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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: rudivn@ife.no

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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