a potpourri * of engineering topics

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A potpourri* of engineering topics

M. S. Tillack,

with help from many others

ARIES Project Meeting27-28 July 2011

*A collection of various things; an assortment, mixed bag or motley.

from the French: “rotten pot”

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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

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ARIES-AT ACT-I ACT-II

Blanket materials SiC/PbLi SiC/PbLi SiC/PbLi

Divertor materials SiC/PbLi W/He W/He

Major radius [m] 5.2 5.5 6.75

Minor radius [m] 1.3 1.375 1.6875

Plasma aspect ratio 4 4 4

Plasma elongation 2.2 2.2 2

Plasma triangularity 0.84 0.7 0.7

Normalized BetaN 5.4 4.5 2.75

Toroidal magenetic field [T] 5.86 5.5 7.25

Greenwald density fraction 1.0037 0.95 0.85

H98 1.349 1.441 1.169

q95 or qcyl 3.552 4.4 4.8

Plasma current [MA] 12.8 10.58 13.28

Bootstrap fraction 0.91 0.8998 0.6066

Max div heat flux OB [MW/m2] 14.7 6.7 7.3

FW surface area [m2] 425.588 504.85 692.63

Max FW heat flux [MW/m2] 0.282 (ave) 0.274 0.257

Blanket volume [m3] 266.902 318.136 414.629

Plasma volume [m3] 308.219 407.739 685.192

Ave. neutron wall load [MW/m2] 3.294 3.07 2.37

Aux. power into plasma [MW] 0 45.1 130.3

CD power to plasma [MW] 35 26.9 121.3

Thermal power [MW] 1982 2065 2332

Fusion power [MW] 1755 1806.5 1958.5

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

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The ARIES-AT blanket concept

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Elements of the SiC/PbLi blanket radial build

Parameter value unit explanation

first wall SiC thickness 1 mm armor, may be W, unrelated to power handling

NO CHANGE

first wall SiC/SiC thickness 4 mm minimum 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 depth 4 mm 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)

5

8

mm

mmrequired to withstand pressure stress due to MHD p. side walls are most challenging.

inner box channel depth 27 cm mainly based on neutronics.

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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 T 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 p3d = k N (v2/2), where N = Ha2/Re = aB2/v; p3d = k (/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

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“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

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2. Vertical Build: coolant circuits 1, 2, and 4 in ARIES-AT

1 2 4

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Contribution of cooling circuits to vertical build

Circuit purpose Thermal power (MW)

Mass flow rate (kg/s)

Flow behind divertor?

Avoidable?

1 series flow through the lower divertor and inboard blanket region

501 6100 lower No

2 series flow through the upper divertor and one segment of the first outer blanket region

598 7270 upper Yes, with He divertor

3 flow through the second segment of the first outer blanket region

450 5470 no –

4 series flow through the inboard hot shield region and first segment of the second outer blanket region

182 4270 upper and lower

No, but flow area could be reduced

5 series flow through the outboard hot shield region and second segment of the second outer blanket region

140 1700 no –

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

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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)

Circuit Mass flow rate (kg/s)

Volume flow rate (m3/s)

Flow area (m2)

Channel depth (m)

1 6100 0.610 5.5 0.25

2 7270 0.727 6.6 0.3

4 4270 0.427 3.9 0.18

Note: LM flow through a pebble bed should be avoided

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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

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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,…)

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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 choice Advantages Disadvantages

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.

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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)

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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 p, and establish design consistency.

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

pins

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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~104 for most of these data)

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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.

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Dimpling works at high Re (we need ~105)

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CFD studies could be performed for our particular design conditions

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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

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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?

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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

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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?

a potpourri * of engineering topics

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