Corrosion and Deuterium Pickup in Zr-2.5Nb: Twenty Years of In-Reactor Testing at the OECD Halden Boiling Water Reactor H.M. Nordin, R. Szőke 19 th International Symposium on Zirconium in the Nuclear Industry May 19 - 23, 2019, Manchester, UK. UNRESTRICTED / ILLIMITÉ -1-
Outline 1. Introduction • CANDU Reactor • Pressure Tube • Pressure Tube Fabrication • Corrosion and Deuterium Ingress 2. Experiment • Materials • Test Loop 3. Results 4. Summary UNRESTRICTED / ILLIMITÉ -2-
CANDU Reactor UNRESTRICTED / ILLIMITÉ -3-
CANDU Reactor Fuel Channel Fast neutron flux Temperature Flow [D] Feeder pipe Pressure Calandria tube tube • Temperature: 250 ° C – 310 ° C • Pressure: 10 MPa UNRESTRICTED / ILLIMITÉ -4- • Flux: 0 – 3.5x10 17 n/m 2 s
Pressure Tube Fabrication Zirconium Feedstock 1960 – 1980’s 1990’s Four vacuum arc melts (Quad Melt) Two vacuum arc melts (Double Melt) ingot ingot Press forge at 1015°C Press forge at 1015°C 1980’s Rotary forge at 815°C Rotary forge at 815°C 1970’s Heat to 1015°C and β -Quench Heat to 1015°C and β -Quench Extrude at 815°C Extrude at 815°C Cold draw 27% Cold draw 27% Steam Autoclave at 400C for 24 hours UNRESTRICTED / ILLIMITÉ -5-
Pressure Tubes Historically, extensive research programs have been under • taken to fabricate improved pressure tubes: ~ 1960’s started investigating Zr -2.5Nb – improved • mechanical properties and corrosion ~ 1980’s introduced β -quenching – improve strength • ~ 1990’s introduced quad melting and lowered initial • hydrogen content – reduce Cl and F for improved fracture toughness ~ 2000’s increased Fe concentration to 1080 ppm and • reduced C concentration to 80 ppm – improve corrosion, deformation and fracture toughness UNRESTRICTED / ILLIMITÉ -6-
Pressure Tubes The extrusion process is known to result in microstructure and • texture variations along the pressure tube which in turn affects deformation, mechanical properties, oxidation and deuterium pickup. UNRESTRICTED / ILLIMITÉ -7-
Corrosion and D Ingress Corrosion and the associated deuterium ingress may be life • limiting degradation mechanisms in Zr-2.5Nb pressure tubes. Corrosion and deuterium uptake in pressure tubes can be • influenced by: - environmental factors (flux, temperature or pH). - material properties (microstructure, microchemistry, texture and state of the β -phase) which are influenced by fabrication processes. To support pressure tube improvement programs, in-reactor • corrosion and deuterium ingress studies were conducted at the OECD Halden Boiling Water Reactor over a 20 year period. Effect of environment and fabrication variables investigated: • - ingot melting (double melted or quadruple melted) non- -quenched versus -quenched - cold work (12% or 27%) - pH - In-flux versus out-flux UNRESTRICTED / ILLIMITÉ -8- -
Materials Corrosion test coupons were machined from twenty-one different • Zr-2.5Nb pressure tubes. - variations in fabrication history (e.g. β -quenched) and minor element concentration, illustrating the development history of pressure tube fabrication processes. The machined coupons tested had different surface finishes: • Pickled + Pre-filmed Pickled 400°C steam for 24 hours HF, HNO 3 and H 2 SO 4 solution Machined Machined + Pre-filmed 400°C steam for 24 hours Note: Many variables! Machined coupons ~ 10 mm wide, 30 mm long and 1 mm thick UNRESTRICTED / ILLIMITÉ -9-
Schematic Diagram of In-Flux Test Loop 9 • Operates under CANDU HTS conditions (pH a 10.2-10.8) • Two independently heated in-flux test channels, three out-flux autoclaves Temperature range: 250 ° C – 335 ° C • Neutron flux: 3-5x10 13 n/cm 2 /s • • Ratio of thermal flux\fast flux: 2:1 UNRESTRICTED / ILLIMITÉ -10-
Oxygen and Deuterium Pickup • Oxidation kinetics were linear after 150 days. UNRESTRICTED / ILLIMITÉ -11-
Effect of Flux on Oxide Growth Rate • The in-flux oxide growth rate tends to be greater than the out-flux oxide growth rate (P-value = 0.0004). • Enhancement of in-flux oxide growth rate dependent on initial microstructure and surface finish. UNRESTRICTED / ILLIMITÉ -12-
Effect of Flux on D Pickup Rate • No effect of flux on deuterium pickup (P-value = 0.96). UNRESTRICTED / ILLIMITÉ -13-
Ingot Production • Oxide growth and deuterium pickup rate similar between Kroll and electrolytic. • Larger extruded tube front-back differences in Kroll ingots. UNRESTRICTED / ILLIMITÉ -14-
Effect of Ingot Melting • Quad melting result in lower deuterium ingress rates. UNRESTRICTED / ILLIMITÉ -15-
Effect of β -Quenching • β -quenching results in lower deuterium ingress rate. UNRESTRICTED / ILLIMITÉ -16-
Effect of β -Quenching Non- β -Quenched β -Quenched • More uniform grain structure in β -quenched material. • Curly nature of non- β -quenched grains may cause β -Zr filaments to be oriented perpendicular to free surface leading to faster oxidation along these filaments. UNRESTRICTED / ILLIMITÉ -17-
Comparison of Fabrication Methods 1990 - 2000 1980 - 1990 2000 - 2005 1960 - 1980 • Fabrication modifications reduced oxide growth rate. UNRESTRICTED / ILLIMITÉ -18-
Comparison of Fabrication Methods 1990 - 2000 1980 - 1990 2000 - 2005 1960 - 1980 • Deuterium ingress reduced by a factor of 5. UNRESTRICTED / ILLIMITÉ -19-
Discussion A large number of confounding variables in tests making • comparison of data and interpretation of the results difficult. The synergistic interactions between fabrication processes, • microstructure, texture, the state of the β -phase and the resulting pressure tube properties are difficult to assess. With the tube improvements, the net total concentration of • hydrogen isotopes has been significantly reduced making Zr-2.5Nb pressure tubes much less susceptible to the deleterious effects of hydrides on fracture properties. UNRESTRICTED / ILLIMITÉ -20-
Conclusions Research programs undertaken to improve pressure tube • properties were successful in reducing corrosion and deuterium ingress. Deuterium ingress reduced by a factor of 5. • This reduction should make Zr-2.5Nb pressure tubes much • less susceptible to the deleterious effects of hydrides on fracture properties. UNRESTRICTED / ILLIMITÉ -21-
Acknowledgements • CNL’s (formerly AECL’s) in -reactor corrosion test program lasted for approximately 20 years. • The contributions of many individuals need to be acknowledged: • From AECL/CNL (including former employees): V. F. Urbanic, R.A. Ploc, G. McDougall, I. J. Muir, G.A. McRae, A. A. Bahurmuz, A.J. Elliott, A. Shaddick, S. Bergin, V. Hilton, C. Davis, M. Seguin, D. Wilkins, R. MacLeod, A. Britton, R. Stuthers, P. Sullivan, D. Irvine, R. Beier, J. Hamel, Y. Andrews and M. Godin. • From the Halden Reactor Project (including former employees): M. A. McGrath, K-L Moum, I. Thoresen, H. Devold, H. Valseth, H. Thoresen, C. Helsengreen, M. Lundgren, K-W. Eriksen, C. Vitanza. UNRESTRICTED / ILLIMITÉ -22-
Heidi.Nordin@cnl.ca Reka.szoke@ife.no UNRESTRICTED / ILLIMITÉ -23-
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