The compositional flexibility of the sodium zirconium phosphate (NaZr2(PO4)3) structure has been exploited in the design of monophasic radiophases capable of immobilizing the most common cations associated with reprocessed high-level commercial waste streams. Highly crystalline, monophasic members of the NaZr2(PO4)3 structural family ([NZP]) have been prepared with conventional processing methods and equipment. These radiophases were tailored to accommodate 10–20 wt % modified PW-4b simulated calcine as single phases isostructural with NaZr2(PO4)3. To meet the challenge of designing monophasic materials capable of accommodating the chemical complexity of PW-4b, an ionic substitution scheme based on crystal chemical principles was developed. The radiophases were prepared with inexpensive, inorganic precursors and a solution sol-gel method; these materials were heat treated and/or sintered under a variety of conditions to determine the optimum conditions for single phase [NZP] formation. X-ray powder diffraction provided valuable information that was used to assess the suitability of the ionic substitution model developed in this investigation. The results of this investigation suggest that monophasic [NZP] radiophases capable of accommodating 10–20 wt % modified PW-4b simulated calcine may be continuously processed with conventional ceramic processing methods and equipment. Moreover, the relatively low temperatures involved and the reproducibility of the process make [NZP] radiophases economically attractive hosts for radioactive and heavy metal industrial wastes.