[en] Material studies were performed in support of the Slagging Pyrolysis Incinerator Project for characterizing the slag product expected from processing low-level waste. The studies included chemical compositional analysis of slag products from waste feed after pyrolysis, slag/refractory interactions, phase and structure of the slag, and chemical leaching. A series of slag compositions were identified using average waste feed and soil. The slags are termed iron-rich basalt vitrophyre. For the materials tests a series of uranium-doped slags were made in the laboratory. Ruby refractory was observed to be the most compatible with the slag series. Structure studies on the slags disclosed that the primary crystalline phases that develop are diopside (CaMgSi₂O₆) and iron oxide. Chemical leach tests performed on the slag series show evidence that the slags have a high resistance to leaching