European nuclear reprocessing plants have discharged radioactive waste into the sea since the early 1950s. The waste material is swept away by ocean currents and can be observed both in sea-ice and sea-water in the Arctic Ocean and at the bottom of the Atlantic Ocean. While discharges of most radioactive species have been reduced the last two decades, discharges of Iodine-129 from Sellafield (UK) and La Hague (France) greatly increased during the 1990s. Naturally occurring concentration of Iodine-129 is insignificant compared to the concentration in the sea after being contaminated by discharges from Sellafield and La Hague.
Ironically, radioactive waste material from these sources has proven to be very useful to infer details of ocean pathways and their timescales. The observed propagation of Iodine-129 from its sources and into the Arctic Ocean and the North Atlantic provides a useful benchmark which ocean models can be tested against. Feeding an ocean model with the historically release rates of Iodine-129 from the reprocessing plants and simulating the subsequent transport by ocean currents, one can directly compare the simulated levels of radioactivity from the model with observed values.
The new publication in Environmental Fluid Mechanics presents a unique comparison of observed and modeled levels of Iodine-129 in the Arctic and Atlantic Oceans. The ocean model developed at the Nansen Center and the Bjerknes Centre shows impressive skills in predicting the magnitude and time history of Iodine-129 in the ocean. In particular, the model representation of Iodine-129 in deep layers in the Atlantic Ocean is fairly accurately captured, thus indicating that the model is able to predict the formation of dense waters ventilating the global oceans.
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| Figure of Iodine-129 in deep layers of the Atlantic Ocean: The map shows the simulated concentration of Iodine-129 (the logarithm of number of Iodine-129 atoms per liter seawater) in the depth of the Atlantic Ocean. |
In addition to using discharged radioactive waste for model validation purposes, the simulated propagation can supplement the limited number of observations to form a more complete picture of the oceanic pathways and timescales of Iodine-129. A model system with the capability documented in this publication could be used to monitor future radioactive releases from Sellafield and La Hague and also monitor and predict the impact of accidental releases of radioactive or toxic waste in the ocean.
This work is a part of the project Arctic Radioactive Contamination, financed by the Research Council of Norway.
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