Long‐Term Corrosion of Carbon‐Steel Casing Used in Deep Geological Radioactive Waste Repository

The study examines the 6‐year corrosion of carbon‐steel casing in Andra's deep geological repository (Bure, France), where steel pipes are embedded in cementitious filling grout (CFG) within Callovo‐Oxfordian claystone. Samples from 0.28, 6, and 15 m depths revealed three corrosion patterns: Type I (Fe(III) oxyhydroxides like goethite, persisting from atmospheric pre‐corrosion), Type II (Fe(II)/Fe(III) phases like magnetite and iron sulfides, indicating deaeration), and Type III (minimal corrosion), likely due to abrasion or limited pre‐exposure. CFG saturation, Cox water ingress, and cell geometry (e.g., Viking seal) drove spatial variability. No significant CPL thickness increase was observed, suggesting limited corrosion progression under most conditions. The atmospheric pre‐corrosion layer acted as a marker of local redox states, while saturated, confined zones promoted magnetite and sulfide formation. This work highlights the heterogeneity of corrosion in geological repositories and the need to account for local environmental factors in long‐term safety assessments.