Potential overestimation of 236U releases from Sellafield reprocessing plant

Abstract This work reveals potential overestimation on uranium-236 (²³⁶U) releases from Sellafield (SF) reprocessing plant in earlier estimations. We report the 40-year time series dataset of uranium isotopes in seaweed seasonally collected from Kattegat, which is at the downstream of radioactive discharges from the European reprocessing plants La Hague (LH) and SF. When comparing the estimated values derived from the previously reconstructed ²³⁶U releases of LH and SF, our observed ²³⁶U concentrations in seaweed demonstrate generally lower levels. Our data analysis suggests nearly one order of magnitude overestimation in the recently reconstructed SF discharge reported by other authors. Such overestimation would introduce large uncertainties when using ²³⁶U as a point-source in environmental tracer applications. We foresee that this work will significantly improve the applications of radioisotope tracers in oceanic studies such as spreading of marine pollutants, ocean mixing and circulation, especially in the regions of North Atlantic and Arctic Ocean.