Host: The Japan Society of Mechanical Engineers
Name : Proceedings of FDR2024 International Topical Workshop on Fukushima Decommissioning Research
Date : October 10, 2024 - October 13, 2024
Ion exchange technology has been used to decontaminate radioactive waste liquids from various sources of the nuclear industry for decades. Both organic and inorganic sorbents are in wide use in both operating nuclear power plants and also in plants under decommissioning. Fortum’s selective NURES® (NUclide REmoval System) ion exchange materials have been successfully used to treat waste liquids produced after the Fukushima accident in addition to the usual treatment of waste streams produced by normal operation of nuclear power plants and decommissioning liquids. In Fukushima ALPS system, two of the four ion exchange materials in NURES® product portfolio were used, CsTreat® and SrTreat®, to remove radiocesium and radiostrontium, respectively, from the waste liquids.
Cesium selective inorganic sorbent, CsTreat®, is based on ferrocyanide structure and provides high decontamination factors and capacity even in complex waste matrices for cesium removal. However, a concern over the potential release of cyanide from the ferrocyanide based materials has been raised especially in connection to the solidification of the used sorbent. As one of the challenges in the overall process of nuclear waste treatment is to secure a final stable state of the waste matrices, the disposal technique needs to be investigated thoroughly to assure a safe state of the waste matrix for decades. The used ion exchange materials are often solidified in various matrices and the chosen technology depends on the waste type, local regulations and power plant preferences. For NURES® materials, Fortum has developed a solidification technique called LOCKIT® which has been tested and optimized for CsTreat® solidification. To prove the final safe state of the LOCKIT® solidification product, the release of cyanide from CsTreat® needs to be assessed. In this work, the potential release of cyanide was investigated in leaching environment and in temperature gradient experiments. The tests aimed to simulate the conditions the solidified material would be exposed to in the final disposal environment. In addition, the temperature gradient tests investigated the potential release of cyanide in elevated temperatures which are relevant during the actual solidification process. The results presented provide information on the stability of the LOKIT® solidification process for ferrocyanide ion exchange material and the long term safety in regards to the potential release of cyanide.
