Protective properties and dissolution ability of the gel formed during nuclear glass alteration

The protective properties and the dissolution ability of different gels formed during alteration from the SON68 glass (nuclear glass R7T7-type) and from two simplified glasses are assessed. The method consists in a first glass alteration in order to form gels at different alteration progresses and, in a second alteration after a renewal of the solution in the same experimental conditions. The kinetics of the second alteration is analyzed in two steps. Firstly, the gel properties are related to its morphological evolution. For the SON68 glass, the increase of the protective properties corresponds to an increase of the thickness of the density gradient within the gel. At high reaction progress, when the gel presents a dense and thin zone located at the gel-glass interface, the protective properties remain constant. Secondly, the ability of the gel to get back its protective properties after the solution renewal is observed. The amount of dissolved gel is calculated and discussed for SON68 glass.