PNNL

Abstract

Sucrose (C12H22O11) has been used in low-activity waste (LAW) melter feeds containing high fractions of nitrates and/or nitrites because of positive effects on foam suppression and denitration. In this study, the effect of sucrose addition in LAW feeds on technetium (Tc) and rhenium (Re) retention was more focused. The amount of sucrose added in feeds was varied to differentiate the carbon to nitrogen mole ratio (C/N ratio). The results show that higher sucrose addition (higher C/N ratio) exhibits enhanced Tc and Re retention. Reducing conditions induced by sucrose decomposition and early chemical reactions between NaNO3/NaNO2 and sucrose are expected to lead to an increase in Tc and Re retention. However, it was observed that high sucrose addition lowered sulfur (S) retention slightly resulting from sodium sulfate decomposition by reducing conditions at lower temperature. This early sulfate decomposition can impact Tc and Re retention because these species can be soluble in sulfate phases. This correlation indicates that less sulfate phases on the glass due to early decomposition can cause less solubility of Tc and Re in the sulfate phases that may result in an increase of Tc and Re retention.