Durability tests on plasma treated surrogate cemented concentrates and resins: Final report

Plasma incineration might be a promising technique for the (re-)conditioning of various radioactive waste streams. Assessing the long-term durability of a plasma slag is essential to assess its performance during disposal. The study presented here investigated the stability of six plasma treated surrogate cemented concentrates or resins in a high pH environment. The slags were crushed (with 2 different granulometries) and immobilized in a cement matrix, after which samples were submitted to long-term durability tests (i.e. investigating their stability in water at 20 °C and in a humid atmosphere at 38 °C) and to an accelerated Alkali-Silica-Reaction (ASR) test (in 1 M NaOH at 80 °C). The results show that the expansion of the cement-slag mixtures remained very limited in the test conditions. Small differences between the different materials and granulometries could be perceived. The mechanical strength of the samples increased during the durability tests, indicating that the water penetration improved their hydration. No visual damage was observed for any of the cemented slag samples. SEM images and mapping show some alteration at the interface between the slag particles and the cement matrix. EDX spot analysis shows that the slag atomic composition remained stable in all samples, even at the interface layer after the durability tests. Changes in atomic composition were found in the cement matrix closer to the slag showing some decalcification, most probably due to calcium leaching. The pore fraction analysis of the SEM images also suggests calcium leaching, showing an increase in porosity in the samples during the durability tests.