High-Temperature Materials Needs for Future Plants

Scott Hsu scott.hsu at hq.doe.gov Program Director, ARPA-E

October 17, 2019 Synergies between this workshop and fusion energy

‣ Need to reduce cost for fusion BoP – ARPA-E aims to help enable commercial fusion power plants within ~20 years with overnight capital cost 50% of capital cost

‣ Significant materials, chemical-compatibility, and -containment challenges for heat exchangers – Synergistic with fission-MSR challenges – Synergistic with challenges for other parts of the fusion power plant, e.g., first wall, fuel-cycle (tritium-processing) system, pumps, etc.

‣ Some ARPA-E-supported fusion concepts are in micro-reactor class (<50 MWe) and require very small footprint for BoP

1 Outline

‣ Fusion energy 101

‣ Summary of high-temperature heat-exchanger and materials challenges for fusion

2 Fusion is the holy grail of energy

the Sun

Attribute Metric

Abundant • Sun will swallow earth fuel before we run out of D • Lithium (>20,000 years) to breed T Carbon-free Net emission is helium

6 4 No long-lived Low-level waste only ( + Li = T + He + 4.8 MeV radioactive activation of structural waste materials) Safe No risk of runaway reaction (but must contain the tritium) Fusion of 132 US tons of DT à primary energy (40 EJ) for 2016 total US electricity generation (source: DOE/EIA/LLNL)

1-kg DT ~4,000,000-kg coal, oil, or gas 3 Fusion “triple product” is a key fusion metric

Fusion Thermal power ≥ losses

“” Must exceed threshold of fuel density ⨉ confinement time

nT! ≳ 8 atm sec High temperatures required means the fusion i E Lawson criterion fuel is in the “” state (ionized gas)

4 Rate of increase of fusion triple product exceeded Moore’s Law and then stalled due to the cost and scale of the next step

Zap Energy

First, form a stable plasma ITER: multi-national to demonstrate/study burning plasmas

5 There are diverse approaches to forming a fusion plasma

tokamak & Highest-performing inertial but expensive confinement approaches fusion (ICF)

Compress to heat and add magnetic field Simplify geometry reach high density and/or reduce field and lower the strength/complexity implosion speed

Z pinches and magnetized- e.g., mirror, FRC, target compression

6 Outline

‣ Fusion energy 101

‣ Summary of high-temperature heat-exchanger and materials challenges for fusion

7 Net energy gain (the “fire”) is necessary but not sufficient for fusion energy–also need materials-centric solutions for everything beyond the plasma (the “fireplace”)

Steam Heat Blanket exchanger Electric Power Superconducting magnets and/or structural vessel Li D –T Plasma T Turbine-Generator Refueling Plasma Coolant facing components

Exhaust Sea water pumping and Condenser Tritium separation extractor extractor advanced power cycle desired

Figure adapted from: H. Yamada, Fusion Energy, in Handbook of Climate Change Mitigation, W.Y. Chen, J. Seiner, T. Suzuki, M. Lackner, eds. (Springer, New York, 2012) 8 Commercially motivated designs share some common features (synergistic with but different than ITER-based design)

General Fusion Zap Energy Commonwealth Fusion Systems

Replaceable Free-surface liquid inner vessel PbLi first walls FLIBE • Thick, liquid PbLi or FLIBE “blanket” ß also serves as coolant immersion - Emphasizes need for corrosion-resistant, high-temp materials blanket • Replaceable first walls - De-emphasizes need to survive neutron irradiation to 100+ dpa

9 Thermal sources and primary coolants (under consideration) in a future fusion power plant

Thermal source Primary coolants Peak under consideration temperature (°C) Blanket PbLi, FLIBE >600 Vacuum vessel PbLi, FLIBE, He >500 Divertor (magnetic He, FLIBE >500 concepts only)

10 A proposed supercritical CO2 power cycle for a large tokamak- based fusion reactor Exploratory concept for EU fusion demo based on “dual coolant lead-lithium” (DCLL) breeder concept

More aggressive, commercially motivated designs prefer higher Must minimize tritium operating temperatures, single coolant (PbLi or FLIBE), fewer loss into power heat exchangers (?), reduced thermal power (≲500 MW total) conversion system

Figure and tables from J. I. Linares, Energy 98, 271 (2016). 11 Heat-exchanger challenges for fusion are synergistic with other high-temperature materials needs for fusion energy

14.1-MeV neutron irradiation Corrosion and Tritium retention or Activation embrittlement permeability First wall & • >1018 /m2/s (>2.6 MW/m2) • Compatibility with PbLi or ≲200-g retention for subsystem Must qualify for structural • up to 50 dpa FLIBE at >950 K (in a 200-MWe fusion plant) low-level waste materials • ~10 appm He per dpa • Flow-assisted (~0.1–10 upon (including (embrittlement, swelling, creep) m/s) corrosion decommisioning divertor*) • Transient heat loads >>10 MW/m2 • ≳2-yr component lifetime Tritium • Same as above • Same as above separation • Permeability of membrane and approaches that of V extraction Pumps and • Same as above • Minimize T leakage into heat power conversion system exchangers • Maximize D & T extraction in plasma-exhaust pumping

Structural/functional integrity Licensing and public acceptance (reducing cost) (reducing tritium inventory)

*Divertor has further challenges due to complex plasma-materials interactions (PMI). 12 General objective is to find the optimum balance between materials innovation and component-replacement schedule

• Materials innovations to overcome challenges (next slide) • New solutions and lower costs Component/replacement lifetime (à LCOE) and tritium through advanced inventory (à ease of licensing) manufacturing

Optimize LCOE, capital cost, development time

13 Additional references and resources (1)

National Academies FESAC report (2018) T. Tanabe (ed.), Tritium: Fuel of Fusion report (2018) Reactors (Springer, Tokyo, 2017).

14 Additional references and resources (2)

‣ ARPA-E Request for Information (RFI) on Enabling Technologies for a Commercially Viable Fusion Power Plant ‣ S. J. Zinkle, “Fusion materials science: Overview of challenges and recent progress,” Phys. Plasmas 12, 058101 (2005). ‣ B. N. Sorbom et al., “ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets,” Fus. Eng. Des. 100, 378 (2015).

15 https://arpa-e.energy.gov

16 Backup: Fusion first-wall and structural materials face unique challenges

From Summary Report on the Fusion Prototypic Neutron From J. Knaster et al., Nucl. Fusion 57, 102016 (2017). Source Workshop, organized by the Virtual Laboratory for Technology for Fusion Energy Science, Gaithersburg, MD, August 20–22, 2018.

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