Fracture toughness and leaching behavior of ion bombarded waste glasses

Abstract

Fracture toughness K lc and fracture surface energy γ were measured on borosilicate waste glasses containing simulated fission products produced in the Institut für Nukleare Entsorgung, KFK. The Hertzian indentation technique with spherical indenters was shown to be a very powerful means with which to study mechanical and fracture properties of small highly radioactive samples. It was tested with Pu-ceramics as well as with Cm-doped glass ceramics. Radiation damage was produced by ion bombardment with Pb or Xe ions of energies up to 300 keV or with He 2+-ions (α-particles) of the cyclotron (KFK) with energies up to 77 MeV. The glasses were used either as-received or else following high-temperature, high-pressure autoclave leaching. The as-bombarded and the leached glasses were analyzed for surface composition and changes by Rutherford backscattering, RBS, with He-ions. In many cases, radiation damage caused an increase in fracture toughness, a very beneficial effect. The leached glasses that were investigated contained surface layers with thicknesses of up to ∼2 μm. RBS showed these layers to be similar in composition to thick layers analyzed by electron microprobe analysis (empa). There was no drastic influence of ion bombardment on the composition or thickness of these layers. The layers themselves caused changes of about ± 10% in the apparent fracture toughness, possibly by absorbing part of the applied energy by plastic deformation or by preventing pre-existing flaws from initiating crack formation.