Degradation of cellulose under disposal conditions: State-of-the-art report

Cellulosic materials are present in significant amounts in Belgian nuclear waste, which is currently envisaged to be disposed of in a surface (low- or intermediate-level short-lived waste) or deep geological repository (intermediate-level long-lived waste) by ONDRAF/NIRAS, the Belgian radioactive waste management organisation. The massive employment of cementitious structural and backfill materials will result in the generation and long-term persistence of a high pH (pH > 12.5) environment within the disposal system. Cellulose is susceptible to both alkaline and radiolytic degradation, which result in the formation of cellulose degradation products. Under highly alkaline conditions, some of these cellulose degradation products (e.g. α-isosaccharinic acid) are able to complex strongly with multivalent radionuclides, thereby possibly enhancing the transport of these radioactive species to the biosphere. This report reviews the current understanding regarding alkaline and radiolytic cellulose degradation processes and the associated kinetics and degradation products. Also the stability of certain degradation products under radioactive waste disposal conditions is addressed briefly.