Geochemical and U-Pb isotopic insights into uranium (U) enrichment in the soil around a nuclear fuel element plant, in Southwest China

Abstract

To assess the impact of nuclear fuel element processing on uranium(U) in the soil environment, a geochemical survey was conducted. The survey provided data on U concentration, speciation, Th/U ratio, and U and Pb isotopic composition in the soil around a nuclear fuel processing plant in Southwest China, which has been operational since 1965, to reveal the enrichment status and sources of U in the soil. The concentrations of Th and Pb in the soil were also compared. The average U concentration was 1.01-1.43 times that of the local background, and U existed primarily as residual U. The enrichment factor value indicates that U is slightly enriched in the soil. The Th/U ratio was higher than the crustal ratio and the world soil average value, indicating that some of the U in the soil has been lost due to surface runoff. The ²³⁵U/²³⁸U ratio distribution shows that a certain amount of ²³⁵U-enriched particles have sedimentation in the downwind direction of the plant soil, which results in a higher ²³⁵U/²³⁸U ratio in this direction. However, in general, the ²³⁵U/²³⁸U ratios were observed to be typical natural values. The ²⁰⁷Pb/²⁰⁶Pb ratio indicates that the U in the U ore enters the soil during nuclear fuel processing.