Generation IV Systems: Key Technological Challenges for Fission Reactors and What It Means for Fusion David Petti R&D Technical Director Next Generation Nuclear Plant Deputy Director Fusion VLT APS-DPP Oct. 31, 2006

Overview A number of Generation-IV nuclear systems are under study worldwide There are many technology challenges that these advanced fission reactors (Generation IV) and fusion have in common. Examples of the overlap are: power conversion technologies, materials corrosion: high temperature materials and coolant compatibility welding and joining technologies, materials response under neutron irradiation, first-principles materials modeling, high temperature materials design rules, and tritium/hydrogen behavior in materials The fusion community can help advance its technology development activities by actively engaging and leveraging much of the common cross-cutting research.

The National Energy Policy Endorses Nuclear Energy as a Major Component of Future U.S. Energy Supplies Existing Nuclear Plants Expedited NRC licensing of advanced reactors Update and relicense nuclear plants Nuclear energy’s role in improved air quality Geologic repository for nuclear waste Price-Anderson Act renewal New Nuclear Plants Advanced fuel cycle/pyroprocessing Next-generation advanced reactors Reprocessing International collaboration Cleaner, more efficient, less waste, more proliferation-resistant

Generation IV Technology Roadmap Identifies systems that are deployable by 2030 or earlier Over 100 concepts were submitted for evaluation Six ‘most promising’ systems that offer significant advances towards: Sustainability Economics Safety and reliability Proliferation resistance and physical protection Each system has R&D challenges. None are certain of success. Summarizes R&D activities and priorities for the systems and lays the foundation for Generation IV R&D program plans http://gif.inel.gov/roadmap Very-High-Temperature Reactor System (safety, hydrogen production) Lead-Cooled Fast Reactor System (sustainability, safety) Gas-Cooled Fast Reactor System (sustainability,economics) Supercritical-Water-Cooled Reactor System (economics) Molten Salt Reactor System (sustainability) Sodium-Cooled Fast Reactor System (sustainability)

Generation IV International Forum (GIF) Brings international perspective: Generation IV Technology Goals Evaluation of Systems and R&D Endorses key elements: Six Gen IV Systems announced Sep ‘02 Generation IV Roadmap Identifies areas of multilateral collaborations and establishes guidelines for collaborations Regularly reviews progress on collaborations Observers from: International Atomic Energy Agency OECD/Nuclear Energy Agency European Commission Nuclear Regulatory Commission Department of State Chartered July, 2001 South Korea U.S.A. Argentina Brazil Canada France Japan South Africa United Kingdom Switzerland European Union

Molten Salt Reactor (MSR) Characteristics Fuel: liquid Na, Zr, U and Pu fluorides 700–800°C outlet temperature 1000 MWe Low pressure (<0.5 MPa) Benefits Waste minimization Avoids fuel development Proliferation resistance through low fissile material inventory

Sodium-Cooled Fast Reactor (SFR) Characteristics Sodium coolant 550°C Outlet Temp 150 to 500 MWe Metal fuel with pyro processing / MOX fuel with advanced aqueous Benefits Consumption of LWR actinides Efficient fissile material generation

Lead-Cooled Fast Reactor (LFR) Characteristics Pb or Pb/Bi coolant 550°C to 800°C outlet temperature 120–400 MWe 15–30 year core life Benefits Distributed electricity generation Hydrogen and potable water Cartridge core for regional fuel processing High degree of passive safety Proliferation resistance through long-life cartridge core

Gas-Cooled Fast Reactor (GFR) Characteristics He or supercritical CO2 coolant High (>800 °C ) outlet temperature High thermal efficiency (>40%) 600-2000 MWth Several fuel options and core configurations Benefits Utilize fuel efficiently through high energy extraction and recycle Destroy long-term radioisotopes efficiently

Supercritical-Water-Cooled Reactor (SCWR) Characteristics Water coolant at supercritical conditions, single phase fluid 550°C outlet temperature 1700 MWe Simplified balance of plant Benefits Efficiency near 45% with excellent economics Thermal or fast neutron spectrum

Very-High-Temperature Reactor (VHTR) Characteristics He coolant (inert, single-phase) 1000°C outlet temperature 600 MWe Solid graphite block core based on GT-MHR Benefits High thermal efficiency Hydrogen production Process heat applications High degree of passive safety

DOE has selected the VHTR system for the Next Generation Nuclear Power (NGNP) Project. The NGNP is the Leading Generation IV Technology for Near-Term Demonstration in Idaho The purpose of the NGNP Project is to demonstrate emissions-free nuclear-assisted electricity and hydrogen production by ~2018-2021

Power Conversion Technology Prismatic Very High Temperature Reactor: Brayton Cycle for Power Conversion ARIES-AT: Brayton Cycle for Power Conversion

Coolant/Structural Material Corrosion Lead cooled fast reactor: corrosion with ferritic steel US ITER TBM: PbLi corrosion with advanced ferritic steel

Coolant/Structural Material Corrosion Very High Temperature Reactor: He impurities effects on high temperature structural materials (Superalloy systems) US ITER TBM: Influence of He impurities effects on high temperature structural material (Superalloy systems)

Welding/Joining Technology Ferritic steels are used in both advanced fission plants (sodium fast reactor, Pb fast reactor) and ITER Test Blanket Modules High temperature Ni superalloys are currently envisioned for heat exchangers at high temperature (> 900°C) Welding and joining technologies are needed for each system Post-weld heat treatments on componments to get proper microstructure Joints in heat exchangers and other components Dissimilar materials weld issues

Material Response Under Irradiation Both fission and fusion systems will be subject to neutron damage Key materials common to both systems include: Advanced ferritic steels (improved creep resistance) Cladding in fast reactors Blanket structure in fusion SiC composites Control rod guide tubes in very high temperature reactors Flow channel inserts in ITER TBM and blanket structure in ARIES-AT Slight differences exist in temperatures and level of damage. Major difference is He/dpa expected in fission versus fusion

First Principles Materials Modeling First principles modeling of material damage phenomena occurring over a range of both space and time scale is recognized as an important element of bridging gaps and filling in uncertainties in material response under irradiation in both fission and fusion systems

High Temperature Materials Design Rules Because of the impact of high temperature on thermal efficiency of both fission and fusion systems, there is a strong push to develop materials that can accommodate high temperature operation (700-1000°C) VHTR for fission DEMO embodiment of ITER TBM and ARIES-AT for fusion High temperature design rules (ASME code case) that account for behavior in nuclear environment and at high temperature are needed US VHTR personnel are starting this activity

Tritium permeation barriers are needed to ensure that at high temperatures permeation through the heat exchanger can meet safety limits of ~ 1-10 Ci/day Very High Temperature Reactor: ternary fission produces about 1 to 2 g of tritium at equilibrium. A key issue is to limit permeation into hydrogen product in hydrogen plant Fusion strives to keep blanket inventory to 100-500 g. High partial pressure of tritium in some blankets makes control of permeation difficult

Summary There are many technology challenges that advanced fission reactors (Generation IV) and fusion have in common. The fusion community can help advance its technology development activities by actively engaging and leveraging much of the common cross-cutting research. Decrease in resources for fusion technology makes this more difficult More integration of the fission and fusion technology communities in the US would help