A new vitrification process for radioiodine has been developed for safe disposal of the spent iodine adsorbent generated from reprocessing off-gas systems. The proposed process consists of the following two steps: (1) separation of radioiodine as AgI from spent iodine adsorbent and (2) vitrification of the separated AgI with silver phosphate. An AgI-Ag2O-P2O5 glass system can homogeneously contain up to 60mol%AgI, which leads to high volume reduction efficiency (approximately 1/25). It also can vitrify the AgI without volatilization of iodine because of its low melting temperature (below 400°C). The leachabilities of iodine from simulated vitrified waste forms were evaluated by the MCC-1 static leach test in an anaerobically controlled glove box, which was purged by nitrogen gas with 3% hydrogen. The leaching behavior of the Agl-Ag2O-P2O5 glass system was influenced by the composition of the actual glass, type of leachant, and redox conditions. When the leach test was carried out using simulated ground wateroriginating from rainfall, the leach rate of iodine from 3AgI-Ag4P2O7 glass was 6×10−8g/cm2/d in the early period of the leach test at 35°C under the reducing condition, after which it decreased to 3×10−9g/cm2/d. This glass showed a lower leach rate in the simulated ground water originating from sea water or cement saturated water, since a precipitation layer was formed on the surface.

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An experimental study on the iodine sorption mechanism onto mixed solid alumina cement and calcium compounds was carried out. The solids were prepared by mixing the alumina cement with Ca(OH) 2 and/or CaSO 4 •2H 2 O. Batch experiments were performed for iodine sorption onto the solid and iodine desorption from the solid that was obtained after a sorption experiment. In order to clarify the hydrates in the solids, X-ray diffraction measurement and scanning electron microscopic observation were adopted. The iodine sorption onto the solid proceeded to replace the OH − in 4CaO•Al 2 O 3 •13H 2 O by I − in solution to form the new hydrate, 3CaO•Al 2 O 3 •CaI 2 •12H 2 O. The results of sorption and desorption experiments showed that the iodine sorption proceeded reversibly and was independent of concentration of iodine up to 1×10 −2 mole/dm 3 in solution.

An experimental study on the iodine sorption mechanism onto mixed solid alumina cement and calcium compounds was carried out. The solids were prepared by mixing the alumina cement with Ca(OH) 2 and/or CaSO 4 ·2H 2 O. Batch experiments were performed for iodine sorption onto the solid and iodine desorption from the solid that was obtained after a sorption experiment. In order to clarify the hydrates in the solids, X-ray diffraction measurement and scanning electron microscopic observation were adopted. The iodine sorption onto the solid proceeded to replace the OH − in 4CaO·Al 2 O 3 ·13H 2 O by I − in solution to form the new hydrate, 3CaO·Al 2 O 3 ·CaI 2 ·12H 2 O. The results of sorption and desorption experiments showed that the iodine sorption proceeded reversibly and was independent of concentration of iodine up to 1×10 −2 mole/dm 3 in solution.