US Department of Energy (DOE) Advanced Gas … Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program UT-BATTELLE ORNL An Overview of the

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


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


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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


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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


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• 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


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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


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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)


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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


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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)


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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


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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


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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


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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


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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


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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


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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


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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.


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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


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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.


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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


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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


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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


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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


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ABAQUS Stress Distributions in SiC layer ofUncracked and Cracked Particles

SiC stress versus time


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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


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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


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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


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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

Documents

US Department of Energy (DOE) Advanced Gas … Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program UT-BATTELLE ORNL An Overview of the