2020 Volume 20 Issue Special_Issue Pages S-1-S-227
The safe management and disposal of radioactive wastes are of critical importance for maintaining a sustainable society. In nuclear waste management, cement and concrete are commonly used to immobilize radioactive waste. Cementation is a common technique used for conditioning low-level and intermediate-level radioactive wastes, which should ensure safe interim storage of waste packages and act as a first long-term barrier during waste disposal. In addition, cement-based materials are utilized for construction and barrier materials in surface disposals for very low-level to low-level waste and deep geological disposals for low-level, intermediate-level, and high-level wastes. Furthermore, recovery from the nuclear disaster at the Fukushima Daiichi Nuclear Power Station (F1NPS) is an important and urgent issue in Japan. To solve the difficult problems associated with radioactive contaminated materials in the plant and in the environment, contributions of cement and concrete technologies are highly expected. The understanding end prediction of the long-term evolution of cement materials interacting with wastes and other barrier materials during interim and final storage is indispensable and needs to be studied by experts from different scientific and engineering disciplines. The very long times associated with the safe disposal of radioactive waste, which are well beyond the lifetime of ordinal engineered structures and therefore not experimentally accessible, make this task even more demanding. n the first part of this special issue, three technical contributions summarize research and development projects for nuclear waste management with cement and concrete technologies in Japan. Nakarai et al. (20-359) and Ichikawa and Hamamoto (19-1275) give general overviews on the use of cement-based materials for low-level radioactive waste (LLW) and for high-level radioactive waste (HLW), respectively. Furthermore, Abe and Iida (20-236) present a comparative discussion of approaches used for LLW in Japan and Belgium. In the second part, the contributions concentrate on processes and applications related to the performance assessment of cement and concrete for nuclear waste management. The scientific papers describe sorption experiments with Cl, I, HTO, and C by Nedyalkova et al. (19-811), diffusion experiments with NaCl of leached cement paste by Kurmisawa et al. (19-426), leaching experiments of cement paste with quick setting admixture by Yokozeki et al. (19-1173), immersion experiments of cement-bentonite samples by Nakarai et al. (19-433, 19-447), and chemo-mechanical modelling of degraded concrete by Oda et al. (19-1075). Finally, the third part contains contributions that investigate, in a broad sense, how cement and concrete technologies can be used to deal with the aftermath of the F1NPS nuclear disaster. At first, a technical paper by Igarashi et al. (19-950) summarizes the outcome of a research initiative that aimed at identifying the cause and extent of radioactive contamination of concrete at the F1NPS. A set of scientific contributions is related to water absorption tests and numerical analysis with a simple moisture transport modeling by Kiran et al. (18-588, 19-168), sorption experiments with Cs and Sr and thermodynamic equilibrium model by Tomita et al. (19-1061), molecular dynamics simulations of Cs sorption by Duque-Redondo et al. (19-95), characterization of calcium aluminate cement containing SrCl2 by Mohammed et al. (19-1296), and diffusion experiments with Cs and Sr by Yamada et al. (19-756). The broad research topics presented in this special issue emphasized the importance of cement and concrete technologies to solve the ongoing issues of radioactive waste management, including F1NPS decommissioning and environmental recovery from radionuclide contamination.