Fission product, cesium-137 with a half-life of approximately 30 years, has been well known as problematic for waste forms. Titanate-based hollandites have long been considered effective phases for sequestering cesium, having the formula A1.33(Ti4+,B)8O16, where A is an alkali/alkaline earth element and B is a metal. Due to the beta decay of 137Cs, hollandites must be energetically stable not only to immobilize cesium, but also to remain stable when it is replaced by its decay product, barium. In this study, we have investigated the structural stability of actinide (U, Np, and Pu)-bearing hollandites, that is, when actinides co-exist at B-sites with titanium, to allow their consideration as both a cesium/barium and actinide waste form. The predicted formation enthalpies from density functional theory have provided insight into the stability of these hollandites as a function of composition which are being used to target synthesis efforts.

Predicting phase stability of potential actinide-bearing hollandite waste forms using first-principles calculations

ACS Fall 2021

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