Oxidation and degradation of Zircaloy-4 in nitrogen- oxygen-steam - PowerPoint PPT Presentation

Oxidation and degradation of Zircaloy-4 in nitrogen- oxygen-steam mixtures at 850°C DENOPI Project High Temperature Corrosion (GRS), July 8-9 2017 Mathilde Gestin, Olivia Coindreau, Michèle Pijolat, Christian Duriez, Véronique Peres Work performed in the frame of the DENOPI project, funded by the French government as part of the “Investment for the Future” Program reference ANR-11-RSNR-0006 Institut Mines-Télécom

Context fuel assembly fuel rod cladding cylindrical fuel pellets “Special Report on the nuclear accident at the Fukushima Daiichi nuclear power station, 2011” Report INPO 11 -005, Institute of Nuclear Power Operations, Atlanta, GA, USA Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 2

Context In SFPs Zircaloy fuel clad = only barrier Fukushima The vulnerability of the spent nuclear fuel pools (SFPs) Post Fukushima French DENOPI Project “Status Report on Spent Fuel Pools under Loss-of-Cooling and Loss-of- Coolant Accident Conditions”, NEA Final Report, CSNI/R(2015)2, May 2015 Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 3

State of the art, Zircaloy-4 in air at 850°C Nitrogen effect on mass and kinetic rate M. Lassere et al, “Study of Zircaloy -4 cladding air degradation at high temperature” Proceedings of the 2013 21st International Conference on Nuclear Engineering ICONE21 July 29- August 2, 2013, Chengdu, China Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 4

State of the art, Zircaloy-4 in air/steam at 900°C Formation of Zirconium nitride (gold colour) Steinbruck et al. Journal of Nuclear Materials 392 (2009) 531 – 544 Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 5

State of the art, Zircaloy-4 pre-oxidized in air at 850°C Normal operation in High temperature reactor oxidation → oxide scale formed → new oxide scale formed As received Pre-oxidized After oxidation in air at 850°C Protective effect of pre-oxide Kasperski et al, Oxidation of Metals January 2017 pp 1 – 13 Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 6

Aims of the study Normal operation in High temperature reactor oxidation → oxide scale formed → new oxide scale formed As received Pre-oxidized After oxidation in air at 850°C Research focus : Oxidation of Zircaloy-4 pre-oxizided in nitrogen-oxygen-steam mixtures at HT Aims of the study: → Understanding the corrosion mechanism → Kinetic analysis for modeling the kinetic rate as a function of the temperature and partial pressures P(O 2 ), P(N 2 ), P(H 2 O) Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 7

Experimental protocol Material Zircaloy-4 : 15*10*0,5 mm Zy-4 Alloy (wt.%) • Pre-oxidation: 250 days O 2 + H 2 O (15% vol.) at 425°C • 1,32 - 1,35 Sn 0,21 • Pre-oxide thickness ≈ 30µm Fe 0,123 - 0,129 O [ H] ≈ 280 ppm • 0,11 Cr Pre-oxide Metal Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 8

Experimental protocol measuring device Apparatus flowing mixture exit furnace Thermogravimetric analysis sample flowing 200 900 mixture Isothermal and isobaric conditions entrance 180 800 160 700 140 600 Experimental conditions: Temperature ( C) Δm /S (g.m -2 ) 120 500 Flow rate 6L/h 100 400 Temperature 850°C 80 300 Pressure P(O 2 ) = 80 hPa 60 P(N 2 ) = 320 hPa 200 40 P(H 2 O) = 50 hPa 100 20 Carrier gas He (balance) 0 0 Rate 10°C/min 0 5000 10000 15000 20000 Time (s) Time 1-10 hours Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 9

Results Thermogravimetric analysis, effect of time 0,035 900 0,035 0,035 900 900 800 800 800 Temperature 0,03 Temperature 0,03 0,03 Temperature 2h05 700 700 700 2h05 isothermal 0,025 0,025 0,025 d( Δm /S)/dt (g.m -2 .s -1 ) d( Δm /S)/dt (g.m -2 .s -1 ) d( Δm /S)/dt (g.m -2 .s -1 ) 4h15 isothermal 600 600 600 Temperature ( C) Temperature ( C) Temperature ( C) 2h05 isothermal 4h15 6h15 isothermal 0,02 0,02 0,02 isothermal 500 500 500 isothermal 400 400 400 0,015 0,015 0,015 300 300 300 0,01 0,01 0,01 200 200 200 0,005 0,005 0,005 100 100 100 0 0 0 0 0 0 0 0 0 5000 5000 5000 10000 10000 10000 15000 15000 15000 20000 20000 20000 25000 25000 25000 30000 30000 30000 Time(s) Time(s) Time(s) Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 10

Results Thermogravimetric analysis, effect of time 0,035 900 0,035 0,035 900 900 800 800 800 Temperature Mixed 0,03 Temperature 0,03 0,03 Temperature Non region: 2h05 700 700 700 protective protective 2h05 isothermal 0,025 0,025 0,025 d( Δm /S)/dt (g.m -2 .s -1 ) d( Δm /S)/dt (g.m -2 .s -1 ) d( Δm /S)/dt (g.m -2 .s -1 ) region 4h15 isothermal & 600 600 600 Temperature ( C) Temperature ( C) Temperature ( C) 2h05 isothermal non 4h15 6h15 isothermal 0,02 0,02 0,02 isothermal 500 500 500 protective isothermal 400 400 400 0,015 0,015 0,015 300 300 300 0,01 0,01 0,01 200 200 200 0,005 0,005 0,005 100 100 100 0 0 0 0 0 0 0 0 0 5000 5000 5000 10000 10000 10000 15000 15000 15000 20000 20000 20000 25000 25000 25000 30000 30000 30000 Time(s) Time(s) Time(s) Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 10

Results Thermogravimetric analysis, effect of time Mixed region: two co-existing regions protective & non protective Optical microscopy of a mixed stage sample Protective ZrN Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 11

Non protective Results Thermogravimetric analysis, effect of time Mixed region: two co-existing regions protective & non protective Optical microscopy of a mixed stage sample Protective ZrN High temperature ZrN oxide Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 11

N 2 (g), O 2 (g), H 2 O (g) Model Mechanism ZrO 2 (porous) pre-oxide Scheme of the degradation process, ZrO 2 (porous) high temperature catalyzed by nitrogen R.1 ZrN ZrO 2 (dense) R.3 R.2 α -Zr(O) H } ZrN + O 2 (g) = ZrO 2 + N i R.1 Oxidation of ZrN PBR ZrO2/ZrN = 1,47 ZrN + 2 H 2 O(g) = ZrO 2 + N i + 2 H 2 → Volume increase ZrO x + N i ↔ ZrN + xO i R.2 Nitridation of metal PBR ZrN/Zr =1,03 → no volume change (2-x)O i + ZrO x ↔ ZrO 2 R.3 Oxidation of metal PBR ZrO2/Zr =1,56 → volume increase Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 12

Model Assumptions validated thanks to experimental Kinetic expression results Does the corrosion proceed in a steady-state? Does the corrosion proceed in a steady-state? • • • • Is the assumption of the rate-determining step Is the assumption of the rate-determining step confirmed? confirmed? • What is the influence of oxygen and nitrogen partial pressures on the kinetic rate and how can it be explained? 𝑒(Δ𝑛 𝑇 ) = 𝐶 0 × Φ 𝑈, 𝑄 × 𝑇 𝑛 𝑢 𝑒𝑢 Φ : areic growth reactivity mol.m -2 .s -1 S m : related to the extent of reaction zone where the rate determining step of growth takes place m 2 . mol -1 n 0 : number of mole of Zy4 𝑜 𝑝 ×𝑁 𝑃 2 S : total surface aera of the specimen 𝐶 0 = Coefficient of proportionality g.m -2 M(O 2 ): molar mass of oxygen 𝑇 Δm : change in mass M. Pijolat and M. Soustelle, Thermochimica Acta, 2008, vol. 478, pp. 34-40 Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 13

𝑒(Δ𝑛 𝑇 ) = 𝐶 0 × Φ 𝑈, 𝑄 × 𝑇 𝑛 𝑢 𝑒𝑢 Model Kinetic, reactivity function Φ Variations of Φ with oxygen, steam and nitrogen partial pressures → jumps method Initial pressure 8% O 2 – 32% N 2 – 5% H 2 O, 850°C 0,035 𝑒 ∆𝑛 0,03 Pressure jump P(1) 11% O 2 𝑇 = 𝐶 0 × 𝛸(𝑄(1)) × 𝑇 𝑛 (𝑢) 0,025 𝑒𝑢 d( Δm /S)/dt (g.m -2 .s -1 ) 𝑏𝑔𝑢𝑓𝑠 𝑒 ∆𝑛 𝐶 0 × 𝛸(𝑄(0)) × 𝑇 𝑛 (𝑢) 0,02 𝑇 𝑒𝑢 𝑐𝑓𝑔𝑝𝑠𝑓 0,015 P(0) 8% O 2 = 𝛸 𝑄(1) P(2) 5% O 2 𝛸 𝑄(0) 0,01 0,005 0 0 5000 10000 15000 20000 25000 Time (s) Variations of Φ divided by F (P(0)) is obtained by scanning a range of given pressures Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 14

1,4 1,2 Model Φ (PH 2 O)/ Φ (P0) = 50 hPa Kinetic, reactivity function Φ 1 0,8 Jumps method, 850°C 0,6 0,4 2 Φ varies with P (H 2 O) Φ varies with P(O 2 ) 1,8 0,2 1,6 0 0 20 40 60 80 100 Φ (PO 2 )/ Φ (P0) = 80 hPa 1,4 PH 2 O (hPa) 1,4 1,2 1,2 1 Φ (PN 2 )/ Φ (P0) = 320 hPa 0,8 1 0,6 0,8 0,4 0,6 0,2 0,4 Φ independent of P(N 2 ) 0 0 50 100 150 200 250 0,2 PO 2 (hPa) 0 0 100 200 300 400 500 600 PN 2 (hPa) Institut Mines-Télécom École des Mines de Saint-Étienne 24/07/2017 15