Crystalline‐Phase Formation in Hot Isostatic Pressing of Nuclear Waste Ceramics with High Zirconia Content

Abstract

Ceramic forms with a significant glass phase have been prepared from Zr‐rich simulated Idaho Chemical Processing Plant high‐level nuclear waste by hot isostatic pressing of redox‐controlled waste and chemical additive calcines. Crystalline‐phase formation in the ceramics is a function of the waste loading, additives, and consolidation temperature. Actinide host phases are controlled by silica‐zirconia crystal chemistry; the composition of the amorphous phase dominates the leaching behavior. Two phase assemblages—one consisting of CaF 2 , ZrO 2 , ZrSiO 4 , and glass, the second of CaF 2 , ZrO 2 , YNaSiO 4 , ZrSiO 4 , and glass—showed leach resistance superior to melter‐processed borosilicate glass forms for uranium and, at waste loadings >80 wt%, offer a factor of up to 3.2 times greater volume reduction. The presence of the designed glass phase in the waste forms makes them more flexible to variations in waste composition and lowers the required hot isostatic pressing temperature for consolidation as compared with polycrystalline waste ceramics, while maintaining the actinide leach resistance of the crystalline phases.