ACCELERATED DEPLOYMENT OF SILICON CARBIDE COMPOSITES FOR AN ATTRACTIVE FUSION ENERGY SOURCE By Dr. Leo Holland Senior Technical Advisor Presented to FESAC-TEC May 31, 2017

Accelerated Deployment of SiC Composites for an Attractive Fusion Energy Source SiC composites have been around a long time in the fusion field They are a favorite of the design community They enjoy a long history of materials research and improvement But SiC remains at TRL2 due to low priority, and the perception that it's not ready for implementation in near-term devices such as FNSF Progress in fission & non-nuclear fields advanced fission TRL to 4-5 Tremendous leverage is available to advance fusion TRL quickly from TRL2 to TRL4 with a modest investment Opportunity exists for US to exert leadership in a forward-looking direction

SiC/SiC the assumed material for the entire blanket assembly SiC/SiC is a Preferred Material in Conceptual Designs of Future Fusion Reactors ARIES-ACT1 blanket SiC/SiC the assumed material for the entire blanket assembly

Why SiC/SiC for Fusion? Unparalleled high temperature strength Practically no irradiation embrittlement Used as a tritium barrier material Low induced activity and decay heat Low neutron absorption Rapidly maturing industrial experiences From Presentation by: Yutai Katoh (ORNL) at the DOE Office of Fusion Energy Sciences Fusion Materials PI Meeting, July 25-29, 2016, Knoxville/Oak Ridge, TN High Strength at High Temperature Low Activation Industrialization of SiC

GA Is Developing SiC-SiC Composites in Support of the DOE Accident Tolerant Fuel Program SiC-SiC composites offer High temperature strength Superior irradiation-resistance Excellent neutronic properties Benefits for LWRs Retains strength to 2000°C No generation of explosive hydrogen in oxidation of metal Benefits for Advanced Reactors (EM2, molten salt, advanced LWRs) High temperature operation High dpa tolerance Coolant compatibility Extended fuel cycle GA SiC-SiC cladding 10µm SiC fiber matrix Westinghouse and GA are developing a uranium silicide fuel with SiC-based cladding. The silicide fuel has much higher thermal conductivity compared to uranium oxide (~10x higher), which offsets the reduced SiC thermal conductivity (as compared to Zircaloy). Uranium silicide has a higher uranium density than UO2, and SiC has a lower neutron absorption cross section than Zircaloy. Westinghouse has done calculations and thinks the fuel could either have more power or a longer life (more U-235 in core –can either burn up more in the same time for more power, or burn for the same power over a longer time). There is also an option where you can get the same fuel life/power for a slightly lower enrichment, and save money on fuel costs. Also, SiC will not creep like Zircaloy does at normal LWR operating temperatures, and without SiC creeping down onto the pellets you postpone any pellet-cladding mechanical interaction, which could allow for a little longer life. These benefits are pretty much based on WEC calculations at this point – we’re still some ways from actual testing of fueled SiC-cladding samples (the first irradiations like that should occur in maybe mid-2017), and I don’t think WEC has decided what they think the optimal route will be (increased power, longer life, or reduced enrichment costs). GA SiC joining

Opportunity to Achieve Class A Waste for the Majority of the Power Core Waste disposal is a controversial topic with unknown future regulatory environment and public perception Class A will help fusion to be more environmentally friendly, and likely will provide substantial cost benefits: 1. Waste lifecycle costs estimates $20/ft3 for Class A LLW $2,000/ft3 for Class C LLW > $ 20,000/ft3 for HLW 2. Low activation may allow substantial cost savings if N-stamp can be avoided, reduce handling costs, reduce cool down times before maintenance operations, etc. L. El-Guebaly and L. Cadwallader, “Lifecycle Waste Disposal and Decommissioning Costs for ARIES Systems Code,” http://aries.pppl.gov/MEETINGS/0805/Elguebaly2.pdf Waste can be a major cost driver if the correct materials are not selected

Worst Case Accidents do not Exceed SiC Limits Loss of flow for PbLi in-vessel breeder/coolant PbLi coolant remains, and increases decay heat source term Loss of water coolant outside the vacuum vessel ARIES-ACT1 Loss of Coolant Study An all SiC/SiC blanket will contain hazardous materials in all scenarios with a simpler, more reliable system Paul W. Humrickhouse, Brad J. Merrill, “ARIES-ACT1 Safety Design and Analysis,” Fusion Science and Technology 67 (2015) 167-178.

High Conversion Efficiency = Lower System Cost ARIES ACT1 Study with SiC Blanket 58% Efficiency (PbLi outlet temperature is 1000˚C) Conversion efficiency of EU water-cooled PbLi (WCLL) Demo blanket M. S. Tillack, et. al., ARIES Team, “Design and Analysis of the ARIES-ACT1 Fusion Power Core,” Fusion Science and Technology 67 (2015) 49-74. Leszek Malinowski, et.al.“Analysis of the secondary circuit of the DEMO fusion power plant using GateCycle,” Fusion Engineering and Design (in press). The SiC/SiC structure in the blanket can allow a nearly 50% increase in revenue from a fusion energy plant

BLANKET STRUCTURAL ALLOYS FOR FNSF Talk by A. F BLANKET STRUCTURAL ALLOYS FOR FNSF Talk by A.F.Rowcliffe to FESS May 2017 SiC/SiC > 1000 > 100 Plan for the sequential development of steels for FNSF My Addition to his slide Development of SiC for the blanket could eliminate some planned development steps and put the US in a leadership position

Risks and Uncertainties Major issues with SiC/SiC: Thermal conductivity is uncertain and too low for high heat flux Experimental work needed to establish SiC use beyond the blanket Hermeticity for high-pressure He GA designing to 20 MPa for ATF Sufficient for blankets including He cooling Transmutation effects and service life are uncertain Joining and coating techniques and properties Being developed for Gen IV Reactor Modeling Results Y. Katoh, et. al., “Current status and recent research achievements in SiC/SiC composites,” Journal of Nuclear Materials 455 (2014) 387–397. SiC/SiC Heat Exchanger Assembly

R&D Development Path 2017 2025 2035 Bench scale mockups single effects Fusion Nuclear Science Facility single effects fully integrated partially integrated Modeling and design studies Blanket Test Facility Fluid Flow and Heat Transfer Corrosion and Redeposition multiple effects Materials development and testing Fabrication & joining, mechanical performance, hermeticity TRL4 TRL2 Current TRL for fission is ~4 TRL6 Begin now to develop a high temperature, low waste blanket system to efficiently support FNSF

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