Interaction of fluoride and phosphate in aluminoborosilicate Hanford site direct-feed high level waste glasses

The coupled effects of fluorine and phosphorus on the structure and crystallization behavior of aluminoborosilicate glasses relevant to Direct Feed High-Level Waste (DFHLW) vitrification at Hanford are investigated. Systematic variation of F and P 2 O 5 contents demonstrates that F alone promotes network depolymerization and induces CaF 2 crystallization above its solubility limit, whereas phosphorus remains largely incorporated without inducing crystallization within the studied range. In contrast, co-addition of F and P 2 O 5 significantly reduces their mutual solubility, resulting in the formation of fluorapatite, Ca 5 (PO 4 ) 3 F. Multi-technique characterization, including F K-edge X-ray absorption spectroscopy, confirms the observed phase assemblages and structural evolution. These results demonstrate that ionic interactions of fluoride and phosphate strongly control crystallization pathways and impose critical compositional constraints on waste loading. The findings highlight the necessity of explicitly incorporating coupled anion effects into predictive vitrification models.