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

1. An Overview of the DOE Advanced Gas Reactor Fuel Development and Qualification Program David Petti Technical Director AGR Program

2. Outer Pyrolytic Carbon Silicon Carbide Inner Pyrolytic Carbon PARTICLES Porous Carbon Buffer Coated Particle COMPACTS Fuel Kernel (UCO, UO2) FUEL ELEMENTS Coated Particle Fuel Performance Is at the Heart of Many of the Key Pieces of the Safety Case for the NGNP Normal Operation Source Term Containment And Barriers And Defense in Depth Mechanistic Accident Source Term Severe Accident Behavior Fuel Safety Limits

3. Why Additional Fuel Work is NeededComparison of German and US EOL Gas Release Measurements from Numerous Irradiation Capsules Only German fuel had excellent EOL performance

4. 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 Key Differences between German and US fuel are related to coating not performance US German Anisotropic PyC Isotropic PyC Weak interface Strong interface Small grained SiC Columnar SiC

5. 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 mm 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 NGNP/AGR Fuel Program Priorities, Requirements and Approach

6. 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) Qualification of TRISO fuel requires two important conditions to be demonstrated

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

8. NGNP/AGR Fuel Program Elements Fuel Supply Post Irradiation Examination & Safety Testing Fuel and Materials Irradiation Coated Particle Fuel Fabrication Fuel Qualification Analysis Methods Development & Validation Fission Product Transport & Source Term Fuel Performance Modeling Program Participants INL, ORNL BWXT, GA

9. Overview of AGR Program Activities Purpose Irradiation Models Safety Tests &PIE Early lab scale fuel Capsule shakedown Coating variants German type coatings Update & Fuel Performance And Fission Product Transport Models AGR-1 AGR-1 feedback Production scale fuel Performance Demonstration AGR-2 AGR-2 feedback Failed fuel to determine retention behavior AGR-3&4 AGR-3&4 Validate Fuel Performance And Fission Product Transport Models Fuel Qualification Proof Tests AGR-5&6 AGR-5&6 Fuel and Fission Product Validation AGR-7&8 AGR-7&8

10. QA Hold AGR-1 Related Activities Certified Data Package Fab baseline & variant particles Characterize Particles Characterization Data Complete Ship to INL Fab & Characterize Compacts Inspect & insert into capsules Complete test train fab Critical dimensions & HM loadings to size gas gap Safety analysis and training Ready to Insert AGR-1 Confirmatory analysis, update pretest prediction, finalize test plan Complete, install & checkout gas control system Begin AGR-1 Irradiation Complete cubicle cleanout Complete checkout & install fission product monitor

11. AGR-1 Baseline and Coating Variants (on 350 µm diameter UCO kernels) All continuous coating Variant 2 Increase Coating Gas Fraction Variant 3b Interrupted between IPyC & SiC Baseline 2 capsules in AGR-1 Variant 1 Increase Coating Temp Variant 3a Deposit SiC with Ar Goal: PyC with low anisotropy and low permeability And acceptable Surface connected porosity CGF = 0.3 T = 1265°C r =1.91 g/cc CGF = 0.3 T = 1265°C r =1.91 g/cc CGF = 0.3 T = 1290°C r =1.85 g/cc CGF = 0.45 T = 1265°C r =1.92 g/cc CGF = 0.3 T = 1265°C r =1.91 g/cc Goal: fine grained SiC 1500°C 1.5% MTS 1500°C 1.5% MTS 1500°C 1.5% MTS ~1425°C ~1.5% MTS 1500°C 1.5% MTS OPyC Layer: Same as IPyC baseline Note: Choice of Variant 3 selection to be based on TCT recommendation supported by batch characterization data.

12. Optimize Sintering ConditionsProduction Line 69302 (AGR-1) 59307 59308 LEUCO for AGR-1 Improved carbon dispersion 1890 4 Hours1890 4 Hours1890 1 Hour 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.

13. Loose kernels AGR-1 Fabrication Sintered kernels LEUCO coated particles Fuel Compact

14. All required characterization capabilities have been established

15. 14March06 Status

16. Vessel Wall He Ne He-3 FPMS H-3 Getter Particulate Filters Silver Zeolite Capsules In-core Grab Sample AGR-1 Experiment Block Diagram

17. 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 Thermocouples Graphite Flux Wire Stack 1 ATR Core Center Stack 2 Stack 3 Hf Shroud SST Shroud Fuel Compact Gas Lines AGR-1 Capsule Design Features

18. 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 Fuel Stack Thermocouple SST Holder Hafnium Shield Capsule Spacer Nub Experiment Conditions

19. 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 Experiment Conditions

20. 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

21. Fission Product Monitors: Assembled equipment for checkout and calibration

22. AGR Fuel Program High Level Schedule

23. 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