Modeling Radiation-Induced Alteration of the Network Structure of Alkali Borosilicate High-level Waste Glass

Abstract

ABSTRACTHigh-level nuclear waste glasses are subject to radiation-induced degradation over very long time scales. In such glasses, bond-breakage and atom displacements occur by both radiolysis (principally from energetic beta-decay electrons) and ballistic mechanisms involving collision cascades initiated by energetic fission nuclei and recoil of alpha-emitting actinide nuclei [1]. This study investigates collision-cascade-induced alteration of the glass network in a simplified sodium borosilicate model nuclear waste glass, using molecular dynamics (MD) codes and efficient topological assessment algorithms. Collision cascades were initiated ballistically (4 keV initial kinetic energy, dissipated elastically) and carried out using MD codes incorporating both two-body Buckingham and three-body Stillinger-Weber potentials verified in the GULP atomistic simulation package. Network topologies of the initial and resulting altered glass structures were determined by enumerating the primitive-ring-based local cluster atom complement at each atom site. The topological description is seen to provide a revealing assessment of network structural changes in the simulated radiation environment that can be potentially related to observable macroscopic changes, such as swelling, viscosity changes, and radiation-induced devitrification.