Levels of radionuclides in plant samples collected around the uranium conversion facility following the criticality accident in Tokai-mura

Concentrations of artificial radionuclides in plant samples collected in the surrounding areas of the uranium conversion facility of JCO Company Limited were studied following the criticality accident in Tokai-mura. Radionuclides detected in plants were 131I, 133I, 140Ba-140La and 137Cs. The highest concentrations of the nuclides were found in samples collected near the facility or its ventilation exhaust and the concentrations decreased sharply with distance. The origins of 140Ba-140La and 137Cs were thought to be from 140Xe and 137Xe, respectively, which were produced in the fission event and released to the atmosphere. The average 131I/133I activity ratio was about 21 (decay-corrected to the end of fission). Levels of the radionuclides in plants outside the JCO grounds were markedly below the intervention levels for foodstuffs in Japan.