Blay, T.

Gatt, Jm.

Henry, R.

Langlois, C.

Meille, S.

Zacharie-Aubrun, I.

English

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Fracture properties characterization of nuclear fuel using micro-cantilever bending

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Fracture properties characterization of nuclear fuel using
micro-cantilever bending
R. Henry, I. Zacharie-Aubrun, Jm. Gatt, T. Blay, S. Meille, C. Langlois
To cite this version:
R. Henry, I. Zacharie-Aubrun, Jm. Gatt, T. Blay, S. Meille, et al.. Fracture properties characterization
of nuclear fuel using micro-cantilever bending. NUMAT2018, Oct 2018, Seattle, United States. ￿cea-
02339463￿
R. HENRY 1, T. BLAY 2, I. ZACHARIE-AUBRUN 2, J.M. GATT 2, C. LANGLOIS 1, S. MEILLE 1
1 Université de Lyon, INSA-Lyon, MATEIS UMR CNRS 5510, 69621 Villeurbanne, France
2 CEA, DEN, DEC, Cadarache, 13108 St Paul Lez Durance, France
With the support of :
1
Fracture properties characterization of nuclear 
fuel using micro-cantilever bending 
Notched micro-cantilever milled in irradiated nuclear fuel (UO2)
16/10/2018
Introduction
I. Context
1. PWR fuel’s behavior under irradiation
2. Mechanical properties at the micro-scale
II. Experimental approach
1. Validation on ZrO2
2. Preparation of µ-cantilevers
3. Mechanical test performed with a nano-indenter
4. Calculation of fracture properties 
III. Results : Fracture properties of fresh and 
irradiated nuclear fuels UO2
1. Fracture stress of nuclear fuels UO2
2. Fracture toughness of nuclear fuels UO2
Conclusion and perspectives
2
CONTENT
Experimental approach ResultsContext
16/10/2018
3INTRODUCTION
16/10/2018
4INTRODUCTION
16/10/2018
Verdon canyon
“Calanque” of Cassis
5INTRODUCTION
CEA
(French) Alternative Energies and 
Atomic Energy Commission
Cadarache Center
Research center for energy :
- Nuclear fission
- Nuclear fusion (ITER : (International 
Thermonuclear Experimental Reactor))
- Nuclear propulsion
16/10/2018
Cadarache
LECA/STAR
A nuclear facility dedicated to 
the irradiated fuel examination
From the whole rod to the microscopic scale
Fuel treatment
(before storage)
Non-destructive examinations
MEGAFOX
(full-length LWR rods)
Fission gas release
Rods cuttings
Micro-analysis laboratory
FIB/SEM, EPMA, SIMS, XRD, TEM
CORALIE :
Fuel rod re-fabrication 
& instrumentation
MEXICOO :
Very high pressure 
furnace
MEYRARG :
Furnace (gas analysis)
CROCODILE 
Furnace (oxidizing conditions)
VERDON :
2 dedicated cells for severe 
accident studies Metallography 
5 dedicated cells
Non-destructive examinations
VENDAUM (experimental pins)
PLACIDE (fuel plates)
DUNCAN : 
Fuel rod cutting 
and machining
6INTRODUCTION
Micro-analyses laboratory
16/10/2018
EPMA    Profilometer FIB / SEM        Storage Cell       SIMS                XRD
TEM
The front shielded wall
FIB /  SEM
The glove box
FIB / SEM
Nano-indenter in situ :
µ-mechanical tests 
7CONTEXT
PWR fuel’s behavior under irradiation
Experimental approach ResultsContext
Cracks
in the fuel
16/10/2018
Modeling of strain location in 
Zircaloy cladding and fuel pellets 
(Pressurized Water Reactor)
 Take it into account in numerical simulations
Fuel modelling :
• Viscoplasticity in the core
• Brittle on the periphery
 Experimental data needed
 Values of :
- Fracture toughness (KIC) 
- Fracture stress (σR)
Fresh nuclear fuel
OK
Irradiated nuclear fuel 
 Impossible to machine 
macroscopic specimens 
for mechanical testing
 PCI (Pellet-Cladding Interaction)
Optical micrograph of a sample 
section of UO2 fuel and its cladding
Irradiated in PWR + power ramp test
Power ramps
Optical micrograph of a UO2 fuel in 
the pellet’s periphery  
Irradiated in PWR + RIA test
Accidental situations
 RIA (Reactivity Insertion Accident)
 LOCA (Loss Of Coolant Accident)
Optical micrograph of a sample 
section of UO2 fuel and its cladding
Irradiated in PWR
Normal operations
PWR = Pressurized Water Reactor 
Optical micrograph of an 
irradiated pellet section
8
CONTEXT 
Mechanical properties at the micro-scale
µ-mechanical tests :
 To avoid cracks (and porosities)
 To measure “intrinsic” properties
Vickers indentation 
on irradiated fuel 
• Handy solution
• Studied and used before
• Sometimes difficult to make a proper 
measurement
Indentation
Notched µ-cantilever for fracture 
toughness measurement (ZrO2)
• Closer to bending test
• Preparation with FIB/SEM(Ga beam)
• Mechanical testing with a nano-
indenter
• Numerical modeling
µ-cantilever bending :
Today’s topic :
Experimental approach ResultsContext
16/10/2018
9EXPERIMENTAL APPROACH
Validation on ZrO2
Notched cantilever
Fracture toughness (KIC) measurement
Un-notched cantilever
Fracture stress (σc) measurement 
ResultsContext Experimental approach
16/10/2018
Setting up the experimental method on cubic zirconia (ZrO2) :
• Crystallographic characteristics close
• Mechanical properties similar (at the macroscopic scale)
R. Henry 1, T. Blay 2, T. Douillard 1, I. Zacharie-Aubrun 2, J-M Gatt 2, C. Langlois 1, S. Meille 1: To be published.
1 Université de Lyon, INSA-Lyon, MATEIS CNRS UMR 5510, 69621 Villeurbanne, France
2 CEA, DEN, DEC, Cadarache, 13108 St Paul Lez Durance, France
Similar fracture toughness 
KIC ≈ 1.5 MPa.m
0.5
 Good agreement with literature 
(macroscopic tests on single crystals)
Higher fracture stress 
σc ≈2 GPa (against ≈200 MPa for macro)
 Scale effect : less defects in a µ-sample
Validation by comparison with literature data :
ϴ EBSD orientation map
Grain’s choice : large 
enough to contain a 
whole cantilever
10
EXPERIMENTAL APPROACH
Preparation of µ-cantilevers
{100}
{111}
{110}
ϴStereographic projection
The targeted 
crystallographic 
plane is normal to 
the sample surface 
ϴ
Positioning
Use of ϴ angle for the 
milling
Specimen
Orientated into a chosen 
crystallographic plane 
Cubic crystal of UO2 and some of its 
crystallographic planes
ResultsContext Experimental approach
16/10/2018
11
EXPERIMENTAL APPROACH
Mechanical test performed with a nano-indenter
Linear load-displacement curve
Corrected from indentation
 Fracture load
ResultsContext Experimental approach
Movies of in situ bending tests
No plasticity : brittle behavior (elastic up to fracture)
16/10/2018
1,0 mN
Fresh UO2
With the support of 
X. Iltis (CEA), N. Tarisien (CEA)
Irradiated UO2
With the support of 
S. Chalal (Carl Zeiss)
12
EXPERIMENTAL APPROACH
Calculation of fracture properties
ResultsContext Experimental approach
16/10/2018
FEM modelling
Calculation inputs :
• Fracture load
• Dimensions of the beam and notch
FEM analysis (Cast3m® (CEA, France)) 
Calculation outputs :
• KIC (fracture toughness)
or
• σc (fracture stress)
Numerical parameter study : 
• Optimization of the test
 Dimensions, positioning, influence of different parameters
• Study of the effect of anisotropic elasticity
13
RESULTS
Fracture stress of nuclear fuels UO2
Context Experimental approach
Standard UO2 (grain size : 10 µm)
Fresh fuel
Large grain UO2 (grain size : 60 µm)
Irradiated fuel (34 GWj/tM)
{100}
{111}
σR= 3.6 ± 0.4 GPa
σR= 2.2 ± 0.4 GPa
σR= 3.4 ± 0.7 GPa
σR= 2.7 ± 0.1 GPa
Fracture surface almost flat
Highest value of stress
Fracture surface flat (higher part)
Lowest value of stress
Results
16/10/2018
{111} family plane seems weaker 
 Coherent with numerical simulations at atomistic scale (MD and DFT)
Scale effect on fracture stress
 ≈3 GPa (micro) against ≈ 150 MPa (macro)
Y. Zhang et al., “Crack tip plasticity in single crystal UO2 : atomistic simulations, Journal of Nuclear Materials, 2012.
14
RESULTS
Fracture toughness of nuclear fuels UO2
Context Experimental approach
Standard UO2 (grain size : 10 µm)
Fresh fuel
Large grain UO2 (grain size : 60 µm)
Irradiated fuel (34 GWj/tM)
Results
Vickers value
KIC≈ 1,0 Mpa.m
0.5
Vickers value
KIC≈ 1,2 Mpa.m
0.5
Macroscopic value 
KIC≈ 1,7 Mpa.m
0.5
{111} family planes weaker
 Cleavage of a fcc crystal
No scale effect on fracture toughness
 Same value as bending tests on macroscopic samples
Values higher than VIF (Vickers Indentation Fracture toughness test)
 Same tendency but higher values
 Calibration of VIF will be considered
16/10/2018
1.6
1.8
Fresh fuel
Irradiated 
fuel (34 
GWj/tM)
Large                
grain size              
(60 µm)
Standard 
grain size 
(10 µm)
Effect of irradiation
Effect of                
µ-structure
15
CONCLUSION / PERSPECTIVES 
ResultsContext Experimental approach
Feasibility of the test showed (despite hard constraints on irradiated fuel)
 Shielded FIB/SEM + glove box + manipulator
• On irradiated fuel with large grains (60 µm)
 First mechanical tests on irradiated in PWR fuel
First results :
• Results on individual grains
 Good complementarity with indentation tests 
• Resistance of crystallographic planes 
 Complement to numerical simulations of surface energies (DFT and MD)
Perspectives :
• Application on irradiated fuel with standard grain size (10 µm)
 Comparison with standard fresh UO2 : irradiation effect
 Evolution of the resistance with the burnup
• Calculation of elastic properties 
 Young Modulus of the cantilever
16/10/2018
05/10/2018
Thank you for your attention
ronan.henry@insa-lyon.fr
Avec le soutien de :
16
17
INDENTATION
µ-éprouvettes IndentationContexte
Nano-indentation Vickers d’un échantillon 
polycristallin de 8Y-FSZ (660 mN)
Nano-indentation Vickers d’un 
monocristal de 8Y-FSZ (400 mN)
c ???
Bifurcation de la fissure
Influence du pore 
sur la fissure
Influence du 
joints de grains 
sur la fissure
06/06/2018


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Fracture properties characterization of nuclear fuel using micro-cantilever bending

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