Properties and structure of vitrified iron phosphate nuclear wasteforms

The structure of vitreous iron phosphates containing up to 35 wt% of one or more common nuclear waste components such as Na2O Cs2O, SrO, UO2 or Bi2O3 have been investigated using Fe-57 Mossbauer, X-ray absorption, X-ray photo electron and Raman spectroscopies and high energy X-ray and neutron diffrac tion techniques. The glass samples investigated were prepared by melting ap propriate chemicals in air at approximately 1200 degrees C for 2 h in alumi na crucibles. The chemical durability of the glasses was investigated by me asuring their dissolution rates in distilled water st 90 degrees C using th e product consistency test (PCT) methodology. The chemical durability of th ese glasses is characterized by dissolution rates of 10-(10)-10-(11) g/cm(2 )/min. The Mossbauer spectra indicate the presence of both Fe(II) and Fe(II I). However, the maximum Fe(II) fraction, Fe(II)/[Fe(II)+ Fe(III)]. was 0.3 4. X-ray absorption data show that, on average, both species of iron ions a re coordinated with approximately 5 near neighbor oxygens and that the iron -oxygen coordination is only slightly (<10%) influenced by the type or the concentration of the waste elements. Iron ions are also coordinated with 4- 6 phosphorous ions in the second shell. Only a minority of the oxygen ions, about 22%, take part in bridging -P-O-P- bonds. Raman spectra show that th e phosphorous-oxygen network, which is dominated by (P2O7)(4-) dimer units, in different samples are similar. (C) 2000 Elsevier Science B.V. All right s reserved.