Treated LAW Feed Evaporation: Physical and Solubility Determination (U)

Abstract

Evaporation is employed in several places in the Waste Treatment Plant pretreatment process to minimize the volume of waste that must be treated in down-stream vitrification processes. Evaporation is the first unit process in pretreatment (Waste Feed Evaporators), applied before LAW vitrification (Treated Feed Evaporator), and concentrates ion exchange eluate (Cs Eluate Evaporator) prior to HLW vitrification. The goal of the Treated Feed Evaporation process is removal of the maximum water content without producing additional insoluble solids. Prior testing of evaporation systems for process feed was completed to support compliance with regulatory permits and to prepare a model of the evaporation system. These tests also indicated a marked tendency for foaming in the WTP evaporators. To date, evaporation testing and modeling have focused on the Treated feed and Cs eluate evaporation systems. This has been the first work performed that investigates evaporation of secondary-waste recycle streams in the Treated LAW Feed Evaporator. Secondary-waste recycles from the LAW off- gas scrubbing system have been the major contributors to the overall Treated Feed Evaporator recycle volume. Experience from Savannah River Site operations suggests that the introduction of silica- laden recycles to an evaporator along with high-sodium treated LAW can significantly increase the likelihood of forming sodium-alumina-silicate precipitates upon concentration. Furthermore, there is considerable interest on the part of the WTP project to evaluate the potential of projected evaporator feed and concentrate blends to produce sodium aluminosilicate precipitates.