Radioactive contamination in sediments near the sunken nuclear submarine Komsomolets, SW of Bear Island in the Norwegian Sea

The Soviet nuclear submarine Komsomolets sank on the 7th of April 1989, 185 km southwest of the Bear Island in the Norwegian Sea to a depth of about 1655 m. The submarine contains one nuclear reactor, containing long-lived radionuclides such as caesium-137 (137Cs) along with other fission and activation products, in addition to two mixed uranium (U)/plutonium (Pu) nuclear warheads containing weapons grade plutonium. The Institute of Marine Research (IMR) has, in cooperation with the Norwegian Radiation Protection Authority (NRPA), monitored the areas adjacent to Komsomolets since 1993, where bottom water and sediment samples have been analysed for 137Cs and plutonium-239, 240 (239+240Pu). Because of the large depth and strong currents in the area, it has not been possible to determine how close to the wreck the samples were taken. The present study has been carried out at the IMR. During sampling from R/V G. O. Sars in April 2013, Komsomolets was precisely located using a Kongsberg EM302 multibeam echosounder, a Simrad EK60 single beam echosounder and an Olex 3D bottom-mapping system. To ensure precise positioning of the sampling equipment, a Simrad MST342 wireless acoustic transponder was attached to the box-corer. The transponder communicated with R/V G. O. Sars' dynamic positioning system, the Kongsberg HiPAP (High Precision Acoustic Positioning), while collecting the sediment samples. An attempt to use the acoustic transponder was also performed in 2012, but due to weather conditions and lack of time, the attempt did not succeed. 1 cm thick slices from fifteen sediment cores collected adjacent to Komsomolets in 2012 and 2013 have been analysed for 137Cs. A selection of the 0-1 and 1-2 cm layers from the 2013 sampling were analysed for 239+240Pu, 238Pu, americium (241Am) and uranium-238 (238U). Further, isotope ratios were determined. Grain size analyses on the 0-1 cm layers of the selected cores were also performed, as well as dating of two cores from the 2012 sampling. No 137Cs peaks was found in any of the cores, neither no elevated activity concentrations of Pu-isotopes, 241Am and 238U. The activity concentrations of 137Cs in the 0-1 cm layers were comparable to 137Cs activity concentrations in surface sediments found in the area adjacent to Komsomolets in previous years. This was also the case for the 137Cs activity concentrations in surface sediments found elsewhere in the Barents Sea and deep areas of the Norwegian and Greenland Seas. Although several model studies have shown that a radioactive leakage from Komsomolets will have insignificant impact on fish and other marine organisms, there are still public concerns about the condition of the submarine and the potential for radioactive leakage