Dissolution of LnYSiAlO glass (Ln=La or Ce) in aqueous media. III. Influence of β irradiation on structure and hydrolysis mechanisms

LnYSiAlO glasses (Ln=La or Ce) are considered as potential matrices for the specific storage of minor actinides. β particles emitted during the disintegration of fission products may cause important modifications to the glass network through electronic excitation and ionization. The influence of these processes on the structure of two analogous compositions of glass, involving La or Ce, and the consequences for their chemical durability were studied. Monoliths of glasses were irradiated with electrons that had been accelerated to 2.5 MeV and samples were then leached in static bidistilled water for one month at 90 °C. Raman spectrometry, 27Al MAS-NMR and EPR spectrometry experiments, performed after irradiation, globally indicated weak structural modifications. The two main effects of irradiation were an increase of the (Al IV)/(Al VI+Al V) ratio and the formation of a paramagnetic center in the case of La-glass ( g≈1.99). The former observation could indicate a slight migration and segregation of the rare earth, preferentially surrounded by highly charged Al V and Al VI units initially. The second point could be correlated with a change in the oxidation state of one of the La-glass component. The reason why no similar paramagnetic center is created during irradiation for Ce-glass is not well understood but a possible charge trapping process involving Ce(III)/Ce(IV) is developped. Finally, leaching solution analysis indicated that normalized elemental releases are almost unchanged after irradiation for both of the La and Ce-glass. The globally weak influence of β irradiation on this family of glass is subsequent to the low mobility of the major components that form high field strength bonds with oxygen.