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

Transcription

1 An Overview of the DOE Advanced Gas Reactor Fuel Development and Qualification Program David Petti Technical Director AGR Program ARWIF Oak Ridge, TN Feb. 16, 2005

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

3 Why Additional Fuel Work is Needed Comparison of German and US EOL Gas Release Measurements from Numerous Irradiation Capsules 1.0E E E E E E E E E E-10 U. S. Fuel German Fuel U.S. German Irradiation temperature ( C) Burnup (%FIMA) Fast fluence (10 25 n/m 2 ) U.S. TRISO/BISO U.S. WAR TRISO/BISO U.S. TRISO/TRISO U.S. TRISO-P German (Th,U)O2 TRISO German UO2 TRISO Only German fuel had excellent EOL performance

4 Impact of IPyC Microstructure Differences on Irradiation Performance Germany: higher coating gas concentrations, higher coating rates, more isotropic coatings, and better survivability under irradiation US: lower coating gas concentrations, lower coating rates, more anisotropic coatings, and IPyC cracking under irradiation which leads to failure of the SiC This may explain much of the difference in irradiation performance of US and German fuel. High coating rates Less isotropic More isotropic IPyC produced at low coating rates

5 Impact of IPyC/SiC Interface Differences on Irradiation Performance German coating was continuous and IPyC had open porosity at the surface, allowing SiC to intrude into IPyC, during coating leading to a strong bond Debonding was never observed under irradiation The US coating was intermittent and the US IPyC had less surface porosity and a more defined interface. The strength of the interface is not well known US irradiation data indicate that sometimes debonding occurs and sometimes it does not. Strong Fingered IPyC/SiC interface in German fuel US IPyC/SiC interface

6 Impact of SiC Morphology on Irradiation Performance Attributed to differences in coating conditions, especially temperature Important impact on fission product retention of fuel, especially under accident conditions Large columnar thruwall SiC grains in US fuel makes fission product migration through the SiC easier Small SiC grains in German fuel makes fission product migration difficult

7 Why Do Additional AGR Fuel Work? Service Conditions In the light of no new plant orders in the 1980s and the TMI-2 accident, safer and less costly HTGRs were envisioned: Passive safety using annular cores and limited power densities Low pressure vented, filtered containments Modular With advances in gas turbine technology in the 1990s, direct cycle modular HTGRs were designed, e.g. the GT-MHR and PBMR designs Optimization of those designs has shown that Higher power density and fuel burnup improves overall economics and reduces the waste volume Higher outlet temperatures improves the overall efficiencies However, designs without high pressure containment require very high quality fuel (~ 10-5 defect level)

8 Why Do Additional AGR Fuel Work? - Comparison of Fuel Service Conditions Germans qualified UO 2 TRISO fuel for pebble bed HTR-Module Pebble; 1100 C, 8% FIMA, 3.5 x n/m 2, 3 W/cc, 10% packing fraction Japanese qualified UO 2 TRISO fuel for HTTR Annual compact; 1200 C; 4% FIMA, 4x10 25 n/m 2, 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, 4-5x10 25 n/m 2, 6-12 W/cc, 35% packing fraction UCO TRISO fuel in compact form Power Density (W/cc) 10 German NGNP 25 Burnup (% FIMA) 2 Packing Fraction Temperature ( C) Fast Fluence (x n/m 2 )

9 Why Do We Need UCO Kernels? High CO Production in UO 2 Fuel The release of excess oxygen by fission in UO 2 fuels causes CO production to become significant at high burnup and accident temperatures Fission produces 2 oxygen atoms Fission products react with about 1.6 oxygen atoms per fission 0.4 excess oxygen atoms react with carbon to form CO Our code predictions are: >10% fuel failure at 20% FIMA and 1100 C Also, CO has been found to react with SiC at accident temperatures if the IPyC layer is permeable or cracked IAEA Benchmark Predictions for EU-1 (European Irradiation of UO 2 to high burnup)

10 Why Do We Need UCO? - Kernel Migration Capsule Max. Avg. Temp. UO 2 Peak Burnup (%FIMA) UO 2 Kernel Migration Max. Avg. Temp. UCO Peak Burnup (%FIMA) UCO Kernel Migration HRB C µm 1100 C 28.6 none HRB-15A 1125 C 28.5% 30 µm in 22% 1110 C 25 none HRB C µm 1105 C 27 none The tendency of UO 2 to migrate up the thermal gradient has been observed in many irradiation experiments The impact for a given reactor design depends on irradiation conditions Not a problem in the German pebble bed (AVR) because of low power density and circulating fuel At the high core power densities and temperature gradients near the inner reflector expected for the NGNP, kernel migration could occur

11 NGNP/AGR Fuel Program Priorities and 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 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 Demonstrate deep burn actinide management capability Demonstrate transmutation actinide management capability

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

13 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

14 Recent Fuel Fabrication Progress Completed fabrication of 4 kg of 350 µm diameter DUO 2 to support coating development at Completed coating studies using 500 µm DUO 2 Deposition of all TRISO layers in an uninterrupted process Met AGR-1 Fuel Product Specifications Fully characterized German reference fuel, HRB-21 fuel, and DUO 2 kernels fabricated at Developed advanced inspection technologies including optical techniques and an ellipsometer for measurement of pyrocarbon 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 low enriched UCO kernels to be coated and compacted for the AGR-1 irradiation

15 Computer- Automated Optical Characterization Uses computer controlled sample positioning and digital imaging plus developed image analysis software Capable of quickly and easily analyzing 1000 s of particles for size and shape with 2 µm resolution Capable of quickly and easily analyzing 100 s of particle cross sections with 1 µm resolution

16 Measurement of Pyrocarbon Anisotropy Preferred crystallographic orientation in pyrocarbon layers can lead to fuel failure. During deposition, the c-axis may tend to line up with the growth direction. The degree and direction of preferred orientation is measured by a scanning ellipsometry technique called the 2- MGEM (2-modulator generalized ellipsometry microscope) developed at OPyC IPyC Diattenuation with Fast Axis Direction Max SiC Min

17 Thermosetting Resin Process for Making Compacts is being Developed 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 overcoated particles Complete warm pressing, heat treatment and carbonization process in FY05 - issue procedure Advantages: No particle-particle contact Uniform die loading Disadvantages: Packing fraction lower than pitch injection process New technology to U.S. Overcoat TRISO surrogate Compacts fabricated using surrogate particles

18 Eight Fuel Irradiations are Planned in the AGR Program Capsule Task/Purpose Cells Location AGR-1 Shakedown and early fuel - confirm understanding from historical database and provide feedback to fabrication multi large - B AGR-2 Performance test fuel - provide feedback to fabrication for a large coater (6 ) multi large - B AGR-3 Fission product transport - 1 multi large - B AGR-4 Fission product transport - 2 single small - B AGR-5 Fuel qualification statistics important multi large - B AGR-6 Fuel qualification statistics important multi large - B AGR-7 Fuel performance model validation multi large - B AGR-8 Fission product transport -3 multi large - B

19 Most of the AGR Irradiations Will Be Conducted in the Large B-holes in ATR Using a Multi-cell Capsule Spectrum is very similar to that in NGNP Modest acceleration - two year irradiation in ATR to simulate three year lifetime for NGNP fuel. Lesson learned from the past.

20 INL Has a Long History of On-line Fission Product Monitoring SystemYear ATR stack 1977 PBF Loop 1979 PBF SFD 1982 LOFT LO 1982 LOFT FP 1985 FLHT-4 & NPR ATR 1998 Lead shield Sample lines Liquid N 2 Dewar HPGe detector assembly

21 Safety Testing There are no accident heatup data for fuel at NGNP conditions (LEU UCO, 15-20% FIMA, C, 4-6x10 25 n/m 2 ) German data on LEU UO 2 at 14% FIMA suggests particle degradation under high temperature accident testing Reason for the behavior is not known with certainty - fission product degradation of the coatings was postulated by the Germans There are important differences between the German fuel particle and NGNP fuel particle that may make a difference (e.g., kernel size (500 vs. 350 micron), lower fission product concentration, UO 2 versus UCO) Results From German Heating Tests

22 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 and structural/mechanical failure mechanisms Additional data are needed to support models for kernel chemistry and carbon monoxide generation Our fuel development program has identified the test programs needed to supply the needed data, including outside R&D (e.g., NERI) Data to support model development will be obtained under controlled conditions that 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 on coated particle fuel technology International code benchmarking exercise with UK, Germany, Russia, France and the US is underway as part of the IAEA CRP

23 PARFUME Capabilities Structural Service Physico-chemical Layer Failure Conditions Models Interactions Evaluation Intact Any user Booth equivalent Monte Carlo particles specified sphere fission gas Amoeba effect based temperature, release using statistical Cracked fluence, Turnbull Fission product sampling layers burnup history diffusivities SiC interactions (e.g. Pd, Cs) Debonded Improved HSC thermolayers thermal dynamic based Thermal Direct model for for CO production for Decomposition numerical Faceted element and any fuel composition integration particles particle Redlich-Kwong Accident EOS conditions Fission product transport across each layer

24 ABAQUS Stress Distributions in SiC layer of Uncracked and Cracked Particles SiC stress versus time

25 PARFUME Calculations on Asphericity Finite element based calculations of stress state Aspect ratio is a function of particle size Influence of pressure is very strong Could become important as coated particle fuel is pushed to high burnup or high temperature (accidents) Failure probability Failure probability 1.0E E E E E E E E E E micron kernel 1.0E E E E E E E E E E-09 Aspect ratio AGR Aspect ratio NPR-1 (p=23.3 MPa) HRB21 (p=15.8 MPa) German (p=10.7 MPa) p = 32.3 MPa p = 27.3 MPa p = 22.3 MPa p = 17.3 MPa p = 12.3 MPa p = 7.3 MPa

26 Debonding: Failure Probability as a Function of Bonding Strength 4.0E E E E E E E E E+00 SiC failures due to debonding Bond strength (MPa) 500 micron kernel 973 K and 1473 K Anisotropy (BAF) = 1.06 and 1.03 T=973K, BAF=1.06 T=973K, BAF=1.03 T=1473K German and US interfacial bonding US - Weak German - Strong

27 Fission Product Transport and Source Term NGNP will use a mechanistic source term that takes credit for all fission product release barriers - kernels, coatings, graphite, primary coolant pressure boundary, reactor building - in order to meet radionuclide control requirements Provide technical basis for source terms under normal and accident conditions 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 under previous 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

28 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