Towards a Mechanistic Understanding of Pellet Cladding Interaction using advanced 3D Characterisation and Atomistic Simulation P. Frankel, A. Garner, A. Plowman, S. Hanlon, C. Gillen, A. Phillion, C. P. Race, J. Donoghue, C. Anghel, A. Ambard, M. Daymond 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK
Why do we study PCI? – PCI failures no longer occur! • Achieved by significant operational constraints • Are these overly conservative? – Increased contribution of renewables • Requirement for load following • Extended reduced power operation Extended reduced power operation 1 Electricity production in Germany (www.energy-charts.de) January 2019 1 S. Béguin PCI-related Constraints on EDF PWRs and Associated Challenges. Nuclear Energy Agency, in:, Pellet- Clad Interact. Water React. Fuels, 2004. 2 Anghel, C. PACE presentation. Westinghouse 2017 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 1
Is PCI understood? • Can we use new tools to improve understanding – Better understanding → operational flexibility/ improved safety – Focus here on chemical effect ( i.e. not PCMI) • Initial assumption that Iodine is responsible fission product • Others fission products may well play a role 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 2
Relating I-SCC cracks to local microstructure • Compared crack paths in: – irradiated sample from mandrel test – Non-radiated in iodine-ethanol solution • Iodine found at crack tip by NanoSIMS 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 3
Relating I-SCC cracks to local microstructure (a) (b) 0 1 2 3 4 0° Unexpected result: 1° 3 2° non-basal cleavage in irradiated sample 3° Radial direction But, 2 too few grains to make conclusive assessment 1 Zr hydride FIB Curtaining [0001] [10-10] 1� mm� 1 μm 1 μm [11-20] Journal of Nuclear Materials, (519) 2019, 166-172. 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 4
Can we quantitatively assess crack path in relation to microstructure? 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 5
I-SCC tests at CNL • Temperature and Iodine control • Various load and sample configs • DCDP measurements TO BUBBLER C276 TOP CAP C276 PULL ROD GLASS TUBE Ar TUBE FURNACE TOP GRIP PRESSURE REGULATOR SPECIMEN 3-WAY STOPCOCK FILTER BOTTOM GRIP GAS FLOW MEASUREMENT AND CONTROL C276 PULL ROD CONDESER C276 BASE CAP 2 WAY VALVE FROM BYPASS FROM TEST CHAMBER METAL TUBING TO GLASS TUBING ADAPTER TYGON TUBING BYPASS TO DIRECT VENT TEST CHAMBER FLASK BUBBLER GLASS STOPPER TO BUBBLER LIQUID LINE HEAT TAPE WRAPPED AROUND EXPOSED GLASS TUBING HEAT BATHS THERMO SCIENTIFIC SAHARA S15 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 6
Track crack progress by potential drop measurements 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 7
Removing cracked volume - PFIB Sample geometry • N.B. Susceptible orientation (b) (a) – i.e. crack in RD 100 μm 100 μm (c) (d) X||ND 200 μm 100 μm Z||RD Y||TD 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 8
Serial sectioning in P-FIB Xe + 100 μm P-FIB conditions • FEI Helios Xe plasma FIB • 30 kV Xe ions – 180 nA • Slice thickness = 300 nm • Rocking mill to reduce curtaining • 30 seconds per slice • 485 slices in total • ~200 μm total thickness 50 μm 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 9
3D chemical data by EDX mapping • Sufficient resolution to identify Cr Fe Cr/Fe in SPPs • Oxygen situated at crack location • No iodine segregation observed – Resolution limit ? – Poor sensitivity in EDX O I – Overlap with Sn – Lost as volatile ZrI 4 ? 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 50µm 10
3D crystallography by EBSD Electron backscatter diffraction • EBSD maps on each slice • Crack path into the page – (i.e. along Z ) Secondary electron imaging 25 μm X 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 11
3D reconstruction of grain volume & crack path • 959 grains in volume • Align crack to microstructure 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 12
Evaluating crack nature Z = 6 μm Z = 26 μm Z = 56 μm Z = 86 μm Z = 140 μm Z = 116 μm 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 13
Grain orientations in analysed volume Transgranular cracked Adjacent to Intergranular crack All orientations Contoured data (58 grains) (35 grains) (959 grains) Z=RD Z=RD Z=RD Y=TD Y=TD Y=TD 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 14
Not just more grains, also spatial information e.g. Crack nature with depth 120 5 4.5 100 4 Transgranular perecentage Average crack width ( μ m) 3.5 80 3 60 2.5 2 40 1.5 Average crack width 1 20 Transgranular percentage 0.5 0 0 Total crack length ( μ m) 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK
Modelling can provide mechanistic understanding What can we do? • Explore how iodine and caesium affect Zr GB properties • Importance of grain boundaries (GBs) • Segregation-induced embrittlement is an atomistic process • First-principles approach (DFT) suitable – chemistry included 1. Pristine GB properties: atomistic environments? 2. Effect of defects: GB weakening? 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 16
Building Boundaries Coincident Site lattice 1) 3) 2) 4) “Σ7” CSL: 7 lattice sites per CSL unit cell 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 17
Building Boundaries Low- Σ GBs: macroscopic degrees of freedom Good range Multiple GB of angles planes Σ Σ Θ /deg Θ /deg Interface Interface Type Type Σ Θ /deg Interface Type 7 7 7 21.79 21.79 21.79 (1 -3 2 0) (1 -3 2 0) (1 -3 2 0) STGB STGB STGB (0 0 0 1) (0 0 0 1) Twist Twist Computationally affordable 13 13 13 27.80 27.80 27.80 (1 -4 3 0) (1 -4 3 0) (1 -4 3 0) STGB STGB STGB for defect studies (0 0 0 1) Twist (0 0 0 1) Twist 19 19 13.17 13.17 (1 -5 4 0) (1 -5 4 0) STGB STGB 19 13.17 (1 -5 4 0) STGB (0 0 0 1) (0 0 0 1) Twist Twist 31 31 31 17.90 17.90 17.90 (1 -6 4 0) (1 -6 4 0) (1 -6 4 0) STGB STGB STGB STGB: symmetric tilt GB 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 18
Building Boundaries Low- Σ GBs: microscopic degrees of freedom Energy landscape Minimum-energy GB expansion 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 19
Building Boundaries Supercells Low- Σ GBs 1. Construct GB supercell and find optimum Σ 7 STGB Σ 13 STGB microscopic configuration Σ 7 Twist GB Σ 13 Twist GB 2. Construct free surface FS 3. Construct bulk supercell Pristine interface properties Defective interface properties Geometry opt. parameters dE/ion 1E-6 eV/atom |F|max 1E-2 eV/Ang Atom shade indicates coordinate in page-normal direction 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 20
Effect of iodine on “strength” of bulk planes Work of separation for Pristine Bulk – Plane more important than Σ – Lowest “strength” for (0001) cleavage For Defective Bulk – All investigated planes weakened by defect • (0001) no longer lowest, but … – Need to account for defect concentration • Different super cell sizes 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 21
Effect of iodine on bulk planes • Normalise by defect concentration → Basal cleavage lowest • Most TG crack close to basal plane 12 Experimental TG crack orientation 10 8 Frequency 6 4 2 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 Angular deviation of cracking plane from basal (°) 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 22
Effect of iodine on GB “Strength” Work of separation for Pristine GBs – (1 -3 2 0) lowest – Plane more important than misorientation For defective GBs – All boundaries “weakened” – Basal least susceptible 21.79 27.80 21.79 27.80 Misorientation /deg 19 th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 23
Recommend
More recommend
