Combined Effects of Alkaline Groundwater and Gamma Irradiation on the Durability of Geopolymer Waste Forms

Abstract

The long-term durability of metakaolin (MK)-based geopolymer waste forms was evaluated under simulated disposal environments. Specimens incorporating Cs, Sr, and Co were fabricated and subjected to ANSI/ANS 16.1 leaching tests in deionized water (DI), concrete-saturated groundwater (CGW), and CGW combined with gamma irradiation (CGW + gamma). Compressive strength, leachability index (LI), microstructure, and surface chemistry were analyzed to evaluate mechanical and chemical stability. All specimens initially satisfied the disposal acceptance criterion (>= 3.45 MPa). The compressive strength remained stable in DI but declined under CGW due to alkali-induced degradation. Under the CGW + gamma condition, severe strength loss occurred, and several specimens fractured completely. Leaching tests revealed substantial LI reduction for Cs, Sr, and Co. Computed tomography imaging showed increased porosity under CGW + gamma, while X-ray photoelectron spectroscopy analysis confirmed Cs and Sr surface enrichment with the reduction of Co3+ to Co2+. These results indicate that while MK-based geopolymers demonstrated strong resistance to individual degradation factors, they experienced significant structural deterioration under combined alkaline and radiation conditions, providing critical insights for the safe disposal of radioactive wastes.