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In pressurised water reactors the cladding tubes in zircaloy-4 are oxidised up to several micrometres on the internal face by direct contact with the UO2 pellets. At the same time, fission products such as 129I are implanted by recoil. Until 1995, the cladding tube pieces called hulls were embedded in concrete. The concrete medium being very basic, this study simulates the corrosion of hulls in the perspective of a long-term disposal in these severe pH conditions. This paper is dedicated to the study of the partial dissolution of the oxide layer, which is the responsible mechanism for the activity release. In order to follow the solid–liquid interface, europium was implanted into the material surface as a marker. Next, the corrosion induced in autoclave at 300°C, 140 bars and in alkaline water was studied. The determination of europium profiles using Rutherford backscattering spectrometry analysis (RBS) allows to deduce the fraction of dissolved ZrO2. It was shown that this dissolution is not homogeneous in porous zirconia and gives rise to the formation of crevices. Using the nuclear microprobe of Pierre Sue laboratory, a more precise study of the specimen surface was performed. |
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