PhD Defense | Emile Mukiza | Effects of gamma irradiation on early age properties of metakaolin-based geopolymer for the immobilization of radioactive waste containing cesium and strontium

Effects of gamma irradiation on early age properties of metakaolin-based geopolymer for the immobilization of radioactive waste containing cesium and strontium

Partitioning of heat and radiation-emitting Cesium (Cs) and strontium (Sr) is regarded as a viable pathway for the safe disposal of spent nuclear fuel and reprocessing waste without exceeding the temperature limits of geological disposal. The partitioned Cs and Sr radionuclides exhibit similar characteristics both being heat and radiation emitters, and could be immobilized together in a suitable matrix. Geopolymer is a potential candidate for the immobilization of Cs and Sr radionuclides, owing to its good thermal performance and radiation resistance. This PhD research explored the possibility for co-immobilization of Cs and Sr by metakaolin-based geopolymer matrix. The results demonstrate that the co-immobilization of Cs and Sr even at higher waste loading (4 wt.% Cs and 4 wt.% Sr) into a single matrix is feasible. However, gamma ionizing radiation and decay heat negatively impacts the strength development and coarsens the pore structure. Despite this, the metakaolin-based geopolymer incorporating Cs and Sr exhibited satisfactory mechanical strength, and the binding phase (N-A-S-H gel) demonstrated chemical stability when simultaneously subjected to a high gamma dose of 4032 kGy at a high dose rate of 6 kGy/h and a temperature of 75 °C. Based on these findings, metakaolin-based geopolymer shows promise for the immobilization of Cs and Sr-containing wastes.

Promoter:

• Geert De Schutter (UGENT)

SCK CEN mentors:

• Quoc Tri Phung
• Suresh Seetharam