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US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
An Overview of the DOE AdvancedGas Reactor Fuel Development
and Qualification Program
David Petti
Technical Director
AGR Program
ARWIF
Oak Ridge, TN
Feb. 16, 2005
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Coated Particle Fuel Performance Is at theHeart of Many of the Key Pieces of the Safety
Case for the NGNP
Normal OperationSource Term
Fuel SafetyLimits
Fuel Kernel(UCO, UO2)
Coated Particle
Outer Pyrolytic CarbonSilicon CarbideInner Pyrolytic CarbonPorous Carbon Buffer
SevereAccidentBehavior
ContainmentAnd
BarriersAnd
Defense inDepth
Mechanistic Accident
Source Term
PARTICLES
COMPACTS
FUEL ELEMENTS
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Why Additional Fuel Work is NeededComparison of German and US EOL Gas ReleaseMeasurements from Numerous Irradiation Capsules
1.0E-101.0E-091.0E-081.0E-071.0E-061.0E-051.0E-041.0E-031.0E-021.0E-01 U.S.
TRISO/BISO
U.S. WARTRISO/BISO
U.S.TRISO/TRISO
U.S. TRISO-P
German(Th,U)O2TRISOGerman UO2TRISO
U. S. Fuel German Fuel
U.S. GermanIrradiation temperature ( C) 930 - 1350 800 - 1320Burnup (%FIMA) 6.3 - 80 7.5 - 15.6Fast fluence (1025 n/m2 ) 2.0 - 10.2 0.1 - 8.5
Only German fuel had excellent EOL performance
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Highcoating
rates
Impact of IPyC MicrostructureDifferences on Irradiation Performance
• Germany: highercoating gasconcentrations, highercoating rates, moreisotropic coatings, andbetter survivabilityunder irradiation
• US: lower coating gasconcentrations, lowercoating rates, moreanisotropic coatings,and IPyC cracking underirradiation which leadsto failure of the SiC
• This may explain muchof the difference inirradiation performanceof US and German fuel.
IPyC produced atlow coating ratesLess
isotropic
More isotropic
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
• German coating wascontinuous and IPyC hadopen porosity at the surface,allowing SiC to intrude intoIPyC, during coating leadingto a strong bond
• Debonding was neverobserved under irradiation
• The US coating wasintermittent and the US IPyChad less surface porosityand a more defined interface.The strength of the interfaceis not well known
• US irradiation data indicatethat sometimes debondingoccurs and sometimes itdoes not.
Strong“Fingered”IPyC/SiCinterface inGerman fuel
US IPyC/SiCinterface
Impact of IPyC/SiC Interface Differenceson Irradiation Performance
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Impact of SiC Morphology on IrradiationPerformance
• Attributed todifferences incoating conditions,especiallytemperature
• Important impacton fission productretention of fuel,especially underaccidentconditions
Small SiC grains inGerman fuel makesfission productmigration difficult
Large columnar thru-wall SiC grains in USfuel makes fissionproduct migrationthrough the SiC easier
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Why Do Additional AGR Fuel Work? –Service Conditions
• In the light of no new plant orders in the 1980s and the TMI-2accident, safer and less costly HTGRs were envisioned:
– Passive safety using annular cores and limited powerdensities
– Low pressure vented, filtered containments
– Modular
• With advances in gas turbine technology in the 1990s, directcycle modular HTGRs were designed, e.g. the GT-MHR andPBMR designs
• Optimization of those designs has shown that
– Higher power density and fuel burnup improves overalleconomics and reduces the waste volume
– Higher outlet temperatures improves the overall efficiencies
• However, designs without high pressure containment requirevery high quality fuel (~ 10-5 defect level)
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Why Do Additional AGR Fuel Work? -Comparison of Fuel Service Conditions
• Germans qualified UO2 TRISO fuelfor pebble bed HTR-Module– Pebble; 1100°C, 8% FIMA, 3.5
x 1025 n/m2, 3 W/cc, 10%packing fraction
• Japanese qualified UO2 TRISO fuelfor HTTR– Annual compact; 1200°C; 4%
FIMA, 4x1025 n/m2, 6 W/cc;30% packing fraction
• Eskom RSA is qualifying pebblesto German conditions for PBMR
• Without an NGNP design, the AGRprogram is qualifying a designenvelope for either a pebble bed orprismatic reactor– 1250°C, 15-20% FIMA, 4-5x1025
n/m2, 6-12 W/cc, 35% packingfraction
– UCO TRISO fuel in compactform
Burnup (% FIMA)Fast Fluence (x 1025 n/m2)
Temperature(°C)
Packing Fraction
Power Density(W/cc)
30
50
10 12501100
5.0
3.0
10
2
25 10
GermanNGNP
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Why Do We Need UCO Kernels? –High CO Production in UO2 Fuel
• The release of excess oxygenby fission in UO2 fuels causesCO production to becomesignificant at high burnup andaccident temperatures
– Fission produces 2 oxygenatoms
– Fission products react withabout 1.6 oxygen atomsper fission
– 0.4 excess oxygen atomsreact with carbon to formCO
• Our code predictions are: >10%fuel failure at 20% FIMA and1100 °C
• Also, CO has been found toreact with SiC at accidenttemperatures if the IPyC layer ispermeable or cracked
IAEA Benchmark Predictions for EU-1 (EuropeanIrradiation of UO2 to high burnup)
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Why Do We Need UCO? - Kernel Migration
• The tendency of UO2 to migrate up thethermal gradient has been observed inmany irradiation experiments
• The impact for a given reactor designdepends on irradiation conditions– Not a problem in the German pebble
bed (AVR) because of low powerdensity and circulating fuel
– At the high core power densities andtemperature gradients near the innerreflector expected for the NGNP, kernelmigration could occur
27
2528.6
UCO PeakBurnup
(%FIMA)
none1105 °C20-55 µm27.81150°CHRB-16
none1110 °C≤ 30 µm in22%
28.5%1125°CHRB-15Anone1100 °C16 µm29.51070°CHRB-14
UCO KernelMigration
Max.Avg.
Temp.
UO2 KernelMigration
UO2 PeakBurnup
(%FIMA)
Max.Avg.
Temp.
Capsule
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
NGNP/AGR Fuel Program Prioritiesand Requirements
• Qualify fuel that demonstrates the safety case for NGNP– Manufacture high quality LEU coated fuel particles in compacts
– Complete the design and fabrication of reactor test rigs forirradiation testing of coated particle fuel forms
– Demonstrate fuel performance during normal and accidentconditions, through irradiation, safety testing, and PIE
– Improve the understanding of fuel behavior and fission producttransport to improve predictive fuel performance and fissionproduct transport models
• Build upon the above baseline fuel to enhance temperaturecapability
• Demonstrate deep burn actinide management capability
• Demonstrate transmutation actinide management capability
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Coated ParticleFuel Fabrication
Fuel Qualification
Analysis MethodsDevelopment &
Validation
Coated ParticleCoated ParticleFuel FabricationFuel Fabrication
Fuel QualificationFuel Qualification
Analysis MethodsAnalysis MethodsDevelopment Development &&
ValidationValidation
Fuel PerformanceModeling
Fuel PerformanceFuel PerformanceModelingModeling
Post IrradiationExamination &Safety Testing
Post IrradiationPost IrradiationExamination &Examination &Safety TestingSafety Testing
Fuel SupplyFuel SupplyFuel Supply
Program Participants
INL, ORNL BWXT, GA
NGNP/AGR Fuel Program Elements
Fission ProductTransport &Source Term
Fission ProductFission ProductTransport &Transport &Source TermSource Term
Fuel andMaterials
Irradiation
Fuel andMaterials
Irradiation
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Fuel Supply• Develop technologies for the manufacture of very
high quality fuel kernels, particles, and compacts– Prepare performance specifications– Manufacture UCO kernels– Conduct laboratory scale coating process
development– Characterize coatings and compare to German
coatings– Coat fuel test articles in ‘full’ size coater– Develop QC methods (both historical and
advanced)– Establish thermosetting resin compacting process– Address automation and other economies for
scaleup
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Recent Fuel Fabrication Progress• Completed fabrication of 4 kg of 350 µm diameter DUO2 to
support coating development at ORNL• Completed coating studies using 500 µm DUO2
– Deposition of all TRISO layers in an uninterrupted process– Met AGR-1 Fuel Product Specifications
• Fully characterized German reference fuel, HRB-21 fuel, andDUO2 kernels fabricated at ORNL
• Developed advanced inspection technologies includingoptical techniques and an ellipsometer for measurement ofpyrocarbon anisotropy
• Developed overcoating process– 165 µm thick overcoat to provide 35% packing fraction– Structurally sound carbonized compacts
• Currently gearing up for fabrication of 350 µm diameter lowenriched UCO kernels to be coated and compacted for theAGR-1 irradiation
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Computer- Automated OpticalCharacterization
• Uses computer controlled samplepositioning and digital imaging plus ORNL-developed image analysis software
• Capable of quickly and easily analyzing1000’s of particles for size and shape with 2µm resolution
• Capable of quickly and easily analyzing 100’sof particle cross sections with 1 µmresolution
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Measurement ofPyrocarbon Anisotropy• Preferred crystallographic orientation in
pyrocarbon layers can lead to fuel failure.
• During deposition, the c-axis may tend toline up with the growth direction.
• The degree and direction of preferredorientation is measured by a scanningellipsometry technique called the 2-MGEM (2-modulator generalizedellipsometry microscope) developed atORNL
OPyC
IPyC
SiC
Diattenuation with Fast Axis Direction
Min
Max
Diattenuation with Fast Axis Direction
Min
Max
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Thermosetting Resin Process for MakingCompacts is being Developed
Compacts fabricated usingsurrogate particles
• New Carbon Materials have been evaluated and qualified
• Overcoating Process has been optimized
• A “hot” new compacting lab was built - now in operation
• Compacts were successfully made from surrogate overcoatedparticles
• Complete warm pressing, heat treatment and carbonization processin FY05 - issue procedure
Overcoat
TRISOsurrogate
Advantages:−No particle-particle contact−Uniform die loading
Disadvantages:− Packing fraction lower than
pitch injection process−New technology to U.S.
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Eight Fuel Irradiations are Planned inthe AGR Program
large - BmultiFission product transport -3AGR-8large - BmultiFuel performance model validationAGR-7
large - BmultiFuel qualification - 2 - statisticsimportant
AGR-6
large - BmultiFuel qualification - 1 - statisticsimportant
AGR-5small - BsingleFission product transport - 2AGR-4large - BmultiFission product transport - 1AGR-3
large - BmultiPerformance test fuel - provide feedbackto fabrication for a large coater (6”)
AGR-2
large - BmultiShakedown and early fuel - confirmunderstanding from historical databaseand provide feedback to fabrication
AGR-1LocationCellsTask/PurposeCapsule
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Most of the AGR Irradiations Will BeConducted in the Large B-holes in ATRUsing a Multi-cell Capsule
• Spectrum is very similar to that in NGNP
• Modest acceleration - two year irradiation in ATR to simulatethree year lifetime for NGNP fuel. Lesson learned from the past.
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
INL Has a Long History of On-lineFission Product Monitoring
SystemYearATR stack 1977PBF Loop 1979PBF SFD 1982LOFT LO 1982LOFT FP 1985FLHT-4 &5 1986NPR-1 1991ATR 1998
Samplelines
HPGedetectorassembly
Leadshield
Liquid N2 Dewar
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Safety Testing• There are no accident heatup data for
fuel at NGNP conditions (LEU UCO, 15-20% FIMA, 1100-1250 °C, 4-6x1025 n/m2)
• German data on LEU UO2 at 14% FIMAsuggests particle degradation underhigh temperature accident testing
• Reason for the behavior is not knownwith certainty - fission productdegradation of the coatings waspostulated by the Germans
• There are important differencesbetween the German fuel particle andNGNP fuel particle that may make adifference (e.g., kernel size (500 vs. 350micron), lower fission productconcentration, UO2 versus UCO)
Results From German Heating Tests
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Fuel Performance Modeling• Performance models that are more mechanistic are needed to assess candidate
particle designs and evaluate source terms for licensing
• The existing coating material property database has large uncertainties
• Additional data are needed to support models for thermochemical andstructural/mechanical failure mechanisms
• Additional data are needed to support models for kernel chemistry and carbonmonoxide generation
• Our fuel development program has identified the test programs needed to supplythe needed data, including outside R&D (e.g., NERI)
• Data to support model development will be obtained under controlled conditionsthat allow for straightforward correlation of model parameters with temperature,burnup, fluence, and other irradiation parameters
• Independent, integral tests will be performed for validation of models
• Work integrated with French INERI on fuel performance modeling and IAEA CRP oncoated particle fuel technology
• International code benchmarking exercise with UK, Germany, Russia, France andthe US is underway as part of the IAEA CRP
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
PARFUME CapabilitiesStructural Service Physico-chemical Layer Failure
Conditions Models Interactions Evaluation
Intact Any user Booth equivalent Monte Carloparticles specified sphere fission gas Amoeba effect based
temperature, release using statisticalCracked fluence, Turnbull Fission product samplinglayers burnup history diffusivities SiC interactions
(e.g. Pd, Cs)Debonded Improved HSC thermo-layers thermal dynamic based Thermal Direct
model for for CO production for Decomposition numericalFaceted element and any fuel composition integrationparticles particle
Redlich-Kwong Accident EOS
conditionsFission producttransport acrosseach layer
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
ABAQUS Stress Distributions in SiC layer ofUncracked and Cracked Particles
SiC stress versus time
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
PARFUME Calculations on Asphericity• Finite element based
calculations of stressstate
• Aspect ratio is afunction of particle size
• Influence of pressure isvery strong
• Could becomeimportant as coatedparticle fuel is pushedto high burnup or hightemperature (accidents)
1.0E-09
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1 1.04 1.08 1.12
Aspect ratioF
ailu
re p
rob
abili
ty
NPR-1 (p=23.3 MPa)HRB21 (p=15.8 MPa)German (p=10.7 MPa)
AGR
1.0E-091.0E-081.0E-071.0E-061.0E-051.0E-041.0E-031.0E-021.0E-011.0E+00
1 1.04 1.08 1.12
Aspect ratio
Fai
lure
pro
bab
ility
p = 32.3 MPap = 27.3 MPap = 22.3 MPap = 17.3 MPap = 12.3 MPap = 7.3 MPa
350 micron kernel
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Debonding: Failure Probability as a Functionof Bonding Strength
SiC failures due to debonding
0.0E+00
5.0E-05
1.0E-04
1.5E-04
2.0E-04
2.5E-04
3.0E-04
3.5E-04
4.0E-04
0 20 40 60 80
Bond strength (MPa)
T=973K, BAF=1.06
T=973K, BAF=1.03
T=1473K
• 500 micron kernel• 973 K and 1473 K• Anisotropy (BAF) = 1.06
and 1.03
German andUS interfacial
bonding
German - StrongUS - Weak
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Fission Product Transportand Source Term
• NGNP will use a mechanistic source term that takes credit for allfission product release barriers - kernels, coatings, graphite,primary coolant pressure boundary, reactor building - in order tomeet radionuclide control requirements
• Provide technical basis for source terms under normal and accidentconditions to support reactor design and licensing
• Technical basis codified in design methods (computer codes)validated by experimental data
• Suite of computer codes operable on PCs developed underprevious DOE programs require model improvement and validation
• Experimental data to be generated by 3 irradiation capsules, PIE,safety testing, out-of-pile loop testing, and in-pile loop testing
US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program
UT-BATTELLEORNL
Summary• AGR Fuel Development and Qualification needed to support NGNP
• Highest priority is to demonstrate the safety case for NGNP
• Fuel is based on reference UCO, SiC, TRISO particles in thermosettingresin (minimum development risk consistent with program objectives)
• Based on Lessons Learned from the past - German coating is thebaseline. Limit acceleration level of the irradiations.
• ‘Science’ based--provides understanding of fuel performance. Modelingis much more important than in the past US programs.
• Provides for multiple feedback loops and improvement based uponearly results
• Improves success probability by incorporating German fabricationexperience