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Improvements to power flow modeling in the ARIES system code. M. S. Tillack. ARIES Project Meeting 25-26 October 2010. Background. Existing models and assumptions need improvement Discrepancies were found within the code (DesignPoint.cpp) The current models are not transparent
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Improvements to power flow modelingin the ARIES system code M. S. Tillack ARIES Project Meeting 25-26 October 2010
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
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.
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.
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.
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
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
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
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
ARIES-ST FW thermal hydraulic design window >600 ˚C wall temperature >5% pumping power
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)
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
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.
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
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.
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