ISA production during hydrolytic degradation of irradiated cellulosic tissues and its sorption on degraded Ordinary Portland Cement: first set of results

Cellulosic materials are widely used in the nuclear industry, and therefore make up a large quantity of certain waste streams. Both during interim storage and final disposal, cellulose will undergo radiolytic and/or hydrolytic degradation in cement water at highly alkaline pH. Under disposal conditions, the α and β isomers of isosaccharinic acid (α- and β-ISA) are important cellulose degradation products. Especially α-ISA has been shown to form complexes with radionuclides, which may facilitate their migration from the waste to the biosphere. On the other hand, sorption of α-ISA on cementitious material present in a disposal facility could counteract the enhancing effect of α-ISA on radionuclide migration. In this study, the effect of pre-irradiation of cellulosic tissues on the production of soluble degradation products, and more specifically ISA, under alkaline conditions was assessed during 3 months, as well as the sorption of α-ISA on Portland cement degraded to state III. The results show that pre-irradiation of cellulosic tissues enhances the production of ISA during hydrolytic degradation. The ISA production rates and yield increased with the absorbed dose applied during pre-irradiation, which can be linked to an increased number of radiolytic chain scissions with increased absorbed dose. Under all test conditions of the degradation study, α- and β-ISA isomers were produced equally. The sorption of α-ISA on cement degraded to state III was found to be lower than previously observed on fresh cement. Moreover, it followed a one-site Langmuir sorption isotherm, with a mild sorption showing a maximum solid/liquid distribution ratio of 109 ± 67 L kg-1.