Presented by A. René Raffray University of California, San Diego

1. Engineering Input to System Code and Trade-Off Studies to Assess Sensitivities of Major Functions to Engineering Parameters Presented by A. René Raffray University of California, San Diego With contribution from S. Malang ARIES Meeting UCSD, La Jolla, CA April 3-4, 2007

2. Input from Utility Advisory Committee on Top-Level Requirements for a Power Plant and on How to Demonstrate Those Engineering Trade-Off Studies and Component Characterization System Code Development and Integration (ARIES-AT as starting point) Physics Input System Level Trade-Off Studies: Path to power plant Phase I Translating Input to: Design Requirements for Next Step Provide Metrics to Help Direct R&D Definition and Pre-Conceptual Design of Next Step Phase II Schematic of ARIES Pathways Study as I Understand It(TBD)

3. Outline • Engineering Input to System Code - Components • Trade-off studies at the function level in conjunction with providing input to system code - Assessing high-leverage engineering parameters to guide integrated trade-off studies to be performed by the system code in the future - Help provide info on R&D direction

4. Engineering Input to System Code • Blanket definitions for different concepts - Materials - Radial Build - Algorithm for performance parameters (nuclear analysis, thermal- hydraulic, stress, coupling to power cycle, etc…) • Input configurations already developed as part of ARIES (recent studies) - Self-cooled Pb-17Li + SiCf/SiC (ARIES-AT) - DCLL (ARIES-CS) - He-Cooled Ceramic Breeder (ARIES-CS) - Flibe? • This would help trade-off runs in system code, with the understanding that the input parameters would have to be refined once a configuration is chosen for more detailed design studies. (UCSD/UW?)

5. Divertor Input to System Code and Trade-Off Studies at the Function Level • Impact of heat flux accommodation on choice of materials and grade level of heat extraction Heat flux (MW/m2): 5 10 15 20 Divertor Pb-17Li+ He-cooled Water-cooled configuration: SiCf/SiC W-alloy Cu alloy (or refractory) Coolant temperature and power cycle efficiency (UCSD/GIT?)

6. Impact of Heat Flux Requirements on Choice of Divertor Configuration • q’’ < 5 MW/m2 (a) Pb-17Li + SiCf/SiC - Negligible pumping power - W-tiles with sacrificial layer ~5 mm - Advanced design, needs substantial R&D - SiCf/SiC temperature < ~1000°C - High-grade heat extraction (b) He-cooled ODS-FS - “low” pumping power - robust and relatively simple plate design - W-tiles with sacrificial layer ~ 10 mm - conservative design, modest R&D - ODS FS temperature < ~ 700°C - Medium-to-high-grade heat extraction

7. Impact of Heat Flux Requirements on Choice of Divertor Configuration (II) • q’’ ~ 5-10 MW/m2 • He-cooled W-alloy (or other refractory, e.g. Ta) - “high” pumping power - more complex plate design, e.g ~100,000 T-tubes or ~400,000 finger-like units - W temperature ~ 700°C (embrittlement) -1300°C (recrystallization) - reliability of plates impacted by limited material choice and large number of difficult joints (impact on availability also) -W-tiles with sacrificial layer ~ 5 mm - Medium-to-high-grade heat extraction - Substantial R&D • q’’ > ~10 MW/m2 • He-cooling and liquid metal cooling increasingly difficult as q’’ is increased past 10 MW/m2 and not feasible at or just above this heat flux level • Low-temperature water with sub-cooled boiling (ITER-like) - heat sink material with high thermal conductivity and large ductility required (e.g. Cu-alloy) - sufficient lifetime under neutron irradiation questionable - activation of heat sink material - W-tiles with sacrificial layer ~ 5 mm - Low-grade heat extraction (divertor power not usable for power conversion system) - modest R&D

8. Changes in Physics and Engineering Parameters Can Substantially Affect Divertor Configuration, Material Choices, Performance, Reliability and R&D Requirements • For example: - Impact of increasing radiation fractions from the core and from the edge - Impact of reducing fusion power for given electric power by utilizing advanced power core design with high power cycle efficiency

9. Power Conversion Trade-Off Studies and Input to System Code • Impact of coolant temperature on choice of materials and grade level of heat extraction Coolant Exit temperature (°C): 420 500 620 800 1000 Power Cycle Low-Perf. High- Perf. Brayton configuration: Rankine Rankine W-alloy Possibility of H2 production Cycle Efficiency: 35% 40% 45% 50% 60% (UCSD/Others?)

10. Choice of Power Conversion System and Impact of High-Temperature Coolant in Advanced Power Core Design Configurations • Coolant exit temperature 420°C-500°C - Low performance Rankine cycle - low or no steam superheating, - potential for chemical reactions between water and LM or Be - Cycle efficiency ~32-40% • Coolant exit temperature 500°C-620°C - High performance Rankine cycle - high steam superheating - 2 or 3 stage steam re-heating, requiring large HX’s (tritium permeation issue) - water/steam pressure > comparable He pressure: high potential for chemical reactions between water and LM or Be - Cycle efficiency ~42-46% • Coolant exit temperature >620°C - Brayton cycle - 2-3 compression stages - highly effective recuperator needed for high perfromance - Cycle efficiency ~45-60% • Coolant exit temperature >~800-900°C - H2 production

11. Tcool,out T superheat 7 Tcool,in 9 reheat Pmax 5 4' 6 4 m Pint 8' 3 8 2' 1-m 2 10' Pmin 1 10 S Example Rankine Cycle with a Steam Generator • • Superheat, single reheat and regeneration (not optimized) • • For example calculations, set: • - Turbine isentropic efficiency = 0.9 • - Compressor isentropic efficiency = 0.8 • - Min.(Tcool–Tsteam,cycle)> 10°C • - Pmin = 0.15 bar

12. Example Brayton Cycle Considered Set parameters for example calculations: - Blanket He coolant used to drive power cycle - Minimum He temperature in cycle (heat sink) = 35°C - 3-stage compression - Optimize cycle compression ratio (but < 3.5; not limiting for cases considered) - Cycle fractional DP ~ 0.07 - Turbine efficiency = 0.93 - Compressor eff. = 0.89 - Recuperator effectiv.= 0.95

13. Comparison of Brayton and Rankine Cycle Efficiencies as a Function of Blanket Coolant Temperature (for example cases) • For this example, ~650°C is the temperature level where it becomes advantageous to choose the Brayton cycle over the Rankine cycle based on cycle efficiency • The choice of cycle needs to be made based on the specific design and including other considerations: - materials - reliabilty - safety - partial power production? - others?

14. For Combination of Power Core Coolant(s) and Cycle, Provide Input to System Code on Efficiency and Pumping Power as a Function of Fusion Power Density E.g., from ARIES-CS study, for DCLL blanket and Brayton cycle:

15. For a Given Power Core Configuration, Increasing the Neutron Wall Load has an Impact on Different Functions • Higher NWL -> shorter life time -> relatively longer replacement time -> lower availability • Higher NWL -> lower coolant exit temperature -> lower gross efficiency in the power conversion system • Higher NWL -> higher pumping power -> lower net efficiency in the power conversion system • Higher NWL -> thicker shielding -> larger radial build in inboard -> larger machine These trade-offs to be done for each power core configuration choice and use as input in system code (UW?)

16. Implications of Waste Treatment on Power Plant Design Requirements • Blanket modules have to be replaced every 3 to 5 years, depending on the maximum NWL • Potential waste treatment methods for the different materials used in the blankets are : - re-use (typical example: liquid metal breeder) - re-cycling (typical example: ceramic breeder, beryllium multiplier) - shallow land burial (typical example: steel structure) • Waste treatments of the different materials requires separating them. Were should this separation be performed, and, for re-cycling, where will the ceramic breeder or the beryllium pebbles be transferred for re-processing? - on the power plant site? - a number of small reprocessing plants would be required. At what cost? - at a central location for a number of power plants? - frequent and difficult shipments of highly activated components with possibly high tritium inventories would be required. (UW?)

17. Implications of Magnetic Field Level on Coil System • Choice of superconducting material - Nb3Sn (<~16 T) - NbTi (< ~8-9 T) - HTS (higher temperature) • Cooling requirements • Coil design • Coil fabrication and assembly • Mechanical support • Nuclear shielding Need input from MIT to include in system code

18. Impact of Power Core Component Design Choice on Reliability and Availability • Number of design units • Number of parts in each unit • Number of welds and joints • Length of welds • Coolant pressure • Maximum stresses compared to allowable limits Can we use a semi-quantitative method as metric for this function when evaluating different design choices? (Boeing/INL?)

19. Impact of Design Choices on Maintenance • Number of cuts and rewelding • Possibility of avoiding cutting/rewelding of coolant lines • Implication on replacement time and power plant availability Can we use a semi-quantitative method as metric for this function when evaluating different design choices? (Boeing?)

20. Impact of Tritium Breeding and Recovery on Fuel Management, Safety and Cost • Tritium breeding - Importance of being able to adjust TBR to meet any operation or uncertainties in design predictions (active knob) - How practical is proposed method (e.g. adjusting 6Li) • Tritium recovery - Maximizing efficiency of the tritium extraction system from the breeder - Implication on tritium inventory - Implication on cost savings in the tritium control system (INL/UW?)