About the ThermChem-FW Project

One of the most challenging aspects of fusion reactor operation is that materials will be continually changing internally due to two powerful and unavoidable driving forces. The first one is the creation of defects due to neutron irradiation. These defects are produced in collision cascades in extraordinarily high concentrations, which eventually leads to their mobilization and migration to microstructural features such as grain boundaries, dislocations, or inclusions. Ultimately, the interactions of these defects with the material’s microstructure results in a number of potentially detrimental phenomena such as hardening, swelling, grain growth, and creep. The second driving force derives from substantial changes in the internal chemistry of the material due to neutron transmutation. This chemistry manifests itself as solid and gaseous transmutants that can give rise to porosity, precipitation, or embrittlement. Perhaps as importantly, these changes in internal chemistry and microstructure during fusion reactor operation lead to alterations in fundamental material properties, such as the elastic constants, thermal and electrical conductivities, heat capacities, molar densities, etc. Due to the absence of suitable materials testing facilities, it is thus crucial to capture these evolving material properties in engineering thermomechanical models of reactor component performance and lifetime. However, the fusion community still lacks accurate models that capture the full thermomechanical response of the structural elements of a reactor, such as the first wall and blanket structures, under realistic fusion conditions.

Thermomechanical modeling of these structural elements is in itself extremely challenging. First wall, blanket, and divertor design concepts all involve several different types of material systems performing distinct functions and separated by multiple interfaces. Developing accurate thermomechanical models with varying material properties thus constitutes a materials science and computational grand challenge, necessitating a multidisciplinary approach with teams of materials and computational scientists working together.

The objective of this project is to develop an integrated computational model linking the materials physics scale with the component-level scale to simulate the thermomechanical response of the full first wall/blanket structures during fusion reactor operation.

To that end, a team of scientists with expertise in materials science at all spatial and temporal scales has been merged with a team of computer scientists specializing in machine learning, high-performance computing, large-scale data processing, and advanced algorithm development. The combined team, assembled into a Center which we call ‘ThermChem-FW’ combines members from academia and National Labs, male and female, early career and established, specifically assembled to benefit from this broad expertise and lead to advances that would not be possible without the sum of all its parts. To assist us in carrying out this work, we will take advantage of opportunities to access leadership-class computational resources offered by DOE. Ultimately, one of the priorities in ThermChem-FW will be to train the workforce of the future in fusion energy and materials by hiring postdoctoral researchers at all participating institutions and involving graduate students at universities in the project.

Schematic diagram of the phenomenology of damage accumulation in plasma-facing materials. The system is subjected to near-surface He and H deposition as well as deep-penetrating fusion neutrons. He/H deposition creates subsurface bubbles that can trap-mutate creating morphological changes in the surface. Neutrons create displacement cascades leading to the formation of voids and interstitial loops, as well as transmutation atom clusters. The shaded area separating both regions connects the near-surface with the material bulk, and is the subject of this proposal. The figure is not to scale.

Modeling and Simulation Packages Used

to be added