Improvements to power flow modeling in the ARIES system code

1. Improvements to power flow modelingin the ARIES system code M. S. Tillack ARIES Project Meeting 25-26 October 2010

2. Background • Existing models and assumptions need improvement • Discrepancies were found within the code (DesignPoint.cpp) • The current models are not transparent • The current models can not be modified; they are based on analysis for specific conditions, and their scalability is suspect • The current documentation is very poor • Topics addressed here: • Thermal conversion efficiency • Pumping power in the blanket and divertor • Power density limits • Pump efficiencies • Fusion power partitioning

3. 1. Thermal conversion efficiencyVASST currently interpolates tables of analysis results from specific blanket/divertor designs (DCLL) (SiC) Z. Dragojlovic, A. R. Raffray, F. Najmabadi, C. Kessel, L. Waganer, L. El-Guebaly and L. Bromberg,
"An Advanced Computational Algorithm for Systems Analysis of Tokamak Power Plants," Fusion Engineering & Design 85 (2), 243-265, 2010.

4. The only real impact of the power core on conversion efficiency comes from bulk coolant temperatures with or w/o intermediate HX Siegfried Malang, Horst Schnauder, and Mark Tillack, 
"Combination of a Self-Cooled Liquid Metal Breeder 
Blanket with a Gas Turbine Power Conversion System," 
Fusion Engineering and Design41 (Sept. 1998) 561.

5. Advanced Brayton Cycle Parameters Based on Present or Near Term Technology Evolved with Expert Input from General Atomics* • Min. He Temp. in cycle (heat sink) = 35°C • 3-stage compression with 2 inter-coolers • Turbine efficiency = 0.93 • Compressor efficiency = 0.88 • Recuperator effectiveness (advanced design) = 0.96 • Cycle He fractional DP = 0.03 • Intermediate Heat Exchanger - Effectiveness = 0.9 - (mCp)He/(mCp)Pb-17Li = 1 * R. Schleicher, A. R. Raffray, C. P. C. Wong, “An Assessment of the Brayton Cycle for High Performance Power Plant,” Fusion Technology39 (2), 823-827, March 2001.

6. Power density limits the bulk outlet temperature due to structure temperature limits and heat transfer DT’s Tmax,structure DTHX DTs~q’’d/k + q’’’ d2/2k Tin (limited by dbtt) DTb Tmax,interface Brayton cycle DTf~q/h Tout

7. BUT the temperature of coolant entering the turbine is determined by blanket internal bulk temperatures Since the time of ARIES-ST, we worked hard to decouple the power cycle from heat flux constraints

8. Other considerations for power density effects on bulk outlet temperature • Can we ignore thermal stress limits on To? • They are very design-dependent • For the metallic structures they seem not to be limiting outlet temperatures (except to the extent structure temperature limits are based on creep) • For SiC, ARIES-AT analysis demonstrated a large margin • I would be surprised if blanket stresses limit To, but we should explore it • Heat flux peaking factors • If heat flux constrains efficiency, then profiles will be important

9. 2. Pumping power • Pressure drop is related to heat transfer, and therefore heat flux limits • Higher pressure drop enables higher heat flux • Diminishing returns when h>k/d • Historically we set 5% Pth as the maximum for the blanket and10% for the divertor, but these are parameters • We need a way to trade increased heat flux vs. decreased net electric

10. ARIES-ST FW thermal hydraulic design window >600 ˚C wall temperature >5% pumping power

11. Current pumping power models in VASST • DCLL blanket • Interploated from tables • DCLL divertor • 0.3415 MW/m2 × surface area • SiC combined blanket/divertor • Interploated from tables • 50/50 split for blanket/divertor • Doesn’t matter in power balance, unless we want to decouple them • New models for both blanket and divertor are needed if we want a He-cooled divertor (DCLL blanket) (SiC blanket + divertor)

12. Power density limits in VASST • Not clear how filters are working in the code • DCLL • Divertor peak heat flux < 8 MW/m2 • FW peak heat flux < 1.0 MW/m2 • Peak neutron wall load < 7.5 MW/m2 • ARIES-AT • Divertor peak heat flux < 8 MW/m2 • FW peak heat flux < 0.625 MW/m2 • Peak neutron wall load < 6 MW/m2

13. Pump efficiencies • Existing DCLL module • Tabular data between 35 and 40% • Depends on Pn and q” (no explanation for this; probably an error) • No distinction is made between PbLi and He pumps • Existing SiC module • Efficiency is input from a data file • Recommendation: • For He, 90% is reasonable for a compressor • For PbLi, it depends on pumping method • 40% for conduction or ALIP EM pump • 80% for a mechanical pump • In either case, this is not “standard” technology • PbLi pumping power is small compared to He, so this parameter probably doesn’t have a large impact.

14. Fusion power partitioning • At present, the power balance uses area fractions to distribute heat to the FWB and divertor • PFC area = FW + total divertor plates • f_geo_div = divertor area / PFC area • Used for both neutron power and core radiation power • This certainly over-estimates power flows to the divertor • First estimate could be q/p • Better estimates from neutronics scaling and radiation models q

15. Discussion and conclusions • New algorithms should provide transparency, scalability and upgradability. • The only complication is the need to trade maximum heat flux against pumping power (plant net efficiency). • Partitioning of neutron and radiation power distribution need to be revisited.

16. UCSD authorship at the 19th TOFE • “Pushing the limits of He-cooled high heat flux concepts,” M. S. Tillack, X. R. Wang, D. Navaei, J. Burke, S. Malang • “Innovative first wall concept providing additional armor at high heat flux regions,” X.R. Wang, S. Malang, M. S. Tillack • “High performance divertor target concept for a power plant: a combination of plate and finger concepts,” X.R. Wang, S. Malang, M. S. Tillack • “Optimization of ARIES T-tube divertor concept,” J. A. Burke, X. R. Wang, M. S. Tillack • “Elastic-plastic analysis of the transition joint for high performance divertor target plate,” D. Navaei, X. R. Wang, M. S. Tillack, S. Malang • “Ratchetting models for fusion component design,” J. P. Blanchard, C. J. Martin, M. S. Tillack, and X. R. Wang • “Development of the lead lithium (DCLL) blanket concept,” S. Malang, M. S. Tillack, C. P. C. Wong, N. B. Morley • “Developing a new visualization tool for the ARIES systems code,” L. C. Carlson, F. Najmabadi, M. S. Tillack