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In-pile testing of CrN, TiAlN and AlCrN
coatings on Zircaloy cladding in
the Halden Reactor
R. Van Nieuwenhove, V. Andersson, J. Balak, B. Oberländer
Sector Nuclear Technology, Physics and Safety
Institutt for Energiteknikk (IFE)
Halden Reactor Project (HRP)
Email: [email protected]
INTRODUCTION
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More demanding conditions
Longer cycles, higher burn-up
Higher initial Lithium hydroxide (LiOH)
More corrosive environment (temperature, chemical)
Need for increased safety
Avoid excessive corrosion and hydrogen release during
accident conditions
Reduction of failures
Avoid fuel failures induced by fretting
Reduction of hydrogen uptake (and embrittlement)
Need for improvement of fuel rod cladding
INTRODUCTION (contd)
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Evolutionary
Modified Zr-based alloys (Opt. ZIRLO,
M5, MDA, NDA, HANA, etc.)
Surface modifications (such as ODS
treatment) and coatings
Revolutionary
SiC, Fe-Cr-Al, metal-ceramic hybrid
cladding, Mo-based alloys (Accident
Tolerant Fuel, Gen IV)
Different approaches
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Approach IFE/Halden
No need for further developments
Cheap
Can be applied to 4 meter rods already now
Coating temperature (PVD) low enough such that
zircaloy properties are not modified
Use commercially available coatings
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History/Highlights of coating research at
IFE/Halden
Year Activity/Highlight Reference (R. Van Nieuwenhove, et al.)
2009 Applied a commercial PVD coating to an
eddy current probe for in-pile use. Proposed
to use commercial PVD coatings on fuel rod
claddings
HWR-918, EHPG, Sandefjord
2010
-
2011
further investigations of coatings (autoclave
tests)
HWR-1028, EHPG, Storefjell,
Norway, 2011
2011 Fukushima accident (and start of accident
tolerant fuel ..)
2011
-
2012
First in-pile testing of PVD coated samples
in BWR land PWR loop.
Excellent corrosion protection with CrN
Internal notes (IFA-731 and IFA-733)
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Year Activity/Highlight Reference
(R. Van Nieuwenhove, et al.)
2013 Testing in supercritical water (Gen-IV)
Excellent corrosion protection with CrN
coating
6th International Symposium on
Supercritical Water-Cooled Reactors
(ISSCWR-6), Shenzhen, China, Paper
13024, March 3-7.
2014 Testing of coatings in liquid lead (Gen-
IV). Excellent corrosion protection with
AlCrN coating
Nuclear Materials Conference,
Clearwater, Florida, October 27-30.
2014 First in-pile testing with coated fuel rods HWR-1106, EHPG, Røros, Norway,
2014 Investigation of the impact of coatings on
hydrogen uptake. Coatings reduce
hydrogen diffusion (> factor 2)
Nuclear Materials Conference,
Clearwater, Florida, October 27-30.
2015-
2016
PIE of coated fuel rods This conference
Previous results of in-pile tests on
coated samples
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Diameter : 5 mm
Length coated part: 10 mm
Coating thickness: 1-2 µm (PVD)
IFA Experiment Loop Total
duration
Exposure
(FPD)
Coatings/samples
731 In-core cladding
corrosion
(2012)
PWR 126
733.1 Crack initiation
(2011-2012)BWR 287
Coated surface
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Condition Thermal fluence Full power
days
TiAlN CrN
Base:
Inconel 600
ZrO2
Base: Inconel 600
BWR 4.5 1020 n/cm2 287 OK (Inconel 600) OK --
PWR 2.1 1020 n/cm2 126
OK for Zr-4
Disappeared on
Inconel 600
OK
Disappeared
Results
IFA-733 (BWR)
CrN coating after irradiation
For detailed linescans
(composition): see HWR-1106
• Protective chromium oxide layer
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Condition Thermal fluence Full power
days
TiAlN CrN
Base:
Inconel 600
ZrO2
Base: Inconel 600
BWR 4.5 1020 n/cm2 287 OK (Inconel 600) OK --
PWR 2.1 1020 n/cm2 126
OK for Zr-4
Disappeared on
Inconel 600
OK
Disappeared
Results
IFA-733 (BWR)
CrN coating after irradiation
For detailed linescans
(composition): see HWR-1106
• Protective chromium oxide layer
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IFA-774: Description of experiment First experiment with coated fuel rods
PWR conditions at 320 ºC (150 days)
Three rods with of coating: TiAlN, CrN, AlCrN (PVD)
One reference rod
Irradiation started on 15.03.2014. Reached now 93 days
(FPD)
No coating
TiAlN
CrN
AlCrN
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Fuel rod characteristics
Double cladding: In view to ease PIE examination of the coated cladding
Outer, coated cladding (Zr-4): 9.5/8.36 mm
Inner cladding, not coated (Inconel 600): 8 / 7 mm
Pellet outer diameter: 6.83 mm
Fuel rod enrichment : 5 %
Fill gas : He
Designed to reach a linear heat rate of 20 kW/m
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Calculated temperature profile for a coated fuel rod
with an inner Inconel 600 cladding and an outer
Zircaloy-4 cladding (20 kW/m)
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1.No
coating
2. TiAlN
3. CrN
4. AlCrN
Installed in rig, before irradiation
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Irradiation history150 FPD
BU = 6.5 MWd/kgUO2
Fast fluence: 1.8 E20 n/cm^2
Visual inspection
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Ref. no coating
TiAlN coating
Did not survive
CrN coating
AlCrN coating
Did not survive
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Bending of downcomer tubes towards fuel rods
increased temperature of cladding
«Accident conditions» over 150 days!
CrN rod
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Look into SEM analysis on un-coated Zircaloy-4 cladding
in order to find an indication of insufficient cooling
Oxide spallation
High porosity of oxide
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Oxide thickness:
About 5.5 µm
SEM backscattered mode – IFA-774, Zry-4, 60mm –
High porosity/circumferential cracks divide the oxide into several layers.
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From visual inspection, the CrN seemed to survive
CrN coatingno coating
No coating
Note: Due to bending of
downcomer tubes, the temperature
of the rods increased
substantially
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CrN coated Zr-4 tube from IFA-774
before irradiation at 30mm
CrN coated Zr-4 tube from IFA-774
after irradiation at 30mm
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CrN coated Zr-4 tube from IFA-774
before irradiation at 30mm
CrN coated Zr-4 tube from IFA-774
after irradiation at 30mm
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CrN coated Zr-4 tube from IFA-774 - After irradiation at 30mm Oxide under coating
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SEM analysis performed on the CrN coated cladding
Hardness measurements
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Rod Hardness before
irradiation
HV0.3
Hardness after
irradiation
HV0.3
Uncoated 200 260
CrN coated 293 305
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Testing in steam (+ air) up to 1000 °C
Note: Corrosion in the presence of nitrogen (+steam) is much
larger than with steam alone. Poster: Martin Steinbrueck (KIT)
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Some results (for Zr-2 substrate):
750 °C, 60 minutes : CrN coating survives
1000 °C, 15 minutes: CrN coating survives
1200 °C, 5 minutes (LOCA test): CrN coating survives
In the presence of cracks, oxide starts forming and can
grow under the coating, pushing the coating outwards
Example:
750°C, 60 minutes
With machined scratch
See also poster of Kevin
Daub (CNL)
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Planned test IFA-796 (PWR) in the Halden reactor
(Joint Halden Program)
Planned irradiation duration: 4-5 years
Expected loading: Autumn 2016
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Conclusions
TiAlN and AlCrN coatings disappeared
CrN coating chemically stable (BWR and PWR)
No reduction in coating thickness
Coatings reduce hydrogen uptake in zircaloy
Coatings can be stretched by 1.5 % before cracking (see
Poster Kevin Daub (CNL))
Despite «accident like» conditions, most of the coating
still intact after 150 days
When a crack occurs, oxide forms underneath and the
expansion leads to further cracking
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