Materials Systems for the Future of Fusion Energy: Radiation Effects in High Heat Flux Materials I
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee, TMS: Additive Manufacturing Committee, TMS: Computational Materials Science and Engineering Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Jason Trelewicz, Stony Brook University; Kevin Field, University of Michigan; Takaaki Koyanagi, Oak Ridge National Laboratory; Yuanyuan Zhu, University of Connecticut; Dalong Zhang, Baylor University

Tuesday 2:30 PM
March 1, 2022
Room: 203A
Location: Anaheim Convention Center

Session Chair: Brian Wirth, University of Tennessee; Jason Trelewicz, Stony Brook University


2:30 PM  
Grain Boundary Softening in Helium Implanted Fine-grained Tungsten: William Cunningham1; Yang Zhang1; Osman El-Atwani2; Jason Trelewicz1; 1Stony Brook University; 2Los Alamos National Laboratory
    Relative to coarse-grained tungsten where helium bubbles promote classical irradiation hardening, ultrafine-grained tungsten experiences biased helium bubble formation at grain boundaries and reported softening. Here, we examine the influence of the helium cavity distribution on the mechanical behavior of fine-grained tungsten using targeted implantation studies. The hardness and modulus, along with helium cavity evolution, are mapped as a function of temperature and fluence in two different tungsten microstructures. At the lowest fluence, the formation of grain boundary cavities is correlated to a reduction in hardness, which is recovered with increasing fluence due to the formation of lattice dislocation loops. Insights from molecular dynamic simulations demonstrate that the observed softening can be attributed to enhanced strain accommodation within the grain boundaries. Specifically, helium bubbles undergo deformation and coalescence at reduced stresses, for which the latter is confirmed through post-mortem TEM imaging of helium bubbles within the plastic zone of residual impressions.

2:50 PM  Invited
Multiscale Materials Modeling of Structural Materials and Plasma Facing Components in the Extreme Fusion Environment: Brian Wirth1; 1University of Tennessee
    Structural materials, breeding blankets and plasma facing components (PFCs) require performance improvements in moving from ITER to future fusion pilot plants. Materials performance is determined by extreme thermal and radiation environment that induces microstructural evolution and property changes, determined by a large span of spatial and temporal scales. Fortunately, recent innovations in computational modeling techniques, increasingly powerful high-performance computing platforms, and improved analytical experimental characterization tools provide the means to develop self-consistent, experimentally validated models of structural materials and PFC performance in the fusion energy environment. This presentation will describe the challenges and opportunities associated with modeling the performance of structural and blanket materials, and divertor PFCs in a next-step fusion materials environment, and provide examples of recent progress to investigate the dramatic surface evolution of tungsten exposed to low-energy He and H plasmas, as well as the coupled He-defect evolutions in bulk structural materials exposed to fusion environments.

3:20 PM  
Evaluating the Temperature Dependence of Bubble Bursting Rate for Low Energy Helium Plasma-exposed Tungsten: Yogendra Panchal1; Sophie Blondel1; Dwaipayan Dasgupta1; Robert Kolasinski2; Brian Wirth1; 1University of Tennessee, Knoxville; 2Sandia National Laboratories
    This work builds upon a bubble bursting model [Blondel et al. 2018, Nuclear Fusion 58, 126034] in Xolotl, a cluster dynamics code for simulating plasma surface interactions in tungsten in a burning plasma fusion environment. In the original bursting model, helium release from over-pressurized bubbles is based on a probability - dependent on bubble size and distance to the surface. This model predicts helium retention behavior that is in quantitative agreement with high implantation flux molecular dynamics (MD) simulations, although the size and depth distribution of bursting has discrepancies with MD. A systematic comparison of Xolotl predictions with a large MD database has led to an improved bursting model, as described in the presentation. Subsequently, the improved model is compared with a set of linear plasma exposure experiments and surface characterization to evaluate the efficacy of the model, and in particular, the temperature dependence of bubble bursting.

3:40 PM  
Macroscopic Elastic Stress and Strain Produced by Irradiation: Luca Reali1; Max Boleininger1; Mark Glbert1; Sergei Dudarev1; 1UKAEA
    Fusion materials swell under neutron irradiation, which can result in significant stresses developing in reactor components. We propose a method for evaluating macroscopic stresses and deformations due to irradiation at the component scale of a fusion power plant. We use a multi-scale approach based on the concept of relaxation volume density, which we show is a particular case of the general notion of eigenstrain. This quantity can be obtained by atomistic modelling or derived from experiment, and implemented into finite element models, closing the length-scale gap. Several case studies illustrate applications of the method that show that the stress state depends primarily on the spatial variation of the neutron exposure. We discuss the radiation-induced stresses in ion-irradiated films, pressurised irradiated tubes, a vacuum vessel and a breeding blanket module.

4:00 PM Break

4:20 PM  Invited
Integrated Multi-physics Modeling of Impurity Migration, Surface Morphology, and Material Evolution in Present and Future Tokamaks: Ane Lasa1; Sophie Blondel1; Timothy Younkin2; David Bernholdt2; John Canik2; Mark Cianciosa2; Wael Elwasif2; David Green2; Phil Roth2; Jon Drobny3; Davide Curreli3; Brian Wirth1; 1University of Tennessee; 2Oak Ridge National Laboratory; 3University of Illinois Urbana-Champaign
    Finding suitable plasma-facing materials is one of the great challenges in designing future fusion reactors, as unprecedented particle and heat fluxes will interact with the first wall, compromising the performance of both the plasma and wall components. These plasma-material interactions involve diverse plasma and materials physics, and thus, are multi-scale in nature. To address this complex system, we have developed a validated, integrated computational model that interprets and predicts plasma-material interactions in plasma-facing materials. The model includes descriptions for the edge plasma, near-surface sheath, impurity erosion and redeposition, particle recycling, surface morphology and sub-surface evolution. Here, we present the latest applications of our model, which has already been used to interpreting experiments in current devices, such as WEST, to predicting the evolution of the ITER divertor under a range of operational conditions, as well as to exploring the impact of plasma impurities in fuel recycling.

4:50 PM  Cancelled
Expanding Irradiation Damage Models to Fusion Conditions: Tackling the Multispecies Paradigm at High Temperatures: Jaime Marian1; 1University of California, Los Angeles
    Fusion energy introduces a wide array of performance issues in structural materials. Several of these are linked to the unique set of operation conditions expected in fusion reactors, which standard materials behavior models struggle to capture. In particular, the consideration of multiple species due to combined effect of cascade damage, neutron transmutation, and exposure to helium and hydrogen presents unique challenges that models must address. As well, the high temperatures expected during operation may enable physical processes not encountered at lower temperatures. In this presentation, we will discuss recent advances in theory and simulation methods to tackle these complex challenges in fusion structural materials, including modeling (i) the effect of transmutation rhenium on the behavior of bulk neutron-irradiated tungsten; (ii) the mechanisms behind the structure of hydrogen thermal desorption spectra in ion-damaged tungsten, and (iii) models of irradiation creep at high temperatures under DEMO conditions in iron.