Thermodynamic assessment of the hollandite high‐level radioactive waste form

Abstract

Ceramic waste forms have been shown to accommodate nearly all constituents in the high‐level nuclear waste (HLW) generated from reprocessing spent nuclear fuel including radioactive and non‐radioactive components and are known to be resistant to hydrothermal leaching. Ceramic waste forms offer better durability and higher waste loadings for some species for which existing HLW glass formulations are inappropriate or inefficient.1‒4 Specifically, titanate ceramics, eg, SYNROC,5 have been extensively studied for use in immobilizing nuclear wastes due to their inherent leach resistance.6‒8 Cs is one challenging radionuclide due to its thermal heat load, volatility at high temperatures, and tendency to form water‐soluble compounds.4 Ti‐substituted hollandite, one of the SYNROC phases, is an alternative candidate for Cs immobilization. In these waste forms, 137Cs (and other constituent radionuclides, ie 137Ba, 87Rb) is incorporated into the crystalline structure.8‒10 Notably, natural analogs of hollandite including ankagite are present in dolomitic marble in the Apuan Alps in Tuscany, Italy, which demonstrates the stability of the hollandite phase over geologic timescales of interest for nuclear waste immobilization. Received: 1 December 2018 | Revised: 20 February 2019 | Accepted: 8 March 2019 DOI: 10.1111/jace.16438