Title : Effect of transition metal oxides in silver tellurite glass
Iodine (I-129) is a radioactive isotope which has half-life of 15.7 million years. The radioactive iodine is produced by nuclear fission in nuclear power plants. Due to iodine has a long half-life with high mobility in the environment, the iodine should be captured and immobilized. In the off-gas treatment system, silver-loaded zeolite filter has been used to collect iodine as a form of AgI, which has been regarded as a durable compound. However, the AgI itself could not be a final waste form because it could not satisfy the waste acceptance criteria. Therefore, it should be immobilized into a suitable matrix. Among the several matrices, silver tellurite glass is considered as a one of the promising candidates of AgI immobilization matrix. In this study, transition metal oxides such as WO3, MoO3 and V2O5 were added to silver tellurite glass (AgI-Ag2O-TeO2), respectively. Their effect was tested as an iodine immobilization matrix. The melt-quenching process was used to produce the glass samples. The mixtures of the glass precursors were melted at 800°C for 1 h in alumina crucibles with ambient atmosphere. The loss of the elements comprising the glass was not significant from the XRF results. The loading of iodine in the immobilization matrix was approximately 13-15 wt%, excluding the oxygen. The normalized releases of all elements obtained by PCT-A were below the order of 10-1 g/m2, satisfying the U.S. regulations (< 2 g/m2). Structural analysis was conducted to reveal the effects of the transition metal oxides on the releases of all elements. The release of iodine decreased with the addition of WO3, MoO3 and V2O5. The transition metal oxides suppressed the release of iodine by densifying the TeO4 polyhedra. The densification of the TeO4 polyhedra resulted in the stabilization of the iodine in the glass matrix. The release of silver depended on the type and concentration of the transition metal oxide. The silver release pattern resulted from the addition of V2O5 was slightly different from those of WO3 and MoO3. However, it was not significantly affected by the increase in the amount of the additives. All the transition metal ions considered in the present study remained stable with the increase in the concentrations of the additives in the silver tellurite glass. It was concluded that densification was occurred by adding transition metal ions such as tungsten, molybdenum, or vanadium into the silver tellurite glass structure. The additives stabilized tellurium ion, a glass network former, to prevent its release from the glass matrix.
Audience Take Away:
- Leaching effect for each additive
- Optimization of glass composition containing radioactive iodine
- How to dispose of radioactive Iodine