Synthesis and characterization of cerium monazite phosphate glass-ceramic for immobilization of nuclear waste salt

Abstract

A phosphate glass-ceramic wasteform incorporating cerium monazite was synthesized through a two-step solid phase sintering methodology, aimed at immobilizing waste salts derived from the pyrochemical reprocessing of spent nuclear fuel. The initial phase involved the synthesis of cerium monazite powder, employing a stoichiometric mixture of CeF₃ and NH₄H₂PO₄ in a molar ratio of mol(Ce:PO₄) = 1:1.4, which was subjected to a thermal treatment at 900°C. Subsequently, the glass-ceramic matrix was fabricated by sintering a composite mixture of the synthesized cerium monazite and iron phosphate glass (IPG) powder at a temperature of 1000°C for a duration of 2 h, resulting in a cerium incorporation exceeding 36.5 wt%. Microstructural analysis and structural characterization of the glass-ceramic sample elucidated the presence of monazite crystallites (CePO₄) with dimensions ranging from .2 to 5.5 µm. The chemical durability of the wasteform was assessed through modified ASTM C1308 tests conducted in deionized water over a period of 28 days, revealing a total elemental leaching rate of 2.58 × 10⁻⁷ g m⁻² min⁻¹.