Materials Issues, Gaps and Research Needs

1. RJ Kurtz1 and the ReNeW Materials Panel 1Pacific Northwest National Laboratory Harnessing Fusion Power Workshop Los Angeles, CA March 2 - 4, 2009 Materials Issues, Gaps and Research Needs

2. ReNeW Materials Panel Members

3. Greenwald Panel Materials Issues Overarching Issue: Understand the basic materials science phenomena for fusion breeding blankets, structural components, plasma diagnostics, and heating components in high neutron areas.

4. Greenwald Panel Materials Gaps

5. ReNeW Panel Materials Issues

6. Materials Research and the Path to Fusion Power • Materials research to identify candidate materials • Radiation damage • Activation • Mechanical & physical properties • Compatibility with coolants and tritium breeders • Large-scale fabrication & joining issues Plasma Physics Confinement Ion Accelerators RTNS Fusion Reactor Concept Definition • Identify and demonstrate approaches to improve material performance • Identify concept specific issues and demonstrate proof-of-principle solutions, e.g. • Design with ferromagnetic material • Methods for design of large, thermo-mechanically loaded structures Fission Reactors ITER IFMIF DEMO Conceptual Designs • Development of materials with acceptable performance and demonstrate to goal life (dpa, He) • Demonstrate solutions to concept specific issues on actual structural materials and prototypic components • Develop design data base, constitutive equations, and models to describe all aspects of material behavior required for design and licensing Component Test Facilities DEMO Final Design & Construction Actual Fusion Environment Test Results Key need is close integration of materials science with the structural analysis-design process.

7. Current Development Status of Fusion Structural Materials Feasibility Tech. maturation Concept Exploration Proof of Principle Performance Extension Unirradiated RAF/M Steels Irradiated Unirradiated V Alloys Irradiated Unirradiated NFA Steels Irradiated Unirradiated SiC/SiC Irradiated Unirradiated W Alloys Irradiated

8. Low-Activation Structural Materials for Fusion Low-activation is a must!! • Materials strongly impact economic & environmental attractiveness of fusion power - basic feasibility. • Many materials are not suitable for various technical reasons. • Based on safety, waste disposal and performance considerations, the three leading candidates are: • RAF/M and NFA steels • Tungsten alloys • SiC composites None of the current reduced or low-activation fusion materials existed 15 years ago.

9. Fusion Materials Relies Heavily on Modeling due to Inaccessibility of Fusion Operating Regime • Extrapolation to fusion regime is much larger for the fusion materials than for plasma physics program. • Lack of an intense neutron source emphasizes the need for a coordinated scientific effort combining experiment, modeling and theory to a develop a fundamental understanding of radiation damage. He and Displacement Damage Levels Steels Spallation neutrons Fusion reactor IFMIF ITER

10. Impact of He-Rich Environment on Neutron Irradiated Materials • A unique aspect of the DT fusion environment is substantialproduction of gaseous transmutants such as He and H. • Accumulation of He can have major implications for the integrity of fusion structures such as: • Loss of high-temperature creep strength. • Increased swelling and irradiation creep at intermediate temperatures. • Potential for loss of ductility and fracture toughness at low temperatures. Grain boundary 316 SS @ 750°C & 100 MPa Voids in F82H at 500°C, 9dpa, 380 appm He

11. Science-Based High-Temperature Design Criteria • Current high-temperature design methods are largely empirical. • Cyclic plastic loading is far more damaging than monotonic loading. • New models of high-temperature deformation and fracture are needed for: • Creep-fatigue interaction. • Elastic-plastic, time-dependent fracture mechanics. • Materials with low ductility, pronounced anisotropy, composites and multilayers. J. Aktaa & R. Schmitt, FZK, 2004

12. Theoretical Strength ~E/50 Future Materials Strength Current Engineering Materials Toughness or Ductility Breaking the High Strength-Low Toughness/Ductility Paradigm • Increased strength is accompanied by reduced toughness (cracking resistance) and ductility. • Strength is increased by alloying, processing and radiation damage. • Low toughness and ductility reduce failure margins. • The benefits of simultaneously achieving high-strength and high ductility/ toughness would be enormous.

13. Fundamentals of Material-Coolant Chemical Compatibility in the Fusion Environment • The traditional approach to corrosion is empirical. • Correlations do not capture basic physics and have limited predictive capability. • Opportunities: • Controlled experiments combined with physical models utilizing advanced thermodynamics & kinetics codes. • Integrated experiments using sophisticated in situ diagnostic and sensor technologies. M. Zmitko / US-EU Material and Breeding Blanket Experts Meeting (2005) J. Konys et al./ ICFRM-12 (2005)

14. 50 keV 10 keV 5 nm 100K, iron Theory and Modeling of Materials Performance Under Fusion Conditions Integration of modeling-theory-experiments-database development is a critical challenge in bridging the multi-physics-length-time scales. • Success - simulations and experiments show high-energy fusion damage events are similar to multiple, lower-energy events - provides fission-fusions dpa damage scaling. • Microstructural evolution in a high-energy neutron, He-rich environment. • Resulting in degradation of performance sustaining properties and stability. • Effects of He are critical. Comparison of 10 and 50 keV displacement cascades in iron

15. 1 •ster LMC: Nuclear LMC: Nuc + Mag (cm ) SANS: Nuc SANS: N+Mag -1 . 0 1 -1 W /d S . 0 0 1 d Fe 0 . 0 0 1 He . . . . . . 0 3 0 0 0 0 1 0 0 2 0 0 0 0 4 0 5 0 6 2 - 2 Å q ( ) Coupling of Modeling and Experiment to Determine He Transport and Fate Experimental characterization SANS/ ASAXS THDS TEM PAS feature ‘signals’ TEM, SANS, Positron theory Multiscale modeling self-consistent ‘understanding’ of He effects predict features simulate observables GR Odette, UCSB & BD Wirth, UCB

16. Compelling Scientific Needs - I • Recent fusion materials R&D efforts have led to the development of high-performance reduced-activation structural materials with good radiation resistance for doses ~30 dpa and ~300 appm He. • The overarching scientific challenge facing structural materials for DEMO is microstructural evolution and property changes (mechanical and physical) that may occur for neutron doses up to ~200 dpa and ~2000 appm He. • Development of high-performance alloys and ceramics including large-scale fabrication and joining technologies is needed. • Current understanding of strength-ductility/toughness relationships is inadequate to simultaneously achieve high-strength and high-ductility and toughness.

17. Compelling Scientific Needs - II • Better mechanistic physical models of thermo-mechanical degradation are needed for development of advanced materials and science-based high-temperature structural design criteria. • The mechanisms controlling chemical compatibility of materials exposed to coolants and erosion of materials due to interaction with the plasma are poorly understood. • Better understanding of radiation-induced and thermo-mechanical property changes in high-heat flux materials (tungsten), magnet, and a host of functional materials is required.

18. Critical Resource Needs - I • Research Scientists and Engineers • Many specialized skills will be needed – physical metallurgists, ceramists, electron microscopists, mechanical property specialists, fracture mechanics, materials evaluation specialists (SANS, PAS, APT, etc.), corrosion scientists, nondestructive evaluation specialists, theory and modeling experts (multiscale materials modeling). • 2003 FESAC Development Plan estimated ~60 FTE/y at peak activity. • Existing talent pool rapidly shrinking! • Materials Science Facilities • Materials evaluation equipment – TEM, SEM, FIB, Auger, APT, etc. • High-temperature materials testing – creep, fatigue, fracture, thermal-shock and fatigue. • Compatibility testing – flow loops for corrosion testing, oxidation. • Physical property measurements – thermal, electrical, optical, etc. • Material fabrication and joining of small to large-scale components. • Hot cells for handling and testing of activated materials.

19. Critical Resource Needs - II • Non-Nuclear Structural Integrity Benchmarking Facilities • Facilities for testing various components such as blanket modules are needed to investigate the potential for synergistic effects that are not revealed in simpler single-variable experiments or limited multiple-variable studies. • Provides data to refine predictive models of materials behavior. • Gives reliability and failure rate data on materials, components and structures to valid codes for designing intermediate step nuclear devices and DEMO. • Test bed to test and evaluate nondestructive inspection techniques and procedures. • Other Facilities • Extensive computational resources will be needed at all phases of fusion materials development to support model development but, in particular, large-scale structural damage mechanics computational capability will be needed to guide and interpret data obtained from component-level test facilities.

20. Critical Resource Needs - III • Fission Reactors • The capability to perform irradiation experiments in fission reactors is essential for identifying the most promising materials and specimen geometries for irradiation in an intense neutron source. • Intense Neutron Source • Overcoming radiation damage degradation is the rate-controlling step in fusion materials development. • Evaluation of radiation effects requires simultaneous displacement damage (~200 dpa) and He generation (~2000 appm). • International assessments have concluded that an intense neutron source with ≥ 0.5 liter volume with ≥ 2 MW/m2 equivalent 14 MeV neutron flux to enable testing up to a least 10 MW-y/m2, availability > 70%, and flux gradients ≤ 20%/cm is essential to develop and qualify radiation resistant structural materials for DEMO.

21. Critical Resource Needs - IV • Component Test Facility • Nuclear facility to explore the potential for synergistic effects in a fully integrated fusion neutron environment. Data and models generated from non-nuclear structural test facilities, fission reactor studies and the intense neutron source will be needed to design this facility.