Ming Tang1

1, Los Alamos National Laboratory, Los Alamos, New Mexico, United States

A series of glass ceramic and crystalline ceramic waste forms were examined as alternative waste forms for glass. These ceramics and glass ceramics are candidate host materials for immobilizing alkaline/alkaline earth (Cs/Sr-CS) + lanthanide (LN) + transition metal (TM) fission product waste streams from nuclear fuel reprocessing. In this study, glass ceramics were fabricated using a borosilicate glass as matrix in which to incorporate CS/LN/TM combined waste streams. The major phases in these multiphase materials are powellite, oxyaptite, pollucite, celsian, and durable residual glass phases. Al2O3 and TiO2 were combined with these waste components to produce multiphase crystalline ceramics containing hollandite-type phases, perovskites, zirconolite/pyrochlores and other minor metal titanate phases. These alternative waste form materials offer increased solubility of troublesome components in crystalline phases compared to glass. This, in turn, leads to increased waste loading. Also the crystalline network formed in these materials results in higher heat tolerance than glass.
For the radiation stability test, selected glass ceramic and crystalline ceramic samples were exposed to charge particles generated by an ion accelerator, which is used to simulate self-radiation in a waste form. Ion irradiation-induced microstructural modifications, volume swelling and microcracking were examined using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and other characterization methods. Our preliminary results reveal very promising radiation tolerance, especially amorphization resistance, in these multiphase nuclear waste forms. However, their stability may be rate dependent which may limit the waste loading that can be employed. To better understand radiation damage effects in nuclear waste forms, several individual crystalline phases in multiphase glass ceramics and crystalline ceramics were fabricated and tested with ex-situ and in-situ ion irradiations. Experimental results show similar radiation damage responses from single crystalline phases and corresponding crystalline phases in multiphase samples. Also, different crystalline phases in these multiphase waste forms exhibit different radiation tolerance under various radiation damage environments.
To investigate radiation damage effects on chemical durability of glass ceramic waste form samples. Static leach testing (28 days/7 days) on non-irradiated and irradiated glass ceramic samples was performed using ASTM C1220 method. Our results suggest that radiation damage definitely affect the chemical durability of glass ceramic samples.