Concentrations of uranium and 235U/238U ratios in soil and plant samples collected around the uranium conversion building in the JCO campus

In order to assess possible contamination by U in the JCO campus following the criticality accident, 10 soil samples and 15 plant samples were collected around the uranium conversion building. Uranium concentrations and isotopic compositions (235U/238U ratio) were determined by ICP-MS. Concentrations of Th in soil were also determined for comparison. Concentrations of U in soils were comparable to the U values for common Japanese soils. However, the U/Th ratios for these soil samples were markedly higher than the control value, suggesting possible contamination by U. The 235U/238U atom ratios in soil and plant samples were notably higher than the natural ratio, 0.00725. The highest values, 0.0162 for soil and 0.0193 for plant, were found in samples collected near the conversion building. However, a relatively high ratio was observed at a site more than 50 m from the building, indicating that enriched U may have been released not only from the conversion building but also from other unknown sources. 235U/238U atom ratios were in general higher in plants than in soils collected at the same points.