The operation of a high-level radioactive waste evaporator was curtailed due to the presence of an aluminosilicate scale that contained sodium diuranate with a uranium-235 enrichment of approximately 3%. Utilizing pervious work, a plan to clean the evaporator system using a heated nitric acid and depleted uranium mixture was developed that addressed numerous safety issues. The sodium aluminosilicate scale was successfully removed during two cleaning cycles, but soluble silicon was not present in measurable quantities in the liquid samples taken during cleaning. Although this phenomenon was not observed in the laboratory tests, silicon was detected in a loose, solid phase discovered in the evaporator cone after the first cleaning cycle.