Thumyat Noe ’23

On March 11^th, 2011, an earthquake in northeastern Japan caused leakage of radionuclides from the Fukushima Daiichi Nuclear Power plant. Fukushima now stores the radioactive waste in designated locations, but there is an immediate need to decrease the radioactivity levels present in the stored wastes to prevent other accidents. Among the radionuclides present in contaminated wastes, scientists have determined radioactive cesium as an important removal target. Previous studies suggest that chlorine-bearing compounds mixed with calcium oxide (CaO) can facilitate the vaporization of radioactive cesium. In this study, researchers at the Chubu University of Japan exposed radioactive cesium-contaminated soil samples from the area near Fukushima Daiichi Nuclear Power plant to thermal treatment with a mixture of CaCl₂ and CaO to determine if this method is able to efficiently remove radioactive cesium in contaminated soil.

Prior to thermal treatment, researchers characterized the dried soil sample with X-ray fluorescence spectrometers. Researchers then mixed the sample with 5%, 10%, or 20%  CaCl₂ or a  mixture of CaCl₂ and CaO with the same CaCl₂ concentrations and an additional 20% CaO. Next, the mixtures underwent thermal treatment in a porcelain boat with lab-scale electrical furnace heating for 30 minutes. During this time, researchers injected 300 mL/ min of air into the reactor through an air pump to remove compounds vaporized from the soil sample. Finally, researchers calculated the removal ratio of radioactive cesium.

Researchers found that at 10% and 20% CaCl₂ addition, an increase in temperature resulted in greater removal of radioactive cesium removal; increasing CaCl₂ % addition at high temperatures also resulted in greater removal of radioactive cesium. Notably, researchers observed that CaO addition enhanced removal of radioactive cesium possibly due to a delay in the decomposition of CaCl₂ in the presence of CaO. Lastly, researchers found that the removal ratio of radioactive cesium is higher in soil with fine particle size. These results suggest that the use of thermal treatment with a mixture of CaCl₂ and CaO is a feasible solution to minimizing risks in storing radioactive waste which in turn could improve environmental wellbeing. 

Works Cited:

[1] F. Jiao, et al., Use of thermal treatment with CaCl₂ and CaO to remove ¹³⁷Cs in the soil collected from the area near the Fukushima Daiichi Nuclear Power Plant. Journal of Hazardous Materials 401, 1-7 (2021). doi: 10.1016/j.jhazmat.2020.123364.

[2] Image retrieved from: https://libreshot.com/nuclear-power-plant/