steam oxidation and post-quench mechanical

Transcription

1 Effect of pre-oxide on Zircaloy-4 4high htemperature t steam oxidation and post-quench mechanical properties Guilbert S., Lacote P., Montigny G., Duriez C., Desquines J., Grandjean C. Institut de Radioprotection et de Sûreté Nucléaire IRSN/PSN-RES/SEREX-LE2M 17 th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb. 213

2 Context and Objectives An experimental oxidation test program was conducted to better understand the influence of the corrosion scale formed during normal operation in case of a high temperature transient. Context: t 1 - The pre-transient corrosion scale is protective (i.e. limits the oxygen supply to the metal) 2 - Oxygen from the pre-transient oxide can diffuse into the metal (chemical reduction of the pre-oxide) Corrosion scale oxygen Chemically reduced oxide 3 - Does the pre-transient oxide favor hydrogen pick-up during HT steam oxidation? Objective: Quantification of these effects Vs the pre-transient scale thickness 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

3 Experimental Design 1.3wt%Sn Zircaloy-4 cladding tubes, PWR 17x17, provided by Cezus (AREVA). 3 steps: 1 - Pre-oxidation at 425 C in O 2 or at (36 C, 15 bars) H 2 O (in autoclave, provided by EDF). 2 - HT oxidation in flowing steam (at 9, 1 or 12 C), Water quenching. 3- Post-tests characterizations Mechanical testing (Ring compression tests at RT). 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

4 Pre-oxidation in O2 at 425 C Horizontal resistive furnace 2 mm specimens for HT steam oxidation H pick-up i k b h by hott extraction Metallographic examination Pre-oxide thickness (µm P m) 1 cm segments, unplugged double side pre-oxidation 64 µm µm Pre-oxidation duration (days) 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

5 Pre-oxidation in O2 at 425 C H pick-up i k b h by hott extraction Metallographic examination P Pre-oxide thickness (µm m) 2 mm specimens for HT steam oxidation 1 Hydrogen Pick-up (wt pp H pm) Horizontal resistive furnace 1 cm segments, unplugged double side pre-oxidation 64 µm µm Pre-oxidation duration (days) 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

6 Metallography after pre-oxidation Optical microscopy Pre-oxidation at 425 C in O 2 2 µm 164 days 17.7 ± 1.3 µm 2 µm 465 days 52.8 ± 2.4 µm 2 µm 2 µm Pre-oxidation at 36 C in autoclave 1112 days 18.1 ±.6 µm 1265 days 3.5 years! 28.3 ± 7µm.7 Higher waviness of the M/O interface at 425 C. At 425 C, above ~3 µm thickness, radial cracks are observed. They do not penetrate down to the metal. 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

7 Comparison with irradiated Zy-4 SEM/BSE images 425 C ino 2 Irradiated, 61 GWd/tU 297 days 5 cycles, span 3 36 C in autoclave 1265 days ~ 3 µm 1 µm 1 µm Bossis, P., et al., Comparison of the high Burn-Up corrosion on M5 and low tin Zy-4. 14th Int. Symp. on Zirconium in the Nuclear Industry, Stockholm 24 1 µm Compared to in-reactor corrosion: Higher radial distance between cracks. More wavy M/O interface. Lateral cracks extension and opening decrease close to the M/O interface. Comparable sub-layer thickness. Sub-layers and cracks distribution are very regular. 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

8 High temperature oxidation in steam Oxidation protocol: St Steam+Ar A 2 mm Furnace heated to the targeted temperature, Steam (1 g/h) + Ar mixture injected from the top, p raised into the hot zone, heat-up p time is ~2-3s Sample at 12 C, Quenching in a water bath. Water bath 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

9 High temperature oxidation in steam Commissioning tests with bare Zy-4 at 9, 1, 11 and 12 C: Weight ga in (g/m²) C 11 C 1 C Brachet 21 (CEA) Hozer 28 (KFKI) Kawasaki 1978 (JAERI) Ozawa 2 (NDC) Billone 28 (ANL) IRSN Cathcart-Pawel Cubic fit 9 C Durations (s) Good agreement with literature data No hydrogen pick-up The oxidation protocol is validated 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

10 Test grids for pre-oxidized specimens Specimens pre-oxidized at 425 C in O 2 For each pre-oxide scale thickness : 7, 12, 18, 32, 41, 53, 64 µm Temperature ( C) 9 C 1 C 12 C Duration 3 and 1 min 15 and 3 min 1 and 6 s 42 tests Specimens pre-oxidized at 36 C in autoclave For each pre-oxide scale thickness : 18 and 28 µm Temperature ( C) 9 C 1 C Duration 1 min 15 min 4 tests 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

11 Weight gain and Hydrogen pick-up during HT steam oxidation 9 C 5 2 /S (g.m -2 ) m autoclaved 1 min 3 min HT m) up during H on (wt ppm H pick-u oxidati autoclaved 1 min 3 min Pre-oxide thickness (µm) Pre-oxide thickness (µm) Low temperature oxide scales are protective regarding HT oxidation. There is good agreement between O 2 oxidized and autoclaved specimens. The protective effect tend to be lost above ~4 µm thickness. The pre-oxide favors H pick-up, specifically above 4 µm. 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

12 Weight gain and Hydrogen pick-up during HT steam oxidation 1 C min /S (g.m -2 ) m HT m) up during H ion (wt ppm 15 autoclaved 1 3 min 15 min H pickoxidati 5 autoclaved 15 min Pre-oxide thickness (µm) Pre-oxide thickness (µm) Low temperature oxide scales are protective regarding HT oxidation. There is good agreement between O 2 oxidized and autoclaved specimens. The protective effect tend to be lost above ~4 µm thickness. The pre-oxide favors H pick-up, specifically above 4 µm. 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

13 Weight gain and Hydrogen pick-up during HT steam oxidation 12 C 2 (*) Le Saux et al., WRFPM, 211, Chengdu, China. 1 m /S (g.m -2 ) autoclaved (*) 6 s 2 s HT m) up during H on (wt ppm H pick-u oxidati s 2 s autoclaved (*) Pre-oxide thickness (µm) Pre-oxide thickness (µm) Low temperature oxide scales are protective regarding HT oxidation. There is good agreement between O 2 oxidized and autoclaved specimens. The protective effect tend to be lost above ~4 µm thickness. The pre-oxide favors H pick-up, specifically above 4 µm. 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

14 Hydrogen pick-up fraction during HT steam oxidation 1 9 C 1 C ) pick-up fr raction (% during HT oxidation H C Pre-oxide thickness (µm) H-pick-up fraction is moderate below 4 µm pre-oxide scale thickness, At 9 and 1 C, for thick pre-oxide scales, hydrogen pick-up fraction reaches 1%. 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

15 Metallographic examination for 64 µm pre-oxide thickness Before HT steam oxidation 5 µm After steam oxidation at 1 C Radial cracks propagation 15 min 5 µm Cracks opening Voids at the M/O interface HT oxide nodules min 3 5 µm Voids favor H accumulation close to the M/O interface. Continuous HT oxide layer (post-breakaway type) Cracks opening promotes oxygen supply through gas phase transport (i.e. as H 2 O molecules) 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

16 Mechanism of voids formation and cracks opening (proposal) Phase 1: Oxygen from the pre- oxide dissolves in the metal: Zr(O) Z(O) Pre-ox 64 µm, 15 min at 1 C Tim e at high temperatu ure 1.1 Chemical reduction of the preoxide, decrease of its thickness, 12Cracks 1.2 lateral spreading formation of voids. Phase 2: New oxygen reaches the metal: 2.1 Formation of HT oxide nodules, which h push on the pre-oxide cracks opening, 2.2 Lateral growth of the nodules, to form a continuous HT oxide layer Zr Zr(O) Zr 1 µm Chemically reduced pre-oxide Pre-ox 64 µm, 15 min at 1 C 5 µm HT oxide nodules Pre-ox 64 µm, 3 min at 1 C 5 µm HT oxide layer Duration of phase 1 is longer for high pre-oxide thickness, thus consequences of pre-oxide reduction are higher. 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

17 Effect of hydrogen on the post-quench ductility Ring Compression Test at room temperature 1 1 C 9 C C Offset strain (%) Hydrogen content after HT oxidation (wppm) It is confirmed that hydrogen content is a key factor influencing the post-quench ductility. 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

18 Summary The high temperature steam oxidation of Zircaloy-4 cladding pre-oxidised at low temperature, in the -65 µm pre-oxide thickness range, has been investigated at 9, 1 and 12 C Low temperature t pre-oxide scales formed at 425 C in O2 are protective ti regarding high h temperature steam oxidation. Protective effect is maximum in the 2-4 µm thickness range. HT oxidation results obtained with pre-oxide scales grown in autoclave at 36 C (2-3 µm thickness) are in good agreement with those obtained with pre-oxide scales formed at 425 C. Above ~4 µm thickness, the pre-oxide scales tend to loose their protectiveness at 9 and 1 C. In the presence of a pre-oxide scale, hydrogen incorporation at high temperature is observed, in condition where no H pick-up is detected with the initially bare alloy. This effect becomes very significant above 4 µm pre-oxide thickness. Effects observed for thick pre-oxide scales may be a consequence of the pre-oxide chemical reduction. 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17

19 Acknowledgments EDF is gratefully acknowledged for providing the autoclaved samples Thank you for your attention 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, 3-7 Feb /17