Diffusion study of implanted iodine in zirconium using ion beams

This study is related to the back end of the nuclear fuel cycle. During nuclear reactor operation, the inner side of the zircaloy cladding tube is implanted by recoil with fission products. Among them, 129I poses a real problem firstly, because it is a volatile element and secondly because it has a very long half-life (T=1.59×107 years). The aim of this paper is to make an analysis of iodine diffusion into zirconium compared to zirconium oxide. In order to analyse the mechanisms involved in iodine migration, stable (127I) and radioactive iodine (131I) species were implanted into zirconium. Diffusion profiles of iodine were followed as a function of successive annealing times (up to several hours) and temperatures (in the range 400–600°C), either by using Rutherford backscattering spectrometry to profile 127I or by γ spectroscopy to measure 131I release. These two techniques allowed us to determine very low iodine diffusion coefficient values (down to 10−17 cm2 s−1) and to extrapolate them to waste storage conditions.