In-pile testing of CrN, TiAlN and AlCrN coatings on Zircaloy cladding in the Halden Reactor

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1 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)

2 INTRODUCTION Need for improvement of fuel rod cladding 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)

3 INTRODUCTION (contd) Different approaches 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)

4 Approach IFE/Halden Use commercially available coatings 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

5 History/Highlights of coating research at IFE/Halden Year Activity/Highlight Reference (R. Van Nieuwenhove, et al.) Applied a commercial PVD coating to an eddy current probe for in-pile use. Proposed to use commercial PVD coatings on fuel rod claddings further investigations of coatings (autoclave tests) Fukushima accident (and start of accident tolerant fuel..) First in-pile testing of PVD coated samples in BWR land PWR loop. Excellent corrosion protection with CrN HWR-918, EHPG, Sandefjord HWR-1028, EHPG, Storefjell, Norway, 2011 Internal notes (IFA-731 and IFA-733)

6 Year Activity/Highlight Reference (R. Van Nieuwenhove, et al.) 2013 Testing in supercritical water (Gen-IV) Excellent corrosion protection with CrN coating 2014 Testing of coatings in liquid lead (Gen- IV). Excellent corrosion protection with AlCrN coating 6 th International Symposium on Supercritical Water-Cooled Reactors (ISSCWR-6), Shenzhen, China, Paper 13024, March 3-7. Nuclear Materials Conference, Clearwater, Florida, October 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 PIE of coated fuel rods This conference

7 Previous results of in-pile tests on coated samples Coated surface Diameter : 5 mm Length coated part: 10 mm Coating thickness: 1-2 µm (PVD) IFA Experiment Loop Total duration Exposure (FPD) 731 In-core cladding corrosion (2012) PWR 126 Coatings/samples Crack initiation ( ) BWR

8 Results Condition Thermal fluence Full power days TiAlN CrN Base: Inconel 600 ZrO 2 Base: Inconel 600 BWR n/cm OK (Inconel 600) OK -- OK for Zr-4 Disappeared PWR n/cm Disappeared on Inconel 600 OK IFA-733 (BWR) CrN coating after irradiation For detailed linescans (composition): see HWR-1106 Protective chromium oxide layer

9 Results Condition Thermal fluence Full power days TiAlN CrN Base: Inconel 600 ZrO 2 Base: Inconel 600 BWR n/cm OK (Inconel 600) OK -- OK for Zr-4 Disappeared PWR n/cm Disappeared on Inconel 600 OK IFA-733 (BWR) CrN coating after irradiation For detailed linescans (composition): see HWR-1106 Protective chromium oxide layer

10 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 Reached now 93 days (FPD) AlCrN CrN TiAlN No coating

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12 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

13 Calculated temperature profile for a coated fuel rod with an inner Inconel 600 cladding and an outer Zircaloy-4 cladding (20 kw/m)

14 Installed in rig, before irradiation 1.No coating 2. TiAlN 3. CrN 4. AlCrN

15 Irradiation history 150 FPD BU = 6.5 MWd/kgUO2 Fast fluence: 1.8 E20 n/cm^

16 Visual inspection Ref. no coating TiAlN coating Did not survive CrN coating AlCrN coating Did not survive

17 Bending of downcomer tubes towards fuel rods increased temperature of cladding «Accident conditions» over 150 days! CrN rod

18 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

19 Oxide thickness: About 5.5 µm SEM backscattered mode IFA-774, Zry-4, 60mm High porosity/circumferential cracks divide the oxide into several layers

20 From visual inspection, the CrN seemed to survive No coating Note: Due to bending of downcomer tubes, the temperature of the rods increased substantially no coating CrN coating 20

21 CrN coated Zr-4 tube from IFA-774 before irradiation at 30mm CrN coated Zr-4 tube from IFA-774 after irradiation at 30mm

22 CrN coated Zr-4 tube from IFA-774 before irradiation at 30mm CrN coated Zr-4 tube from IFA-774 after irradiation at 30mm

23 CrN coated Zr-4 tube from IFA After irradiation at 30mm Oxide under coating

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25 SEM analysis performed on the CrN coated cladding 25

26 Hardness measurements Rod Hardness before irradiation HV0.3 Hardness after irradiation HV0.3 Uncoated CrN coated

27 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)

28 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)

29 Planned test IFA-796 (PWR) in the Halden reactor (Joint Halden Program) Planned irradiation duration: 4-5 years Expected loading: Autumn

30 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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