© 2017 Electric Power Research Institute, Inc. All rights reserved.
Aylin Kucuk, EPRI – PI
Ioan Arimescu, AREVA – Co-PI
Yang-Pi Lin, GNF – Co-PI
Nuclear Science User Facilities FY2017
Annual Program Review, Germantown, DC
November 14-15, 2017
Improved Understanding of
Zircaloy-2 Hydrogen
Pickup Mechanism in
BWRs
2© 2017 Electric Power Research Institute, Inc. All rights reserved.
Hydrogen Impacts in Zirconium Alloy Materials
Many fuel issues are affected by hydrogen pickup of Zircaloy fuel cladding and fuel components
– Loss of Coolant Accidents (LOCA)
– Reactivity Initiated Accidents (RIA)
– Seismic Events
– BWR Channel Distortion
– PWR Fuel Assembly / Bundle Distortion
– Hydrogen Embrittlement / Hydride-induced Cracking
– Secondary Degradation
– Dry Cask Storage and Transportation
Need to better understand phenomena:
– Corrosion
– Hydrogen Pickup
Alloying Effects
– Hydrogen Diffusion, Migration & Precipitation
– Enhanced Corrosion (rims)
– Mechanical Property Changes (strength, ductility)
– Dimensional Changes
Creep; H-Assisted Irradiation Growth
– Hydride Embrittlement
– Water Chemistry Effects
– Hydride Reorientation (stress, temperature)
– Hydrogen Redistribution (thermal & stress gradients)
Oxide spallation, delamination, peeling and blistering
– Delayed Hydride Cracking
Pending Loss of Coolant Accident (50.46c) Rule
(Allowable clad corrosion during postulated accident)
0
5
10
15
20
25
0 200 400 600 800 1000
Equ
ivla
net
Cla
d R
eac
ted
(%)
Hydrogen Concentration (ppm)
DuctileBrittleLab A-DuctileLab A-BrittleNRC Proposed LimitCurrent Limit 50.46b
Forthcoming Limit 50.46c
Eq
uiv
ale
nt C
lad
Re
acte
d (
%)
More important than burnup or alloy!
3© 2017 Electric Power Research Institute, Inc. All rights reserved.
High Hydrogen Pickup and Variability at High Burnup in BWRs
Zircaloy-2 material show high hydrogen pickup and variability later in life but Zircaloy-4 does not.
– The main difference is Ni. What is the role of Ni on hydrogen pickup?
Previous Work
– EPRI NFIR and Channel Distortion Programs co-funded the HYDRanZeA project
HYDRanZeA (HYDRogen and Zr-Based Alloys)
BWR Fuel Cladding BWR Zircaloy Structural Materials
Miyashita et al., ANS LWR Fuel Performance Conference, San Francisco, 2007Geelhood et al. 2011 Water Reactor Fuel Performance Meeting, Chengdu, China, 2011
4© 2017 Electric Power Research Institute, Inc. All rights reserved.
NFIR/CDP HYDRanZeA Project Plan
GNF
Zirc-2 water rods
Zirc-2 and Zirc-4 channels
Westinghouse
Zirc-2 and Zirc-4 channels
AREVA
Zirc-2 and Zirc-4 channels
Electron
Microscopy
Pre-irradiated
Zircaloys from
BWRs
Synchrotron
techniques
Objectives:
• Determine why Zirc-4 HPUF is lower than Zirc-2 HPUF in
BWRs at high burnup
• Determine why Zirc-2 in BWRs show high hydrogen pickup at
high burnup
Scope:
• Compare pre-irradiated Zircaloy-2 and Zircaloy-4 alloy and
oxide structures at low and high fluence
3D Atom
Probe
5© 2017 Electric Power Research Institute, Inc. All rights reserved.
Irradiated BWR Chanel and Water Rod Materials in
Commercial BWRs
Zr-2 and Zr-4 channel materials Zr-2 water rod samples with various exposure and fluence
Both channel and water rod samples will be studied in the NSUF funded project. Remaining
parts of the studied samples will be donated to the NSUF material library.
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12
Hyd
roge
n P
ickup
Fra
ctio
n (
%)
Fluence (x1021 n/cm2 E>1 MeV)
Zircaloy-4 Channels Zircaloy-2 Channels
1400
1600
1800
2000
2200
2400
2600
2800
3000
0.0 5.0 10.0 15.0 20.0
Exp
osu
re T
ime
(da
ys)
Fluence (x1021 n/cm2 E>1 MeV)
Zircaloy-2 Water Rod
6© 2017 Electric Power Research Institute, Inc. All rights reserved.
Confirm or Refute the “Ni-band” Hypothesis
Developed a decision flow chart to design and focus the project
Metal
Zr2(FeNi) SPP
Ev.tetrag.oxide
Barrier
Layer
Porous
Oxide
Layer
Oxidized
SPP
a) Low burnup b) High burnup
Fe & Ni in
Forced solution
Metallic
Bands at
Oxide GB
“Ni-band” Hypothesis: After Ni
containing SPPs are dissolved under
irradiation at high burnup, metallic Ni
segregates at grain boundaries (oxide
and/or metal) and act as H window by
resulting accelerated hydrogen pickup.*
* Garzarolli et al., 16th ASTM Zr Symposium, 2010.
7© 2017 Electric Power Research Institute, Inc. All rights reserved.
HYDRanZeA Project FindingsQuestions Answers Concerns
Are Ni containing SPPs
dissolved in Zr-2 showing high
HPUF?
(TEM & 3DAP)
Yes. SPPs dissolve as a function of fast
fluence. Ni dissolves slower than Fe. 3DAP
showed high Ni content in metal matrix in
high HPUF materials.
TEM results were too qualitative with poor
statistics. 3DAP results were quantitative but too
localized. Need more examinations to confirm the
correlation.
Any segregation of Ni at grain
boundaries or other defects in
the metal?
(TEM & 3DAP)
Yes. Ni and Fe nano segregations observed
in irradiated metal matrix.
What happens to these nano segregations when
they are incorporated into the oxide? Stay metallic?
Any segregation of Ni at oxide
grain boundaries?
(TEM & 3DAP)
No. Conflicts with the previous findings.
Does Ni stay metallic in the
oxide?
(XANES)
Yes. High HPUF materials show up metallic
Ni up to 5-10 micron in the oxide while low
HPUF materials do not.*
More measurements are needed to strengthed the
correlation. Is high HPUF caused by metallic Ni or
metallic Ni is caused by high H content in the
oxide?
“Ni band” hypothesis could not be confirmed systematically. • Many supporting evidences were observed but no “Ni bands” are found in the oxide.
• A different form of the hypothesis may be in play.
• More measurements should be performed to fully understand the role of Ni in HPUF.
* A. Shivprasad et al., 18th ASTM Zr Symposium, 2016
8© 2017 Electric Power Research Institute, Inc. All rights reserved.
Oxide Resistivity vs. Hydrogen Pickup
Is this correlation also valid for irradiated Zircaloy-2
materials?
– How about the metallic Ni measured in high hydrogen
pickup Zircaloy-2?
1. It is verified that experimentally
𝜌ZrO2
EIS (ZrNb) < 𝜌ZrO2
EIS (Zr4)
2. There is a clear correlation between
𝜌𝑍𝑟𝑂2EIS and 𝑓𝐻
𝑖
Couet et al., 18th ASTM Zr Symposium, 2016
9© 2017 Electric Power Research Institute, Inc. All rights reserved.
Project Objective and Approach
Objective To understand why Zircaloy-2 material exhibit high
hydrogen pickup and a large variability in BWR environments by investigating a correlation between the irradiated Zircaloy-2 oxide layer resistivity and hydrogen pickup.
Approach Perform in-situ EIS measurements on pre-
irradiated BWR channel and water rod samples
– Focus tests on determining if the irradiated Zircaloy-2 oxide layer resistivity is correlated to the hydrogen pickup.
Perform PIE of same materials using TEM and SEM
– To complement the electrochemistry measurements, detailed oxide microstructure of the tested materials such as cracks and porosity will be determined.
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12
Hyd
roge
n P
ickup
Fra
ctio
n (
%)
Fluence (x1021 n/cm2 E>1 MeV)
Zircaloy-4 Channels Zircaloy-2 Channels
1400
1600
1800
2000
2200
2400
2600
2800
3000
0.0 5.0 10.0 15.0 20.0
Exp
osu
re T
ime
(da
ys)
Fluence (x1021 n/cm2 E>1 MeV)
Zircaloy-2 Water Rod
10© 2017 Electric Power Research Institute, Inc. All rights reserved.
Industry Activities on Hydrogen Pickup Issue
FRP
SHIZAM
NFIR-7
HYDRanZeA
Phase 2
MUZIC-3
Utilities
• Many PhDs on characterization of irradiated
Zircaloy materials and testing to understand the
HPU mechanism (PWRs and BWRs)
• In-situ EIS measurements in-reactor on
irradiated cladding (BWR and PWR)
• Advanced Modelling
• Hot cell examination
• Test Reactor experiments
• NDE method development
• Funds MUZIC-3
• Funds HYDRanZeA Phase 2
• Coordinates the interaction between MUZIC-3
and HYDRanZeA Phase 2
Same materials tested in the
HYDRanZeA project will be
characterized in the MUZIC-3
program.
DOE
NSUF
11© 2017 Electric Power Research Institute, Inc. All rights reserved.
Project Collaborators
Roles Responsible Party
Lead PI Aylin Kucuk, EPRI
Co-PIs Ioan Arimescu, AREVA
Yang-Pi Lin, GNF
PNNL NSUF Technical Lead Dave Senor, PNNL
Technical Staff at PNNL
NSUF
Olga Marina, PNNL
Dan Edwards, PNNL
3 year program
Complementary test program to
the HYDRanZeA Phase 2 project
– Focused on the irradiated Zircaloy-2
and Zircaloy-4 non-heat transfer
materials
Some key industry experts will
review progress through NFIR-VII
steering committee
12© 2017 Electric Power Research Institute, Inc. All rights reserved.
Benefits of HYDRanZeA Phase 2 Tests to Industry
Empirical hydrogen pickup models have been developed for forthcoming NRC LOCA rulemaking
– Especially challenging for BWR Zircaloy-2 due to significant HPU variability at later in life
Empirical models are only valid for conditions that they are benchmarked to
Any mechnanistic understanding of the hydrogen pickup phenomenon would be a supporting basis
of these empirical models
– May facilitate regulators’ timely licensing of new materials (e.g., HPU models)
0
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15
20
25
0 200 400 600 800 1000
Equ
ivla
net
Cla
d R
eac
ted
(%)
Hydrogen Concentration (ppm)
DuctileBrittleLab A-DuctileLab A-BrittleNRC Proposed LimitCurrent Limit
50.46b
Proposed Limit
50.46c
New LOCA rule
requires industry
to develop HPU
models
AREVA’s HPU Model Results on Zircaloy-2 in BWRs
Equiv
ale
nt C
lad R
eacte
d (
%)
13© 2017 Electric Power Research Institute, Inc. All rights reserved.
Project Status and Plan
Channel sample selection is completed.
Water rod samples will be transferred from ORNL to PNNL by the end of the year.
– Paperwork is in-progress
Project team will meet in Charlotte on November 16 to discuss about the testing details.
FY18 FY19 FY20
Select fuel channel samples X
Transfer water rod samples from ORNL to PNNL X X
Setup EIS measurements for various irradiated materials X X
SEM/TEM characterization of irradiated materials X X X X X
Begin autoclave testing and EIS measurements X X X X X
SEM/TEM of autoclave samples X X X X
Complete autoclave testing and EIS measurements X X
Finish characterization of tested materials and EIS data analysis X X X
Final report X X