ORNL is managed by UT-Battelle, LLC for the US Department of Energy
An Overview of the Material-Salt Compatibility
Program at ORNL
Stephen Raiman
with J. Keiser, N. Gallego, C. Contescu,J. McMurray, A. Willoughby, J. Startt,J. McDuffey, D. Ezell-Bull, S. Sham, and others
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Materials in molten salts degrade by chromium depletion
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Stability of Metals in Chloride Salts
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KClLiCl
NaClCaCl2
MgCl2
AlCl3CrCl2
FeCl2NiCl2
MoCl4
MnCl2
Redox condition
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Chromium reacts at salt-metal interface, diffuses outward from bulk, and leaves porous layer
! Salt impurities react with structural alloys
2HF(d) + Cr(s) CrF2(d) + H2(d)
! Metallic halides
Cr(s) + FeF2(d) CrF2(d) + Fe(s)
! Fuel
Cr(s) + 2UF4(d) CrF2(d) + 2UF3(d)
Similar reactions in Cl salt, just replace F with Cl
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Our objective is to understand degradation of structural alloys in molten salts
Enabling…
! Optimized chemistry-material choices
! Accurate models of in-reactor behavior
! Development of advanced materials
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“Calibrating” how salt chemistry affects the lifetime of salt-facing components
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Outline
! Corrosion testing methods
! Advanced material development
! Graphite and SiC compatibility
! Modeling
! Irradiation accelerated corrosion
! Infrastructure development and future plans
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Capsule testing
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Flowing salt with a thermal gradient is required to accurately reproduce MSR conditions
! Temperature-dependent equilibrium constants drive mass transfer
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Hot leg: reaction moves to right (dealloying)
Cold leg: reaction moves to left(deposition)
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Thermal convection loops have been used at ORNL since the MSRE days
! Salt is introduced at top
! Flow is driven by thermal gradient
! Coupons are hung in both the hot leg and cold leg
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Fluoride salt preparation
! Hydrofluorination process
! Capacity of ~ 3.3 L (6.6 kg) per batch
! Ability to produce a variety of salts including fuel salts and FLiBe
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! Dehydration" Carnallite method (NH4Cl)
! Carbochlorination" CCl4 @ T = 750°C
! Metal & oxide content verified analytically
! Capacity:" Current: 0.5 L (0.8 kg) /batch" Expanding to 1.5 L / batch
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Chloride salt preparation
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Outline
! Corrosion testing methods
! Advanced material development
! Graphite and SiC compatibility
! Modeling
! Irradiation accelerated corrosion
! Infrastructure development and future plans
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Understanding how commercial alloys perform in molten chlorides and fluorides
Alloy Ni Fe Cr Mo
316H SS 10 68 17 3Hastelloy N 71 4 7 16Alloy 800H 33 45 20 0Haynes 230 57 !"#$% 22 2Inconel 600 75 7 15 0
Hastelloy C-276 61 4 22 9Haynes 242 57 5 16 16
Hastelloy N 71 4 7 16
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Advanced materials
! New alloys with enhanced properties" Includes Hastelloy-N variants
! Cladded materials" Corrosion resistant materials cladding joined to code-qualified
structural materials
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Fusion Welding of Ni on 316H Stainless
! Nickel cladding on 316H steel
! Total 12 passes, 50% overlay
! High quality arc welding cladding of Ni on 316H is relatively easy to achieve
! Multiple layers of cladding will be carried out next"
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Characterization
Source (Sam Sham)
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Capsule testing of alloy-N variants and potential cladding materials
Raiman, (unpublished)
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Metallography of samples
Cu plating
M49 Alloy-N
Damage layer
316L
Damage layer
M52
10 !m
Raiman, (unpublished)
Cu plating
Cu plating
Cu plating
Alloy
Alloy
Alloy
Alloy
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Outline
! Corrosion testing methods
! Advanced material development
! Graphite and SiC compatibility
! Modeling
! Irradiation accelerated corrosion
! Infrastructure development and future plans
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Nuclear graphite requirements
! High purity: Neutronics (low B content), oxidation resistance
! High density: Greater neutron moderator capacity
! High irradiation stability: Low dimensional changes
! High thermal conductivity, high strength, low elastic modulus, low CTE
! Low anisotropy: Less than 1.1 defined by ratio of thermal expansion
! Low salt infiltration
! Small grain size/pore size: Ultrafine (<10 !m) / microfine grains (<2 !m)
! Low gas fission products permeation
! Chemically inert: low tritium and fluorine chemisorption
! Electrochemically passive: need to minimize galvanic corrosion of metals/alloys in the presence of graphite
! Low cost
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Low wettability observed on fine-grained graphite
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Significant wetting observed on SiC sample exposed to FLiBe
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New pressure-vessel testing apparatuswith antechamber
Crucible
Gas inlet and outlet
Ball valve
Filled and sealed in glovebox
Alternate gas inlet
Sample holder
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Outline
! Corrosion testing methods
! Advanced material development
! Graphite and SiC compatibility
! Modeling
! Irradiation accelerated corrosion
! Infrastructure development and future plans
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Development of thermodynamic models
Basic models will be extended to include the highly multicomponent systems that inevitably occur with MSRs.
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Modeling surface energy at the alloy-salt interface with density functional theory (DFT)
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Outline
! Corrosion testing methods
! Advanced material development
! Graphite and SiC compatibility
! Modeling
! Irradiation accelerated corrosion
! Infrastructure development and future plans
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Irradiation effect on corrosion
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Likely no radiolysis effect in salt
Possible effect of radiation
enhanced diffusion
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Capsule irradiation in OSU reactor
! KCl-MgCl2 salt" “aggressive” salt with ~1% oxide
to ensure measurable corrosion during short exposure
" “clean” salt with <30 ppm oxide to ensure impurity effect doesn’t mask irradiation
Irradiated UnirradiatedAggressive salt Alloy N 316 SS Alloy N 316 SS
Clean salt Alloy N 316 SS Alloy N 316 SS
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Reactor insertion
! Capsules irradiated for 21 hours at 800"C! Currently awaiting examination at ORNL! Proof of concept for future irradiations
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Outline
! Corrosion testing methods
! Advanced material development
! Graphite and SiC compatibility
! Modeling
! Infrastructure development and future plans
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Reliable data on molten salt corrosion?
Raiman, Lee, J. Nucl. Mater. (2018)
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Data, data, data
! as a basis for salt chemistry guidelines
! to guide material selection and development
! to validate models
Collected data must be both! Useful! Repeatable
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Efforts in progress to increase experimental throughput
Furnace banks devoted to capsule testing
MSR Campaign Review
Filled and sealed in glovebox
Pressure vessel with
antechamber for high quality static
exposures
Lots of high quality salt!
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Summary
! Multi-faceted program to understand compatibility of structural alloys and graphite with molten salts
! Computational models in development
! Infrastructure improvements to allow data generation with high reliability and high throughput
! Irradiation-corrosion program to understand combined effects in MSR cores
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FY19 plans - summary
! Continue exposures of commercial alloys in F and Cl salts" Find effect of temperature
" Impurity effects on corrosion (Redox)
" Fission product effect
! Corrosion in flowing salt" Thermal convection loops
! Model development" Atomistic modeling to find interface behavior
" Thermodynamic modeling to understand salt chemistry effect on corrosion
! Graphite infiltration
! Advanced material studies" Advanced Ni superalloys
" Cladded materials
" Structural ceramics
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Supplementary
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Graphites for MSR… “grading”Grain
size [!"#Pore size
(um) Density Billet size Purity Cost Country of origin
Irradia-tion data
Irradiation lifetime Isotropic
Still manufac-
tured
AG
C-C
am
pa
ign
H-451 Medium 5-100 1.71 SGL USA Low dose Extruded
NBG-17 Medium 8-30 1.86 Large < 5 ppm $ SGL (Germany/ France) Low dose Vibro-
molded
NBG-18 Medium 5-50 1.87 Large < 5 ppm $ SGL (Germany/ France) Low dose Vibro-
molded
PCEA Medium 5-100 1.79 Large < 5 ppm $ GrafTech (USA) Low dose Extruded
IG-110 Fine < 100 <1 1.76 Large < 5 ppm $ Toyo (Japan) Low dose Iso-molded
IG-430 (dropped) Fine < 100 <1 1.80 Large < 5 ppm $ Toyo (Japan) Low dose Iso-molded
2114 (added) Fine < 100 Large < 5 ppm $ Mersen
(France-USA) Low dose
MSRE CGB Medium 1.86 Small Union Carbide (USA) Extruded
OTH
ER fi
ne g
rain
gra
phi
tes
POCO-ZXF-5Q
Microfine < 2 0.3 1.78 Small < 5 ppm $$ USA Low dose Iso-pressing
POCO-AXF-50
Ultrafine < 10 0.8 1.78 Small < 5 ppm $$ USA Low dose Iso-pressing
POCO-TM Ultrafine < 10 1.5 1.82 Small < 5 ppm $$ USA Few data Iso-pressing
G347A Ultrafine < 10 1.85 Large < 5 ppm Tokai (Japan) High dose Iso-pressing
IGS743NH Superfine < 50 1.80 Large Nippon
(Japan) Low dose Iso-molded
ITU10 Fine < 100 Ibiden (Japan?)
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Experiment Types
Crucible Sealed Capsule Thermal Loop Pumped Loop
Sealed from contaminants No Yes Yes Yes
Access for instrumentation Yes No Yes Yes
Hot and cold sections No No Yes Maybe
Precise flow control No No No Yes