Abstract: In order to suppress the "yellow phase" often found in the vitrificationmelter for processing sulfate-containing HLW, waste loading of glass had to belowered sharply, resulting in poor economy. A method is presented here that candecompose the sulfate in HLW by adding a reducing agent into the melter, andthe decomposed gases are then trapped by soda solution in the washing tower tobe treated as intermediate level liquid waste. Sulfate distribution in the processunder different operation conditions is given, and the effect of sulfate contentbuild-up in the process system caused by feeding back condensate on processgieration is discussed.