Removal of radioactive substances using tannic acid resin

TEPCO operates an 'Advanced Liquid Processing System (ALPS)' as the treatment of contaminated water generated by the Fukushima Daiichi Nuclear Power Station accident. The authors carried out improvement and development using an adsorbent mainly made of tannic acid that is capable of adsorbing various nuclides from contaminated water. They applied condensation polymerization to gallic acid, which is the decomposition product of tannic acid, in porous silica beads to obtain tannic acid resin supported with porous silica. As the nuclide adsorption property of tannic acid resin, it was effective for element group of many fission products such as actinide elements, rare earth and so on. However, it was not able to adsorb anions such as iodide ion, and it had little effect on cesium and strontium. In addition, although tannic acid resin is available in seawater, it is not suitable for use under acidic condition. In order to strengthen the function of tannic acid resin and enable to adsorb more nuclides, the synthesis of tannic acid resin based on ion exchange resin was investigated. The complex adsorbent combined with imidazole type anion exchange resin was effective for I^- and IO^3-, and also effective for many elements such as rare earth elements and actinoids as with tannic acid resin alone, Furthermore, a new complex adsorbent is under development, but in the future it is also necessary to develop carriers considering post-disposal. (A.O.)