A Review of Cellulose Degradation and the Fate of Degradation Products Under Repository Conditions

The disposal of long-lived intermediate- and some low-level wastes (ILW/LLW) in vaults backfilled with cementitious material is one of a number of generic disposal concepts under consideration in the UK. The employment of a cementitious backfill results in the generation and persistence of a high pH (pH 12.5 to 10.5) environment within the disposal system. These conditions are favourable in terms of reducing the mobility of some radionuclides, however they also promote the chemical degradation of cellulosic materials present in some wastes. This alkaline chemical degradation of cellulose results in the generation of a range of soluble products some of which are able to complex radionuclides and potentially enhance their mobility (e.g. iso-saccharinic acid). This report reviews the current understanding regarding alkaline cellulose degradation and the associated impacts of radiolytic and microbial processes. Conceptual and mathematical models developed to describe alkaline cellulose degradation are also outlined and discussed. The nature and extent of alkaline cellulose degradation products are discussed together with their stability towards microbial and chemical degradation under repository and geosphere conditions