Plutonium-238 alpha-decay damage study of a glass-bonded sodalite ceramic waste form

An accelerated alpha-decay damage study of a glass-bonded sodalite ceramic waste form has been completed recently. The study was designed to investigate the physical and chemical durability of the waste form after exposure to ²³⁸Pu alpha decay The alpha-decay dose at the end of the four year study was approximately 1.0 × 10¹⁸ decays/gram of material. The ceramic waste form (CWF) was developed to immobilize fission products accumulated during the treatment of spent nuclear fuel from the Experimental Breeder Reactor II performed at Argonne National Laboratory-West in Idaho. Small quantities of actinide elements are also found in the waste form. The CWF is currently undergoing qualification testing and characterization for acceptance by the Office of Civilian Radioactive Waste Management for geologic disposal. Methods used to monitor the ²³⁸Pu-loaded CWF material in this study included: immersion density determination to measure possible macroscopic swelling, chemical durability by leach testing, microstructural analysis by scanning and transmission electron microscopy, and phase composition and stability by powder x-ray and electron diffraction. After four years of exposure to alpha decay, the investigation observed little alteration to the CWF. Specifically, the ²³⁸Pu-loaded CWF maintained its physical integrity, the density remained constant, no cracking or phase debonding was observed by microscopy, and the material's chemical durability did not change significantly over the duration of the study. The only significant measured change was an increase of the unit-cell lattice parameters of the plutoniurn oxide and sodalite phases of the material, but these were very small and did not lead to any loss of waste form durability.