Investigation of radiocesium volatilization from soil by in-situ ground heating

Department of Partnership Operations for Environmental Remediation, Headquarters of Fukushima Partne; Ningyo-toge Environmental Engineering Center; Vitrification Technology Development Department, Tokai Reprocessing Technology Development Center; Environmental Protection Section, Radiation Protection Department

After the Fukushima nuclear accident, extensive area was contaminated with radionuclides from the Fukushima Daiichi Nuclear Power Plant and various methods have been investigated to remedy such contamination. To understand potential of in-situ ground heating and radionuclide desorption, behaviors of ground temperature and of radiocesium volatility by in-situ heating was investigated. More than 15 minutes was necessary to accomplish melting temperature of several cesium compounds by heating using portable burner and maximum temperature was about 700 degree in Celsius. At the time ground surface temperature was about 600 degree, the temperature at 1cm depth was about 300 degree, whereas the temperature at 5cm depth was 50-60 degree. Under the condition of heating temperature of 600-1,300 degree and heating period of 5-60 minutes, activity of Cs-134 and Cs-137 varied in the range of -9.8 to +14.0% after heating using electric furnace and any volatility of radiocesium was not recognized. TG/DTA analysis for soil and zeolite (mordenite) which mixed with nonradioactive Cs compound each were also carried out to understand chemical form and volatility behavior of radiocesium. It is suggested that chemical compound e.g., CsAlSiO would be formed when SiO and AlO3 were composed in the system and radiocesium would remain in soil under the high temperature condition, whereas Cs in CsCO would be volatized in the SiO and/or AlO free system.