Submersible media filters and submersible columns for use in removing radioactive isotopes and other contaminants from a fluid stream, such as a fluid stream from the primary coolant loop of a nuclear reactor system or a fluid stream from a spent-fuel pool. Generally, these submersible media filters and submersible columns are adapted to be submersed in the fluid stream, and additionally the filters are adapted to be vitrified after use, resulting in a stabilized, non-leaching final waste product with a substantially reduced volume compared to the original filter. In several embodiments, the submersible media filters and submersible columns include isotope-specific media (ISM).