Melt processed single phase hollandite waste forms for nuclear waste immobilization: Ba1.0Cs0.3A2.3Ti5.7O16; AÂ =Â Cr, Fe, Al

Cs is one of the more problematic fission product radionuclides to immobilize due to its high volatility at elevated temperatures, ability to form water soluble compounds, and its mobility in many host materials. The hollandite structure is a promising crystalline host for Cs immobilization and has been traditionally fabricated by solid state sintering methods. This study presents the structure and performance of Ba1.0Cs0.3A2.3Ti5.7O16; A = Cr, Fe, Al hollandite fabricated by melt processing. Melt processing is considered advantageous given that melters are currently in use for High Level Waste (HLW) vitrification in several countries. This work details the impact of Cr additions that were demonstrated to (i) promote the formation of a Cs containing hollandite phase and (ii) maintain the stability of the hollandite phase in reducing conditions anticipated for multiphase waste form processing.