Thermal decomposition of Ru adsorption resin in the presence of steam and evaluation of migration behavior

抄録

Radioactive wastes containing water, such as operational wastes caused by decommissioning of the Fukushima Daiichi Nuclear Power Station and secondary wastes generated from the Advanced Liquid Processing System (ALPS), need to be stored in a stable condition for the long term. For ALPS-treated secondary wastes with high radioactivity levels among the radioactive wastes, intermediate treatment is thought to be one measure to reduce the potential hydrogen generation risk and storage capacity. It was found that the characteristics of secondary wastes include concerns about hydrogen generation from radiolysis and the need to reduce the volume of the waste in consideration of potential changes in composition and storage.(Oniki, T., et al., 2019) It was found that in this study, the applicability of pyrolysis technology using steam, which is expected to provide high volume reduction, stabilization and control of nuclide volatilization, to resin-based adsorbents and chelating resins used as Ru adsorption resins was evaluated. （Parruzot, B., et al., 2023 ;Miyatake, K., et al., 2008）

Resin-based adsorbent and chelating resin, which are used as Ru adsorption resins in ALPS, were heated to 1000°C, by TG-DSC, TG-MS. XAFS was used to evaluate the effect of steam addition and the structure of the residue after heating. To confirm the effect of steam addition, heating in an Ar atmosphere was also performed for comparison. In both cases, not so much increase in weight loss was observed. In the case of the resin-based adsorbent, it was confirmed that the gas generation temperature during heating became lower with the addition of water vapor, and weight loss occurred from the lower temperature. It was also confirmed that Ru in the residue was reduced to metal in both Ar and water vapor atmospheres when heated to 500°C. In the case of chelating resin, it was confirmed that the gas generation temperature during heating became partly lower when water vapor coexisted. It was also confirmed that Ru in the residue existed as an oxide when heated at 500°C in an Ar atmosphere but was reduced to a metal when heated at 500°C in a steam atmosphere. This result suggests that heating in a steam atmosphere may inhibit volatilization by reducing Ru, although the weight reduction rate does not increase so much.