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

2. 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

3. 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

4. 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

5. 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

6. 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,”
Waste can be a major cost driver if the correct materials are not selected

7. 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)

8. 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)
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

9. 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

10. 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

11. 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

12. Questions
&
Discussion