Study on contaminated water decontamination method based on solvent extraction method using incombustible HFC

As for the treatment of contaminated water generated by the Fukushima Daiichi Nuclear Power Station accident, a certain progress is seen in reducing the amount of contaminated water using a second Cs adsorption apparatus that uses an adsorbent and a multiple nuclides separation/removal facility. On the other hand, a large amount of secondary waste such as adsorbents accumulates, and this treatment is a future task. The authors propose a compact solvent extraction method with high removal performance without discharging secondary waste, which is capable of deploying on the fields. The crown ether diluent that has been studied so far is flammable and highly toxic, so there is a problem that the load on the environment is large. The authors investigated crown ether as extractant, perfluoro ether as co-extractant, and nonflammable hydrofluorocarbon (HFC) as diluent, and found the optimum combination against Sr and Cs. As a result, the following have become possible: aqueous phase after removal of metallic ions is discharged, organic layer is distilled to recover HFC via distillation, and residue with low volume is treated as high radioactive waste. This is a simple method where selectively extracted radioactive materials can be isolated through the distillation operation of HFC without operation like reverse extraction and can be sent directly to waste treatment such as glass solidification. Thus, the solvent extraction method is capable of regenerating and reusing water and HFC, and has expandability to debris processing in the future. (A.O.)