Cladding Interaction using advanced 3D Characterisation and - - PowerPoint PPT Presentation

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Cladding Interaction using advanced 3D Characterisation and - - PowerPoint PPT Presentation

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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,

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK 19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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
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19th 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

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Extended reduced power operation1

  • 1S. Béguin PCI-related Constraints on EDF PWRs and Associated Challenges. Nuclear Energy Agency, in:, Pellet-

Clad Interact. Water React. Fuels, 2004. 2Anghel, C. PACE presentation. Westinghouse 2017

Electricity production in Germany (www.energy-charts.de) January 2019

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Relating I-SCC cracks to local microstructure

  • Compared crack paths in:

– irradiated sample from mandrel test – Non-radiated in iodine-ethanol solution

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  • Iodine found at crack tip by NanoSIMS
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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

1 mm

[0001] [10-10] [11-20]

Radial direction

1

1 μm

2

Zr hydride

(b) (a) 1 μm

FIB Curtaining

3

1 2 3

4

0° 1° 2° 3°

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Relating I-SCC cracks to local microstructure

Journal of Nuclear Materials, (519) 2019, 166-172.

Unexpected result: non-basal cleavage in irradiated sample But, too few grains to make conclusive assessment

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Can we quantitatively assess crack path in relation to microstructure?

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

I-SCC tests at CNL

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C276 TOP CAP C276 PULL ROD TOP GRIP SPECIMEN BOTTOM GRIP GLASS TUBE TUBE FURNACE

Ar

METAL TUBING TO GLASS TUBING ADAPTER 3-WAY STOPCOCK FLASK PRESSURE REGULATOR GLASS STOPPER

TYGON TUBING BYPASS TO DIRECT VENT TEST CHAMBER

HEAT BATHS THERMO SCIENTIFIC SAHARA S15

2 WAY VALVE

BUBBLER CONDESER LIQUID LINE FILTER GAS FLOW MEASUREMENT AND CONTROL HEAT TAPE WRAPPED AROUND EXPOSED GLASS TUBING C276 PULL ROD C276 BASE CAP TO BUBBLER TO BUBBLER FROM BYPASS FROM TEST CHAMBER

  • Temperature and Iodine control
  • Various load and sample configs
  • DCDP measurements
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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Track crack progress by potential drop measurements

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Removing cracked volume - PFIB

100 μm 100 μm 100 μm 200 μm (a) (b) (c) (d)

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Z||RD Y||TD

X||ND

  • N.B. Susceptible orientation

– i.e. crack in RD

Sample geometry

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Serial sectioning in P-FIB

100 μm

9 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

Xe+

50 μm

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

3D chemical data by EDX mapping

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Cr

  • Sufficient resolution to identify

Cr/Fe in SPPs

  • Oxygen situated at crack location
  • No iodine segregation observed

– Resolution limit ? – Poor sensitivity in EDX – Overlap with Sn – Lost as volatile ZrI4?

50µm Fe I O

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

3D crystallography by EBSD

Electron backscatter diffraction Secondary electron imaging

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25 μm

X

  • EBSD maps on each slice
  • Crack path into the page

– (i.e. along Z )

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

3D reconstruction of grain volume & crack path

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  • 959 grains in volume
  • Align crack to microstructure
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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Evaluating crack nature

Z = 6 μm Z = 26 μm Z = 56 μm Z = 86 μm Z = 116 μm Z = 140 μm

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Grain orientations in analysed volume

Z=RD Y=TD

All orientations (959 grains) Transgranular cracked (58 grains) Adjacent to Intergranular crack (35 grains)

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Z=RD Y=TD Z=RD Y=TD

Contoured data

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Not just more grains, also spatial information e.g. Crack nature with depth

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 20 40 60 80 100 120

Average crack width (μm) Transgranular perecentage Total crack length (μm)

Average crack width Transgranular percentage

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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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?
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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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Building Boundaries

Coincident Site lattice

1) 2) 3) 4)

“Σ7” CSL: 7 lattice sites per CSL unit cell

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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Building Boundaries

Low-Σ GBs: macroscopic degrees of freedom

STGB: symmetric tilt GB

Multiple GB planes Good range

  • f angles

Σ Θ /deg Interface Type 7 21.79 (1 -3 2 0) STGB (0 0 0 1) Twist 13 27.80 (1 -4 3 0) STGB (0 0 0 1) Twist 19 13.17 (1 -5 4 0) STGB (0 0 0 1) Twist 31 17.90 (1 -6 4 0) STGB Σ Θ /deg Interface Type 7 21.79 (1 -3 2 0) STGB (0 0 0 1) Twist 13 27.80 (1 -4 3 0) STGB (0 0 0 1) Twist 19 13.17 (1 -5 4 0) STGB (0 0 0 1) Twist 31 17.90 (1 -6 4 0) STGB Σ Θ /deg Interface Type 7 21.79 (1 -3 2 0) STGB 13 27.80 (1 -4 3 0) STGB 19 13.17 (1 -5 4 0) STGB 31 17.90 (1 -6 4 0) STGB Computationally affordable for defect studies

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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Building Boundaries

Low-Σ GBs: microscopic degrees of freedom

Energy landscape Minimum-energy GB expansion

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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Building Boundaries

Supercells

Geometry opt. parameters dE/ion 1E-6 eV/atom |F|max 1E-2 eV/Ang

  • 1. Construct GB supercell and find optimum

microscopic configuration

  • 2. Construct free surface FS
  • 3. Construct bulk supercell

 Pristine interface properties  Defective interface properties

Low-Σ GBs

Σ7 STGB Σ13 STGB Σ7 Twist GB Σ13 Twist GB Atom shade indicates coordinate in page-normal direction

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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Effect of iodine on “strength” of bulk planes

Work of separation for Pristine Bulk For Defective Bulk

– Plane more important than Σ – Lowest “strength” for (0001) cleavage – All investigated planes weakened by defect

  • (0001) no longer lowest, but …

– Need to account for defect concentration

  • Different super cell sizes
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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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Effect of iodine on bulk planes

2 4 6 8 10 12 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90

Frequency Angular deviation of cracking plane from basal (°)

Experimental TG crack orientation

  • Normalise by defect concentration

→ Basal cleavage lowest

  • Most TG crack close to basal plane
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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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Effect of iodine on GB “Strength”

For defective GBs Work of separation for Pristine GBs

– (1 -3 2 0) lowest – Plane more important than misorientation

21.79 27.80 Misorientation /deg 21.79 27.80

– All boundaries “weakened” – Basal least susceptible

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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Comparing model with experimental observations: GBs

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Relative frequency Misorientation angle (°)

All boundaries 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Relative frequency Misorientation angle (°) All boundaries Cracked boundaries

Experimental: misorientation of IG cracked boundaries 21.79 27.80 Misorientation /deg 21.79 27.80

  • Experimental data shows good agreement

for simulated GBs → higher IG at 20-25 deg → no IG cracks at 25-30 deg

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Limitations of using GB misorientation

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  • For 2D slice, GB only defined by

misorientation

– i.e. average orientation of one grain compared to adjacent grain

  • Real boundaries much more

complex

  • DFT shows crack plane more

important than misorientation

  • Each grain has many boundary

planes

  • Crack adjacent to particular ones
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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

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Crack resistant grains

  • Some grains are observed to deflect the crack
  • Basal planes oriented away from loading direction

Z=RD Y=TD

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK Average intragranular misorientation

0.25 5 10 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 >10

Relative frequency Average intragranular misorientation (°) Bulk Transgranular Intergranular Deflectors

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Misorientation within grains

  • Bulk < IG < TG < crack deflectors
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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Summary

  • I-SCC was successfully performed in gaseous I2 using CNL Rig.
  • 3D analysis provides meaningful correlation between

microstructure and crack path, insight into I-SCC crack propagation.

– Primarily trans-granular (0001) observed for the material studied – Some grains are particularly resistant to cracking despite showing large malorientation/deformation.

  • DFT can provide understanding of relative susceptibility of different

planes (TG) and grain boundaries (IG) to weakening by aggressive species such as iodine.

  • For the limited boundaries simulated, modelling and experimental

show good qualitative agreement regarding the most succeptible boundaries and planes

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Acknowledgements

  • This work was funded by the EPSRC - PACIFIC [EP/L018616/1]

Programme and is supported by EPSRC Centre for Doctoral Training in Nuclear Fission- Next Generation Nuclear [EP/L015390/1]. It has been carried out as part of the PACE consortium on Pellet Cladding Interaction.

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PACE Pellet Assisted Cladding dEgradation

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Next steps

  • Simulate effects for more boundaries
  • Test “less susceptible” orientations
  • Effect of proton & neutron irradiation on crack path

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PACE Pellet Assisted Cladding dEgradation

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

2 4 6 8 10 12 14 16

Number of twins Total crack length (μm) Bulk Close to crack (b) Crack propagation direction 31

Proximity of twining to crack

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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

1 mm

[0001] [10-10] [11-20]

Radial direction

1

1 μm

2

Zr hydride

(b)

1 mm

[0001] [10-10] [11-20]

1 μm

2 3 4

(c) (d)

1

(a) 1 μm 1 μm

Zr twin

5

FIB Curtaining

3

1 2 3

4

0° 1° 2° 3°

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Relating I-SCC cracks to local microstructure

Journal of Nuclear Materials, (519) 2019, 166-172.

Gaseous Iodine ( Mandrel test)

  • TG and IG cracks
  • Non-basal TG cracks
  • Intergranular attack in iodine-ethanol solution
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19th International symposium on zirconium in the nuclear industry, May 20-23 2019, Manchester, UK

Misorientation/deformation around crack in 3D

Intragranular misorientation (Misorientation of each voxel within a grain with respect to average orientation)

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