B. KURSTEN, SCK • CEN (Mol, BELGIUM)

1. Corrosion Evaluation of Metallic Materials for Long-Lived HLW/Spent Fuel Disposal Containers – review of 15-20 years of research B. KURSTEN, SCK•CEN (Mol, BELGIUM) EURADWASTE ’04 (6th EC Conference on the Management and Disposal of Radioactive Waste) 29 March – 1 April 2004, Luxembourg

2. 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, 30th March 2004 2 / 15

3. 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, 30th March 2004 3 / 15

4. Background • Deep underground disposalin 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 varies from 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, 30th March 2004 4 / 15

5. Geochemical Composition of Potential Disposal Environments within various EU-Countries EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 5 / 15

6. Materials Selection of Candidate Container Materials within various EU-Countries EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 6 / 15

7. Parameters, techniques and modes of corrosion EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 7 / 15

8. Scientific Approach Screening Studies • Laboratory Experiments • immersion • electrochemical • radiochemical • In Situ Experiments Detailed Studies • Parametric Studies • T • pH • Conc. aggressive ions •  Demonstration Tests 1-1 scale welding procedure Modelling Natural analogues EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 8 / 15

9. Main Results (1/5) Salt Environment • Carbon steel(TStE 355) • corrodes actively in MgCl2- and NaCl-brines • vCORR (µm/y) • influence of pH • no significant effect on vCORR in MgCl2 (pH=3-7) and in NaCl (pH=1-5) • vCORR decreased in NaCl from 50 µm/y (pH=1) to 26 µm/y (pH=10) • influence B(OH)4-, H2O2, ClO-, Fe3+(salt impurity, radiolytic prods., corr. prod.) • 90°C : 5 µm/y  236 µm/y (NaCl) • 170°C : 70 µm/y  120 µm/y (MgCl2) • effect of welding (in MgCl2) • 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 • MgCl2 (150°C) : 47 µm/y (no )  72 µm/y (10 Gy/h) • Ti-alloy (Ti99.8-Pd) • vCORR < 1 µm/y • not susceptible to pitting or SCC • no influence of , H2O2 and ClO- EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 9 / 15

10. 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) 2,700 - 7,200 mg/L (France) • production of H2: enhanced transport pathways for radionuclides • Ni- and Ti-alloys • vCORR < 0.1 µm/y • resistant to pitting corr.: T = 140°C; [Cl-] = 50,000 mg/L; [S2O32-] = 200 mg/L • susceptible to crevice corr.: oxic cond.; T = 140°C; [Cl-] > 20,000 mg/L • Carbon steel • vCORR • Stainless steels • vCORR < 0.1 µm/y • resistant to pitting under ‘normal’ repository cond. ([Cl-] < 100 mg/L; [S2O32-] = 17 mg/L) • T=140°C, oxic cond., [Cl-]>10,000 mg/L : pitting (ECORR>ENP) • T=140°C, anoxic cond., [Cl-]=50,000 mg/L: no pitting (ECORR<<ENP) • Effect of T: drastic shift of ENP in the active direction (ENP << ECORR) pit depth and pit density increases with increasing T EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 10 / 15

11. Main Results (3/5) Granitic Environment (Spain) • Carbon steel(TStE 355) • vCORR = 6 µm/y (90°C); 14 µm/y (120°C) • susceptible to pitting at 120°C (dmax = 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, 30th March 2004 11 / 15

12. Main Results (4/5) Granitic Environment (Sweden/Finland) • Lifetime predictions for copper canisters EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 12 / 15

13. Main Results (5/5) Cementitious Environment • Large amounts of concrete present in repositories (structural materials) • Carbon steel(BS4360) • vCORR (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) • vCORR (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 S2O32- adding 3,360 mg/L S2O32- to 17,750 mg/L Cl- led to SCC (80°C) EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 13 / 15

14. 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, 30th March 2004 14 / 15

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 EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 15 / 15