Abstract
Cementation of the secondary aqueous wastes from TEPCO Fukushima Daiichi Nuclear Power Plant is challenging due to the significant strontium content and radioactivity, leading to a potential risk of hydrogen gas generation via radiolysis of water content. The present study investigates the reduction of water content in calcium aluminate cement (CAC) with/out phosphate modification by a heat-treatment during the solidification. The reduction of water in the CAC was found restricted by the rapid formation of crystalline hydration phases, whereas the phosphate-modified system allowed the gradual reduction of water, achieving the reduction of 60% water content at 95 °C. Curing at 60–95 °C also eliminated the significant cracks found at 35 °C in the phosphate system. The possible difference in the amorphous products, NaCaPO4∙nH2O type at 35 °C and Ca(HPO4)∙xH2O type at 60–95 °C, may have contributed to the improvement in the microstructure together with the change in the pore size distribution.
Highlights
The processing of contaminated water from Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Plant results in a large amount of secondary aqueous wastes with a high strontium content and a significant radioactivity [1]
The present study investigates the application of a heat-treatment during the solidification process of a calcium aluminate cement (CAC) with/out phosphate modification to produce a cementitious material with reduced water content
Reduction of water content The weight of samples decreased during the curing period at all temperatures both in the CAC and CAP systems
Summary
The processing of contaminated water from Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Plant results in a large amount of secondary aqueous wastes with a high strontium content and a significant radioactivity [1]. To assure the safe storage of these wastes, they must be converted into a form that has a reduced risk of leakage as well as a minimised fire risk due to the hydrogen gas generation [2,3]. Such wastes can be encapsulated in cement matrices based on the Portland cement (PC). If these secondary aqueous wastes are encapsulated using a conventional cementing process based on PC, the risk of hydrogen gas generation would remain, due to the radiolysis of the water intrinsically present in the cement matrix both in the pore solution and the hydrated products
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