Characterization of Long-Term, In-Reactor Zircaloy-4 Corrosion Coupons and the Impact of Flux, Fluence, and Temperature on Oxide Growth, Stress Development, Phase Formation, and Grain Size Brendan Ensor a , Gene Lucadamo a , John Seidensticker a , Ram Bajaj a , Zhonghou Cai b , and Arthur Motta c The Naval Nuclear Laboratory is operated for the U.S. Department of Energy by Fluor Marine Propulsion, LLC, a wholly owned subsidiary of Fluor Corporation a Naval Nuclear Laboratory, b Argonne National Laboratory, c The Pennsylvania State University 19 th International Symposium on Zirconium in the Nuclear Industry
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Characterization of Long-Term, In-Reactor Zircaloy-4 Corrosion Coupons and the
Impact of Flux, Fluence, and Temperature on Oxide Growth, Stress Development,
Phase Formation, and Grain Size
Brendan Ensora, Gene Lucadamoa, John Seidenstickera, Ram Bajaja,
Zhonghou Caib, and Arthur Mottac
The Naval Nuclear Laboratory is operated for the U.S. Department of Energy by Fluor Marine Propulsion, LLC,
a wholly owned subsidiary of Fluor Corporation
aNaval Nuclear Laboratory, bArgonne National Laboratory, cThe Pennsylvania State University
19th International Symposium on Zirconium in the Nuclear Industry
Outline
2
• Introduction
• Effects of temperature, neutron flux, and neutron fluence on Zircaloy-4 corrosion, transition, and irradiated induced breakaway
• Results
• SEM, FIB-SEM serial sectioning, crack morphology, metal-oxide interface morphology
• Synchrotron µXRD experiments (grain size and phase fraction)
• Discussion
• Tetragonal phase stability
• Proposed theory on cause of irradiation induced breakaway/transition corrosion behavior
• Summary and Conclusions
Zirconium Alloy Corrosion• Zr alloys used as structural materials
• Good high temperature corrosion resistance and neutron transparent
• Needles of oxide observed at the metal-oxide interface• Seen elsewhere…(Zircaloy-2 BWR 9-cycle1, Baris et al, Journal of
Nuclear Materials, 2018)
• Perhaps a precursor to unstable oxide growth?• Similar morphology seen in Crystal Bar Zr in air (600°C) and autoclave
(360°C) prior to breakaway oxidation2
1A. Baris, R. Restani, R. Grabherr, Y.-L. Chiu, H. E. Evans, K. Ammon, M. Limback and S.
Abolhassani, "Chemical and Microstructural Characterization of a 9 cycle Zircaloy-2 cladding
using EPMA and FIB Tomography," Journal of Nuclear Materials, vol. 504, pp. 144-160, 2018. 2B. Ensor, "The Nature of Unstable Oxide Growth in Zirconium and Zirconium Alloys," PhD
Thesis in Nuclear Engineering: The Pennsylvania State University, 2016.
FIB/SEM Characterization – Irradiated Samples
12
Synchrotron µXRD Experiments – Irradiated Samples
13
Figure 1- Left, reconstructed FIB serial section acquired from H337J (no flux, 1139 days, 355°C, 25.6 µm) and Right, H421J
(1.37x1013 n/cm2/s, 537 days, 355°C, 25.7 µm). The capping layer is red, the cracks are dark blue, and the Zircaloy-4 is rendered
in green. The oxide is semi-transparent.
5 mm 5 mm
• Three thick oxide film Zircaloy-4 samples were examined using
Grain Diameter as a Function of Temperature (Outer Oxide, Zircaloy-4)
Monoclinic Phase Oxide
Tetragonal Phase Oxide
- From previous work1
- Increasing temperature leads to increasing monoclinic grain size
- Temperature has no effect on tetragonal grain size- Indicative of a critical size, above which tetragonal transforms to monoclinic
1B. Ensor, D. J. Spengler, J. R. Seidensticker, R. Bajaj, Z. Cai and A. T. Motta, "Microbeam
synchrotron radiation diffraction and fluorescence of oxide layers formed on zirconium alloys
at different corrosion temperatures," Journal of Nuclear Materials, vol. TBD, p. TBD, 2019.
Results – Grain Size (Autoclave)
21
0
5
10
15
20
25
30
35
40
45
3.53.02.52.01.51.00.50.0
Gra
in S
ize
Dia
met
er (
nm
)
Distance from Metal-Oxide Interface (µm)
H1187R, H2287J, H1190R, and H1406J Grain Size Diameter
360°C
274°C
Monoclinic Grains
Tetragonal Grains
- From previous work1
- Smaller monoclinic grains at metal-oxide interface (MOI), larger away
- Larger tetragonal grains at MOI, smaller away- Indicative of stress stabilization of the tetragonal phase at the MOI
1B. Ensor, D. J. Spengler, J. R. Seidensticker, R. Bajaj, Z. Cai and A. T. Motta, "Microbeam
synchrotron radiation diffraction and fluorescence of oxide layers formed on zirconium alloys at
different corrosion temperatures," Journal of Nuclear Materials, vol. TBD, p. TBD, 2019.
Results – Grain Size (ATR)
22
271-274°C
352-355°C
352-355°C
271-274°C
- Still no change in
tetragonal phase grain size
- Hard to see temperature
effect
- Instead, much larger
neutron flux/fluence effect
observed
- Increasing the neutron flux
or fluence leads to larger
monoclinic grain size
0
5
10
15
20
25
30
35
40
45
50
H381J
(272°C)
H977J
(314°C)
H1240J
(337°C)
H944J
(339°C)
H337J
(355°C)
H421J
(355°C)
H657J
(352°C)
H920J
(353°C)
Gra
in s
ize
(nm
)
Average Tet d Average 111m d
Results – Grain Size (ATR)
23
- Monoclinic and
tetragonal grain size
evolution through oxide
consistent with
autoclave observations
- Same stable (~15 nm)
tetragonal grain size as
autoclave
- Noticeable effect of
neutron flux or fluence
on monoclinic grain
size
- No observed effect on
tetragonal grain size
ResultsPhase Composition
24
Results - Phase Composition
25
- Highest fT at MOI with fTdecreasing away from
MOI- As observed previously1
- No effect of temperature1
- Observable effect of
neutron flux and fluence- Higher fT at MOI
- Lower fT in bulk
- Decrease away from
MOI consistent with
grain growth
- fT at MOI thought to be
related to metal stress
accommodation
(Irradiation hardening?)
R² = 0.3951
R² = 0.51490
0.05
0.1
0.15
0.2
0.25
0.3
0 10 20 30 40 50 60 70 80 90
Tet
ragon
al F
ract
ion
, f T
Fluence (1020 n/cm2; >1 MeV)
Tetragonal Fraction (Bulk and Max) vs Fluence
Max
Bulk
1B. Ensor, D. J. Spengler, J. R. Seidensticker, R. Bajaj, Z. Cai and A. T. Motta, "Microbeam synchrotron radiation diffraction and fluorescence of
oxide layers formed on zirconium alloys at different corrosion temperatures," Journal of Nuclear Materials, vol. TBD, p. TBD, 2019.
Grain growth
Stress at MOI
Results – Phase Composition
26
1 B. Ensor, D. J. Spengler, J. R. Seidensticker, R. Bajaj, Z. Cai and A. T. Motta,
"Microbeam synchrotron radiation diffraction and fluorescence of oxide layers formed
on zirconium alloys at different corrosion temperatures," Journal of Nuclear Materials,
vol. TBD, p. TBD, 2019.
- Two key factors: grain
size and stress
- Previous results have
linked the tetragonal
phase fraction1 to stress
in the oxide layer2
- Macroscopic
compressive stress
influences the formation
of fT
- Resulting t → m and
cracks influence
observations
2 H. Swan, M. S. Blackmur, J. M. Hyde, A. Laferrere, S. R. Ortner, P. D. Styman, C. Staines, M. Gass, H. Hulme, A. Cole-Baker
and P. Frankel, "The measurement of stress and phase fraction distributions in pre and post-transition Zircaloy oxides using
nano-beam synchrotron X-ray diffraction," Journal of Nuclear Materials, vol. 479, pp. 559-575, 2016.
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 1 2 3
Tet
ragon
al P
has
e F
ract
ion
, f
T
Distance from Oxide-Water Interface (µm)
Zircaloy-4 Average Tetragonal Phase Fraction
Average of all
Samples
Average of all
360°C Samples
Average of
H1406J (360°C)
Peak at metal-
oxide interface
DiscussionTheory
27
Stress and Thermodynamics
28
∆𝐺𝑡→𝑚 = ∆𝐺𝑐ℎ𝑒𝑚𝑖𝑐𝑎𝑙𝑡→𝑚 + ∆𝑊𝑚𝑎𝑡𝑟𝑖𝑥
𝑡→𝑚 + 𝑆𝑡𝑤𝑖𝑛𝑡→𝑚 + 𝜎𝑚𝑎𝑐𝑟𝑜𝑁𝐴𝜐
𝑡𝜅0 +𝑁𝐴𝜂(𝜐
𝑡)1/3[ 𝜐𝑚23𝛿𝑚 − 𝜐𝑡
23𝛿𝑡]
(𝑉𝑡)1/3
1 Qin, W., C. Nam, H.L. Li, and J.A. Szpunar. "Tetragonal phase stability in ZrO2 film formed on
zirconium alloys and its effects on corrosion resistance." Acta Materialia 55 (2007): 1695-1701.
Free energy to
change from the
tetragonal to the
monoclinic
phase
Chemical free
energy
driving force
Matrix
strain
Work against the
macroscopic
compressive
stress
Tetragonal phase
grain size term
Alloying elements Stress Grain Size
No effect seen
at MOI
• Why higher tetragonal fraction at MOI?
• Thermodynamics1 of t → m
Redistribution2 of
Fe…but so much
more Sn in matrix
Irradiation
hardening of
matrix
Twin
boundary
energy term
2 B. Ensor, "The Nature of Unstable Oxide Growth in Zirconium and Zirconium Alloys," PhD Thesis in
Nuclear Engineering: The Pennsylvania State University, 2016.
Stress and Thermodynamics
29
• Why higher tetragonal fraction at MOI?
• Irradiation hardening• Metal matrix less able to accommodate oxide growth stresses, leading to
higher stresses at MOI and higher fT• Levels off around 4-5 dpa
• What about irradiation induced creep?• Irradiation induced creep would relieve σ, thus leading to lower fT• Larger enough to offset hardening?
• All material here is recrystallized alpha-annealed Zircaloy-4
• Cold-worked/stress-relief annealed Zircaloy-4 creeps more in-flux
• So would expect less fT in irradiated CW/SRA Zircaloy-4
Theory
30
- A proposed model includes the basics of protective oxide layer growth and is
consistent with the findings from these studies
- The oxide growth can be split into four distinct phases:
(1) Oxide nucleation from the metal grains
(2) Growth of protective oxide layer (i.e., barrier layer)
(3) Breakdown of protective oxide during transition and formation of a new barrier
layer
(4) Irradiation induced transition (distinct from the cyclic transition process
described in steps 1-3) to post-transition oxide growth
0
50
100
150
200
250
300
350
400
450
0 500 1000 1500 2000 2500
Weig
ht G
ain
(m
g/d
m2)
Exposure time (days)
Neutron Irradiated Zircaloy-4 Weight Gain
0
20
40
60
80
100
120
140
0 100 200 300 400 500
We
igh
t G
ain
(m
g/d
m2 )
Days @ 360°C in Autoclave
Transitions
Cyclic Process
Zircaloy-4, 360°C water
43
12
3
12
3
12
Discussion – Cyclic Corrosion Regimes
31
(1) Oxide nucleates as small, equiaxed grains, postulated to be driven partly by matching to the
metal lattice; higher corrosion rate• Equiaxed oxide grains, higher fT, thinner suboxide layer, and more uniform grain size (larger tetragonal
phase grains and smaller monoclinic phase grains) as compared to oxide grown in the next phase
(2) Favorably-oriented monoclinic grains grow into larger, columnar oxide grains, driven by the
need to reduce stress accumulation, slower corrosion rate• Lower fT (increases as the oxide approaches transition), a significant suboxide layer (the size increases
as transition is approached and oxide growth slows), and a divergence in the grain size of the
monoclinic and tetragonal phases (monoclinic grains become larger, while tetragonal grains transform to
monoclinic phase above a critical size)
(3) Oxide transition; the protective nature of the oxide layer is lost due to a breakdown in the oxide• Leads to easy access of the metal to the oxidizing species (made possible by a percolation of porosity)
• Occurrence of the transition is characteristic of an alloy and oxidation conditions
• Once it occurs, the process begins again at (1).
➢Phases (1) and (2) governed by the alloying elements and precipitates➢Efforts to model this behavior based on the potential across the oxide and space charge compensation1
➢Phase (3), oxide transition, is governed by stress accommodation and a critical stress of the
protective oxide layer
1A. Couet, A. Motta and A. Ambard, "The coupled charge compensation model for zirconium
alloy fuel cladding oxidation, I. Parabolic oxidation of zirconium alloys," Corrosion Science, vol.
100, pp. 73-84, 2015
Discussion – Irradiation Induced Transition
32
(4) An irradiation induced transition to enhanced corrosion rates
• Described well by Kammenzind et al. for Zircaloy-41
• Appears to be related to a synergistic effect between thick oxide films and irradiation effects
on SPPs/alloying element redistribution• Heterogeneous radiolysis could not cause a transition prior to the existence of the thick film →
magnitude of the acceleration once in the post-transition regime
• Led to 30-40x accelerated corrosion rates in post-transition at temperatures similar to those
examined above
• Exposure to various levels of neutron fluence did accelerate the time at which the material
transitioned from pre-transition (1)-(3) to post-transition (4)• SPPs/alloying element could also effect the onset to (4)
➢ The two corrosion regimes (pre-transition (1)-(3) and post-transition (4)) and the time at which
the corrosion transitions from one to the other are the key descriptors of in-reactor Zircaloy-4
corrosion
• Note distinction between ‘irradiation induced transition (4)’ and the ‘transition (3)’ ascribed to
cyclic behavior often observed out-of-reactor
1 B. F. Kammenzind, J. A. Gruber, R. Bajaj and J. D. Smee, "Neutron irradiation effects on the
corrosion of Zircaloy-4 in a PWR environment," 18th International Symposium on Zirconium in
the Nuclear Industry ASTM STP 1597, pp. 448-490, 2018
Discussion – Irradiation Induced Transition Cause
33
➢ It is hypothesized that the oxide growth induced stress accommodation
of the Zircaloy-4 metal while irradiated could be the cause of the
transition from the pre-transition regime (1)-(3) to the post-transition
regime (4)
• Further testing is needed to understand and describe this mechanism
in detail and how other alloy systems (such as Zr-Nb) show
resistance to this enhanced corrosion regime
➢ Additional accelerating factors, such as acceleration due to hydrogen
concentration1, can also impact the corrosion rates observed in all
regimes (1)-(4)
1B. Ensor, A. M. Lucente, M. J. Frederick, J. Sutliff and A. T. Motta, "The role of hydrogen in
zirconium alloy corrosion," Journal of Nuclear Materials, vol. 496, pp. 301-312, 2017.
Ability of Metal to
accommodate oxide
growth stresses
Effects on
Precipitates
Creep
properties
Irradiation
Hardening
Irradiation
Induced
Transition
Else?
Summary of Observations
34
Characterization
- Irradiated Zircaloy-4 samples had similar oxide peaks, intensities, and variations as the samples
that were corroded in autoclave, suggesting similar corrosion mechanisms
- Two samples exposed at the same temperature to the same oxide thickness (355°C, ~26 µm),
but at different neutron flux levels (0 vs. 1.37x1013 n/cm2/s) had similar oxide layer spacing and
crack morphology despite the 2x corrosion rate of the in-flux sample; - Suggests that the in-cycle corrosion kinetics, rather than the transition oxide layer spacing, was most
influenced by the irradiation at this temperature and low total fluence (~1 dpa)
- One sample corroded at a low temperature (272°C) had accelerated corrosion after ~26 dpa,
which was correlated with a decrease in crack spacing, and change in crack morphology- Needles observed in sample close to entering similar regime (~12.5 dpa)
Grain Size
- Monoclinic grain size is larger for higher neutron fluxes and fluences, growing continually away
from the metal-oxide interface
- Average tetragonal grain size constant as a function of temperature and neutron flux/fluence;
above ~15 nm, the tetragonal phase is not stable and transforms to the monoclinic - Supported by a decrease in fT in the bulk of the oxide as a function of neutron fluence
Tetragonal Phase Fraction, fT- Maximum fT occurs near the MOI and increases as a function of neutron fluence
- Saturates around ~4-8 dpa, and likely occurs because of irradiation hardening limiting the
amount of stress the metal can accommodate, leading to higher stress accumulation at the MOI
Acknowledgements
35
- Ashley Lucente and Robert Etien III for their help coordinating the
sample preparation.
- Arash Parsi and Robert Rees for their help in sample preparation for
APS, acquiring the FIB serial section images, SEM imaging, and
conventional XRD measurements at Westinghouse, Churchill.
- This research has been authored by the Naval Nuclear Laboratory
under Contract No. DOE-89233018CNR000004 with the U.S.
Department of Energy.
- This research used resources of the Advanced Photon Source, a
U.S. Department of Energy (DOE) Office of Science User Facility
operated for the DOE Office of Science by Argonne National
Laboratory under Contract No. DE-AC02-06CH11357.
- This research was performed (B. Ensor) under appointment to
the Rickover Fellowship Program in Nuclear Engineering sponsored
by Naval Reactors Division of the U.S. Department of Energy.
Thank you for your attention
Questions?
36
37
EXTRA SLIDES
Synchrotron µXRD Experiments - Beamline Data
14
H657J
352°C, 230 days,
8.1 x 1013 n/cm2/s
9.50 µm
Metal-oxide
Interface
(-111)m
(111)m
(101)T
(002)T
(020)m
(002)m
(0002)α-Zr
{110}m
(002)m
(200)m
(020)m
Planes // to
Metal-oxide
interface
Planes ┴ to
Metal-oxide
interface
(002)t in
irrad too
{200}m chi
location
H977J
314°C, 1206 days,
4.23 x 1013 n/cm2/s
25.1 µm
Stress and Thermodynamics
39
• All material here is RXA Zircaloy-4
• Cold-worked/SRA Zircaloy-4 has stronger substrate out-of-flux…
• …creeps more in-flux
• So would expect less fT in CW/SRA Zircaloy-4
• …but less fT in autoclave tests too?
1B. Ensor, "The Nature of Unstable Oxide Growth in Zirconium and Zirconium Alloys," PhD Thesis in Nuclear
Engineering: The Pennsylvania State University, 2016.
Synchrotron µXRD Experiments – Autoclave Samples• Tested 11 Zircaloy-4 (some β-quenched) samples corroded at a variety of
temperatures, all prepared in cross-section
*H1190R, H1312J, and H1313J were corroded for 3 days at 360°C prior to listed exposure, <0.8 µm of the
oxide for all
**Oxide thickness is average thickness based on the weight gain of the sample
Exposure Condition* Time (days) Oxide thickness (μm)**
274°C water 3003 2.05, 2.35
316°C water 3113 13.1
360°C water 20 1.14
360°C water 120 2.09
360°C water 170 3.03, 4.02
400°C steam 41, 259 3.5, 9.1
413, 427°C steam 200, 203 7.8, 13.6
0
3
6
9
12
15
0
45
90
135
180
225
0 500 1000 1500 2000 2500 3000
Oxid
e T
hic
kn
ess
(µm
)
Wei
gh
t G
ain
(m
g/d
m2)
Time (days)
H2287J
H1187R
H1406J
H1312J
H1313J
H1405J
N2513
H1372J
H3017J
H3035J
H1190R
400-413°C
360°C
316°C
274°C
●: Zircaloy-4
427°C
15
B. Ensor, D. J. Spengler, J. R. Seidensticker, R. Bajaj, Z. Cai and A. T. Motta, "Microbeam
synchrotron radiation diffraction and fluorescence of oxide layers formed on zirconium alloys
at different corrosion temperatures," Journal of Nuclear Materials, vol. TBD, p. TBD, 2019.
Results – Grain Size (ATR and Autoclave)
41
20
25
30
35
40
45
50
270 290 310 330 350 370 390 410 430
Gra
in S
ize
(nm
)
Corrosion Temperature (°C)
Grain Size Data
ATR data Autoclave data Autoclave Fit
B. Ensor, D. J. Spengler, J. R. Seidensticker, R. Bajaj, Z. Cai and A. T. Motta, "Microbeam
synchrotron radiation diffraction and fluorescence of oxide layers formed on zirconium alloys
at different corrosion temperatures," Journal of Nuclear Materials, vol. TBD, p. TBD, 2019.
42
Results – Grain Size (Autoclave)
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10 12 14 16 18 20
Gra
in S
ize
Dia
met
er (
nm
)
Average Oxide Thickness (µm)
Monoclinic Grains
Tetragonal Grains
427ºC
413ºC
400ºC
360°C
316ºC
274°C
B. Ensor, D. J. Spengler, J. R. Seidensticker, R. Bajaj, Z. Cai and A. T. Motta, "Microbeam
synchrotron radiation diffraction and fluorescence of oxide layers formed on zirconium alloys
at different corrosion temperatures," Journal of Nuclear Materials, vol. TBD, p. TBD, 2019.
Results - Phase Composition (Autoclave)
43
0
0.05
0.1
0.15
0.2
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Tet
ragon
al F
ract
ion
Distance from the Metal-Oxide Interface (µm)
Average Tetragonal Fraction for Different Corrosion Temperatures
427ºC
413ºC
400ºC
360°C
316ºC
274°C
All
0.04
0.06
0.08
0.1
0.12
0.14
0 0.5 1 1.5 2 2.5 3
Tet
ragon
al P
has
e F
ract
ion
Distance from the Oxide-Water Interface (µm)
Towards metal-oxide interface
(oxide growth direction)
Oxide first formed Approximate
transition location
- Highest fT at MOI- Around 15%
- Decreases away from MOI- Around 7.5%
- No effect of temperature- Creep could have made fT
less for higher temp
- Higher corrosion rate
previously linked to higher fT- Competing?
- Plot as function of O/W
interface to see change
within transition layer
- Noticeable periodicity
(“dinosaur bones” theory)
B. Ensor, D. J. Spengler, J. R. Seidensticker, R. Bajaj, Z. Cai and A. T. Motta, "Microbeam
synchrotron radiation diffraction and fluorescence of oxide layers formed on zirconium alloys
at different corrosion temperatures," Journal of Nuclear Materials, vol. TBD, p. TBD, 2019.
Results - Phase Composition (ATR)
44
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
26 27 28 29 30 31 32 33 34 35 36 37 38 39
Inte
nsi
ty (
cps)
Position (°2θ)
H381J 1° i.a.
H381J 2.5° i.a.
H920J 1° i.a.
H920J 2.5° i.a.
(-111)m
(101)T
(111)m
272°C
353°C
Results - Phase Map (Autoclave & ATR)
45
(a) (-111)m Diffraction Intensity
(d) Tetragonal Fraction, fT
(b) (111)m Diffraction Intensity
(c) (101)T Diffraction Intensity
Metal-oxide interface
Oxide-water interface
Oxide
Metal
Oxide-water interface
Oxide-water interface
Metal-oxide interface
Metal-oxide interface
Oxide
Metal
Metal-oxide
interface
Oxide-water
interface - Created µXRD/XRF
maps on two samples
(one autoclave, one
irradiated)
- Shows typical metal-
oxide interface
undulations
- Can create oxide peak
intensity maps
- And grain size,
tetragonal fraction, etc.
- Highlights variability,
reproducibility, and
consistency of data
locally
B. Ensor, D. J. Spengler, J. R. Seidensticker, R. Bajaj, Z. Cai and A. T. Motta, "Microbeam
synchrotron radiation diffraction and fluorescence of oxide layers formed on zirconium alloys
at different corrosion temperatures," Journal of Nuclear Materials, vol. TBD, p. TBD, 2019.
Results - Phase Map (Autoclave & ATR)
46
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 1 2 3 4
Tet
ragon
al F
ract
ion
, f T
, at
Met
al-O
xid
e In
terf
ace
Oxide Layer Thickness (µm)
Irradiated
H1490J
8.29x1013 n/cm2/s, 1138 days
274°C, 1.60 µm0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 1 2 3 4
Tet
ragon
al F
ract
ion
, f T
, at
Met
al-O
xid
e In
terf
ace
Oxide Layer Thickness (µm)
Non-Irradiated
H1187R
Autoclave, 170days
360°C, 3.03 µm
0
0.05
0.1
0.15
0.2
0.25
0 0.5 1 1.5 2 2.5 3 3.5
Tet
rago
nal
Ph
ase
Fra
ctio
n
Distance from Metal-Oxide Interface (µm)
H1187R Map Average Tetragonal Phase Fraction
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.5 1 1.5 2 2.5
Tet
rago
nal
Fra
ctio
n, fT
Distance from Metal-Oxide Interface (µm)
H1490J Map Tetragonal Fraction• Irradiated vs. Autoclave comparison
1B. Ensor, "The Nature of Unstable Oxide Growth in Zirconium and Zirconium Alloys,"
PhD Thesis in Nuclear Engineering: The Pennsylvania State University, 2016.
Results – Previously published by Kammenzind et al
47
1 B. F. Kammenzind, J. A. Gruber, R. Bajaj and J. D. Smee, "Neutron irradiation effects on the
corrosion of Zircaloy-4 in a PWR environment," 18th International Symposium on Zirconium in
the Nuclear Industry ASTM STP 1597, pp. 448-490, 2018
Precipitate Oxidation
(Presented at NuMat 2018, October 2018)
48
49
µXANES Results - Fe in Zircaloy-4 - Autoclave
0%
25%
50%
75%
100%
-2 -1 0 1 2 3 4 5
Per
cen
tage
Met
allic
, No
rmal
ized
Distance to the Metal-Oxide Interface (mils)
274°C316°C360°C
Metal Oxide
- Zr oxidizes preferentially
to Fe
- Overall similar behavior
of Fe metallic fraction
when corroded in water
- Difference between 274-
360°C water and 400-
425°C steam, with
plateau of unoxidized Fe
- Attributed to increased
corrosion kinetics in
steam at higher
temperatures0%
25%
50%
75%
100%
-2 -1 0 1 2 3 4 5 6 7 8
Per
cen
tage
Met
allic
, No
rmal
ized
Distance to Metal-Oxide Interface (µm)
Metal Oxide
316°C 400°C413°C 425°C
2B. Ensor, A. T. Motta, R. Bajaj, J. R. Seidensticker, Z. Cai, "XANES analysis of iron in Zircaloy-4 oxides formed at different temperatures
studied with microbeam synchrotron radiation," ANS LWR Fuel Performance Meeting, TopFuel 2015, A0151 (2015).
1B. Ensor, "The Nature of Unstable Oxide Growth in Zirconium and Zirconium Alloys," PhD Thesis in Nuclear
Engineering: The Pennsylvania State University, 2016.
Synchrotron µXRD Experiments – Autoclave Samples
50
Sample AlloyExposure
Condition
Time
(days)
Oxide Thickness
(μm)
C1757P Zr-2.5Nb360°C water
680°F20 1.55
C1758P Zr-2.5Nb360°C water
680°F170 3.12
C5031P Zr-2.5Nb454°C steam
850°F200 39.9
• Three Zr-2.5Nb samples were corroded in autoclave with pure
water or steam for up to 200 days at 360°C and 454°C
B. Ensor, M. Moorehead, J. R. Seidensticker, R. Bajaj, A. Couet, and A. T. Motta, “XANES
Study of Fe and Nb Oxidation in Zr-2.5Nb Oxide Layers," Transactions of the American
Nuclear Society, vol. 117, p. 527-530, 2017.
51
µXANES Results – Fe in Zircaloy-4 and Zr-2.5Nb
0%
25%
50%
75%
100%
-1 0 1 2 3
Pe
rce
nt
of
Fe M
etal
lic, N
orm
aliz
ed
Distance to the Metal-Oxide Interface (µm)
Metal Oxide
Zr-2.5Nb
Zircaloy-4
360°C
• Fe oxidizes closer to the Metal-Oxide Interface in Zr-2.5Nb than Zircaloy-41
• Smaller precipitates (surface area) and more Fe in solid solution
1B. Ensor, A. T. Motta, R. Bajaj, J. R. Seidensticker, Z. Cai, "XANES analysis of iron in
Zircaloy-4 oxides formed at different temperatures studied with microbeam synchrotron
radiation," ANS LWR Fuel Performance Meeting, TopFuel 2015, A0151 (2015).
B. Ensor, M. Moorehead, J. R. Seidensticker, R. Bajaj, A. Couet, and A. T. Motta, “XANES Study of Fe and Nb
Oxidation in Zr-2.5Nb Oxide Layers," Transactions of the American Nuclear Society, vol. 117, p. 527-530, 2017.
52
µXANES Results – Fe & Nb in Zr-2.5Nb
0%
25%
50%
75%
100%
-1 0 1 2 3 4 5 6 7
Perc
ent
of
Fe o
r N
b M
etal
lic, N
orm
aliz
ed
Distance to Metal-Oxide Interface (µm)
360°C450°C
● NbΔ Fe
Metal Oxide
• Fe and Nb oxidize at similar distances to the Metal-Oxide Interface in Zr-2.5Nb
• Difference seen in water (360°C) vs. steam (454°C), more “delayed”
• Consistent with studies of ZIRLO®1
• Space charge (Fe3+ vs. Nb5+)
1A. Couet, A. T. Motta, B. de Gabory, Z. Cai, "Microbeam X-ray Absorption Near-
Edge Spectroscopy study of the oxidation of Fe and Nb in zirconium alloy oxide
layers," J. Nucl. Mater, 452, 614 (2014).
B. Ensor, M. Moorehead, J. R. Seidensticker, R. Bajaj, A. Couet, and A. T. Motta, “XANES Study of Fe and Nb
Oxidation in Zr-2.5Nb Oxide Layers," Transactions of the American Nuclear Society, vol. 117, p. 527-530, 2017.
53
µXANES Results – Effect of Irradiation
0
0.25
0.5
0.75
1
-2 -1 0 1 2 3 4 5 6 7 8 9 10
Fra
ctio
n o
f M
eta
llic F
e
Distance from Metal-Oxide Interface (µm)
Non-irradiated
Zircaloy-4
(H337J)
Irradiated
Zircaloy-4
0
0.25
0.5
0.75
1
-1 0 1 2 3 4 5
Fra
ctio
n o
f M
eta
llic F
e
Distance from Metal-Oxide Interface (µm)
352-355°C
Fe in non-irradiated sample is
oxidized further into the oxide
than Fe in the irradiated samples
0
0.25
0.5
0.75
1
-1 0 1 2 3 4 5
Fra
ctio
n o
f M
eta
llic F
e
Distance to the Metal-Oxide Interface (µm)
274°C
316°C
360°C
Autoclave
Iso
therm
al
1B. Ensor, "The Nature of Unstable Oxide Growth in Zirconium and Zirconium Alloys," PhD Thesis in Nuclear
Engineering: The Pennsylvania State University, 2016.
54
µXANES Results – Effect of Irradiation
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 20 40 60 80 100
Oxid
e P
ositio
n w
he
re F
e is m
ostly O
xid
ize
d (
µm
)
Neutron Fluence (1020n/cm2, E > 1 MeV)
Oxide Position where Fe is mostly Oxidized vs Neutron Fluence
Average of autoclave
samples corroded in water
One additional
sample at (217.1, 1)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 4 8 12
Oxid
e P
ositio
n w
he
re F
e is m
ostly O
xid
ize
d (
µm
)
Neutron Flux (1013n/cm2/s, E > 1 MeV)
Oxide Position where Fe is mostly Oxidized vs Neutron Flux
Average of autoclave
samples corroded in water
352-355°C
337-339°C
314°C
271-274°C
- There is a clear Neutron Flux and Neutron Fluence correlation to the
position in the oxide where Fe is mostly oxidized
1B. Ensor, "The Nature of Unstable Oxide Growth in Zirconium and Zirconium Alloys," PhD Thesis in Nuclear
Engineering: The Pennsylvania State University, 2016.
352-355°C
337-339°C
314°C
271-274°C
55
µXANES Results – Effect of Irradiation
Hypothesis: redistribution of Fe from precipitates
to matrix caused by irradiation leads to higher
surface to volume ratio and more Fe oxidation
closer to the MOI
1B. Ensor, "The Nature of Unstable Oxide Growth in Zirconium and Zirconium Alloys," PhD Thesis in Nuclear
Engineering: The Pennsylvania State University, 2016.