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Removing radioactive cesium following Fukushima

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Published: September 3, 2013

A new decontamination process developed at Tokyo Tech may prove vital in the removal of radioactive cesium from the land around Fukushima

Current decontamination methods for removing radioactive nuclides from the environment are not effective enough to cope with the scale of the Fukushima Daiichi nuclear disaster. Following calls for new research, Kenji Takeshita and Hideharu Takahashi at Tokyo Institute of Technology, together with scientists and engineers at CDM Consulting and the Radwaste and Decommissioning Center (RANDEC), have developed a novel methodology for the effective and efficient removal of radioactive cesium from soils and sewage sludge.1,2

Takeshita's team combined two techniques - a hydrothermal process followed by so-called coagulation settling (Fig.1). Firstly, they added water to contaminated solids and heated the solution to 200℃-260℃ whilst stirring in a closed container. The organic materials in the solids began to decompose under hydrothermal conditions attained by the rising heat and pressure. Next, the remained solid material was washed, small amounts of inorganic coagulant and adsorbant powders (Ferric Ferrocyanide) added and the cesium removed as a precipitate. In this way, the researchers successfully removed 96% of cesium from sewage sludge sampled in Fukushima city.

Removing contaminants from soils proved more difficult. The team extended the process to include 'blasting' - releasing the pressure in the hydrothermic solution suddenly by opening a valve, further fragmenting the decomposing solids. By blasting the solution twice, followed by coagulation settling, over 90% of cesium was removed from the soils.

The new process is highly effective and leaves little secondary waste, and the team are hopeful it will help in the decontamination of Fukushima.

Fig. 1: Tokyo Tech scientists and co-workers have developed a new combined methodology for removing radioactive cesium from soil and sewage sludge using hydrothermal and coagulant settling processes. .

Reference:

1. K. Takeshita, H. Takahashi, Y. Jinbo & A. Ishido. Restoration of water environment contaminated by radioactive cesium released from Fukushima Daiichi NPP. Proceedings of GLOBAL 2013, Salt Lake City, 2013.
2. News Focus, 'Cooling a Hot Zone', Science 339, 1028-1029
DOI: 10.1126/science.339.6123.1028
http://www.sciencemag.org/content/339/6123/1028.full

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