Geopolymers as an Immobilization Matrix for Radioactive Waste

Geopolymers, also known as alkali-activated aluminosilicate cements or binders, were initially discovered in the early 20th century. Over time, they have been progressively developed for various industrial applications, such as construction, radioactive waste immobilization and encapsulation, ceramics, fireproofing, and patching materials. The process of manufacturing geopolymers is similar to that of standard Ordinary Portland Cement (OPC), but it benefits from using readily available aluminosilicate materials that interact with different activators.
In recent years, immobilization and/or encapsulation of radioactive waste within a geopolymer matrix has gained global interest as an alternative to standard Portland cement (OPC) blends. This is due to geopolymer's high strength, adaptable gel network, and overall low environmental impact. Recent research has extensively explored formulation development in this field, resulting in various potential waste immobilization formulations. These often consist of metakaolin or slag-based systems, demonstrating significant promise in stabilizing diverse waste streams.
However, to ensure that any waste form, cement or geopolymer, aligns with relevant storage and disposal Waste Acceptance Criteria (WAC), a series of tests are necessary. These tests establish the durability performance of the waste form over extended time periods, in conditions that simulate representative storage and disposal conditions. Since international standards for geopolymers are lacking in both construction and nuclear sectors, researchers from different Member States have employed various testing protocols—primarily those established for cementitious matrices—to evaluate waste form performance. These protocols have yielded varying results due to differences in implementation of the test procedures, which makes it challenging to compare outcomes across Member State organizations.
To address this challenge, the IAEA has proposed this Coordinated Research Project (CRP). The project aims to benchmark established cementitious protocols against emerging procedures developed for geopolymer matrix testing. The goal is to facilitate the establishment of future waste form testing protocols for using geopolymers as matrices for immobilizing radioactive waste.