Storyboard: Radionuclide dispersion

Radioactive contamination of the Arctic Ocean

In recent decades, radioactive contamination of the Arctic Ocean from various sources, including dumped materials and sunk submarines, has been a significant concern. Dumped materials include solid and liquid wastes, as well as reactor cores. They are the greatest sources of radioactivity in the Arctic Ocean, exceeding the contribution from reprocessing plants (IAEA, 2015).

Sources and transfer of radioactivity may be affected by climate change. In particular, nuclear testing between 1957 and 1963 on the Novaya Zemlya archipelago deposited long-lived radionuclides on glaciers. Melting of glaciers due to global warming could result in the release of long-lived radionuclides into the sea, threatening human and environmental health.

Dispersion of radionuclides in a marine system

The exchanges between dissolved and solid (suspended matter and bed sediments) phases, along with advection/diffusion, are important for many radionuclides.

In addition, these processes, especially near the sources, can be far from equilibrium. These factors should be taken into account when the dispersion of radionuclides is considered.

Our approach

To simulate the transport of radionuclides in the Arctic Ocean, the output from circulation model NEMO was used to run a 3D Lagrangian radionuclide transport model based on particle tracking and random walk algorithms.

A novel probabilistic approach for transforming particles’ states, including radioactive decay, adsorption-desorption in bed and suspended sediments, erosion, and deposition, was developed (Brovchenko et al., 2024).

Kolmogorov equations for the state transition probabilities were applied to pre-calculate a matrix of all possible particle states during a time step. The

Monte-Carlo method was used to determine the new state of each particle at the next time step.

Probability distribution for historic and projection case studies of ¹³⁷Cs dispersion from sunk submarines and ice sheet

1. The Lagrangian simulations of ¹³⁷Cs transport in the Arctic Ocean seas demonstrate varied pathways depending on source locations and climate change of ocean circulation. The most important factor influencing the path of spread was the depth of the radioactivity outflow.
2. Whereas in the deep-water scenario of submarine “Komsomolets”, a portion of the caesium ending up in the bottom sediments is less than 1% of the activity, this part reaches 89% in the “K-29” scenario for in shallow Abrosimov fjord in the Kara Sea and
3. Qualitatively, the dispersion of ¹³⁷Cs is similar for historical and projection calculations. However, a portion of activity ending up in the bottom for historical and projection scenarios can differ by more than 50%.

Radionuclide transfer from the bottom sediment to the marine organisms can be an important radiological factor in Arctic

Implications for polar systems, the Earth System and society

Based on model simulation, we showed that the bottom deposit is an important source of radioactivity in the benthic zone in the shelf seas of the Arctic Ocean. Transfer of activity in the marine food chain that includes pathways from bottom sediment through deposit feeders can result in doses for biota and humans.

Recommendations

Currently, no significant radioactive leaks from locations of dumped materials and sunk submarines have been detected in the Arctic Ocean. However, such sources may emerge in the future, particularly as a result of melting coastal glaciers on Novaya Zemlya. Therefore, monitoring of these locations including bottom sediments is necessary in the next decades.

Future research priorities

A specific problem is the role of ice in the transport of radioactivity, both through the entrainment of highly radioactive particles from bottom sediments during ice formation and through the transport of contaminated particles in the ocean. Although this problem, as it applies to the Kara Sea, has already been examined in several studies, it is necessary to revisit it.