Nuclear corrosion and materials: achievements and challenges
Résumé
Corrosion and material sciences face challenges which involved and still need increases of knowledge and understanding in light water nuclear power plants.In pressurized water reactors (PWRs), the performances of the two first barriers for the plant safety (cladding for the fuel and steam generator tubing for the primary circuit) have key importance and their performances have been improved through the better knowledge of their corrosion behaviors. This leads for cladding to the evolution of zirconium alloy composition with addition of niobium. Stress corrosion cracking of nickel base alloys has been a great challenge for PWRs which has been solved progressively by evolutions of Alloy 600 from Meal Annelled (MA) to thermally treated (TT) materials and then to evolution of the alloy composition with less nickel and more chromium (Alloy 690), based on corrosion results. SCC mechanisms are still in progress for a better prediction of the nickel base alloy susceptibility, linked to the extension of the service time of nuclear power plants from 40 years, as initially planned, to 60 years and probably more as expected now, In secondary circuits of PWRs, like for boiling water reactors, flow accelerated corrosion (FAC) has been and is still an industrial challenge linked to the design of the apparatus, thermohydraulics and water chemistry. The chemical composition of low alloyed steels (chromium content) is a major parameter for FAC. These 3 corrosion phenomena (general corrosion of cladding alloys, stress corrosion cracking of nickel base alloys and flow accelerated corrosion) sustain researches and developments to model corrosion phenomena at various scales, from atoms to components.
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