Silicon Carbide Tritium Permeation Barriers for Steel Structural Components, Phase II Ultramet Matt Wright(PI) Test Support: Sandia Rion Causey, Rob Kolasinski Design and Modeling and Test Support: Sandia Dennis Youchison DOE Technical Monitor Gene Nardella Program Duration: 2 Years (August, 2008 – August, 2010) FNST Meeting August 12-14, 2008

Background International Thermonuclear Experimental Reactor (ITER) requires development of advanced materials for breeder blankets Tritium confinement is one of the most important safety objectives Aluminized coatings work well in the laboratory but fail in relevant environments.

Background CVD SiC permeability ~10-10 lower than that of 316 SS. After PbLi/ irradiation, alumina permeability is poorer than even the stainless steel substrate, mainly because of cracking [3] Tritium/hydrogen permeability comparison of Al2O3 and SiC with 316 SS [1,2] 1. R.A. Causey et al., J. Nucl. Mater. 203 (1993), 196-205. 2..R.M. Roberts et al., J. Am. Ceram. Soc. 62 (1979), 495-499. 3. D.L. Smith et al., Fusion Eng. Des. 61-62 (2002), 629-641.

Background Aluminized coatings are NOT chemically compatible with PbLi Al2O3 + 2Li → 2LiAlO2 + O CVD SiC has no reaction with PbLi. Large differences in tritium barrier coating performance have been attributed to superficial coating damage, i.e., microcracks [4]. However, because of CTE mismatch, SiC cannot be directly applied to steel (microcracking). CTEs: CVD SiC: 4.5 ppm/K ferritic steel F82H: 10.37 ppm/K Alumina range: 5.50 ppm/K - 9.60 ppm/K Avoidance of microcrack formation in tritium barrier coatings is therefore of utmost importance. 4. A. Aiello et al., Fusion Eng. Des. 58-59 (2001), 737-742.

Phase I Program Phase I investigated a dense CVD SiC coating (tritium barrier), bonded to ferritic steel using SiC foam. Foam compliant interlayer between steel and SiC barrier. Optical micrographs (cross-sections) of SiC foam bonded to low-activation steel with braze.

Phase I Program Results Foam steel bondline characterization continued... Higher magnification optical micrographs (cross-sections) of SiC foam bonded to low-activation steel with ABA

Phase I Program Results Resistance to high temperature thermal cycling and thermal shock was demonstrated through furnace testing, RT to 700°C, 10X Thermal cycling of SiC foam-steel bonded samples in controlled atmosphere tube furnace

Phase I Program Results Dye penetrant and SEM characterization after high temperature thermal cycling and thermal shock Dye penetrant testing of TPB coating after thermal cycling and shear test, showing no microcracking SEM images of thermal cycled development specimen, showing interface between SiC foam and solid SiC coating (Left) and higher magnification view within SiC coating (Right)

Phase I Program Results Foam to steel bond strength was established through shear testing. Qualitatively determined that foam to steel joint was at least as strong as the foam Failure was random throughout the foam SiC foam-steel test specimen after thermal cycling and shear test

Phase I Program Results Feasibility demonstrator specimens for deposition of non-porous CVD coating of SiC on SiC foam 10.1-cm diameter disks of 10% dense CVD SiC foam with 1.0 mm thick CVD SiC permeation barriers (Left) and side view of specimens (Right)

Phase I Program Results TPB on foam demonstrator hardware, cont. SEM images (cross-sections) of CVD SiC permeation barrier on CVD SiC foam

Phase I Program Results TPB on foam demonstrator hardware, cont. High-magnification SEM images (cross-sections) of CVD SiC permeation barrier on SiC foam, showing no porosity in coating

Phase I Program Results A matrix of dense SiC wafers was fabricated for deuterium permeation and tritium plasma testing. Representative CVD SiC coating (Left) on 3-cm diameter graphite disk (Right), fabricated for deuterium permeation testing

Phase I Program Results A matrix of dense SiC wafers was fabricated for deuterium permeation and tritium plasma testing. CVD SiC coatings on 5.1-cm diameter graphite disks, fabricated for tritium plasma testing

Phase I Program Results TPE was not available during the performance period. Deuterium permeation test results indicate the concept has high potential for meeting ITER tritium barrier requirements for TBMs. Gas analysis over duration of deuterium permeation test Gas analysis results for deuterium permeation test performed at 250̊C

Phase I Conclusions The primary objective of bonding solid CVD SiC tritium barrier coating to low-activation steel through use of a compliant SiC foam interlayer, was clearly achieved. Thermal and mechanical test results showed good potential for the structure to meet TPB requirements. Initial bonding procedures were established and thermal cycling tests were performed. The results showed no degradation of the foam-to-steel bond or the solid SiC coating. Without the foam interlayer, SiC coatings bonded directly to steel would microcrack severely during thermal cycling as a result of CTE mismatch. Preliminary D permeation testing performed at Sandia showed promising results, demonstrating a hermetic boundary.

Phase II Plans TPB Process Optimization and Property Characterization: Expand the scope to include compliant open-cell Mo and V metallic foam interlayer- thereby minimizing thermally induced stress that would otherwise damage the SiC permeation barrier coating. TPB Modeling and Model Validation: Sandia will perform detailed thermostructural modeling of a tubular TPB structure consisting of a ferritic steel outer tube, an open-cell foam interlayer, and a CVD SiC internal tritium barrier. Validated by producing strain gauge-instrumented rectangular coupons of the most promising multilayered barrier structures and applying a temperature gradient between the TPB coating and the steel substrate using the EB-60 electron beam at the Sandia Plasma Materials Test Facility (PMTF).

Phase II Plans Mechanical and thermal property testing: performed as required to support the modeling and design High temperature permeation rig construction- High temperature furnace, control system, mass spectrometer assembled and fitted with molybdenum tubes on each side of the seal. allowing testing to 1000°C Surface roughness was a factor in sealing samples to the gasket material, will be addressed by – Surface polishing by magnetorheological finishing (MRF) Sample surface metallization-Ti/Pt/Au for brazing/soldering to copper gaskets. Sputtering or evaporation of gold

Deuterium Permeation Setup Phase II Plans Deuterium Permeation and D/T Plasma Testing: Deuterium permeation testing will be performed on flat TPB structures up to 1000°C at Sandia Livermore, and plasma testing will be performed in the STAR facility at Idaho National Engineering Laboratory. To show that SiC retains its integrity with plasma exposure. Plasma Experiment Target Holder Deuterium Permeation Setup

Phase II Plans Fabrication of Steel Tube Prototype with TPB ID Liner: Following the Sandia design, material and process optimization at Ultramet, and deuterium permeation and plasma testing, the optimal TPB prototype structure will be fabricated. Prototype Testing: Tubular prototypes will be instrumented with thermocouples and a hydrogen gas delivery system. The TPB tube liner will be heated to 1000°C any hydrogen leakage past the permeation liner will be monitored with a residual gas analyzer. Compliant foam interlayer (SiC, Mo or V) Ferritic steel tube SiC TPB coating 76.2 × 350 mm TPB mockups