Computational Materials Science and Engineering of Materials in Nuclear Reactors: Poster Session
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Dilpuneet Aidhy, Clemson University; Michael Tonks, University of Florida; Mahmood Mamivand; Giovanni Bonny, Belgian Nuclear Research Center
Monday 5:30 PM
February 24, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr
E-33 (Invited): Development of a New Thermochemistry Solver for Multiphysics Simulations of Nuclear Materials: Parikshit Bajpai1; Max Poschmann1; David Andrs2; Chaitanya Bhave3; Michael Tonks3; Markus Piro1; 1Ontario Tech University; 2Idaho National Laboratory; 3University of Florida
Nuclear materials are highly complex multiscale, multiphysics systems and an effective prediction of nuclear reactor performance and safety requires simulation capabilities that exhibit a very tight coupling between different physical phenomena. The Idaho National Laboratory’s Multiphysics Object Oriented Simulation Environment (MOOSE) provides the computational foundation for performing such simulations and currently consists of the continuum scale fuel performance code BISON and the mesoscale phase field code Marmot. A new application called Yellowjacket is under development to directly couple thermodynamic equilibrium and kinetics in order to model corrosion in advanced reactors. As part of Yellowjacket, a thermochemistry code is being developed to provide rapid access to thermodynamic databases and perform thermochemical equilibrium calculations for a range of different materials, which is currently in its infancy. This paper describes the recent progress towards development of Yellowjacket and presents the plans for developing capabilities of practical interest to the nuclear industry.
E-34: Ab-initio Modelling of Iodine Defects in Strained Zirconium and Ordered Zirconium-oxygen Suboxides: Vlad Podgurschi1; Daniel King1; Jana Smutna1; Mark Wenman1; 1Imperial College London
In water reactors, iodine stress corrosion cracking is the main cause of pellet cladding interaction failures but the mechanism and chemistry are debated. The protective effect of oxygen is also not fully understood. Density functional theory calculations were performed to investigate the formation energy of iodine defects in bulk zirconium under the effect of hydrostatic strain (-3% to 3%). The formation energy of iodine interstitial defects decreased with increasing strain and became favourable (-0.44 eV) at a strain of 3%. The substitutional energy of iodine was found to be relatively insensitive to strain. In order to gain an understanding into the protective effect of oxygen, various ordered zirconium-oxygen suboxides were considered (Zr6O, Zr3O and Zr2O). The formation energy of iodine defects increased as the oxygen content increased (2.67, 3.51 and 4.82 eV respectively), supporting the idea that oxygen has a protective effect at a stress corrosion crack tip.
E-36: ICME Modeling of U-10%wt Mo Alloys: A Linkage between Microstructure Evolution and Process Modeling: Chao Wang1; Zhijie Xu1; William Frazier1; Ayoub Soulami1; Saumyadeep Jana1; Kyoo Sil Choi1; Curt Lavender1; Vineet Joshi1; 1Pacific Northwest National Laboratory
Low-enriched uranium alloyed with 10wt% molybdenum (U-10Mo) has been recognized as a promising candidate to replace high-enriched uranium fuel due to its ability to meet the neutron flux demands of U.S. high power research reactors and initial experimental evaluations of irradiation performance. Manufacturing the U-10Mo alloy involves a complex series of thermomechanical processing steps, including homogenization, hot rolling, annealing, cold rolling, and hot isostatic pressing. As part of this project, several models/modeling methods have been developed for the individual processes. The interaction and coupling between individual processes use the concept of ICME which aims to bridge the information passing between interacting models and investigates the impact of manufacturing processes on material microstructure evolution. The ICME framework is demonstrated by combining all the individual processes. It is shown that the implementation of ICME leads to improved predictions, better understanding of microstructure across multiple processes, and accelerated and more cost-effective development effort.
E-37: Machine Learning-assisted Risk-informed Sensitivity Analysis for ATF Under SBO: Jianguo Yu1; Cole Blakely1; Hongbin Zhang1; 1Idaho National Laboratory
ATF fuel rods have been designed to have similar or improved behavior in normal operation and provide increased coping time during design basis accidents (DBA) and beyond DBA. A key aspect in the evaluation of the ATF designs is the determination of potential increases in coping time with respect to advancements in fuel and cladding materials. After Fukushima Daiichi nuclear power plant accident, station blackout (SBO) has been widely recognized as one of the most severe postulated events and the fuel rod behavior should be effectively evaluated in the operations of nuclear power plants. However, the studies on fuel rod performance such as the cladding failure under SBO are still scarce. In this work, we will present our recent progress on machine learning-assisted risk-informed sensitivity analysis for ATF under SBO. We will demonstrate that it is feasible to estimate the coping time as ATF fuel and cladding are chosen.
E-38: Mesoscale Modeling of High Burn-up Structure (HBS) Formation and Evolution in U-Mo Alloys: Karim Ahmed1; Daniel Schwen2; Yongfeng Zhang2; 1Texas A&M University; 2Idaho National Laboratory
U-Mo and other nuclear fuels develop a unique microstructure under irradiation usually known as the High Burn-up Structure (HBS). Recrystallization was proposed as a mechanism that facilitates HBS formation. A phase field model was utilized to study irradiation-induced recrystallization. The model takes into consideration the chemical energy of gas atoms, interfacial energies of grain boundaries and bubble surfaces and strain energy associated with dislocations. This renders the model capable of simulating the formation and growth of sub-grains and bubbles concurrently. The model predicts a strong effect of magnitude and distribution of dislocation density, grain boundary energy, and bubble surface energy on the formation of sub-grains. A systematic study of the effects of temperature, grain size, dislocation density/burn-up, bubble size and fraction on the overall kinetics of HBS formation and evolution was conducted. The model predictions agree well with reported data in literature.
E-39: Molecular Dynamics and Phase-field Study of Anisotropic Grain Growth Behavior in UO2: Jarin French1; Yipeng Gao2; Xian-Ming Bai1; 1Virginia Tech; 2Idaho National Laboratory
UO2 is the primary nuclear fuel in light water reactors. The fuel performance while in-reactor can be significantly affected by the fuel’s grain growth behavior. Using a combination of molecular dynamics and phase-field simulations, we have systematically investigated microstructural evolution in UO2 as influenced by anisotropic grain boundary (GB) properties. Molecular dynamics simulations are conducted to study the misorientation- and rotation-axis-dependent anisotropy in GB energy and GB mobility in UO2. Our results show that GB mobility has a strong anisotropy, while GB energy is not sensitive to these two GB characters. In general, the GBs with a <111> rotation axis have higher mobility than other rotation axes. Phase-field simulations are performed to elucidate the effect of anisotropic GB properties on grain growth behavior at the mesoscale.
E-40: Origin of Hardening in Spinodally-decomposed Fe-Cr Binary Alloys: Tomoaki Suzudo1; Takeshi Toyama2; Yoshiyasu Nagai2; 1Japan Atomic Energy Agency; 2Tohoku University
Spinodal decomposition in thermally aged Fe-Cr binary alloys leads to significant hardening, which is the direct cause of the so-called 475C-embrittlement. Our previous study has discovered that the hardness scales linearly with short-range-order parameter; this suggests that Cr-Cr neighboring pairs formed by phase separation cause hardening. To understand the atomistic origin of hardening, we conducted a series of numerical simulations, in which an edge dislocation interacts to spinodally-decomposed structure. By removing specified Cr-Cr pairs from the system, we investigated the contribution of these Cr-Cr pairs to hardening. The result indicated that Cr-Cr pairs either cut or compressed by the moving dislocation significantly contribute hardening, and the influence from the remaining pairs is minor.
E-41: Recrystallization and Grain Growth Simulations for Multiple-pass Rolling and Annealing of U-10Mo: William Frazier1; Chao Wang1; Shenyang Hu1; Zhijie Xu1; Vineet Joshi1; 1Pacific Northwest National Laboratory
A simulation model of recrystallization and grain growth has been developed to investigate grain structure evolution during deformation and heat treatment in polycrystalline UMo fuel. SEM images of microstructures were directly used as input for closed loop simulations of multiple rolling and annealing passes. FEM calculations of deformation and Potts Model simulations of recrystallization and grain growth were used iteratively to inform each subsequent stage of simulation. The model was then applied to predict the grain structure evolution during multiple-pass hot rolling of U-10Mo, and benchmarked against experimentally observed U-10Mo recrystallization behavior. The results showed that our model is able to capture the coupling between deformation and recrystallization, and quantitatively reproduce the observed U-10Mo recrystallization and grain growth kinetics with respect to time and temperature. A separate model of post-recrystallization U-10Mo grain growth is also discussed.
E-44: The Contribution of Li Vacancies to the Evolution of Thermal Conductivity in Irradiate LiAlO2: Seyed Aria Hosseini1; Tina Mirzae1; Eric Peraza2; Alex Greaney1; 1University of California, Riverside; 2Pacific Northwest National Laboratory
Lithium aluminate (LiAlO2) is a target material for the production of tritium by transmutation of lithium. We aim to understand the evolution of the thermal conductivity of LiAlO2 under irradiation. To this end, the intrinsic phonon transport properties for LiAlO2 — its phonon dispersion and phonon-phonon scattering lifetime — were computed from first principles calculations and used to inform Boltzmann transport simulations used to predict the anisotropic thermal conductivity tensor of single crystal LiAlO2 at temperatures from 300 to 1200 K. The ab initio computed intrinsic phonon properties were also used to calibrate calculations of thermal conductivity from classical molecular dynamics (MD) simulations using the Green-Kubo method. The MD simulations were extended to defected structures to compute the additional scattering rate due to the presence of irradiation induced Li-vacancies. The results are compared with Rayleigh scattering models for impurity scattering.
E-45: Thermodynamics of Hydrogen Pickup in Zr Alloys: Vidur Tuli1; Christopher Jones2; Katie Moore2; Michael Preuss2; Magnus Limback3; Antoine Claisse3; Patrick Burr1; 1The University of New South Wales; 2University of Manchester; 3Westinghouse Electric Sweden AB
Hydrogen pick-up of zirconium alloys is a life-limiting concern for nuclear fuel cladding. We have used a combination of NanoSIMS imaging of deuterated and corroded samples and ab-initio atomic scale simulations to shed light on H distribution in Zr alloys. We observe that deuterium hotspots are co-located with second phase particles, but we provide evidence that it is thermodynamically unfavourable for hydrogen to dissolve in Zr(Fe,Cr)2 SPPs compared to the bulk α-Zr. It is proposed that H is attracted to the interface between the SPPs and the Zr matrix, and that local strain plays a key role. We also find that the solubility of H in metals can be predicted by a description of the local (nearest neighbour) chemistry, thus enabling predictions for any alloy system without the need for explicit ab-initio atomic-scale simulations. For instance, H prefers tetrahedral interstitial sites that maximise Zr and minimise Fe as nearest neighbours.