Alkaline hydrolysis of radio-oxidized aliphatic polymers
Résumé
To ensure the safety of the French deep geological repository, the degradation of organic molecules which can be found in long-lived intermediate-level waste (LL-ILW) packages has to be very well understood. In a first period, these molecules which include polymers are radio-oxidized because they are in contact with radionuclides. In a second period, water will diffuse inside the site to the packages and radio-oxidized polymers will suffer alkaline hydrolysis. The objective of this article is to evaluate the parameters of influence when polyolefins suffer leaching at high pH; aliphatic polymers being chosen because of their relative importance, in quantity, in the LL-ILW packages.
In this work, we have evaluated the influence of the materials’ composition (nature of the resin, presence of charges and fillers) and of the irradiation conditions (nature of the irradiation, linear energy transfer LET and dose). We observed that degradation is influenced by the molecular structure of the polymer, but also by the presence of inorganic fillers and organic charges. Degradation of the materials under study increases with dose and LET (in the case of comparison between ions irradiations), the most penalizing conditions being encountered using low LET ionizing rays compared to swift heavy ions irradiation. We observe that the higher the oxidation rate, the higher the polyolefins sensitivity to alkaline hydrolysis.