kernels of Irradiated AGR-1 and AGR-2 TRISO Fuel Particles by Using Atom Probe Tomography - FY 2020 RTE 2nd Call, #4217

Understand the Fission Products Behavior and Irradiation Effects in UCO Fuel Kernels of Irradiated AGR-1 and AGR-2 TRISO Fuel Particles by Using Atom Probe Tomography - FY 2018 RTE 3rd Call, #1593

Understand the Fission Products Behavior and Irradiation Effects in UCO Fuel Kernels of Irradiated AGR-1 and AGR-2 TRISO Fuel Particles Using Titan Themis 200 with ChemiSTEM Capability - FY 2018 RTE 1st Call, #1257

Understand the Fission Products Behavior in UCO Fuel Kernels of safety tested AGR2 TRISO Fuel Particles by Using Titan Themis 200 with ChemiSTEM Capability - FY 2019 RTE 3rd Call, #2893