PNNL

Abstract

During vitrification of radioactive wastes excessive foaming reduces processing rates within melters by hindering heat transfer from the molten glass pool to the reacting melter feed. Formulations of low-activity waste (LAW) melter feeds, for vitrification at the Waste Treatment and Immobilization plant at the Hanford Site, conventionally include addition of sucrose to mitigate excessive foaming by hastening the denitration process. However, incomplete combustion of sucrose produces organics such as acetonitrile (C2H3N) that may exceed bounding limits of downstream effluent treatment facilities. Using boron nitride (BN) as an alternate reductant to sucrose, in a representative LAW melter feed, avoided excessive foaming and 90% of the C2H3N production by preventing of the low-temperature sucrose-nitrate reactions. Due to the higher decomposition temperature of BN than H3BO3, foaming was suppressed by delaying the reaction of a large fraction of boron with the transient glass-forming melt until above the foam onset temperature, thus reducing the quantity and viscosity of the connected melt and trapping less gas in the foam layer.