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After the Fukushima nuclear power plant accident, radionuclides containing fission products were released from the fuel debris into the cooling water. For the treatment of the contaminated cooling water, the Advanced Liquid Processing System (ALPS) facility has been operating for 7 years. Most of the cationic species of fission products are well eliminated in ALPS by sorption and/or co-precipitation. On the contrary, anionic species of the fission products are still unknown to eliminate or not. Especially iodine-129 having a high toxicity and an extremely long half-life (16M years), is present as different chemical species of iodide (I-), iodate (IO3-), and/or organo-iodine (org-I). Thus, sorption of I-129 should be studied by controlling chemical speciation. Here we report the sorption behaviors of IO3- species on the several sorbents involving activated carbon, CeO2-modified activated carbon, Ag-attached zeolite, titanate attached activated carbon, and MgO. In addition, the solidification of IO3- with alkaline-activated metakaolin (AAMK), so-called geopolymer, were studied. We measured distribution coefficients by the sorbents, leaching behavior from the I doped AAMK into a distilled water and into a sea water. We analyzed chemical species of IO3- in sorbents and AAMK by XANES using synchrotron X-ray, and position of I and chemical components present with I in the sorbents and AAMK were analyzed by SEM.
Sorption of IO3- showed that high distribution coefficients could be obtained in acid solution for activated carbon, CeO2-modified activated carbon, Ag-attached zeolite, and titanic acids attached activated carbon, and in alkaline solution for MgO. XANES analysis showed that the sorbed I was present as IO3-. SEM analysis dis not detect I within the sorbents. These results indicate that IO3- is associated by sorbents with outer sphere complexes. Almost all IO3- was solidified with AAMK. The leaching test showed that less than 1% of I in AAMK were released into distilled water and into sea water. The XANES spectrum of I in AAMK was nearly the same as that of the KIO3 standard, indicating that I is present as IO3- ion in AAMK. These results indicate that I as the chemical species of IO3- is well recovered by the sobents in acid solution, and is also well solidified in AAMK.
