Identification of Radiolytic and Hydrolytic Degradation Products from Cellulosic Materials in Radioactive Waste Disposal Environments

Cellulose and hemicellulose, both widely present in radioactive waste, undergo combined radiolytic and hydrolytic degradation during disposal under the highly alkaline conditions imposed by the cementitious waste matrices and engineered barriers. This combined process generates water-soluble organic compounds that can complex with radionuclides, thereby potentially enhancing their migration from the waste to the biosphere. Identification of these degradation products formed by cellulosic materials is essential for assessing their complexation potential and predicting their impact on radionuclide mobility. In this work, degradation products resulting from sequential radiolytic and alkaline degradation of cellulosic tissues, realistically present in radioactive waste, were identified using multiple advanced techniques, i.e., Electrospray Ionization Time-of-Flight Mass Spectrometry, Ion Chromatography Mass Spectrometry, and Nuclear Magnetic Resonance spectroscopy. Our results confirm that isosaccharinic acid (α-ISA and β-ISA) is the major end product from cellulose degradation, while xylo-isosaccharinic acid (XISA) indicates hemicellulose degradation. Furthermore, significant concentrations of formic and lactic acid were detected, alongside minor products including glycolic, acetic, propionic, malonic, and oxalic acids, with malonic and oxalic acids appearing only after irradiation at high irradiation doses and under air (malonic) or argon (oxalic). Additional unquantified compounds, such as glutaric acid, 2-hydroxybutyric acid, and oligosaccharides, were observed as well. These findings advance our insight into the degradation of end products of cellulosic materials in radioactive waste and establish a foundation for future research on their complexation potential and impact on radionuclide mobility, especially for compounds where data are lacking.