Materials in Nuclear Energy Systems (MiNES) 2021: Material Properties Evolution- Session II
Program Organizers: Todd Allen, University of Michigan; Clarissa Yablinsky, Los Alamos National Laboratory; Anne Campbell, Oak Ridge National Laboratory
Thursday 8:00 AM
November 11, 2021
Room: Allegheny
Location: Omni William Penn Hotel
Session Chair: Benjamin Eftink, Los Alamos National Laboratory
8:00 AM Invited
Mesoscale Simulations of Interactions between Dislocation Loop and Point Defects in bcc Iron: Haixuan Xu1; Ziang Yu1; 1University of Tennessee
Dislocation loops play a critical role in irradiation-induced microstructural evolution of structural materials. Conventional understanding of the interaction between dislocations loops and point defects (PD), particularly at mesoscale, is challenging and limited. In this study, the capture efficiency and bias factor of dislocation loops are determined using a recently developed method based on the lifetime of point defect computed using kinetic Monte Carlo simulations in a model bcc iron system. Bias factors and maximum swelling rate from this approach are compared with both neutron and ion-irradiation experiments and previous theoretical results. The effects of loop densities, loop sizes and temperatures are systematically examined. Comparative analysis of dislocation loop bias and dislocation bias has also been carried out. This approach also applies to many other mesoscale processes and a variety of microstructure features, such as grain boundaries and interfaces.
8:40 AM
Mechanical Response of HT9 and T91 under Dual-ion and Neutron Irradiations: Pengcheng Zhu1; Shradha Agarwal1; Steven Zinkle1; 1University of Tennessee, Knoxville
9-12% Cr ferritic/martensitic steels are promising candidate structural materials for Generation IV fission reactors. HT9 and T91 alloys were subjected to dual-ion (9 MeV Fe3+ and 3.42 MeV He2+, 445 and 520 ℃) and BOR60 reactor irradiations to quantify the possibility of using ion irradiation to simulate neutron irradiation in microstructures and mechanical properties. Nanoindentation hardness testing was performed with Berkovich indenter to obtain information on the bulk hardness of the dual-ion irradiated samples due to limited damage volumes. For the neutron irradiated samples, both nanoindentation and Vickers hardness testing were conducted. An accurate way to extract bulk mechanical properties form nanoindentation data will be used based on our previous study on FeCr binary alloys. The results of TEM characterization of the bubbles and dislocation loops will be summarized, and detailed comparisons will be provided on the predicted (dispersed barrier hardening superposition) vs. measured strength values of the irradiated specimens.
9:00 AM
Rapid Simulation of the Irradiated Microstructure in Flux Thimble Tubes to High Dose Using Ion Irradiation
: Miao Song1; Kevin Field2; Cem Topbasi3; Gary Was2; 1Shanghai Jiao Tung University; 2University of Michigan; 3Electric Power Research Institute
Flux Thimble Tubes (FTTs) removed from a PWR were subjected to self-ion irradiation to increase dpa to match the 100 dpa peak in the FTT. Ion irradiated microstructures were compared to those created in reactor to determine the extent to which ion irradiation can be used to predict the microstructure evolution in life extension timeframes. FTT samples were taken from regions of the tube with 38 dpa and 74 dpa and irradiated with 8 MeV Ni3+ at 390 and 410°C and a damage rate of ~ 10-3 dpa/s. Ion irradiation of reactor irradiated samples at 410℃ resulted in the same size and number density of nanocavities, loops, and clusters, and RIS at 100 dpa as in the FTT section at the same dose with the exception of Ni-Si-Mn cluster dissolution during ion irradiation. Extension of damage to 160 dpa resulted in precipitation at grain boundaries and grain boundary migration.
9:20 AM Cancelled
Atomistically Informed Cascade Overlap Model to Predict Alloy 800H Microstructure Evolution during High-dose Neutron Irradiation: Samuel Morris1; Brian Wirth1; 1University of Tennessee Knoxville
High-dose neutron or self-ion irradiation of Ni-base alloys has been shown to produce large quantities of immobile defects, such as interstitial Frank loops. Irradiation experiments have shown the number densities of these defects tend to saturate after doses on the order of a few dpa. However, cluster dynamics modeling substantially overpredicts in these alloys the Frank loop number density at higher doses due to its lack of accounting for cascade overlap effects, which may alter the amount and type of stable damage generated in new cascades, as well as the size or Burgers vector of existing defects. In this work, we use the results of atomistic simulations of cascade overlap in fcc Ni to develop a cascade overlap model suitable for incorporation into cluster dynamics. The model considers changes in cascade-generated damage and changes in size and Burgers vector of existing defects due to cascade overlap.
9:40 AM
Solute Segregation and Precipitation Across Damage Rates in Dual Ion Irradiated T91 Steel: Stephen Taller1; Valentin Pauly2; Zhijie Jiao2; Gary Was2; 1Oak Ridge National Laboratory; 2University of Michigan
Dual ion irradiations using 5.0 MeV defocused Fe2+ ions and co-injected He2+ ions were conducted on ferritic-martensitic steel T91 to 17 dpa in a damage rate range 5×10-5 to 3×10-3 dpa/s at 445°C followed by characterization using scanning transmission electron microscopy. Ni/Si clusters and radiation induced segregation were quantified using energy dispersive x-ray spectroscopy (EDS) at each condition and compared with the same material in the as-received condition and irradiated in the BOR-60 reactor at 376°C. The density of Ni/Si clusters and magnitude of Ni and Si enrichments were found to decrease monotonically with damage rate. No significant Cr segregation was found with dual ion irradiation. Rate theory calculations suggest the increased recombination at higher ion damage rates reduced the segregation and Ni/Si cluster density compared to BOR-60. This work highlights the importance of irradiation damage rate when using ion irradiation to simulate reactor irradiation.
10:00 AM Break