Radioactive Wastes Cementation during Decommissioning Of Salaspils Research Reactor

This paper deals with information on the radioactive wastes cementation technology for decommissioning of Salaspils Research Reactor (SRR). Dismantled radioactive materials were cemented in concrete containers using tritiated water-cement mortar. A laboratory tests system was developed to meet the waste acceptance criteria for disposal of containers with cemented radioactive wastes in near-surface repository "Radons". We studied the viscosity of water-cement mortar, mechanical tests of solidified mortar’s samples, temperature changes during solidification, and leakage of Cs-137 and T-3 radionuclides for different water-cement compositions with additives. The pH and electro conductivity of solutions during leakage tests were controlled. Results indicated that the water/cement ratio significantly influences water-cement mortar’s viscosity and mechanical stability of solidified samples. Increasing the water ratio from 0.45 to 0.62 decreased viscosity from 1100 mPas to 90 mPas and mechanical stability from 23 N/mm2 to 12 N/mm2. The role of additives, such as fly ash and Penetron admix, in reducing solidification temperature was discussed. Addition of fly ash reduced solidification temperature from 81 oC to 62 oC. Leakage tests showed complex radionuclide release curves, and the experimental results indicated that fly ash facilitated tritium and cesium leakage in the water phase. Further directions of investigations are drafted.