Immobilization of cesium and iodine into Cs 3 Bi 2 I 9 perovskite-silica composites and core-shell waste forms with high waste loadings and chemical durability.

•Develop pervoskite ceramic waste forms with high I and Cs loading and excellent chemical durability.•Consolidate Cs3Bi2I9-silica composite and core-shell structures into dense pellet by spark plasma sintering.•Understand the surface alteration and passivation mechanisms and their impacts on chemical durability.