Role of lithium in enhancing radiation tolerance under γ-irradiation in lithium borosilicate waste glasses

Lithium-containing borosilicate glasses are used for the safe containment of high-level nuclear waste in the UK. Glasses were fabricated with varying Li2O contents and irradiated to a total γ-dose of 80 MGy to probe the relationship between Li2O contents and γ irradiation-induced defects. Semi-quantitative X-band Electron Paramagnetic Resonance (EPR) measurements revealed the formation of boron-oxygen hole centres (BOHC), electron-trap centres, Oxy radicals and hole centres (HC1) defects after γ-radiation. The results highlight the beneficial impact lithium has on the glass network against the formation of paramagnetic defects by transforming BO3 sites to [BO4]-. Experimental evidence from EPR and Nuclear Magnetic Resonance (NMR) spectroscopy indicated that the primary defects formed in the 4-component and 7-component glasses are BOHCs on bridging oxygens of the BO3 sites and Oxy radicals linked to silicon atoms, respectively. All glass compositions reached defect saturation around 25 MGy suggesting that the number of components in the glass network or Li2O content does not significantly influence saturation dose, however, no change in the environment or connectivity of the boron, sodium or silicon subnetworks was observed by multinuclear NMR.