[H-CG24] Nuclear Energy and Geoscience

[HCG24-P09] Manufacturing and design rationale of alkali activated materials using molten fly ash

*Yusuke Ohya¹, CHAERUN Raudhatul Islam¹, Hirohisa Yamada², Isamu Kudo³, Tatsumi Kuroki³, Nobuyuki Sekine³, Masahiro Taniguchi⁴, Kikuchi Ryosuke⁵, Tsubasa Otake⁵, Tsutomu Sato⁵ (1.Graduate School of Engineering Hokkaido university, 2.National Institute of Advanced Industrial Science and Technology, 3.FUJI ELECTRIC CO., LTD, 4.TAISEI CORPORATION, 5.Faculty of Engineering Hokkaido university)

A large amount of radioactive cesium (Cs) was released into the environment and contaminated the surrounding soil and plants in the accident at Fukushima Daiichi Nuclear Power station (FDNPS). The Cs-contaminated soil was removed and classified based on its properties, while the Cs-contaminated plants were burned into ash. The molten fly ashes are heavily contaminated by Cs which is easily extracted by water. Therefore, stabilization and solidification of the ash are urgent issue for safety storage and disposal. Many previous studies have investigated a cement material as a matrix of the waste form, which matrix could immobilize radioactive nuclides. However, unfortunately, Cs retention cannot be expected for cement waste based on the result of previous published studies. On the other hand, geopolymer matrix recently attracts rising for radionuclide immobilization. Geopolymer is an interlinked tetrahedral polymer containing amorphous alumina-silicate (Si-O-Al) with alkali cations (K⁺) as a charge balance. Geopolymer is typically made by condensing a mixture of metakaolin binder and alkali-activator solutions. The chemical compositions of Cs-contaminated ashes contain reactive Si and Al, therefore replacing metakaolin with Cs-contaminated ash were considered in this study. However, manufacturing geopolymer using ash as a binder to immobilize Cs is more complex than that using metakaolin due to its high reactive calcium (Ca) content. When Ca-content ash is mixed with alkali-activator, cement phases such as Ca silicate hydrate might be produced and affect Cs immobilization.
This study investigated how to manufacture geopolymer waste using the molten fly ash and improve Cs immobilization in the waste. Recipe for the manufacturing of the specimens which have high flowability for agitation, strength, and immobilization capacity of Cs. In this presentation, the authors will present about the process of acquiring the recipe that resulted from various trials.