Polyphase Ceramic for Consolidating Nuclear Waste Compositions with High Zr‐Cd‐Na Content

Abstract

The development of dense polyphase tailored ceramic forms for the immobilization of high‐level nuclear wastes has been extended to an Idaho Chemical Processing Plant Fluorinel composition. The ceramic was designed to maximize waste loading and subsequent waste volume reduction without sacrificing chemical durability in aqueous environments. The ceramic, fabricated by hot isostatic pressing, consists of four main crystalline phases, calcium fluoride, zirconia, an apatite‐structured solid‐solution phase, and sphene. The form also contains a designed borosilicate glass phase, a Ni‐Cd alloy, and a minor amount of crystalline zircon. The crystalline apatite solid‐solution phase is the major host for incorporating the actinide simulants U, Ce, and Y, while the glass phase contains Cs and Sr. The calcium fluoride and sphene phases provide microstructural isolation of the radionuclide‐containing phases. Since the glass and crystalline components of the ceramic are not phase compatible at all temperatures, the exact phase content is determined by the tailoring additives, consolidation temperature, and oxidation state control during processing. The simulated HLW ceramic has a density of 3.3 g/cm 3 at a waste loading of 73 wt%.