Nepheline Crystallization in Nuclear Waste Glasses: Progress Toward Acceptance of High‐Alumina Formulations

Historical data have been critically compiled and analyzed for investigating the quantity of nepheline ( NaAlSiO 4 ) precipitated as a function of composition in simulated nuclear waste glasses. To understand compositional effects two primary methods were used: (1) investigating the Al 2 O 3 – SiO 2 – Na 2 O ternary while filtering for different B 2 O 3 levels and (2) creating a quadrant system consisting of compositions reduced to two representations: (i) the nepheline discriminator ( ND ) which depends only on the SiO 2 content by weight normalized to the total weight of the Al 2 O 3 – SiO 2 – Na 2 O submixture and (ii) the optical basicity ( OB ) which contains contributions from all constituents in the glass. Nepheline precipitation is expected to be suppressed at high SiO 2 levels ( ND > 0.62) or at low basicities ( OB < 0.55–0.57). Changes in sodium aluminosilicate glass OB values due to additions of CaO and B 2 O 3 correlate with the observed effects on nepheline formation. It is proposed that additional composition space is available for formulating high waste loading, high‐ Al 2 O 3 nuclear waste glasses when consideration is given to location on the Al 2 O 3 – SiO 2 – Na 2 O submixture as well as OB .