Update on ARIES ACT2 Power Core Design and Engineering X. R. Wang, M. S. Tillack, C. Koehly ARIES Project Meeting 18 September2013 ARIES UC San Diego UW Madison PPPL Boeing INL GIT GA

Progress was made in several areas since May ACT2 power core configuration and CAD drawings, including blanket internal details Primary stress analysis of the reference blanket MHD heat transfer in the DCLL blanket, detailed thermal analysis of the steel structures Thermal stress analysis of the reference design Alternative “small module” blanket concept o Pressure stress analysis and parametric studies, comparison of small module with full sector blanket Power cycle definition Next steps

ACT-2 power core CAD drawings (now available on the web) were generated using physics point Plasma major radius 9.75m Plasma aspect ratio 4 Plasma minor radius m SOL at midplane (IB,OB)10cm IB blanket thickness65cm first wall3.8cm breeding zone58.2cm back wall3cm OB-I blanket thickness40cm first wall3.8cm breeding zone33.2cm back wall3cm OB-II blanket thickness60cm front wall3cm breeding zone54cm back wall3cm 9 inboard PbLi feed pipes

Definition of the divertor target plates and slots was performed in the same manner as ACT-1 Inboard divertor target to x-Point >~0.48 m Outboard divertor target to x-Point > ~0.76 m

Internal details were generated based on 3D analysis: 1. Layout and radial build of the reference IB blanket ZoneDescriptionThickness (cm) 1 First wall FW cooling channel Second wall Stagnant Pb-Li SiC insert Breeding channel SiC insert Stagnant Pb-Li Separation plate Stagnant Pb-Li SiC insert Breeding channel SiC insert Stagnant Pb-Li Back plate 3.0 Total 65 For R=9.75 m Breeding cell layout: 9 toroidal, 2 radial Dimensions of cell: ~0.306 m (toroidal) x m (radial) Thickness of grid plate: 1.8 cm

2. Layout and radial build of outboard Blanket-I ZoneDescriptionThickness (cm) 1First wall0.4 2FW cooling channel3.0 3Second wall0.4 4Stagnant Pb-Li0.5 5SiC insert0.5 6Breeding channel SiC insert0.5 8Stagnant Pb-Li0.5 9Separation plate1.8 10Stagnant Pb-Li0.5 11SiC insert0.5 12Breeding channel SiC insert0.5 14Stagnant Pb-Li0.5 15Back plate3.0 Total40 Breeding cell layout: 16 toroidal Dimensions of OB-I cell: ~0.297 m(tor.)x0.166 m(rad.) Dimensions of OB-II cell : ~0.31 m(tor.)x0.27 m(rad.) Thickness of grid plate: 1.8 cm tor. pol. rad.

3. Radial build of outboard Blanket-II Zone Description Thickness (cm) 1 First wall FW cooling channel Second wall Stagnant Pb-Li SiC insert Breeding channel SiC insert Stagnant Pb-Li Separation plate Stagnant Pb-Li SiC insert Breeding channel SiC insert Stagnant Pb-Li Back plate 3.0 Total 60

Material compositions of the DCLL outboard blankets from CAD model (Sector Design) BOTTOM SECTIONMIDDLE SECTIONAVERAGE OVER POLOIDAL LENGTH Blanket-I (40 cm) Blanket-II (60 cm) Blanket-I (40 cm) Blanket-II (60 cm) Blanket-I (40 cm) Blanket-II (60 cm) Front Plate 3.8 cm / 3.0 cm 33.6% F82H 66.4% He (3.8 cm) 46.5% F82H 55.5% He (3 cm) 33.6% F82H 66.4% He (3.8 cm) 38.7% F82H 61.3% He (3 cm) 33.6% F82H 66.4% He (3.8 cm) 42.6% F82H 57.4% He (3 cm) Breeding Zones 33.2 cm (OB-I) 54 cm (OB-II) 72.0% LiPb 7.6% F82H 8.5% SiC 11.9 % He 79.2% LiPb 6.4% F82H 7.0% SiC 7.4 % He 76.3% LiPb 6.2% F82H 7.8% SiC 9.7 % He 82.9% LiPb 5.0% F82H 6.1% SiC 6.0 % He 74.2% LiPb 6.9% F82H 8.2% SiC 10.7 % He 81.1% LiPb 5.7% F82H 6.5% SiC 6.7 % He Back Plate 3 cm 74.2% F82H 25.8% He 76.3% F82H 23.7% He 73.8% F82H 26.2% He 75.1% F82H 24.9% He 74.0% F82H 26.0% He 75.7% F82H 24.3% He

Load conditions and design limits for primary stress Helium operating pressure is 8 MPa Pb-17Li static pressure at bottom: ~1.6 MPa front, ~1.5 MPa back (MHD pressure drop of 0.1 MPa was assumed ) Stress allowables for F82H steel: o Average membrane stress < 1 S m o Primary membrane plus bending stresses < 1.5 S mt (2/3 of min. creep stress to rupture) o Thermal stresses < 1.5 S mt o Combined primary and secondary stresses < 3 S m S m, MPaS t, MPa1.5 S mt, MPa 425 ˚C ˚C ˚C ˚C ˚C Allowable stress for RAFS (F82H) steel (S t at t=100,000 h)

3D stress analysis was performed at several locations Primary stress analysis was performed at middle and bottom cross sections for IB, OB1, and OB2 (cf. ARIES-CS, which looked only at one location, and omitted weight of PbLi) Boundary Conditions: a. At bottom plane, z-displacement = 0 b. Free expansion and free bending c. Symmetry at the vertical plane (poloidal-radial plane at 11.25˚)

Inboard blanket primary (membrane + bending) stress using 1.6 MPa in PbLi, 8 MPa He Peak stress concentration ~228 MPa We assume local stress can be reduced (below 216 by adding welding fillers. Rad. Pol. Tor. location , MPa maximum228 first wall90 second wall153 separation plate144 grid plate98 back plate45

Excluding local concentrations, the inboard blanket can accommodate internal pressure up to 2.5 MPa Peak stresses away from local concentrations (that we believe can be easily fixed) Limit at 500 C Limit at 475 C Allowable pressure

Cross-section at bottomCross-section at middle plane First WallFront grid plate Back grid plate Separation plate Back plate1.5 S mt, Primary stresse at bottom, MPa Primary stress at middle, MPa Primary (membrane + bending) stresses in the OB blanket are manageable (1.6 MPa PbLi pressure)

Modeling of MHD heat transfer is needed to provide heat flux boundary conditions into steel structures 2D radial/vertical geometry modeled, including PbLi and SiC Boundary temperatures provided by ANSYS; heat fluxes solved iteratively for use in thermal and thermal stress analysis at blanket top and bottom Iterative solver used previously for ACT1:

Peak heat flux (FW) is MW/m 2. FW He inlet/outlet temperature reduced to 385/436 C (from 429/509), and blanket He exit temperature is ~470 C. LiPb inlet/outlet temperature is ~460/647 C. Heat transfer coefficient on FW is ~8600 W/m 2 -K (roughing wall is assumed), ~4300 W/m 2 -k for all others (smooth walls). Maximum structure temperature must be lower than 550 C (thermal creep strength) and LiPb/F82H steel interface must be lower than 500 C (compatibility) Heat flux from the PbLi breeder into the steel structures can cause interface temperature limits to be exceeded (k SiC =5 W/mK) W/m 2 q1bot52874 q2bot39962 q3bot q4bot103370

q > 10 5 W/m 2 K can cause difficulty maintaining steel within acceptable temperature range k = 2 W/mK provides acceptable temperatures The highest leverage on grid plate heat flux comes from k SiC

Experiments have been performed on unirradiated SiC foam for flow channel inserts In ARIES-ST we assumed k SiC could be easily degraded Recent R&D (Ultramet, Sharafat) suggests 2 W/mK is achievable Shahram Sharafat, Aaron Aoyama, Neil Morley, Sergey Smolentsev, Y. Katoh, Brian Williams, and Nasr Ghoniem, “Development status of a SiC-foam based flow channel insert, for a U.S.-ITER DCLL TBM,” Fusion Science and Technology 56 ( ) 2009.

Uniform inlet temperature = 460 ˚C Slug flow Zone 1 outlet continues into zone 2, “inside-out” k SiC = 2 W/mK Final thermal results using k=2 W/mK Zone 1Zone 2 T1top491 C T1bot488 C T2top491 C T2bot488 C T3top491 C T3bot495 C T4top491 C T4bot495 C From ANSYS

Thermal stress analysis of OB Blanket-I at bottom section shows requirements are met (k SiC = 2 W/mK) Maximum FW temperature is well below 550˚C limit. Maximum LiPb/F82H interface temperature ~495 C (within design limit of 500˚C). Maximum thermal stress is ~144 MPa (1.5 S mt =203 MPa at T=500˚C) 144 MPa W/m 2 q1bot5907 q2bot-4187 q3bot52657 q4bot54750

Thermal stresses in outboard blanket-I at the middle section are also well within limits 133 MPa 0.9 mm Distribution of total deformation  Maximum thermal stress is ~133 MPa, well below 1.5 S m stress limit (203 MPa at 500˚C) Distribution of thermal stress

Alternative Blanket Design Option for ACT-2 DCLL (no sector side wall supports) 6 modules/sector each module is fed by one Pb-Li access pipe Stress model model Bottom view

Primary (membrane plus bending) stress for the small blanket (Inner Module) indicates a minimum of 8 needed 6 modules per sector 8 modules per sector The inner modules have Pb-Li static pressure balanced on both sides. The total stress of the inner module for the case of 8 modules per sector meets 1.5 S mt design limit. The 6 modules/sector design exceeds the allowable stress. Max. σ=167 MPa Max. σ=268 MPa Tor. Pol. Rad.

The outer module also meets the 1.5 Sm limit using 8 modules per sector  8 modules per sector (22.5 toroidal degree)  6 modules per sector (22.5 toroidal degree) Local stress σ= 399 MPa Local stress σ= 370 MPa σ= 290 MPa σ = 199 MPa 6-module design exceeds allowable (1.5 S mt =203 MPa) Local stress increased a lot vs. sector design, but can be reduced by adding welding fillers. 6 modules per sector 8 modules per sector

Parametric studies were performed to explore variations of the FW of the alternative design  8 module design results in too much steel for TBR  We attempted to find a solution with 6 modules by adjusting the dimensions of the FW channels 38 mm A (reference) 38 mm mm B (thick back wall) C (thick He channel)

Option A primary stress results (6 modules) Allowable primary membrane plus bending stress=203 MPa at T=500 C Allowable total pressure load is ~1.4 MPa Option A can not accommodate the weight of Pb-Li (~1.6 MPa). 38 mm Limit at 475 C Limit at 500 C

Maintain the total thickness of a FW panel (3.8 cm) unchanged, increase the thickness of the second wall from 4 mm to 6 mm. Allowable total pressure load increased from 1.5 to ~2.1 MPa 38 mm Option B primary stress results (6 modules) Limit at 475 C Limit at 500 C

Maintaining the thickness of the second wall unchanged, increasing the total FW panel from 3.8 cm to 4.0 cm (suggested by Siegfried). Allowable total load is ~1.5 MPa 40 mm Option C primary stress results (6 modules) Limit at 475 C Limit at 500 C

Comparison of Material Compositions for DCLL Inboard Blanket Design Options ARIES-CS (2m x 2m module) ACT2 DCLL (Sector) ACT2 DCLL (6 Modules-A) ACT2 DCLL (6 Modules-B) ACT2 DCLL (6 Modules-C) ACT2 DCLL (8 Modules) First Wall 3.8 cm 8% ODS FS 27% F82H 65% He 5.3% ODS FS 28.4% F82H 66.3% He 35.5% F82H 64.5% He (4/30/4 mm) 39.3% F82H 60.7% He (4/28/6 mm) 37.3% F82H 72.8% He (4/32/4 mm) 35.5% F82H 64.5% He Breeding Zone 58.2 cm 77% LiPb 7% F82H 3.7% SiC 12.3% He 79.2% LiPb 6.1% F82H 6.2% SiC 8.5 % He 72.3% LiPb 8.7% F82H 5.3% SiC 13.7 % He 72.3% LiPb 9.5% F82H 5.3% SiC 12.9 % He 69.8% LiPb 9.0% F82H 5.2% SiC 15.3 % He 65.5% LiPb 10.9% F82H 5.8% SiC 17.8 % He Back Plate 3 cm 80% F82H 20% He 84.1% F82H 15.9% He 35.6% F82H 64.4% He 37.9% F82H 62.1% He 36.8% F82H 63.2% He 35.6% F82H 64.4% He Max. Pr Load, MPa (PbLi pressure not considered in ARIES-CS)  Maximum primary membrane plus bending stress should be below 1.5 Sm (209/189 MPa for T=500/550 C).  The sector design option provides the largest LiPb fraction in the breeding zone and can accommodate the highest pressure load up to 2.5 MPa.  The 6-module per sector design has advantages for fabrication, but lower LiPb fraction in the breeding zone.  6-module A &C options can not support the weight of PbLi.  All of the small-module designs have reduced breeding capability.

Brayton cycle efficiency is degraded due to the low inlet temperature required to maintain steel/PbLi interface below 500 C operating point,  =45%

PbLi divertor plates FWFW grid plates divertor structure SR Power flows and temperature matching in the heat exchanger We reduced the HX  T in order to increase the inlet temperature

What’s next? Any revisions based on feedback from this meeting We need final PF coil locations ASAP A few minor details added in the CAD drawings (e.g. maintenance paths) One journal article to be prepared on ACT2 power core engineering No work to extend beyond calendar 2013