Baselga-Cervera, and 4 co-authors, reported in late 2018 that as a normal result from the nuclear fuel cycle, large amounts of depleted uranium (DU) tails are piling up, waiting for possible re-use or final disposal. To date, the recovery of the residual 235U isotope contained in DU has been conducted only marginally by physical processes. Relative isotope abundances are often mediated by biological processes, and the biologically driven U isotopic fractionation has been previously identifed in reducing bacteria. The authors' results indicate that the cells of two microalgal strains (freshwater Chlamydomonas sp. (ChlGS) and marine Tetraselmis mediterranea (TmmRU)) took up DU from the exposure solutions, inducing U isotopic fractionation with a preference for the fssile 235U isotope over 238U. The n(235U)/n(238U) isotopic fractionation magnitudes (δ235) were 23.6±12.5‰ and 370.4±103.9‰, respectively. These results open up new perspectives on the re-enrichment of DU tailings, ofering a potential biological alternative to obtain reprocessed natural-equivalent uranium.
Additionally, their findings present implications for identifying biological signatures in the geologic records. The authors concluded that the preferential accumulation of the fssile 235U isotope in sediments might be a proxy for the activity and presence of microalgae. U fractionation biological fngerprints in ancient sedimentary rocks would provide insights into ancient microbial activity and establish temporal constraints. Additionally, the authors' fndings might provide insights into the Oklo phenomenon on the assumption of a microbial contribution in the initiation of the natural nuclear reactions. Several factors probably contribute to these unique chain reactions.
Two thousand million years ago – the same time proposed for Oklo’s event – 235U made up approximately 3% of the natural U, a condition that makes possible the starting of a fission reaction. However, a U-rich mineral deposit needs to be formed to obtain a critical mass. Most likely, the presence of increasing oxygen in the Earth’s atmosphere enabled the U fux and subsequent concentration in U ore bodies. The direction and magnitude of the observed microalgal U isotopic fractionation during bioaccumulation could support the biological hypothesis of the origin of the natural nuclear reactions.
Managed & Built by I2M Consulting, LLC | © 2010-
