Radioactive Nuclides in the Incinerator Ashes of Municipal Solid Wastes before and after the Accident at the Fukushima Nuclear Power Plant

Abstract

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). Incinerator ash samples were collected in northern Kyushu, Japan, which is located approximately 1200 km west-southwest (WSW) of the Fukushima nuclear power plant, from April 2006 to March 2007 and from March 2011 to October 2011. ⁴⁰K, ¹³⁷Cs, ²⁰⁸Tl, ²¹²Pb, ²¹⁴Pb, ²¹²Bi, ²¹⁴Bi, and ²²⁸Ac were identified in the ashes before the accident (∼February 2011) and ¹³⁴Cs 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 ¹³⁴Cs and ¹³⁷Cs 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 ¹³⁴Cs and ¹³⁷Cs in 1st fly ash of municipal solid waste; one half of ¹³⁴Cs existed as water soluble salts and the other half as carbonate compounds, whereas 75% of ¹³⁷Cs 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.