1. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 1 Oxidation of Zircaloy in prototypic air-steam mixtures M. Steinbrück, P. Severloh, U. Stegmaier, T. Ziegler Institute for Materials Research I Forschungszentrum Karlsruhe Postfach 3640, 76021 Karlsruhe, Germany

2. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 2 Motivation Scenarios for air ingress: Residual fuel elements Breach in the primary circuit RPV rupture Open RPV lid 1) Late phase after failure of RPV2) Mid loop operation 3)… Consequences: Strong exothermal reaction ( R H air >> R H steam ) Less cooling effect Detrimental effect of nitrogen on oxide scales Higher oxygen activity in the core Temperature escalation Degradation Oxidation of fuel FP release and transport What are prototypical atmospheres? 1) First steam, then air (sequential) 2) Mixed air-steam atmospheres For both no data are available so far

3. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 3 Motivation Oxygen Parabolic oxidation kinetics 1200 °C

4. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 4 Motivation Oxygen Nitrogen Parabolic oxidation kinetics 1200 °C

5. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 5 Motivation Oxygen Nitrogen Air Parabolic oxidation kinetics Parabolic reaction kinetics ~ Linear oxidation kinetics 1200 °C Oxidation rate in air is much higher than in oxygen or steam

6. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 6 Oxidation of Zircaloy-4 in mixed air-steam atmospheres

7. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 7 BOX Rig for oxidation experiments under controlled atmosphere

8. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 8 BOX Rig for oxidation experiments under controlled atmosphere Furnace Controlled Evaporator Mixer Controller for gas and water Heated pipe to MS Mass spectrometer Air lock

9. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 9 BOX Rig: Sample holder with Zry-4 cladding segment ZrO 2 rod Zry-4 cladding segment Heated flange

10. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 10 Test matrix 1 hour or 10 min, isotherm 3 temperatures: 800, 900, 1000, 1100, 1200, 1300, 1400, 1500 °C 9 compositions: air/steam mixtures with 0, 2.7, 5, 10, 30, 50, 70, 90, 100 vol.% air 81 tests

11. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 11 Test conduct and MS results of the series at 1500 °C Input rates: Rates measured by MS:

12. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 12 Metallographic post-test appearance of specimens after 1 hour isothermal oxidation at 800 °C Air0.9 air / 0.1 H 2 O0.7 air / 0.3 H 2 O0.5 air / 0.5 H 2 O0.3 air / 0.7 H 2 O 0.1 air / 0.9 H 2 O0.05 air / 0.95 H 2 O0.03 air / 0.97 H 2 OH2OH2O 800 °C 1 h

13. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 13 Air0.9 air / 0.1 H 2 O0.7 air / 0.3 H 2 O0.5 air / 0.5 H 2 O0.3 air / 0.7 H 2 O 0.1 air / 0.9 H 2 O0.05 air / 0.95 H 2 O0.03 air / 0.97 H 2 OH2OH2O 900 °C 1 h Metallographic post-test appearance of specimens after 1 hour isothermal oxidation at 900 °C

14. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 14 Air0.9 air / 0.1 H 2 O0.7 air / 0.3 H 2 O0.5 air / 0.5 H 2 O0.3 air / 0.7 H 2 O 0.1 air / 0.9 H 2 O0.05 air / 0.95 H 2 O0.03 air / 0.97 H 2 OH2OH2O 1000 °C 1 h Metallographic post-test appearance of specimens after 1 hour isothermal oxidation at 1000 °C

15. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 15 1300 °C 10 min Air0.9 air / 0.1 H 2 O0.7 air / 0.3 H 2 O0.5 air / 0.5 H 2 O0.3 air / 0.7 H 2 O 0.1 air / 0.9 H 2 O0.05 air / 0.95 H 2 O0.03 air / 0.97 H 2 OH2OH2O Metallographic post-test appearance of specimens after 10 min isothermal oxidation at 1300 °C

16. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 16 1300 °C, 10 min, 0.3 air/ 0.7 H 2 O Metallographic post-test appearance of specimens after 10 min isothermal oxidation at 1300 °C in 30% air + 70% steam

17. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 17 10 min in air 1200°C1300°C 1400°C 1500°C Metallographic post-test appearance of specimens after 10 min isothermal oxidation various temperatures in air

18. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 18 10 min in steam 1200°C1300°C 1400°C 1500°C Metallographic post-test appearance of specimens after 10 min isothermal oxidation various temperatures in steam

19. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 19 Oxidation of Zircaloy-4 in mixed air-steam atmospheres First influence of air in mixtures on oxidation behaviour at 900 °C (locally) Increasing degradation of oxide scale with temperature and air concentration (local layer) Reversal at 1500 °C: almost no impairment of the oxide scales by air 1 h 10 min

20. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 20 Sequential oxidation of Zircaloy-4 first in oxygen and then air or nitrogen

21. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 21 Test rig with thermal balance and mass spectrometer

22. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 22 Comparison between oxidation in O 2, N 2, and air Oxidation in air is not the sum of the reaction in oxygen and nitrogen!

23. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 23 Pre-oxidation in oxygen suppresses the influence of nitrogen during subsequent oxidation in air Comparison between oxidation in O 2, N 2, and air: Influence of pre-oxidation

24. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 24 Pre-oxidation in oxygen causes an increase of the reaction rate in nitrogen Comparison between oxidation in O 2, N 2, and air: Influence of pre-oxidation

25. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 25 Significant higher oxidation rates at 1000 °C in comparison to 1100 °C! Comparison between oxidation in O 2, N 2, and air: Influence of breakaway at 1000 °C

26. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 26 Comparison between oxidation in O 2, N 2, and air: Post-test appearance of specimens

27. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 27 1100 °C, air 1100 °C, O 2 1100 °C, N 2 1100 °C, PO, air 1100 °C, PO, N 2 Comparison between oxidation in O 2, N 2, and air: Metallographic PT examination With pre-oxidation (PO)

28. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 28 Little pre-oxidation in oxygen (steam) causes a significant reduction of the detrimental effect of subsequent oxidation in air Isothermal tests at 1200 °C in air in dependence on the degree of pre-oxidation

29. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 29 Oxidation rates in oxygen and in air after significant pre-oxidation are almost identical Isothermal tests in air at 1200 °C in dependence on the degree of pre-oxidation

30. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 30 1200 °C No PO Air 1200 °C 3 s PO in O 2 Air 1200 °C 10 min PO in O 2 Air 1200 °C 10 s PO in O 2 Air Isothermal tests in air in dependence on the degree of pre-oxidation: Post-test metallography

31. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 31 Reaction rates in nitrogen are higher after pre-oxidation in oxygen, but seem to be independent on the degree of pre-oxidation Isothermal tests in nitrogen at 1200 °C in dependence on the degree of pre-oxidation With pre-oxidation Without pre-oxidation

32. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 32 1200 °C No PO N 2 1200 °C 3 s PO in O 2 N 2 1200 °C 10 min PO in O 2 N 2 1200 °C 10 s PO in O 2 N 2 Isothermal tests in nitrogen at 1200 °C in dependence on the degree of pre-oxidation

33. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 33 Oxidation of zirconium without pre-oxidation in: Oxygen:parabolic kinetics Nitrogen:parabolic kinetics (very slow) Air:linear kinetics (very fast, nitride formation at metal/oxide phase boundary) Oxidation of zirconium with pre-oxidation in: Nitrogen:linear kinetics, nitride formation at external oxide surface Air:parabolic kinetics like in oxygen (as long as oxide scale is dense) Nitride formation only in the absence of oxygen and in the presence of oxide! Sequential oxidation of Zircaloy-4 in oxygen and air/nitrogen

34. Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft M. Steinbrück, FZK/IMF-I 11th Int. QUENCH Workshop, Karlsruhe, October 25-27, 2005 34 Future work Experiments on sequential oxidation in various atmospheres at 800, 1000, 1200, and 1400 °C; test of new specimens avoiding external+internal oxidation (diploma thesis) Kinetic tests on the oxidation of Zircaloy in mixed air-steam atmospheres Tests on oxidation of pre-existing external nitride scales in steam Further experiments necessary for model development