Mechanical Behavior of Nuclear Reactor Materials and Components III: Modeling
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Assel Aitkaliyeva, University of Florida; Clarissa Yablinsky, Los Alamos National Laboratory; Osman Anderoglu, University of New Mexico; Eda Aydogan, Middle East Technical University; Kayla Yano, Pacific Northwest National Laboratory; Caleb Massey, Oak Ridge National Laboratory; Djamel Kaoumi, North Carolina State University

Tuesday 2:30 PM
March 21, 2023
Room: 28D
Location: SDCC

Session Chair: Clarissa Yablinksy, Los Alamos National Laboratory; Assel Aitkaliyeva, University of Florida


2:30 PM  Invited
A Mesoscale Model of Creep in Monolithic UMo Fuels: Shenyang Hu1; Benjamin Beeler2; 1Pacific Northwest National Laboratory; 2North Carolina State University
    Experiments show that creep is one of failure modes in monolithic UMo fuels. Because gas bubbles act as sinks of defects and has different elastic-plastic properties from that of UMo matrix gas bubble structures (volume fraction, spatial and size distributions) not only affect defect concentrations, but also stresses, hence, the creep. In this talk, we will present a mesoscale model of creep by integrating a microstructure-dependent cluster dynamics model, a phase-field model of nonequilibrium gas bubbles, and crystal plasticity theory. The integrated model aims to capture the multi-physics coupling of radiation defect evolution, gas bubble evolution, and diffusion-controlled creep. The effect of radiation conditions, inhomogeneous kinetic properties of defects, and applied stresses on gas bubble swelling and creep rate in polycrystalline UMo and Zr layer structures will be presented. The results are important inputs in the development of creep rate model for predicting the fuel performance.

3:00 PM  
Modeling Long-term Radiation Effects on the Concrete Biological Shield: Amani Cheniour1; Yann Le Pape1; Eva Davidson1; Mehdi Asgari1; Benjamin Spencer2; Tara Pandya1; Mark Baird1; Benjamin Collins3; Andrew Godfrey1; 1Oak Ridge National Laboratory; 2Idaho National Laboratory; 3University of Texas at Austin
    The concrete biological shield (CBS) surrounding the reactor pressure vessel in light water reactors (LWRs) is exposed to neutron and gamma radiation. Concrete aggregates swell due to the amorphization of their minerals under neutron irradiation. Different minerals expand at different rates, which causes significant mismatch strains. Consequently, at high radiation doses, fracture is likely to occur at interfaces between mineral grains as well as in the cement paste due to its lower strength, which deteriorates the concrete’s mechanical properties. In this work, radiation damage in concrete is modeled at the structural scale to assess the extent of damage in the CBS and its long-term structural integrity in the perspective of subsequent license renewals of LWRs. We use the finite element-based code Grizzly, aided by radiation transport data from VERA-Shift, to model the evolution of radiation-induced expansion, creep, and damage in concrete with neutron fluence and temperature in 3D.

3:20 PM  
Robust Constitutive Modeling with Artificial Neural Networks: Qing-Jie Li1; Mahmut Cinbiz2; Yin Zhang1; Geoffrey Beausoleil II2; Ju Li1; 1Massachusetts Institute of Technology; 2Idaho National Lab
    Structural materials in nuclear energy applications are often subjected to simultaneous evolutions in compositional, structural, and environmental condition spaces, imposing significant challenges on mechanical behaviors modeling. In this work, a new artificial neural network architecture, consisting of temporal convolutional neural network and fully connected neural network (TCN-FCN), was applied for learning complex stress-strain data. The causal convolution operation implemented in this TCN-FCN architecture can correlate the most informative loading history information to current stress state in a high-dimensional material parameter space. The TCN-FCN models were benchmarked with similar gated recurrent unit (GRU)-based recurrent neural network models and showed ~50% error reduction in modeling complex loading histories and high-dimensional dependencies (e.g., temperature, strain rate, materials conditions, etc.). Such TCN-FCN architecture demonstrates excellent generalization ability and universal capability in modeling high-dimensional complex stress-stress data, thus offering a robust alternative to conventional empirical/semi-empirical models for nuclear materials modeling and optimizations.

3:40 PM  Cancelled
Liquid Lead Embrittlement: Experiments and Molecular Dynamics Simulations: Alberto Fraile1; Simon Middleburgh1; Nicholas Barron2; Paolo Ferroni3; Michael Ickes3; 1Nuclear Futures Institute; 2National Nuclear Laboratory Limited ; 3Westinghouse Electric Company
     Liquid metal corrosion can be accelerated along the grain boundaries (GB) or other microstructural features that can act as preferential diffusion pathways. Hence, we focus on the effect of Pb inside the GBs of Fe and Ni as model systems. The dependence of the mechanical properties (Young’s modulus, toughness and ultimate strength) of Fe and Ni polycrystals with the amount of Pb atoms in the GBs was examined. The atomistic aspects of embrittlement through GBs were determined and a model is being developed to understand the damage produced by Pb atoms in metals and alloys. This work combines theoretical and experimental efforts. A state-of-the-art liquid Pb corrosion facility is operational in the Nuclear Futures Institute, offering a unique piece of equipment to investigate corrosion by flowing and static liquid Pb with velocities up to 4 m/s and temperatures up to 600°C, and oxygen control system. Further details will be presented.

4:00 PM Break

4:20 PM  
Simulating Irradiation Induced Creep with Coupled Rate Theory and Plasticity Models: Aaron Kohnert1; Laurent Capolungo1; 1Los Alamos National Laboratory
    Creep deformation can occur in radiation environments well below the temperatures and stresses where similar behavior is seen thermally. This work introduces a modeling framework capable of directly simulating irradiation induced creep by attaching a rate theory approach to treating vacancy and self-interstitial fluxes directly to a dislocation dynamics model to capture plastic flow. The simulations are fully resolved in 3d, and include the elastic interactions between point defects and dislocations which drive preferential partition of defects between sinks. From these simulations, we examine dislocation network morphologies and microstructure evolution in bcc Fe crept in both thermal and radiation environments. Additionally, quantitative flow rates are extracted at a variety of temperatures and stress levels, providing the expected magnitude of irradiation induced creep for a range of conditions.

4:40 PM  
Molecular Dynamics Studies of Helium Bubble Effects on Grain Boundary Fracture Vulnerabilities in an Fe70Ni11Cr19-1%H Austenitic Stainless Steel: Xiaowang Zhou1; Michael Foster1; Ryan Sills1; 1Sandia National Laboratories
    Comprehensive molecular dynamics simulations have been performed to study the delamination of seven grain boundaries/cleavage planes (Sigma1{111}, Sigm3{111}, Sigm5{100}, Sigm7{111}, Sigm9{411}, Sigm11{311}, and R{100}/{411}) containing a helium bubble. A variety of strain rates, system dimensions, bubble densities, bubble radii, bubble pressures, and temperatures were explored. We found that in general, grain boundaries absorb less energies with decreasing strain rate but increasing bubble areal density, bubble pressure, bubble radius, and temperature. The propensity of grain boundary delamination is sensitive to grain boundary type: The random grain boundary R{100}/{411} is one of the most brittle boundaries whereas the Sigm1{111} cleavage plane and the Sigm3{111} twin boundary are two of the toughest boundaries. The sorted list of grain boundary fracture vulnerability obtained from dynamic tensile test simulations and decohesion energy calculations does not match, confirming the important role of plastic deformation during fracture. Detailed mechanistic analyses are performed to interpret the simulated results.