A potpourri * of engineering topics

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

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

3. Comparison of AT, ACT-I and ACT-II parameters

4. The ARIES-AT blanket concept

5. Elements of the SiC/PbLi blanket radial build

6. Thermal hydraulic and MHD considerations for blanket box sizing • Two changes with largest impact: 15% high thermal power, 50% higher B2 • Thermal power • Keep overall DT fixed (maintain temperature windows) • 15% increase in Pthermal 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 • Dp3d = k N (rv2/2), where N = Ha2/Re = saB2/rv; Dp3d = k (s/2) avB2 • ‘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. “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. 2. Vertical Build: coolant circuits 1, 2, and 4 in ARIES-AT 1 2 4

9. Contribution of cooling circuits to vertical build 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. 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) • Note: LM flow through a pebble bed should be avoided

11. 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. 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. 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)

14. 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. 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~105 • Limited effort was given to design the roughness, determine exact values of h and dp, and establish design consistency.

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

17. Enhancement beyond ~2x comes with increasing friction factor penalty • (Re~104 for most of these data) • P. M. Ligrani and M. M. Oliveira, Comparison of Heat Transfer Augmentation Techniques, AIAA Journal 41 (3) March 2003.

18. 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. Dimpling works at high Re (we need ~105)

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

21. 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. 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. 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/m2 (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. 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?