1. page 1 of 12 A potpourri * of engineering topics M. S. Tillack, with help from many others ARIES Project Meeting 27-28 July 2011 * A collection of various things; an assortment, mixed bag or motley. from the French: “rotten pot”

2. page 2 of 12 Topics 1.ARIES-AT, ACT-I and ACT-II blanket radial builds 2.ARIES-AT, ACT-I and ACT-II vertical builds ( i.e., coolant routing behind the divertor) 3.Vacuum vessel materials selection 4.Heat transfer enhancement by roughening 5.Tantalum

3. page 3 of 12 ARIES-ATACT-IACT-II Blanket materialsSiC/PbLi Divertor materialsSiC/PbLiW/He Major radius [m]5.25.56.75 Minor radius [m]1.31.3751.6875 Plasma aspect ratio444 Plasma elongation2.2 2 Plasma triangularity0.840.7 Normalized BetaN5.44.52.75 Toroidal magenetic field [T]5.865.57.25 Greenwald density fraction1.00370.950.85 H981.3491.4411.169 q95 or qcyl3.5524.44.8 Plasma current [MA]12.810.5813.28 Bootstrap fraction0.910.89980.6066 Max div heat flux OB [MW/m 2 ]14.76.77.3 FW surface area [m 2 ]425.588504.85692.63 Max FW heat flux [MW/m 2 ]0.282 (ave)0.2740.257 Blanket volume [m 3 ]266.902318.136414.629 Plasma volume [m 3 ]308.219407.739685.192 Ave. neutron wall load [MW/m 2 ]3.2943.072.37 Aux. power into plasma [MW]045.1130.3 CD power to plasma [MW]3526.9121.3 Thermal power [MW]198220652332 Fusion power [MW]17551806.51958.5 Comparison of AT, ACT-I and ACT-II parameters

4. page 4 of 12 The ARIES-AT blanket concept

5. page 5 of 12 Elements of the SiC/PbLi blanket radial build Parametervalueuni t explanation first wall SiC thickness1mmarmor, may be W, unrelated to power handling NO CHANGE first wall SiC/SiC thickness4mmminimum for structural integrity, dominated by pressure stress (surface heat fluxes nearly identical in all designs); MHD pressure drop will be different, but gravity loads dominated in ARIES-AT NO REASON TO CHANGE annular channel depth4mm sized for flow rate to provide heat removal and bulk  T, similar surface heat fluxes, but more power in ACT-II inner box thickness (curved) inner box thickness (straight) 5858 mm required to withstand pressure stress due to MHD  p. side walls are most challenging. inner box channel depth27cmmainly based on neutronics.

6. page 6 of 12 Thermal hydraulic and MHD considerations for blanket box sizing Two changes with largest impact: 15% high thermal power, 50% higher B 2 Thermal power Keep overall  T fixed (maintain temperature windows) 15% increase in P thermal  15% increase in flow rate Need either higher velocity ( inboard ) or deeper channels ( outboard ) Higher velocity “may” require additional structure for pressure stresses (ARIES-AT was conservative) MHD  p 3d = k N (  v 2 /2), where N = Ha 2 /Re =  aB 2 /  v;  p 3d = k (  /2) av B 2 ‘a’ can be reduced in the FW channel  50% more rib structure ‘v’ can be reduced in the FW channel with larger ‘d’  50% more fluid. But, lower ‘v’ and larger ‘d’ will impact h

7. page 7 of 12 “MHD flow conditioning” Analogous to ordinary flow conditioning But based on completely different physics I suggested this to the UCLA group as a useful geometry to test and/or model

8. page 8 of 12 2. Vertical Build: coolant circuits 1, 2, and 4 in ARIES-AT 124

9. page 9 of 12 Contribution of cooling circuits to vertical build CircuitpurposeThermal power (MW) Mass flow rate (kg/s) Flow behind divertor? Avoidable? 1series flow through the lower divertor and inboard blanket region 5016100lowerNo 2series flow through the upper divertor and one segment of the first outer blanket region 5987270upperYes, with He divertor 3flow through the second segment of the first outer blanket region 4505470no– 4series flow through the inboard hot shield region and first segment of the second outer blanket region 1824270upper and lower No, but flow area could be reduced 5series flow through the outboard hot shield region and second segment of the second outer blanket region 1401700no– A. R. Raffray, L. El-Guebaly, S. Malang, I. Sviatoslavsky, M. S. Tillack, X. Wang, and The ARIES Team, "Advanced power core system for the ARIES-AT power plant,” Fusion Eng. and Design 80 (2006) 79–98

10. page 10 of 12 Flow area and depth of manifolds Assume same nominal velocity as blanket: 11 cm/s (MHD pressure drop is extremely uncertain) Assume R=3.5 (rough approximation) Constant v ✕ B to avoid MHD effects (need to tailor channels for changing B: higher v at larger R) CircuitMass flow rate (kg/s) Volume flow rate (m 3 /s) Flow area (m 2 ) Channel depth (m) 161000.6105.5 0.25 272700.7276.6 0.3 442700.4273.9 0.18 Note: LM flow through a pebble bed should be avoided

11. page 11 of 12 3. Vacuum vessel material selection Recent history Issue raised by Malang a couple of months ago: Ferritic steels suffer from low-T embrittlement and PWHT issues. Austenitic steels (316) will not meet class C. Engaged Team members in email discussions. Materials community took interest in this topic, highlighting it as an important near term issue for the program (Kurtz, FNS-PA July 2011) Report by Malang distributed, report by Rowcliffe expected. A review and assessment is underway : Requirements Material choices Activation (El-Guebaly) R&D needs

12. page 12 of 12 Vacuum vessel material choices ITER chose SS316 due to: Easy fabrication, welding of thick elements, no post-weld heat treatment required No impact on the magnetic field (not ferromagnetic) Compatible with water coolant (typical conditions are T < 150 C and p < 1 MPa) No embrittlement by neutron irradiation, even at irradiation temperatures < 200 C But… 316SS can not be used in a power plant due to: Relatively high neutron activation, even at the low fluence at the VV Potential for swelling, even at low neutron doses Material choices considered for ARIES: Standard austenitic steel (for example SS 316) Modified austenitic steel (for example, Ni replaced by Mn) Ferritic steels (either with 2 – 3 % Cr, or 14 – 18 % Cr) Ferritic/Martensitic steel (F82H, Eurofer) (typical 8-9% Cr) Simple ferritic steel (Fe with small amounts of C, Mn, Si…, widely used in industry) Others (Inconel, Cu-alloys, Al-alloys,…)

13. page 13 of 12 Comparison of material options G. Piatti, P. Schiller, “Thermal and Mechanical Properties of the Cr-Mn (Ni-free) Austenitic Steel for Fusion Reactor Applications”, J. Nuclear Materials vol. 141-143, p. 417-426 (1986) Y. Suzuki, T. Saida and F. Kudough, “Low activation austenitic Mn-steel for in-vessel fusion materials”, J. Nuclear Materials vol. 258-263, Part 2, p. 1687- 1693 (Oct. 1998) Material choiceAdvantagesDisadvantages Simple carbon steels as widely used in the industry Low cost Easy welding No PWHT required Reduction of ductility by low temperature irradiation may require periodic in-situ annealing. Suitable coatings or effective water chemistry required to avoid corrosion. Ferritic steel with higher chromium content Relatively low cost No problems with welding No PWHT required Reduction of ductility by low temperature irradiation may require periodic in-situ annealing. Probably corrosion resistant only if Cr content > 10 %. Austenitic steel with Ni replaced by Mn Can be qualified as low activation material, waste class A Probably no impact of irradiation on ductility and swelling Probably no problem with welding Probably no PWHT required Large development/qualification effort may be required. Fabrication (hardness?) and corrosion resistance unknown.

14. page 14 of 12 Comments on low-Cr FS and FM steel Post-weld heat treatment (PWHT) is required for low-Cr content and ferritic/martensitic steels. Welding would be needed after initial fabrication and after any maintenance rewelding. Friction stir welding is a low-temperature alternative to TIG welding, and may eliminate the need for PWHT. However, these are high-performance steels developed for in-vessel service. Would we want to use them in the vacuum vessel? Higher fabrication cost. Lower development cost (already under development for blanket). Tailored for high temperature operation, not below 200 C. Glenn Grant and Scott Weil, “Friction Stir Welding of ODS Steels – Steps toward a Commercial Process,” Workshop on Fe-Based ODS Alloys: Role and Future Applications, UC San Diego La Jolla, CA (Nov 17 – 18, 2010). (http://www.netl.doe.gov/publications/proceedings/10/ods/Glenn_Grant_FSW.pdf)

15. page 15 of 12 4. FW heat transfer enhancement (He cooling) Since the time of ARIES-ST, we took credit for 1-sided roughening ~ 2x higher h assumed Friction increased on only one wall (assumed no effect on other walls) Large margin on 5% pumping power requirement when using desired bulk velocity. Typically Re~10 5 Limited effort was given to design the roughness, determine exact values of h and  p, and establish design consistency.

16. page 16 of 12 Several types of 2d and 3d structures are possible: roughness, ribs, scales, dimples, pins

17. page 17 of 12 Enhancement beyond ~2x comes with increasing friction factor penalty P. M. Ligrani and M. M. Oliveira, Comparison of Heat Transfer Augmentation Techniques, AIAA Journal 41 (3) March 2003. (Re~10 4 for most of these data)

18. page 18 of 12 Roughness on side and back walls affects h P. R. Chandra, C. R. Alexander and J. C. Han, “Heat transfer and friction behaviors in rectangular channels with varying number of ribbed walls,” International Journal of Heat and Mass Transfer, Volume 46, Issue 3, January 2003, Pages 481-495.

19. page 19 of 12 Dimpling works at high Re (we need ~10 5 )

20. page 20 of 12 CFD studies could be performed for our particular design conditions

21. page 21 of 12 Performance metrics Roughening features have corresponding heat transfer factor (j) and friction factor (f) Hold two of the 3 ratios on left constant to evaluate the performance of each roughness Holding Pumping Power and Area Constant… * R. L. Webb and N. H. Kim (2005) Principles of Enhanced Heat Transfer

22. page 22 of 12 5. Tantalum Assessed in previous IFE and MFE studies: high temperature capability, industrial experience, good database. Used in the current ARIES divertor design due to its high ductility, even after irradiation. If W alloys do not succeed, then is Ta-alloy or some compound structure employing Ta a reasonable option?

23. page 23 of 12 Tantalum characteristics vs. W Melting temperature (hence temperature window): 3290 vs. 3695 K Activation, afterheat: a concern, but better than W Transmutation: becomes 10% W after 10 MW-yr/m 2 (LIFE) Thermal neutron absorption: may be problematic for TBR Thermal conductivity: 57 vs. 173 W/m-K Hydrogen inventory: strong getter at 1000 C, outgases at 1500 C Hydrogen hardening and embrittlement Oxygen and nitrogen chemistry: impurity control required Raw material cost: $300/kg vs. $200 for W

24. page 24 of 12 Tantalum temperature windows Allowable plastic strain for Ta is >15% at room temperature and >5% at 700 ºC (based on Steven Zinkle emails). Not much literature on this, and no information on fracture toughness. Should we press for more information?