Corrosion Evaluation of Metallic Materials for Long-Lived HLW/Spent Fuel Disposal Containers – review of years of research B. KURSTEN, SCKCEN (Mol, BELGIUM) EURADWASTE 04 (6 th EC Conference on the Management and Disposal of Radioactive Waste) 29 March – 1 April 2004, Luxembourg

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Corrosion Evaluation of Metallic Materials for Long- Lived HLW/Spent Fuel Disposal Containers Acknowledgements Co-authors : E. Smailos (FZK.INE, Germany) I. Azkarate (INASMET, Spain) L. Werme (SKB, Sweden) N.R. Smart (Serco Assurance, UK) G. Marx (GNF.IUT, Germany) M.A. Cuñado (ENRESA, Spain) G. Santarini (CEA/SACLAY, France) Funding : National authorities and institutions European Commission

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Corrosion Evaluation of Metallic Materials for Long- Lived HLW/Spent Fuel Disposal Containers Background Geochemical composition of potential disposal environments Materials selection Parameters, techniques, modes of corrosion Main results Salt Clay Granite Cement Conclusions Future R&D Modelling

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Background Deep underground disposal in stable geological formations (e.g. salt, clay, granite) favoured option that is being pursued worldwide to deal with long-lived radioactive waste in a feasible and safe manner disposal concept variesfrom country to country according to type of waste multibarrier concept : a series of natural (geosphere) and engineered (man-made) (waste matrix, metallic container, buffer) barriers that act in concert to isolate radionuclides to retard radionulide release from the waste to the biosphere Metallic container is one of the principal engineered barriers two different approaches : corrosion-allowance concept (corrode uniformly, predictable corrosion rate, thick-walled) corrosion-resistant concept (high corrosion resistance, low corrosion rate, thin-walled, risk for localised attack)

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Geochemical Composition of Potential Disposal Environments within various EU-Countries

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Materials Selection of Candidate Container Materials within various EU-Countries

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Parameters, techniques and modes of corrosion

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Scientific Approach Screening Studies Detailed Studies Laboratory Experiments immersion electrochemical radiochemical In Situ Experiments Parametric Studies T pH Conc. aggressive ions Demonstration Tests 1-1 scale welding procedure ModellingNatural analogues

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Main Results(1/5) Salt Environment Carbon steel (TStE 355) corrodes actively in MgCl 2 - and NaCl-brines v CORR (µm/y) influence of pH no significant effect on v CORR in MgCl 2 (pH=3-7) and in NaCl (pH=1-5) v CORR decreased in NaCl from 50 µm/y (pH=1) to 26 µm/y (pH=10) influence B(OH) 4 -, H 2 O 2, ClO -, Fe 3+ (salt impurity, radiolytic prods., corr. prod.) 90°C : 5 µm/y 236 µm/y (NaCl) 170°C : 70 µm/y 120 µm/y (MgCl 2 ) effect of welding (in MgCl 2 ) reduction of corrosion resistance severe localised attack in weld region and HAZ stress relief treatment improves the corrosion resistance slight sensitivity to SCC and loss of ductility in NaCl very low strain rates : not expected in a real repository influence of NaCl (150°C) : no effect MgCl 2 (150°C) : 47 µm/y (no ) 72 µm/y (10 Gy/h) Ti-alloy (Ti99.8-Pd) v CORR < 1 µm/y not susceptible to pitting or SCC no influence of, H 2 O 2 and ClO -

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Main Results(2/5) Clay Environment Two different approaches low-alloy or unalloyed steels (e.g. France) passive Fe-Ni-Cr-Mo alloys (e.g. Belgium) Parameters risk of localised corr.: [Cl - ] = 100 mg/L (Belgium) 2, ,200 mg/L (France) production of H 2 : enhanced transport pathways for radionuclides Ni- and Ti-alloys v CORR < 0.1 µm/y resistant to pitting corr.: T = 140°C; [Cl - ] = 50,000 mg/L; [S 2 O 3 2- ] = 200 mg/L susceptible to crevice corr.: oxic cond.; T = 140°C; [Cl - ] > 20,000 mg/L Carbon steel v CORR Stainless steels v CORR < 0.1 µm/y resistant to pitting under normal repository cond. ([Cl - ] < 100 mg/L; [S 2 O 3 2- ] = 17 mg/L) T=140°C, oxic cond., [Cl - ]>10,000 mg/L : pitting (E CORR >E NP ) T=140°C, anoxic cond., [Cl - ]=50,000 mg/L: no pitting (E CORR <<E NP ) Effect of T: drastic shift of E NP in the active direction (E NP << E CORR ) pit depth and pit density increases with increasing T

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Main Results(3/5) Granitic Environment (Spain) Carbon steel (TStE 355) v CORR = 6 µm/y (90°C); 14 µm/y (120°C) susceptible to pitting at 120°C (d max = 280µm) parent and weld material are resistant to SCC at 90°C Stainless steel (AISI 316L) resistant to SCC no loss of ductility, but isolated pits could be observed near the fracture zone

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Main Results(4/5) Granitic Environment (Sweden/Finland) Lifetime predictions for copper canisters

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Main Results(5/5) Cementitious Environment Large amounts of concrete present in repositories (structural materials) Carbon steel (BS4360) v CORR (µm/y) pitting is expected to be limited (propagation only a few mm deep) availability of water prior to re-saturation supply of oxygen after re-saturation Stainless steels (AISI 304L, 316L) v CORR (µm/y) resistant to pitting corrosion room T: [Cl - ] = 100,000 mg/L 45°C, 70°C: [Cl - ] = 50,000 mg/L SCC strong synergistic effect of Cl - and S 2 O 3 2- adding 3,360 mg/L S 2 O 3 2- to 17,750 mg/L Cl - led to SCC (80°C)

Conclusions Salt environment CARBON STEEL: corrosion-allowance concept Ti99.8-Pd: corrosion-resistant concept (negligible general corr.; high resistance to loc. corr. and SCC) Clay environment STAINLESS STEELS, Ni- and Ti-ALLOYS: corrosion-resistant concept CARBON STEEL: corrosion-allowance concept Granitic environment COPPER, CARBON STEEL: corrosion-allowance concept Cementitious environment CARBON STEEL: low general corrosion rates STAINLESS STEELS: very low general corrosion rates; resistant to pitting corr. (up to 50,000 mg/L Cl - at 70°C) EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15

EURADWASTE 04, Session VI – Waste Characterisation & Corrosion Studies, 30 th March / 15 Future R&D Microbially influenced corrosion (MIC) Atmospheric corrosion (interim storage) Effect of fabrication aspects and container design on corrosion Long-term metallurgical modifications Influence of radiation effects Influence of nitric acid on the integrity of the container Archeological analogues Modelling