– New Studies on Mystery ‘Black Substances’ Released: Fuel core materials from Fukushima plant detected — Plutonium, Uranium-236, Curium discharged into environment likely in form of fine particles (PHOTO) (ENENews, March 7,2 014):
Environmental Science & Technology (ACS Publications), March 6, 2014: Isotopic compositions of 236U and Pu isotopes in “Black Substances” collected from roadsides in Fukushima Prefecture: fallout from the Fukushima Dai-ichi Nuclear Power Plant accident — Black colored road dusts were collected in high radiation areas in Fukushima Prefecture. Measurement of 236U and Pu isotopes and 134,137Cs in samples was performed in order to confirm whether refractory elements such as U and Pu from the fuel core were discharged […] The concentrations of 134,137Cs in all samples were exceptionally high, ranging from 0.43 to 17.7 MBq/kg, respectively. 239+240Pu was detected at low levels, ranging from 0.18 to 1.14 Bq/kg and with high 238Pu/239+240Pu activity ratios of 1.64 to 2.64. 236U was successfully determined in the range 0.28 to 6.74 x10^-4 Bq/kg. The observed activity ratios for 236U/239+240Pu were in reasonable agreement with those calculated for the fuel core inventories, indicating that trace amounts of U from the fuel cores were released together with Pu isotopes, but without large fractionation. The quantities of U and 239+240Pu, emitted to the atmosphere were estimated as 2.3×10^9 Bq (150 g) and 3.9×10^6 Bq (580 mg), respectively. […] fractionation between volatile and refractory radionuclides associated with the dispersal/deposition processes with distance from the [FDNPP] was found.
Journal of Environmental Radioactivity, June 2014: Isotopic Pu, Am and Cm signatures in environmental samples contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident — Dust samples from the sides of roads (black substances) have been collected together with litter and soil samples at more than 100 sites contaminated heavily in the 20-km exclusion zones around Fukushima Dai-ichi Nuclear Power Plant (FDNPP) (Minamisoma City, and Namie, Futaba and Okuma Towns), in Iitate Village located from 25 to 45 km northwest of the plant and in southern areas from the plant. Isotopes of Pu, Am and Cm have been measured in the samples to evaluate their total releases into the environment […] When these activity ratios were compared with those for fuel core inventories in the FDNPP accident estimated by a group at JAEA, except 239,240Pu/137Cs activity ratios, fairly good agreements were found, indicating that transuranic nuclides, probably in the forms of fine particles, were released into the environment without their large fractionations. […]