Department of Energy (DOE) Advanced Reactor ......and Property Changes due to Fast Neutron...
Transcript of Department of Energy (DOE) Advanced Reactor ......and Property Changes due to Fast Neutron...
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Nuclear Graphite Research Needs
Will WindesIdaho National Laboratory
DOE-NE NEET Cross-cut Coordination Meeting August 15-16, 2016
Department of Energy (DOE)Advanced Reactor Technologies (ART) R&D Program
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Why Research Graphite? Lessons we’ve learned from other graphite core reactor programs
– After Reactor Start-up…• Interestingly - fuel is not considered life limiting component after start-up• Graphite is life limiting component of reactor
– Degradation issues of graphite – normal and accident operations– Changes resulting from irradiation – structural integrity, cracks (irradiation creep)
– NRC will require understanding of the primary structural core material• Material properties needed for license approval before reactor start-up, and • Predicting core behavior during normal and off-normal operation
Primary objectives of graphite components– Must keep the fuel safe
• Must keep temperature “low” – thermal conductivity• Must maintain structural integrity – strength and irradiation behavior
– Creep behavior → Reduces cracks resulting from irradiation stresses– Provides core structure
• Cooling channel integrity, control rod insertion, and stable fuel configuration
− After Reactor Start-up…• Interestingly - fuel is not considered life limiting component after start-up• Graphite is life limiting component of reactor
• Degradation issues of graphite – normal and accident operations• Changes resulting from irradiation – structural integrity, cracks (irradiation creep), fracture
− NRC will require understanding of the primary structural core material• Material properties needed for license approval before reactor start-up, and • Predicting core behavior during normal and off-normal operation
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Primary function of Graphite R&D activities Defines the safe working envelope for nuclear graphite
− Current and future nuclear graphite components− Applicable for multiple DOE reactor designs (cross-cutting):
• HTR (both PB and Prismatic) and MSR designs
Data/analysis will be codified− Data will be used in new ASME Code− Code requires use of irradiation data and high
temperature behavior
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Graphite Core Components
ComponentMax.
Normal Operation
Off-Normal DPA
Graphite fuel block 900-1200ºC ~1400ºC ~ 0.8/yr
Reflector blocks 600-900ºC ~1200ºC ~ 0.5/yr
Core support columns 1000-1200ºC ~1200ºC ~0.001/yr
Other components 250 - 350ºC ~300-600ºC Varies
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Material Issues
Degradation
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∆L/L
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dose, dpa
1100 C900 C700 C500 C300 C
0.40.50.60.70.80.9
11.11.21.31.4
-5 5 15 25C
TE/C
TEo
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Property changes from irradiation and environment
O id ti i iti
Fission product transport/retention
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Main Material Properties of Interest
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Irradiation Dimensional
Change
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Main Material Properties of Interest
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Irradiation Dimensional
Change
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Main Material Properties of Interest
Irradiation Dimensional
Change
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Main Material Properties of Interest
Irradiation Dimensional
Change
G. Haag,” Properties of ATR-2E Graphite and Property Changes due to Fast Neutron Irradiation”, Juel-4183, 2005
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Main Material Properties of Interest
Irradiation Dimensional
Change
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Irradiation creep
(Residual stress remover)
Irradiation Dimensional
Change
Main Material Properties of Interest
Dose, dpa
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Structural failure
Low Thermal Conduct
Relieves stress Irradiation
creep(Internal stress
remover)
Longer component
lifetime
Structural failure
Turnaround
Higher core temperature
Main Material Properties of Interest
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Internal stress build-
up
Cracking&
Fracture
Irradiation Dimensional
Change
Larger block gaps (lowers
thermal transport)
Thermal properties
Thermal expansion
change
Lower Failure
Degradation
StrengthlossLower
ThermalTrans KIc
Extends turnaround
Strengthdecrease
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USA’s 5 different research areas
Graphite R&D Program
Defines the safe working envelope for nuclear graphite and
protection of fuelBehavior models- Predicts irradiated
material properties and potential degradation issues
- Irradiation behavior for continued safe operation
Mechanisms and Analysis- Data analysis and interpretation- Understanding the damage mechanisms
is key to interpreting data
Irradiation- Determines irradiation
changes to material properties- Irradiation behavior for
continued safe operation
Virgin Properties- (Statistically) Establishes as-
received material properties- Baseline data used to
determine irradiation material properties
Licensing & Code- Establishes an ASME
approved code (for 1st time)- Develops property values
for initial components and irradiation induced changes
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AGC Experiments
Irradiation Testing:• Creep Specimens• Button “piggyback”• Changes to properties• Irradiation of new materials• Fundamental irradiation damage
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AGC Experiment : Irradiation changes
AGC - 3
AGC - 5
Database for previous nuclear graphite grades
800 ºC
1100 ºC
600 ºC
1400 ºC
AGC - 4
AGC - 6
Dose (dpa)1 3 4.5 6
HTV
AGC - 1AGC - 2
• By comparing between test series• Property change by dose• Property change by temperature • Property change by stress
• Three pairs of test capsules• 3 Temperatures • 3 Stress levels• Continuous dose (0.5 – 7 dpa)
ε, σ
, ρ, α
, E, C
TE
Dose (dpa)
Tirr = 600, 800, 1100Cσ = 14, 17, 21 MPa
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Areas of pertinent graphite research DOE-ART focusing on large program activities
– Irradiation (AGC), Unirradiated data, Oxidation, ASME Code
Areas of maximum interest– Fundamental (i.e., small) irradiation studies
• Irradiated defect structures - creep mechanisms– Material property changes
• Affect of irradiation and molten salt– Fracture and strength
• Fracture toughness and multi-axial fracture behavior– Degradation (oxidation – salt erosion)
• Development of oxidation/degradation models• Development of new oxidation resistant grades/components
(dopants and coatings)– NDE flaw detection
• Flaw prediction and evolution during irradiation or degradation
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Fundamental irradiation studiesA real need to determine irradiated defect structures and how they affect behavior/performance.
• Grains shrink parallel to planes and grow in perpendicular direction
• Overall volume shrinkage
Cracks formed during fabrication accommodate swelling – for a while
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Creep - Dislocation climb/glide
• Intriguing TEM images under electron beam
– ║to Basal planes
– Interaction of basal planes under irradiation
– Does this show dislocation glide possibilities?
• Not supposed to happen in current model
C. Karthik et al. J. Nuc Mat 412 (2011) 321–326
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2 IL bonds
3 IL bonds
Dislocation climb/glide
2 IL bonds3 IL bonds
T. Trevethan et al, U of Sussex & U of Leeds, INGSM-13, Sept 2012
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Evidence of irradiation damage in graphite
A. Asthana et al, J. Appl. Cryst., (2005) 38, 361-367
• Tirr = 333 K (60°C)
• φlow 0.004 dpa
• φhigh 0.24dpa
Unirr
γlow
γhigh
No indication of sub-plane formation Different from current model
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Questions• What /Which defect structure affects material properties
– What are real creep mechanisms? Defect structures– What defect structures affect strength/modulus?
– How does this affect fracture behavior?– How is thermal diffusivity/conductivity affected?– Thermal expansion doesn’t match up with current explanation of
microstructure/defect changes. Why?• How does defect structure behave/interact
– Microstructure evolution• How does the defect microstructure change over increased dose
and temperature?• Defect accumulation
– How is porosity affected?• Pore generation in tertiary creep – but how/why?
• Irradiated specimens - at National Labs (INL/ORNL)– Collaborations and sharing of irradiated specimens is a priority– Independent (small) studies with university reactors is needed, too
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Material Property Changes
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Irradiation shown to affect graphite properties− Dimensional changes, internal stress− Increased stiffness and strength− Dramatic decrease in thermal diff.
What about Molten Salt?− If salt infiltrates graphite pores− Are basic properties the same?− Combination effects from irradiation and salt?
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Fracture and Strength Irradiation shown to affect graphite
strength− Initial strength due to dislocation pinning
from point defects− But what about pore structure?
− Microstructure evolution over dose?
− Increased flaw population must change fracture behavior
How does molten salt penetration into pores affect fracture behavior?− Solidification of salt inside pores will create high
internal tensile stresses− Pore/crack growth will result.− Exacerbates fracture?
G. Haag,” Properties of ATR-2E Graphite and Property Changes due to Fast Neutron Irradiation”, Juel-4183, 2005
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Degradation - oxidation
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PCEA
IG-110
NBG-18
Pure PCEA NBG-17
Wei
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PCEA
NBG-18
• Lots of data and studies on graphite oxidation
• Need to develop improved models based on new data
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Radioactivity – tritium and fp build-up• Build-up of tritium
− Especially important for dissolved fuel
• Does graphite retain it? Diffusion rate?− Any build-up?
• Important for HTR design as well− Source term for accident calculations.
− Waste disposal issues− How does temperature affect release rates (accident)?− Diffusion rate at accident temperatures?
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Nondestructive Evaluation of Graphite• Desperately need development of NDE Technologies for large components
and In-Service Inspection (ISI)• Conventional NDE Inspection technologies applicable to Graphite
– Eddy Currents, X-Ray Radiography, and Ultrasonics
Ultrasonics
Laser Based UT
Contact UT
X-Ray Source
X-Ray Radiography
Induction CoilAC Magnetic Field
Eddy Currents
Test Piece
Eddy Currents
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Will Windes Idaho National [email protected] (208) 526-6985