Gas Reactor TRISO-Coated Particle Fuel Modeling Activities at the - PowerPoint PPT Presentation

Idaho National Engineering and Environmental Laboratory Gas Reactor TRISO-Coated Particle Fuel Modeling Activities at the Idaho National Engineering and Environmental Laboratory David Petti, Gregory Miller, John Maki, Dominic Varacalle, and Jacopo Buongiorno Paris, France October 12, 2001

Idaho National Engineering and Environmental Laboratory Outline • Fuel Performance Model Objectives • Structural Modeling – Normal particle – Property Database – Debonded particle – Cracked particle • Chemistry module – Fission Gas and CO Release Model • Comparison of PARFUME predictions to recent US irradiations • Preliminary predictions from PARFUME for German LEU particle at high burnup • Future Work

Idaho National Engineering and Environmental Laboratory PARticle FUel ModEl (PARFUME) • Objective: To develop a mechanistic fuel performance model that – Describes the relevant behavior of TRISO-coated fuel during irradiation – Explains past poor performance for US gas reactor fuel – Can be used as a design tool to develop improved coated particle fuel – Can be used to establish a linkage between acceptable in-reactor performance and a fuel product/process fabrication specification

Idaho National Engineering and Environmental Laboratory Structural Properties •fracture strength Multidimensional Multidimensional •elastic modulus Statistical Finite Element •poisson's ratio Fit Of Stress Structural •creep constants Results Analysis •Interfacial bond strength Physio-chemical Behavior Under Irradiation •Fission Gas Release and Swelling Integrated •Fission Product Chemistry Behavior Mechanistic (Diffusion, Migration, and Segregation) Fuel •Gas production (CO and CO 2 ) Performance •Irradiation-induced dimensional changes of Model the coating layers •Kernel Migration •Restructuring and grain growth

Idaho National Engineering and Environmental Laboratory Examination of NPR Fuel indicates that asymmetric radiation shrinkage is important Radial crack in IPyC Debonding of IPyC from SiC SiC crack near IPyC crack Need to consider cracking and debonding in model development Photomicrograph of failed NPR fuel particle

Idaho National Engineering and Environmental Laboratory Three Conceptual Models for Particle Failure OPyC SiC IPyC Standard 3 3 Layer Cracked 3 Layer Layer Model Model Debonded Model

Idaho National Engineering and Environmental Laboratory ABAQUS Results from Standard and Cracked Models Standard/Nominal Particle is in Standard Particle compression; Particle with Cracked IPyC has SiC layer in tension Principal 200 stress Cracked Particle (MPa) 0 Normal Particle Cracked Particle -200 SiC Layer -400 Stress Concentration at Crack Tip -600 0 2 4 6 8 10 12 Time (x 10 6 seconds) Note: Model contains ~ 800 nodes and takes about 2- 8 hours to run

Idaho National Engineering and Environmental Laboratory ABAQUS results for debonded particle SiC Stress Stress Concentrations at Edge of Debonding

Idaho National Engineering and Environmental Laboratory PyC shrinkage is a function of temperature, Bacon Anisotropy Factor (BAF), density and fluence Radial (BAF=1.08) Tangential (BAF=1.08) Data - 910°C 20 0 Fit 910°C Data - 700°C 15 -3 Fit 700°C Data - 1215°C 10 -6 Fit 1215°C Data 910°C Fit 910°C 5 -9 Data 700°C Fit 700°C 0 -12 Data 1215°C Fit 1215°C -5 -15 0 2 4 6 8 0 2 4 6 8 Fluence (x 10^25 n/m*2) Fluence (x 10^25 n/m*2) Radial Change at 1032°C Tangential Change at 1032°C 0 BAF=1.28 3 BAF=1.17 -1 2 BAF=1.08 -2 BAF=1.02 1 -3 BAF=1.02 -4 0 BAF=1.08 -5 -1 BAF=1.17 -6 BAF=1.28 -2 -7 0 1 2 3 4 0 1 2 3 4 Fluence (*10^25 n/m*2) Fluence (*10^25 n/m*2)

Idaho National Engineering and Environmental Laboratory Pyrocarbon irradiation induced creep rate has large influence on stress in IPyC and stress concentration in SiC Using new creep value of 1.4*10 27 (psi-nvt) -1 based on broad assessment of data from GA in 1993 Using historical creep value of 3.29 *10 27 (psi-nvt) -1 from GA SiC Stress in Cracked Model at 1200°C Note: STRESS3 code using different PyC creep data uses 3.4 *10 27 (psi-nvt) -1

Idaho National Engineering and Environmental Laboratory Development of Key Parameters and Levels • KEY PARAMETERS Low Medium High – Temperature (K) 873 1073,1273 1473 – IPyC Thickness (um) 30 40 50 – IPyC Anisotropy (BAF) 1.0 1.16 1.33 – IPyC Density (g/cc) 1.8 1.9 2.0 – SiC Thickness (um) 30 40 50 – OPyC Thickness (um) 33 43 53 972 calculations! Statistical fit good to 0.5%

Idaho National Engineering and Environmental Laboratory Effect of Temperature: Differences in PyC creep have large differences in calculated stress in IPyC and SiC IPyC Layer In SiC near crack tip ---- 600 °C ---- 1200°C

Idaho National Engineering and Environmental Laboratory Fission Gas Release Model • Release fraction considerations – Fission recoil contribution based upon range distributions tabulated by Littmark and Ziegler – Diffusion coefficient used in the equivalent sphere model based upon the correlation developed by Turnbull et al. This correlation is the sum of three contributions: • At high temperatures, intrinsic diffusion dominates • At intermediate temperatures, radiation enhanced vacancy diffusion dominates • At low temperatures, an athermal radiation induced contribution dominates (possibly ascribed to a knock-out mechanism)

Idaho National Engineering and Environmental Laboratory CO Generation and Release Model • CO yield comparison for UO 2 fuel: – NPR review: CO yield may be as high as 0.38 based upon available oxygen – ORNL compilation: CO yield is approximately 0.13 but may be as high as 0.40 depending on thermodynamic calculations – GA model for LEU fuel: (yield) CO = 1.64 exp(-3311/T) where T = temperature (K) at 1273 K, (yield) CO = 0.12 • CO gas release is temporarily using the GA model: – For UCO fuel, (yield) CO = 0 – For LEU UO 2 fuel, (yield) CO = 1.64 exp(-3311/T) where T is temperature in degrees K - For UO 2 fuel, (release fraction) CO = 1

Idaho National Engineering and Environmental Laboratory Model results for German particle 6 Total internal pressure 5 4 CO partial pressure 3 2 Fission gas partial pressure 1 0 0 500 1000 1500 Irradiation Time (days)

Idaho National Engineering and Environmental Laboratory Chemistry Model • Physics results – Power density and burnup for 4%, 8%, 12%, 16%, and 20% enrichment – Used HTR module as design point (no inner reflector or mixing zone) • ORIGEN2 calculations are complete – Elemental fission product concentrations as a function of initial uranium loading in the pebble and burnup – Use either lookup tables or statistical fits to develop input for HSC chemistry calculations • Chemistry calculations expected this fall • Goal is to get fission gas release and CO pressure as a function of O/C ratio in kernel and state of important fission products in the kernel (oxide versus carbide)

Idaho National Engineering and Environmental Laboratory Comparison of Ceramographic Observations from Recent US Irradiations to PARFUME Calculations for TRISO Coated Fissile Fuel Particles • Fuel Compact % Cracked % Cracked Fast Fluence Irradiation Burnup 10 25 n/m 2 temperature % FIMA • IPyC layer SiC layer ° C • PIE PARFUME PIE PARFUME • NPR-2 A4 65 100 3 8.2 3.8 746 79 • NPR-1 A5 31 100 0.6 1.6 3.8 987 79 • NPR-1 A8 6 100 0 4.9 2.4 845 72 • NPR-1A A9 18 100 1 0.9 1.9 1052 64 • HRB-21 1C 1 100 0 7.7 1.5 800 14 • HRB-21 2B 3 100 0 1.9 2.3 980 18 • HRB-21 4A 33 100 5 1.6 3.5 1000 22.5 • NPR fuel is UCO, 93% U-235 • HRB-21 fuel is UCO, 20% U-235

Idaho National Engineering and Environmental Laboratory Increase of creep coefficient by a factor of 2 to 3.5 will give results that are in much better agreement with the data and is more consistent with creep values used previous fuel performance codes NPR-2 A4 NPR-1 A5 120 120 Calculated Calculated 100 100 Data Data 80 80 60 60 40 40 20 20 0 0 1 2 3 4 5 1 2 3 4 5 Factor Applied to Creep Coefficient Factor Applied to Creep Coefficient NPR-1A A9 NPR-1 A8 120 120 100 100 Calculated 80 Data Calculated 80 Data 60 60 40 40 20 20 0 0 1 2 3 4 5 1 2 3 4 5 Factor Applied to Creep Coefficient Factor Applied to Creep Coefficient

Idaho National Engineering and Environmental Laboratory Preliminary PARFUME Predictions of Structural Behavior of German LEU Particle at High Burnup End-of-life burnup (%FIMA) SiC layer in 0 5 10 15 20 25 compression under all 0 -100 conditions SiC Stress (MPa) -200 CEGA creep -300 Amplified creep -400 -500 End-of-life burnup (%FIMA) 0 5 10 15 20 25 -600 0 -50 700 C SiC Stress (MPa) 900 C -100 1100 C -150 -200 -250 -300