Radioactive nuclides in the incinerator ashes of municipal solid wastes were determined by γ-ray spectrometry before and after the accident at the Fukushima nuclear power plant (March 11, 2011 214 Bi, and 228 Ac were identified in the ashes before the accident (~February 2011) and 134 Cs was identified along with these eight nuclides in the ashes after the accident (March 2011~). A sequential extraction procedure based on a modified Tessier method with added water extraction was used for 1st fly ash sampled in August 2011 because the highest activity concentrations of 134 Cs and 137 Cs were observed for this sample. The speciation of radioactive nuclides in the fly ash was achieved by γ-ray spectrometry and powder X-ray diffractometry for the extraction residues. Little variation was observed in the distribution of the chemical forms of 134 Cs existed as water soluble salts with the remainder as carbonates(10%) and sulfides (15%). These results show that 88% of the total radioactive Cs existed in water soluble and ion extractive forms and might be at risk for elution and diffusion with rain and wind.
The use of standard fly ash was developed and evaluated for gamma-ray spectrometry of radioactive cesium. Fly ash from municipal solid waste incineration was sampled at Fukushima prefecture. Standard fly ash was prepared by pulverization, sieving, and homogenization. The homogeneity and conservation of prepared standard sample were estimated using variance analysis after the Cochran test.Results show that the relative standard deviations of radioactivity were 3.0 % for 134 Cs and 0.94 % for 137 Cs. No significant difference was found for within-bottle and the between-bottle variances. Elemental analysis of the fly ash sample was done using X-ray fluorescence analysis. Concentrations of radioactive cesium corrected based on self-absorption coefficient were evaluated using component analysis results.This method, prepared for standard fly ash, is expected to be useful to assess fly ash containing radioactive cesium.Keywords : fly ash of municipal solid waste incineration, radioactive cesium, standard sample, gamma-ray spectrometry, homogeneity test 藤井 健悟 ・ 大渕 敦司 ・ 岩鼻 雄基 ・ 萩原 健太 ・ 小池 裕也
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