Hot isostatically pressed Y2Ti2O7 and Gd2Ti2O7 pyrochlore glass-ceramics as potential waste forms for actinide immobilization

Abstract

Both Y2Ti2O7 and Gd2Ti2O7 pyrochlore glass-ceramics (GCs) have been prepared with an oxide route and consolidated via hot isostatic pressing (HIPing) as waste forms for actinide immobilization. The crystallization of Y2Ti2O7/Gd2Ti2O7 pyrochlore as the major actinide host phase in the residue glass has been confirmed with XRD, SEM-EDS and Raman spectroscopy. The static leaching tests confirmed that both GCs are chemically durable with normalized Y/Gd and Ti leach rates ∼10−4–10-5 g m-2 d-1 after 28 days. In addition, the interactions between the 316L stainless steel (SS) HIP-can and the GCs have been investigated. Interactions occur at the interface with a layer of mixed Cr/Ti oxide and CrTi2O5 crystals observed for the Y2Ti2O7 GC and a layer (∼10 μm) of Cr2O3 observed for the Gd2Ti2O7 GC as the reaction fronts from the SS cans. Furthermore, a layer (∼10 μm) of Gd-(Si/Ti)-oxide phase formed on the GC side of the interface.