Concentrations of uranium and U-235/U-238 ratios in soil and plant samplescollected 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 collect ed around the uranium conversion building. Uranium concentrations and isoto pic compositions (U-235/U-238 ratio) were determined by ICP-MS. Concentrati ons 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 cont rol value, suggesting possible contamination by U. The U-235/U-238 atom rat ios 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 foun d in samples collected near the conversion building. However, a relatively high ratio was observed at a site more than 50 m from the building, indicat ing that enriched U may have been released not only from the conversion bui lding but also from other unknown sources. U-235/U-238 atom ratios were in general higher in plants than in soils collected at the same points. (C) 20 00 Elsevier Science Ltd. All rights reserved.