Uranium isotope ratios in the environmental samples collected after a criticality accident in the uranium conversion facilities of JCO

Soil and botanical (grass and leaf) samples collected inside and in the vicinity of the uranium conversion facilities, in which a critical accident occurred on September 30, 1999, were analyzed for uranium concentration and 235U/238U isotope ratio by inductively coupled plasma mass spectrometry. Extractable uranium showed high 235U/238U ratios in contrast to uranium in the silicate fractions which had the natural isotope ratio. One of the leaf samples gave the highest 235U/238U ratio of 2.2 which limits the minimum isotope ratio of the contaminant. The impact of the enriched uranium was estimated using the observed 235U/238U ratios and uranium concentrations by assuming the mixing of two components (natural and enriched uranium). The impact systematically increased with decreasing distance of the sampling site from the laboratory where the accident occurred, providing a clue to source identification of the enriched uranium.