PNNL

Abstract

A novel nuclear waste form was synthesized for the disposal of electrorefiner salt from pyrometallurgical reprocessing of used nuclear fuel. Its synthesis constitutes two steps: waste salt dehalogenation via ion exchange with H-Y zeolite, followed by thermal treatment for phase transition and consolidation. Salt cation-loaded zeolite exhibiting greater than 90% dehalogenation was sintered for 12 hours at 925°C and achieved 3 vol% porosity (determined via Archimedes method). Microstructural imaging and structural characterization revealed a multiphase assemblage of alkali aluminosilicate and mixed oxide phases. Chemical durability experiments were performed using modified ASTM C1308 tests in demineralized water and different silica solutions. Si-containing species appear to exhibit congruent dissolution, while the release behaviors of alkali elements appear to include diffusion-limited contributions. The 4-day cumulative releases for DSWF are less than 33% of those measured for the baseline glass-bonded sodalite advanced ceramic waste form (GBS ACWF). Furthermore, the dehalogenation and consolidation processing steps provide a 35% decrease in required storage volume for a given waste salt mass relative to the GBS ACWF.