ORNL is managed by UT-Battelle for the US Department of Energy Progress on R&D of SiC FCI for DCLL Prepared for Presentation at 2 nd EU-US DCLL Workshop November 14-15, 2014, Los Angeles Yutai Katoh Leader, Fusion Materials & Nuclear Structures Materials Science and Technology Division Oak Ridge National Laboratory With contributions from: L.L. Snead, T. Koyanagi (ORNL) R.J. Shinavski (Rolls-Royce HTC) S. Sharafat (UCLA), B. Williams (Ultramet) T. Nozawa, K. Ozawa (JAEA)

2 Katoh on SiC FCI for Fusion DCLL Blankets Introduction FCI is among key components for liquid metal-cooled/bred fusion blankets –Proposed by Malang (1991) and adopted in conceptual blanket designs. –Mitigates MHD pressure drop –Enables high temperature operation –Makes DCLL concept attractive Two important FCI functions in DCLL –Thermally insulate steel structures from Pb-Li –Electrically insulate Pb-Li from steel structures FS GAP FCI Pb-Li 100 S/m 20 S/m  FCI = 5 S/m Temperature Profile for Model DEMO Case Smolentsev

3 Katoh on SiC FCI for Fusion DCLL Blankets Key FCI Requirements 1.Minimize Impact on Tritium Breeding 2.Adequate thermal insulation – K th = 2~5 W/m-K for US DCLL TBM 3.Adequate electrical insulation –  el = 5~100 S/m for US DCLL TBM 4.Compatibility with Pb-Li – Up to 470 º C for US DCLL TBM, >700 º C for DEMO – In a flow system with large temperature gradients 5.Leak Tight for Liquid Metal / disconnected porosity – Pb-Li must not “soak” into cracks or pores, must remain isolated in small pores even if cracked 6.Mechanical integrity – Primary and secondary stresses must not endanger integrity of FCI 7.Retain Requirements 1 – 5 during operation – Neutron irradiation in D-T phase ITER, and extended to DEMO – Developing flow conditions, temperature & field gradients – Repeated mechanical loading under VDE and disruption events Sharafat and Katoh, Discussion summary from 8th IEA International Workshop on SiC/SiC Ceramic Composites for Fusion Applications, 2009, Daytona Beach.

4 Katoh on SiC FCI for Fusion DCLL Blankets R&D Needs for SiC-based FCI (Katoh, 2007) Present Status (Radiation-resistant SiC/SiC) R&D Goal (Property-adjusted SiC/SiC) Thermal insulation -Insufficient unirradiated insulation (5-10 W/m-K) -Substantial change during irradiation -Maintain W/m-K throughout operation -Validate radiation effect model Electrical insulation -May meet requirement (<~ 20 S/m) -Controllability questionable -Radiation effect unknown -Establish control scheme -Address radiation effect Chemical compatibility -Static testing underway -Results so far promising -Perform validation Liquid metal leak tightness -No serious concern-Perform validation Mechanical integrity -Cracking stress likely limits  T -Stress induced by differential swelling may dictate secondary stress -Survive  T > 200K throughout operation -Determine differential swelling effect and irradiation creep -Confirm other radiation effects

5 Katoh on SiC FCI for Fusion DCLL Blankets FCI Design Space Considerations

6 Katoh on SiC FCI for Fusion DCLL Blankets SiC-based Materials for FCI Property2D SiC/SiCPorous SiC + CVD SiC Thermal conductivity>~2 W/m-K irradiatedHighly tailorable Electrical conductivity10 – 100 S/mHighly tailorable Pb-Li compatibilityGood Leak tightness, BOIGood Strength, flexure ~200 MPa  -cracking ~100 MPa Young’s modulus200 GPa M’, 500°C, BOL~400K~200K Sharafat

2. Eliminate interlaminar shear stresses at corners of FCI insert by using continuous inner electrical FCI with minimal temperature drop through-thickness & outer architechurally designed thermal FCI composed of non-rigidly attached corners (Smolentsev and Malang ) Inner Electrical FCI Outer Thermal FCI SiC/SiC Composites for Flow Channel Inserts SiC/SiC composites produced from near stoichiometric SiC fibers and a CVI SiC matrix have demonstrated excellent stability under neutron radiation similar to monolithic CVD SiC SiC/SiC composites possess pseudo- plasticity because reinforcing fibers provide a high strain to failure (compared to monolithic ceramics). An insensitivity of the mechanical properties to temperature also exists DoE funded SBIR with Hyper-Therm HTC examining the feasibility of SiC/SiC composites for flow channel inserts Benefits: Two properties identified do not meet requirements: 1. Unacceptably high through thickness thermal conductivity (15-23 W/m/K in 800ºC-ambient prior to irradiation) would result in too high of a heat loss and/or insufficient thermal protection of the ferritic steel flow channel; 2. High interlaminar shear stresses at corners due to through thickness thermal gradient may cause matrix cracking and Pb-Li permeability Solutions: 1. Architectural construction of the SiC/SiC composite to reduce through- thickness thermal transport Two fluted core technology demonstrators FEA modeling indicates fluted core SiC/SiC can achieve equivalent through thickness thermal conductivity of 1.4 W/m/K Zinkle, ICFRM-14

Results: Comprehensive thermomechanical modeling was performed and correlated with experimentally derived performance. At 700 o C the composite structure exhibited low thermal (~ 3 to 6 W/m-K) and electrical conductivity (< 0.1 S/m). Immersion testing of development specimens in PbLi for 100 hours at 0.7 MPa and 600°C resulted in no metal ingress. FCI prototype segments up to 100 x 100 x 300 mm long were successfully fabricated along with a segment joint coupling FCI prototype thermal testing showed a high thermal gradient across the wall at steady-state with 600°C ID and 453°C OD. Immersion testing of a FCI prototype in PbLi at 560°C, at ambient pressure, for 6 hours resulted in no metal ingress. Ultramet – Department of Energy SBIR Phase-II (DE-FG02-05ER84193): Flow Channel Inserts for Dual-Coolant ITER Test Blanket Modules Objective: Demonstrate the feasibility of a silicon carbide, open-cell-foam-core flow channel insert that will: Provide thermal insulation between high temperature liquid Pb-17Li tritium breeder and structural material Provide electrical insulation between the Pb-17Li and structural material to mitigate magneto-hydrodynamic effects Ultramet (Materials and Structures) B. Williams, M. Wright Digital Material Solutions (Design and Modeling) S. Sharafat, A. Aoyama, N. Ghoniem DOE (COTR) G. Nardella Open-cell SiC Foam SiC Foam/SiC Facesheet Development Specimen SiC Foam/SiC Facesheet FCI Prototype Segment (100 x 100 x 300 mm long) 10 mm Electrical Conductivity Thermal Conductivity

9 Katoh on SiC FCI for Fusion DCLL Blankets Thermal Conductivity: Irradiation Effect Thermal conductivity of 2D SiC/SiC composites falls around W/m-K (Hi-Nicalon™ Type-S) to W/m-K (Tyranno™-SA3). Thermal conductivity of irradiated SiC/SiC exhibits very weak temperature dependence at T < T irrad

10 Katoh on SiC FCI for Fusion DCLL Blankets Enhanced Thermal Insulation by Architectural Approach Recent SBIR effort by Hypertherm HTC demonstrated fabrication and effectiveness of fluted panels for improved insulation. Shinavski

11 Katoh on SiC FCI for Fusion DCLL Blankets Electrical Conductivity “Intrinsic” electrical conductivity for 2D SiC/SiC appeared to be 2 – 20 S/m through-thickness at RT - 800°C. Neutron irradiation slightly increased electrical conductivity to 10 – 20 S/m.

12 Katoh on SiC FCI for Fusion DCLL Blankets Electrical Conduction Model and Analysis Direction of unperturbed field Volume fraction of interphase which is aligned in favor of conduction In interphase-dominated condition: Through-thickness conductivity due to interphase bypass: Efficiency of short-circuit conduction (related with probability of inter-connection)  tt meas. [S/m]  ip meas. [S/m]  ip model [S/m]  S/W Nicalon-S ML (~100 nm) 5.5 (±0.8 for 8 samples) ~2.8% P/W Tyranno-SA3 PyC (~150 nm)4.5550~0.8% P/W Tyranno-SA3 PyC (~50 nm)2.6180~1.4% T=RT Interphase conductivity 1/T 

13 Katoh on SiC FCI for Fusion DCLL Blankets Secondary Stress Issues Thermal stress due to  T Swelling-induced stress Saturated swelling: ~8x10 -6 K -1 at ~500ºC Thermal expansion: ~4.5x10 -6 K -1 Thermal expansion: ~4.5x10 -6 K -1 Flexural strain due to instantaneous thermal expansion Flexural strain due to differential swelling Typical cracking strain for SiC T M = 773K In presence of  T, secondary stress induced by differential swelling is likely more intense than instantaneous thermal stress. Understanding irradiation creep may change situation. Katoh, 2010

14 Katoh on SiC FCI for Fusion DCLL Blankets Critical Gaps - Design and Failure Issues: Statistical Failure Assessment related to Fission Product Transport No-Leak Leak Need to understand whether matrix micro- cracking relates to failure (= failure criteria) The permeation studies to date have been performed on as- fabricated specimens If the fully-ceramic structural reliability is challenging, what are mitigation strategies?

15 Phase II Objective Expand upon the success of previous SiC foam/SiC facesheet FCI work and address two primary areas: –Develop an internal filler material (carbon or oxide aerogel) to allow the FCI to continue functioning in the event of SiC facesheet damage. –Continue design optimization and prototype component fabrication such that testing can be performed in a representative, flowing PbLi environment.

16 Phase II Results

17 Phase II Results (2)

18 Phase II Conclusions (3) Views of aerogel-filled foam specimens (nominally 30 cm long, 6 x 6 cm ID, 8 x 8 cm OD) on the reactor coating stand following the first SiC facesheet deposition run. A B

19 Phase II Conclusions (4) Increased-length Phase II demonstrator, composed of three, nominally 30 cm FCI sections linked together using CVD SiC-coated graphite couplings.

20 Katoh on SiC FCI for Fusion DCLL Blankets Concluding Remarks SiC-based materials present advantages in technological maturity except specific nuclear aspects –Insulating properties are adequate for use in DCLL. –Likely survive  T largely exceeding 200K. Critical issues are related with transmutation –Solid transmutation effects on insulating performances and corrosion resistance –Note that extent of concern strongly depends on high energy tail of fusion neutron spectra (e.g. FW vs. most other blanket portions) Qualification requirements? –Failure criteria and acceptable failure probability need to be established

21 Katoh on SiC FCI for Fusion DCLL Blankets

22 Katoh on SiC FCI for Fusion DCLL Blankets Development of Insulating Interphase Composite Hypertherm HTC developed PyC/SiCN multilayer interphase replacing PyC/SiC. Interphase becomes insulating when Si-N bond dominates. Insulating interphase should lower through-thickness composite conductivity below the matrix SiC conductivity. Shinavski

23 Katoh on SiC FCI for Fusion DCLL Blankets Secondary Stress Evolution Considering Irradiation Creep of SiC Swelling-coupled creep was found for SiC n = 1 D tr ~42 at 300ºC ~66 at 500ºC ~120 at 800ºC Largest magnitude of secondary stress is anticipated upon cooling after swelling saturation is reached. DT = 300K will be close to the cracking limit for SiC. T M =773K  T=400K T M =773K  T=200K B 0 = 3E-7 dpa -1 MPa -1 Intermittent cooling Katoh, submitted Typical cracking limit

24 Results: Comprehensive thermomechanical modeling was performed and correlated with experimentally derived performance. At 700 o C the composite structure exhibited low thermal (~ 3 to 6 W/m-K) and electrical conductivity (< 0.1 S/m). Immersion testing of development specimens in PbLi for 100 hours at 0.7 MPa and 600ºC resulted in no metal ingress. FCI prototype segments up to 100 x 100 x 300 mm long were successfully fabricated along with a segment joint coupling FCI prototype thermal testing showed a high thermal gradient across the wall at steady-state with 600ºC ID and 453°C OD. Immersion testing of a FCI prototype in PbLi at 560°C, at ambient pressure, for 6 hours resulted in no metal ingress. Objective, using silicon carbide, open-cell- foam-core develop FCI prototype that: Provides thermal insulation between high temperature liquid Pb-17Li tritium breeder and structural material Provides electrical insulation between Pb-17Li and structural material to mitigate MHD effects Electrical Conductivity Thermal Conductivity Recent Progress on SiC-Foam Based FCI SiC Foam/SiC Facesheet FCI Prototype Segment (100 x 100 x 300 mm long) Zinkle, ICFRM-14

Program Team Ultramet: Brian Williams (PI), Jim Selin Digital Materials Solutions: Shahram Sharafat, Nasr Ghoniem, Aaron Aoyama UCLA: Sergey Smolentsev, Tomas Sketchley, Neil Morley DOE Technical Monitor: Barry Sullivan Ultramet/Department of Energy SBIR Phase II (DE-SC ): Optimization and Simulated Testing of Flow Channel Inserts for Dual-Coolant ITER Test Blanket Modules

26 Katoh on SiC FCI for Fusion DCLL Blankets Phase II Conclusions The program was clearly successful in continuing to establish the feasibility of Ultramet’s SiC foam-based FCI for use as electrical/thermal insulation in DCLL blankets. High electrical/thermal insulation performance was demonstrated using development specimens and 30 cm long SiC foam/SiC facesheet components filled with vitreous carbon and silica aerogels to enhance insulation behavior were successfully fabricated. For the first time, a component was tested for electrical insulating performance in flowing PbLi for one month, and components were tested in static PbLi at both high pressure and temperature. Although dynamic testing of a 30cm FCI segment in flowing PbLi performed using the magnetohydrodynamic PbLi loop MaPLE at UCLA was shown to be highly complex in terms of the test procedure and data interpretation, the results were very promising. Monitoring of the temperature and flowrate in the loop for 30 days did not reveal any significant changes that would indicate metal ingress and deterioration of the FCI electroinsulating properties, and analysis of the MHD pressure drop indicated that the FCI performed as required, reducing the MHD pressure drop in the PbLi flow to a level that matched 3D theoretical predictions. Extrapolation of these results to actual blanket conditions, suggested a pressure drop reduction factor in the range of

27 Katoh on SiC FCI for Fusion DCLL Blankets Phase II Conclusions (2) Thermochemical and thermomechanical survivability of FCI segments under worst- case-scenario conditions was performed at UCLA in static PbLi at high pressure (1MPa) as well as high temperature (700˚C) for 100 hours. The test proved to be very demanding because specimens were subjected to a sudden initial temperature change from room temperature to 400˚C (submersion of ambient temperature FCI into 400˚C PbLi). An FCI segment would not encounter this thermal shock in actual use. However, the testing provided useful information under off-normal conditions for specimens with differing aerogel filler materials, with and without dense SiC facesheets. One specimen exhibited no metal ingress wheras other specimens exhibited varying degrees of ingress (no specimen exhibited full ingress). It is speculated that ingress in some areas may be caused by mechanical failure of the aerogel (exposed to high pressure), rather than chemical reactivity with the PbLi, and that use of higher density aerogels may reduce or eliminate metal ingress in all areas as long as thermal/electrical conductivity remains within requirements. Based on these results, UCLA recommends continued development, testing, and analysis of the SiC foam-based FCI for use as electrical insulation in DCLL blankets. Although significant progress has been made, additional FCI materials/processing development and testing is clearly required to optimize performance of this critical component.