Abstract: A study of sulphur whereabouts in vitrification process of simulated HLW-hearing high SO42- ontent with GC-12/9B formulation is described in this paper. Analyses of sulphur distribution indicate that the sulphur content in glass products is 0.12-0.53 wt%. This is in good agreement with the results obtained by other authors 20-30% of sulphur in HLW go into glass, and 70-80% into off-gas in the form of SO3. The mechanism of eliminating yellow phase is reduction-decomposition of sulphate. The compositions of glass ro-ducts are analysed and compared with, original specimens.