An Overview of the DOE Advanced Gas Reactor Fuel Development and Qualification Program

US Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program

UT-BATTELLEORNL

An Overview of the DOE Advanced Gas Reactor Fuel Development

and Qualification Program

David PettiTechnical Director

AGR Program


UT-BATTELLEORNL

Coated Particle Fuel Performance Is at the Heart of Many of the Key Pieces of the Safety

Case for the NGNPNormal Operation

Source 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


UT-BATTELLEORNL

Why Additional Fuel Work is Needed Comparison of German and US EOL Gas Release Measurements 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


UT-BATTELLEORNL

Key Differences between German and US fuel are related to coating not performance

• Coating rate used to make PyC (affects permeability and anisotropy of layer; US is low which reduces permeability and increases anisotropy; German is high which reduces anisotropy and increases permeability)

• Nature of the coating process. US used interrupted coating. Germans used uninterrupted coating. Interrupted coating and tabling led to metallic inclusions (from the tabling screens) in the SiC layer creating weak particles

• Nature of the interface between SiC and IPyC (German fingered interface is strong and US is weak which causes debonding)

• Microstructure of SiC (German is small grained and US is large columnar grained; difference is largely due to temperature used during SiC coating step)

• US had significant iron contamination of compact matrix which attacked the SiC and caused failures

USGerman

Weak interfaceStrong interface

Columnar SiCSmall grained SiC

Isotropic PyC Anisotropic PyC


UT-BATTELLEORNL

NGNP/AGR Fuel Program Priorities, Requirements and Approach

• The gas reactor in the US must demonstrate high integrity in-reactor and accident performance at any operating envelope envisioned the VHTR to have a chance of being commercialized. The fuel is the sine qua non of the VHTR.

• 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 for irradiation testing of coated particle fuel forms

– Demonstrate fuel performance during normal and accident conditions, through irradiation, safety testing, and PIE

– Improve the understanding of fuel behavior and fission product transport to improve predictive fuel performance and fission product transport models

• Build upon the above baseline fuel to enhance temperature capability• Lowest risk path to successful coated-particle manufacturing is to “replicate” the proven German coating

technology to the extent possible in an uninterrupted manner on the AGR particle design (350 m UCO), incorporating the lessons learned from prior U.S. fabrication and irradiation experience

• Irradiations of more that one type of fuel (variants) are required to provide improved understanding of the linkage between fabrication conditions, coating properties and irradiation performance


UT-BATTELLEORNL

Qualification of TRISO fuel requires two important conditions to be demonstrated

• Production of high quality fuel at a manufacturing scale with very few manufacturing defects (~ 1E-05) - this is the difficult part

– Disciplined control of coating process– Statistical demonstration (nature of the CVD process) of irradiation and

accident behavior– Currently cannot establish satisfactory fuel product specification to cover all

aspects of fuel behavior» Some process specifications are required. Thus, we are qualifying the

coater and the process.• Satisfactory performance for the service/performance envelope. The historical

database suggests this is attainable.– Normal conditions (temperature, burnup, fast fluence, packing fraction and

power density)– Accident conditions (hundreds of hours @ 1600°C with no fission product

release)


UT-BATTELLEORNL

Why Do Additional AGR Fuel Work? - Comparison of Fuel Service Conditions

• Germans qualified UO2 TRISO fuel for 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 fuel for HTTR

– Annual compact; 1200°C; 4% FIMA, 4x1025 n/m2, 6 W/cc; 30% packing fraction

• Eskom RSA is qualifying pebbles to German conditions for PBMR

• Without an NGNP design, the AGR program is qualifying a design envelope for either a pebble bed or prismatic reactor

– 1250°C, 15-20% FIMA, 4-5x1025

n/m2, 6-12 W/cc, 35% packing fraction

– UCO TRISO fuel in compact form

Burnup (% FIMA)Fast Fluence (x 1025 n/m2)

Temperature(C)

Packing Fraction

Power Density(W/cc)

30

50

10 1250

1100

5.0

3.0

10

2

25 10

GermanNGNP


UT-BATTELLEORNL

Coated Particle Coated Particle Fuel FabricationFuel Fabrication

Fuel Fuel QualificationQualification

Analysis Analysis Methods Methods

Development Development && ValidationValidation

Fuel Fuel Performance Performance

ModelingModeling

Post Post Irradiation Irradiation

Examination & Examination & Safety TestingSafety Testing

Fuel SupplyFuel Supply

Program Participants

INL, ORNL BWXT, GA

NGNP/AGR Fuel Program Elements

Fission Product Fission Product Transport & Transport & Source TermSource Term

Fuel and Materials

Irradiation


UT-BATTELLEORNL

Overview of AGR Program ActivitiesPurpose Irradiation Safety Tests &PIE Models

AGR-1

AGR-2

AGR-3&4

AGR-5&6

AGR-7&8

Early lab scale fuelCapsule shakedown

Coating variantsGerman type coatings

Fuel and FissionProduct Validation

Fuel QualificationProof Tests

Failed fuel to determineretention behavior

Production scale fuelPerformance Demonstration

AGR-1

AGR-2

AGR-3&4

AGR-5&6

AGR-7&8

Update &Fuel

PerformanceAnd Fission

ProductTransportModels

ValidateFuel

PerformanceAnd Fission

Product Transport

Models

feedback

feedback


UT-BATTELLEORNL

AGR-1 Related ActivitiesFab baseline & variant

particlesCharacterize

Particles

Fab & CharacterizeCompacts

Ship toINL

Inspect & insertinto capsules

Complete test train fab

Complete, install & checkout gas control system

Complete checkout & install fissionproduct monitor

Complete cubiclecleanout

Safety analysisand training

BeginAGR-1

Irradiation

Critical dimensions & HMloadings to size gas gap

Ready to Insert

AGR-1

Certified Data Package

Confirmatory analysis,update pretest prediction,

finalize test plan

Characterization Data

Complete

QA Hold


UT-BATTELLEORNL

AGR-1 Baseline and Coating Variants (on 350 µm diameter UCO kernels)

CGF = 0.3T = 1265°C =1.91 g/cc

1500°C1.5% MTS

~1425°C~1.5% MTS

OPyC Layer: Same as IPyC baseline

All continuous

coating

Note: Choice of Variant 3 selection to be based on TCT recommendation supported by batch characterization data.

Goal: PyC with low anisotropy

and low permeabilityAnd acceptable

Surface connected porosity

CGF = 0.3T = 1290°C =1.85 g/cc

CGF = 0.45T = 1265°C =1.92 g/cc

CGF = 0.3T = 1265°C =1.91 g/cc

Baseline2 capsules in

AGR-1

Variant 1Increase

Coating Temp

Variant 2Increase

Coating GasFraction

Variant 3aDeposit

SiC with Ar

1500°C1.5% MTS

1500°C1.5% MTS

1500°C1.5% MTS

CGF = 0.3T = 1265°C =1.91 g/cc

Goal: fine grained SiC

Variant 3bInterrupted between

IPyC & SiC


UT-BATTELLEORNL

Optimize Sintering ConditionsProduction Line

Kernel improvement is primarily due to better carbon dispersion during kernel forming, and less grain growth most likely due to the shorter sintering time at 1890oC.

69302 (AGR-1) 59307 59308 LEUCO for AGR-1 Improved carbon dispersion 1890 4 Hours 1890 4 Hours 1890 1 Hour


UT-BATTELLEORNL

AGR-1 Fabrication

LEUCO coated particles

Fuel Compact

Loose kernelsSintered kernels


UT-BATTELLEORNL

All required characterization capabilities have been established

Density

Dim

ensions

Microstructure/

Ceram

ography

Sphericity

BET Surface A

rea

Anisotropy

Permeability

Crystallite/G

rain Size

Porosity

Uranium

Dispersion

Heavy M

etal Contam

ination

Missing B

uffer Fraction

Defective SiC

Fraction

Defective O

PyC Fraction

Impurities

KernelBufferIPyCSiCOPyCParticleCompact

– Completed – In Progress – Not applicable/required


UT-BATTELLEORNL

14March06 Status

ProductTRISOBatch

Fabrication

TRISOBatch

Characterization

Blend toForm

Composite

TRISOComposite

Characterization

CompactFabrication

CompactCharacteriza

tion

Baseline - pass - pass In Process

Variant 1 - pass - pass In Process

Variant 2 - pass In Process

Variant 3 In Process


UT-BATTELLEORNL

AGR-1 Experiment Block Diagram

Vessel Wall

CapsulesIn-core

HeNeHe-3

SilverZeolite

ParticulateFilters

H-3Getter

Grab Sample

FPMS


UT-BATTELLEORNL

AGR-1 Capsule Design Features• 6 Capsules with individual

temperature control and fission product monitoring

• Fuel compacts– 3 fuel compacts/level – 4 levels/capsule– Total of 12 fuel

compacts/capsule – Encased in graphite

containing B4C• 3 thermocouples/capsule• Thermal melt wires for

temperature back-up• Fast and thermal flux wires• Hafnium & SST shrouds

ATR Core Center

Graphite

Fuel Compact Gas Lines

Thermocouples

Flux Wire

Hf Shroud

SST Shroud

Stack 1

Stack 3

Stack 2


UT-BATTELLEORNL

Experiment Conditions• Minimum compact average burn-up > 14 %

FIMA (134.5 GWd/t)

• Maximum capsule burn-up > 18 % FIMA (172.8 GWd/t)

• Maximum fast neutron fluence < 5 x 1025 n/m2 (E>0.18 MeV)

• Minimum fast neutron fluence > 1.5 x 1025

n/m2 (E>0.18 MeV)

• U-235 enrichment 19.7 wt%

• Packing Fraction 35% (about 1410 particles/cc)

Gas Line

Thermocouple

Fuel Stack

Hafnium Shield

SST Holder

Capsule Spacer

Nub


UT-BATTELLEORNL

1

2

3

NT11

+1.605e+03+1.662e+03+1.718e+03+1.775e+03+1.832e+03+1.888e+03+1.945e+03+2.001e+03+2.058e+03+2.115e+03+2.171e+03+2.228e+03+2.285e+03

Experiment Conditions• Maximum temperature

<1400 ºC

• Time average peak temperature of 1250 ºC

• Time average volume average temperature of 1150 +30/-75 ºC

• Particle power not to exceed 400 mW/particle

• Only graphite (with boron carbide) may contact fuel specimens


UT-BATTELLEORNL

Welding of mockups of an AGR-1 capsule and brazing of tubes to the end cap

These two mockup capsules are straight within about .010 inch


UT-BATTELLEORNL

Fission Product Monitors: Assembled equipment for checkout and calibration


UT-BATTELLEORNL

AGR Fuel Program High Level Schedule


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 thermosetting resin (minimum development risk consistent with program objectives)

• Based on Lessons Learned from the past - German coating is the baseline. Limit acceleration level of the irradiations.

• ‘Science’ based--provides understanding of fuel performance. Modeling is much more important than in the past US programs.

• Provides for multiple feedback loops and improvement based upon early results

• Improves success probability by incorporating German fabrication experience

Documents

An Overview of the DOE Advanced Gas Reactor Fuel Development and Qualification Program