Enhanced Hydrogen Uptake und Reaction Kinetics During Oxidation of Zircaloy-4 in Nitrogen Containing Steam Atmospheres M. Grosse, S. Pulvermacher, M. Steinbrück (KIT – IAM) B. Schillinger (TU Munich) KIT / Institut für Angewandte Materialien 19th International Symposium on Zirconium in the Nuclear Industry 1/21 www.kit.edu Manchester UK, May 19-23 2019
Introduction Why the reaction of Zircaloy in steam-nitrogen mixed atmospheres is an 𝑎𝑠𝑃 2 issue? ➢ Air ingress during SFP accidents and after vessel failure in severe reactor accidents. ➢ It is well known that the presence of nitrogen can accelerate the reaction of zirconium alloys with oxygen or steam. Basic reactions, strongly simplified : 800 N2 conc., % with oxygen 𝑎𝑠 + 𝑃 2 → 𝑎𝑠𝑃 2 0 0.1 0.2 with steam 𝑎𝑠 + 2𝐼 2 𝑃 → 𝑎𝑠𝑃 2 + 2𝐼 2 0.5 600 0.7 with nitrogen 2𝑎𝑠 + 𝑂 2 → 2𝑎𝑠𝑂 1 H 2 O 2 + 5 m, g/m² N 2 Re-oxidation of nitrides : 10 400 50 70 ZrN + O 2 → ZrO 2 + N 80 90 100 200 H 2 O Mass gain of Zircaloy-4 oxidized at 800°C N 2 0 in steam-nitrogen mixtures, 0 5000 10000 15000 20000 (Steinbrück et al., NUMAT 2014) time, s 19th International Symposium on Zirconium in the Nuclear Industry 2/21 Manchester UK, May 19-23 2019
Introduction If ZrN precipitate, cracks are formed and 𝑎𝑠𝑃 2 the ZrO 2 layer is not longer protective against further oxidation. 𝒂𝒔𝑶 The behavior of the reaction of zirconium with oxygen, steam and nitrogen was investigated in a large number of experiments. 𝒂𝒔 Modeling in severe accident codes is not yet satisfying. The results of tests using different experimental setups are contradictory. One reason for the differences are different gas flow rates applied in the tests. A model describing the influence of the gas flow rates on the reaction behavior was developed at KIT. 19th International Symposium on Zirconium in the Nuclear Industry 3/21 Manchester UK, May 19-23 2019
Flow rate model [M. Grosse et al. ICAPP 2016] Basic reactions with steam if an oxide layer is already formed + 2+ )(𝑝𝑦) = 𝑎𝑠𝑃 2 ox + 2𝐼 𝑏𝑒 𝐼 2 O g + (Zr𝑃 + 𝑊 𝑃 2+ + 2𝑓 − ) 𝑃 𝑃 𝑝𝑦 + 𝑎𝑠 𝑛 = (𝑎𝑠𝑃 + 𝑊 𝑃 Wagner, C., Die Löslichkeit von Wasserdampf in ZrO 2 -Y 2 O 3 -Mischkristallen, Ber. Bunsen-Ges. Phy. Chem., Vol. 72, 1968, pp. 778-781 19th International Symposium on Zirconium in the Nuclear Industry 4/21 Manchester UK, May 19-23 2019
Flow rate model [M. Grosse et al. ICAPP 2016] Basic reactions with nitrogen if no oxygen or steam is available 2+ + 2𝑓 − (𝑝𝑦) = 2𝑎𝑠𝑃 2 (𝑝𝑦) + 2ZrN (ox) 𝑂 2 () + 4 𝑎𝑠𝑃 + 𝑊 𝑃 2+ + 2𝑓 − ) 𝑃 𝑃 𝑝𝑦 + 𝑎𝑠 𝑛 = (𝑎𝑠𝑃 + 𝑊 𝑃 19th International Symposium on Zirconium in the Nuclear Industry 5/21 Manchester UK, May 19-23 2019
Flow rate model [M. Grosse et al. ICAPP 2016] 2+ + 2𝑓 − (𝑝𝑦) = 2𝑎𝑠𝑃 2 (𝑝𝑦) + 2ZrN (ox) 𝑂 2 () + 4 𝑎𝑠𝑃 + 𝑊 𝑃 4 for the reaction of N 2 with Zr(O) Experimental evidence: reaction rate K ~ x O 0.9 900°C 0.8 1000°C 1100°C 0.7 1200°C 1300°C 1/4 0.6 -1 ) -2 s 0.5 ( , gm 0.4 0.3 0.2 0.1 0.0 1 2 3 4 5 6 7 Oxygen concentration, wt% 19th International Symposium on Zirconium in the Nuclear Industry 6/21 Manchester UK, May 19-23 2019
ሶ ሶ ሶ ሶ ሶ Flow rate model [M. Grosse et al. ICAPP 2016] Do we know the oxygen vacancy flux to the surface? 𝐿 𝑜𝑝𝑦 Yes, we know! 𝑜 𝑊 2+ = ሶ 𝑜 𝑝𝑦𝑧𝑓𝑜,𝑠𝑓𝑏𝑑𝑢 = 2 𝑢 ∗ 𝑃 𝐿 𝑜𝑝𝑦 𝑜 𝑃2 𝑜 𝑂 2 = 2 𝑢 ∗ − 2 − ሶ 𝑜 𝐼 2 𝑃 /4 How many nitrogen reacts? 𝑙 𝑜 𝑃 𝑜 𝑃 2 2 𝑢 ∗ − 2 + ሶ 𝑜 𝐼 2 𝑃 Molar concentration of 𝑜 𝑂 = න 𝑒𝑢 + 𝑜 0 𝑂 𝑜 𝑃 2 nitrogen taken up: 2 2 + ሶ 𝑜 𝐼 2 𝑃 𝑢 19th International Symposium on Zirconium in the Nuclear Industry 7/21 Manchester UK, May 19-23 2019
ሶ ሶ ሶ Flow rate model [M. Grosse et al. ICAPP 2016] ❑ Number of cracks can be assumed to be proportional to the number of ZrN precipitates. ❑ No hints that the size of the ZrN precipitates depend on time or temperature. ❑ Therefore, the fraction of cracks should be proportional to the nitrogen concentratiion in the oxide. 𝐿 𝑜 𝑃 𝑜 𝑃 2 2 𝑢 ∗ − 2 + ሶ 𝑜 𝐼 2 𝑃 𝑔 𝑑𝑠𝑏𝑑𝑙𝑡 = 𝐵 න 𝑒𝑢 + 𝑜 𝑂 0 𝑜 𝑃 2 2 2 + ሶ 𝑜 𝐼 2 𝑃 𝑢 ❑ The reaction rate is weighted sum of the reaction rate of positions with cracked and undisturbed oxide. 𝐿 𝑜 𝑃 𝑜 𝑎𝑠 = 𝑔 𝑗𝑜𝑢𝑓𝑠𝑔𝑏𝑑𝑓 𝑑𝑠𝑏𝑑𝑙𝑓𝑒 𝐿 𝑜 𝑎𝑠 + 1 − 𝑔 𝑗𝑜𝑢𝑓𝑠𝑔𝑏𝑑𝑓 𝑑𝑠𝑏𝑑𝑙𝑓𝑒 2 𝑢 ∗ 19th International Symposium on Zirconium in the Nuclear Industry 8/21 Manchester UK, May 19-23 2019
ሶ ሶ Flow rate model [M. Grosse et al. ICAPP 2016] 𝐿 𝑜𝑝𝑦 𝑜 𝑃2 Determining parameter: quantity 𝑜 𝑂 2 = 2 𝑢 ∗ − 2 − ሶ 𝑜 𝐼 2 𝑃 /4 of steam and oxygen starvation 2 x 2 kinds of starvation • total starvation (starvation of all gases reacting): The lower the oxygen, steam and nitrogen flow rate, the lower is the reaction rate • partial starvation (starvation only of oxygen and stream): The lower the oxygen and steam flux, the higher is the reaction rate. • global starvation : starvation at the whole material • local starvation : starvation only at locations with increased reaction rate (e.g. cracks) or if oxygen and steam was already consumed by the material located before in flow direction. 19th International Symposium on Zirconium in the Nuclear Industry 9/21 Manchester UK, May 19-23 2019
Experimental validation of the model 150 SF1 The lower the oxygen and 2 SF2 m, g/m steam flow rate the earlier is the SF4 SF6 transition in the reaction kinetics 100 SF8 and the higher is the reaction SF10 rate after the transition. 50 0 0 500 1000 1500 2000 2500 3000 Time, s INFLUENCE OF THE STEAM AND OXYGEN FLOW RATE ON THE REACTION OF ZIRCONIUM IN STEAM/NITROGEN AND OXYGEN/NITROGEN ATMOSPHERES, (M. Grosse et al., ICAPP 2016) 19th International Symposium on Zirconium in the Nuclear Industry 10/21 Manchester UK, May 19-23 2019
Neutron radiography Which are the consequences for the hydrogen uptake and why can we study these processes by in-situ neutron radiography? Crack formation in the zirconium oxide layer is connected with enhanced hydrogen uptake by the metallic zirconium. Hydrogen concentration is a marker for oxide cracks. 1600 Zircaloy-4, 1000°C 1400 1200 c H , wppm 1000 800 600 400 200 M. Grosse et al., 0 Nucl. Instr. & Meth. A 651 (2011). 253 0 3600 7200 10800 14400 18000 oxidation time, s 19th International Symposium on Zirconium in the Nuclear Industry 11/21 Manchester UK, May 19-23 2019
Basis Neutron radiography Intensity measured at the detector pixel x,y: ( ) = = − total I ( x , y ) T ( x , y ) I ( x , y ) I ( x , y ) exp s 0 0 Total macroscopic neutron cross section: = i i ( x , y , t ) N ( x , y , t ) total total i − = + + + Zry 4 H H N N O O ( x , y ) N ( x , y , t ) N ( x , y , t ) N ( x , y , t ) total total total total 3,5 3,0 2,5 -1 2,0 total , cm 1,5 900°C 1000°C 1,0 1100°C 1200°C 0,5 1300°C 0,0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 H/Zr atomic ratio 19th International Symposium on Zirconium in the Nuclear Industry 12/21 Manchester UK, May 19-23 2019
Experiments - Antares beam line (FRM-2) Experiments were performed at the ANTARES neutron imaging beamline at the FRM-2 research reactor (TU Munich, Garching, Germany) using the KIT-INRRO furnace Lateral resolution: ~ 0.25 mm (l ~ 225 mm, L/D ≈ 971) exposure time: 29 s readout time: 1.2 s 19th International Symposium on Zirconium in the Nuclear Industry 13/21 Manchester UK, May 19-23 2019
Test matrix of experiments with different flow rates Steam-air-tests 4 temperatures Several tests with 40% air and 800°C 10% steam with 24 l/h and 60 l/h, 900°C respectively, at 800°C 1000°C 2 in-situ with 24 l/h tests, 1100°C respectively, at 800°C and 1000°C 5 flow rates The oxidation times applied 24 l/h depended on temperature. 36 l/h Analysis of the reaction gases 48 l/h 60 l/h by mass spectrometry in the 72 l/h pre-tests, Analysis of the hydrogen 50 % argon absorption by in-situ neutron 10 % steam imaging at Antares (FRM-2) 40 % nitrogen 19th International Symposium on Zirconium in the Nuclear Industry 14/21 Manchester UK, May 19-23 2019
In-situ Neutron imaging – influence of flow rate steam-nitrogen 900°C 24 l/h 36 l/h 48 l/h 72 l/h 19th International Symposium on Zirconium in the Nuclear Industry 15/21 Manchester UK, May 19-23 2019
Results 900°C released hydrogen absorbed hydrogen 19th International Symposium on Zirconium in the Nuclear Industry 16/21 Manchester UK, May 19-23 2019
In-situ Neutron imaging – different atmospheres steam-nitrogen steam steam-air 800°C 1000°C 19th International Symposium on Zirconium in the Nuclear Industry 17/21 Manchester UK, May 19-23 2019
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