Computational Materials Science and Engineering of Materials in Nuclear Reactors: Multiscale Modeling II
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
Thursday 2:00 PM
February 27, 2020
Room: Theater A-9
Location: San Diego Convention Ctr
Session Chair: Eva Zarkadoula, Oak Ridge National Laboratory; Dilpuneet Aidhy, University of Wyoming
2:00 PM
Molecular Dynamics Studies of Thermal Conductivity Degradation of UO2 due to Dispersed Xe Atoms and Xe Bubbles: Weiming Chen1; Michael Cooper2; Ziqi Xiao1; David Andersson2; Xian-Ming Bai1; 1Virginia Polytechnic Institute and State University; 2Los Alamos National Laboratory
Thermal conductivity uranium dioxide (UO2) is a critical nuclear fuel performance property. In reactor fuels, Xe fission gas can be trapped by vacancies to form dispersed Xe or aggregate to form Xe bubbles, both of which can significantly impact the fuel thermal transport properties. In this work, molecular dynamics simulations are conducted to study the phonon scattering effects by dispersed Xe atoms and Xe bubbles in UO2. At a given Xe concentration, it is found that the fuel thermal conductivity increases with bubble size initially then reaches a saturated value, indicating dispersed Xe atoms can cause more thermal conductivity reduction than their clustered form. However, when the Xe content in a bubble is high, the thermal conductivity reduction is stronger than an empty void. Detailed analysis reveals that the high bubble pressure can displace bubble surface atoms andcause additional phonon scattering effect.
2:20 PM
A Micromechanics-based Modeling Approach to Predict the Mechanical Properties of Zircaloy with Hydride Precipitates: Varun Gupta1; Yulan Li1; Shenyang Hu1; Arun Devaraj1; David Senor1; 1Pacific Northwest National Laboratory
The formation of hydride precipitates in zirconium-based alloys have a significant impact on their strength and ductility. The heterogeneous microstructures in these Zircaloys limit the application of phenomenological or smeared continuum damage models for accurately predicting their mechanical performance. In this work, a microstructure-based finite element modeling framework has been developed to predict the mechanical properties of Zircaloy. Quantitative microstructural details extracted from scanning electron microscopy (SEM) images was used to generate heterogeneous microstructures including the morphology and spatial distribution of hydrides. The talk will also feature a phase field modeling approach to study stress-enhanced hydrogen diffusion and hydride formation in polycrystalline Zirconium, and material property degradation.
2:40 PM
Microstructure-based Finite Element Model to Investigate the Effect of Grain Size and Homogenization on Hot-rolled U-10Mo: Ayoub Soulami1; Aaron Fortier2; Curt Lavender1; Vineet Joshi1; 1Pacific Northwest National Laboratory; 2RWTH Aachen
Low-enriched uranium with 10wt% molybdenum (U-10Mo) is being developed and qualified by the NNSA to replace high-enriched uranium due to its ability to meet the neutron flux requirements in U.S. high performance research reactors. During hot rolling, cast U-10Mo ingots are sandwiched between two thin zirconium (Zr) sheets and loaded into a steel can. Experimental observations after hot rolling indicate Zr thickness variations in the final fuel foil product. Non-homogenized molybdenum in the uranium matrix and coarse U-10Mo grains lead to variation in the Zr interlayer thickness. The purpose of this work is to investigate the effects of microstructural attributes on thickness variation in the resultant Zr interlayer. A microstructure-based finite-element model was developed, and a study on the effect of U-10Mo grain size, can materials, and homogenization on the Zr interlay variation was conducted. The model successfully predicted the experimentally observed variations in the Zr interlayer.
3:00 PM
Reduced Order Modeling of Thermal Creep in 316H Stainless Steel: Aaron Tallman1; M Arul Kumar1; Laurent Capolungo1; 1Los Alamos National Laboratory
Hierarchical multiscale modeling has been pursued as a means of bridging the gap between the scale of physics-based material models and the engineering scale. While more efficient than direct numerical simulation, hierarchical methods still retain a numerical expense greater than engineering models. To further reduce the expense of physics-informed simulation, a reduced-order method is proposed. Here, primary and secondary thermal creep of 316H stainless steel are captured using a constitutive model in a viscoplastic self-consistent (VPSC) framework. A reduced-order model (ROM) is proposed which emulates VPSC simulation results using polynomial regression over a reduced number of degrees of freedom, including internal state variables. An application domain is defined, i.e. temperature and applied stress range. A design of experiments is used to ensure fidelity of the ROM to VPSC within the entire chosen domain. Invertible mappings are employed to mitigate compounding errors. The ROM is applied at the engineering scale.
3:20 PM Break
3:40 PM
Application of Variational Bayesian Monte Carlo Method for Improved Prediction of Doped UO2 Fuel Performance: Yifeng Che1; Koroush Shirvan1; 1Massachusetts Institute of Technology
Chromia-doped UO2 fuel has been shown to effectively promote grain growth and suppress fission gas release (FGR) under transient operating conditions. The most recent FGR model for the Chromia-doped UO2 fuel improves the FGR prediction, while is still not perfect due to missing physics as well as the inherent uncertain nature of the FGR process. This work intends to further improve the BISON FGR model for Chromia-doped UO2 fuel in Bayesian framework using the available Halden experimental data. Dimensionality reduction is first performed using principal component analysis to deal with the time-dependent FGR series data. Kriging is then used as metamodel of the computationally expensive code BISON. A novel optimization framework, Variational Bayesian Monte Carlo (VBMC), is utilized to improve the predictability of the most recent BISON FGR model. The performance of VBMC and the traditional statistical Markov Chain Monte Carlo sampling (MCMC) is compared and discussed.
4:00 PM
Zirconium Alloy Cladding Burst Mechanisms under LOCA with Burnup Extension: Jianguo Yu1; Cole Blakely1; Hongbin Zhang1; 1Idaho National Laboratory
Extending the authorized fuel burnup level to the proposed new limit of 75 GWD/MT can provide significant economic benefits to enhance the commercial competitiveness of the current fleet of operating light water reactors (LWRs). However, to ensure the integrity of fuel rods with high burnup fuel, there are still a number of technological challenges posed by higher burnups that need to be remedied. One of the main obstacles associated with burnup extension is the fuel rod behavior such as burst during design basis accident (DBA) condition analyses, especially for large-break loss-of-coolant (LBLOCA) and reactivity insertion accident (RIA). In this work, fuel rod burst mechanisms with the proposed new burnup limit under the LBLOCA conditions are investigated using the advanced fuel performance code Bison. Results for four fuel rod burst criteria will be presented in this comparative study: overstrain, plasticity instability (PI), overstress (OS), and combination of OS/PI.
4:20 PM
Shape and Stability of Voids and Fission Gas Bubbles in UO2: Conor Galvin1; Michael Rushton2; Michael Cooper3; David Andersson3; Robin Grimes4; Patrick Burr5; 1UNSW + Imperial; 2Bangor University; 3Los Alamos National Laboratory; 4Imperial College London; 5UNSW Sydney
The formation of fission gas bubbles is a performance limiting factor in nuclear fuel as it degrades mechanical properties and leads to fuel swelling. However, there are significant gaps in the knowledge of the properties of fission gas bubbles. Many experimental studies report faceted voids and bubbles, but MD studies have only considered spherical shapes for simplicity. Here we systematically construct all Wulff shapes composed of {100}, {110} and {111} planes, and identify the most stables void/bubble geometries. MD simulations were performed for different sizes (up to 10 nm), pressures (up to 1.25 Xe/Schottky) and temperatures. We show that faceted bubbles and voids are always more thermodynamically favorable over spherical counterparts, however the energy difference decreases with increasing temperatures and decreasing pressure. The optimal ratio of {111}:{100} also varies with temperature.The results can inform higher-order models and fuel performance codes to predict fission gas behavior in fuel.