Determination of uranium isotopes in soil core samples collected on the JCO grounds after the criticality accident.
To evaluate the impact of the 1999 criticality accident in Tokai-mura on the U isotope composition in soils, U isotopes (235U and 238U) were determined with inductively coupled plasma-mass spectrometry (ICP-MS) for soil core samples collected on the JCO grounds after the accident. The 235U/238U ratios were higher than the natural ratio in most samples. The highest ratio observed was 0.0262. Although vertical profiles of the 235U/238U ratio differed among the soil cores, the ratios tended to be high at the surface and decreased with depth. The U concentration also changed with depth. The percentages of 235U in the excess U, estimated from the positive correlation between U concentration and the 235U/238U ratio in soil samples, were less than 4% by mass (mostly 1-3%) and were much lower than the enrichment of the U used in the uranium conversion building at the time of the criticality accident (18.8%). These findings indicate that enriched U had been released before the criticality accident during the U processing at JCO in connection with the reconversion of light water reactor fuel. Since the range of the U concentrations found was comparable to the range of uncontaminated Japanese surface soils, the amount of U added to the soil was judged negligible from a radiation protection viewpoint.
Yoshida
S
S
Environmental and Toxicological Sciences Research Group, National Institute of Radiological Sciences, Chiba-shi, Chiba, Japan. s_yoshid@nirs.go.jp
Muramatsu
Y
Y
Tagami
K
K
D007564:Japan; D013058:Mass Spectrometry; D018788:Radioactive Hazard Release; D011868:Radioisotopes / Q000032:analysis; D012987:Soil / Q000032:analysis*; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D017974:Uranium Compounds / Q000032:analysis*; D014878:Water Pollution, Radioactive / Q000032:analysis*
D011868:Radioisotopes; D012987:Soil; D012990:Soil Pollutants, Radioactive; D017974:Uranium Compounds