Secondary wind transport of radioactive materials after the Fukushima accident

Abstract

Data from the radiation monitoring network surrounding the FukushimaDai-ichi Nuclear Power Plant (FNPP) revealed that the radiation levelsgenerally decayed faster at a highly-contaminated area than atneighboring moderately-contaminated areas during the first month afterthe Fukushima nuclear accident in March, 2011. Two possible mechanismsare considered: secondary transport of radioactive dust by wind or rain,and nonuniform radionuclide ratio of contamination between radioiodine(I-131) and radiocesium (Cs-134 and Cs-137). The composition data fromsoil does not favor the latter scenario, except for the local coastalregion south of the FNPP, while inter-regional transport from thehighly-contaminated area to the moderately-contaminated areas explainsboth the general difference in the decay rate in the entire area and therelatively slow decay at a high-dose rate anomaly 40 km northwest of theFNPP.