April 25, 2026: After 37 years on, there are no signs of leakage from plutonium warheads. Two recent studies of seabed sediments near the sunken nuclear submarine Komsomolets/K-278 in the Norwegian Sea revealed that no plutonium contamination beyond natural background levels. Given Russian submarines, this is welcome news. One Russian sub was nick-named “Hiroshima” by its nervous crew.

The submarine included one nuclear reactor and two plutonium warheads. The vessel sat on the seafloor approximately 250 kilometers southwest of Bear Island. Since its sinking in early 1989, there have been fears that radioactive leakage could affect the marine environment.

The Norwegian and Barents Seas are among the world’s most productive marine ecosystems and support some of the largest fish stocks on the planet. Nevertheless, two recent studies by Russia and Norway found no evidence of weapons-grade plutonium in residues or seawater near the wreck.

The Russian study, conducted by scientists from the Russian Academy of Sciences, is based on samples collected during the 68th expedition of the research vessel Akademik Mstislav Keldysh. The vessel visited the wreck site numerous times since the early 1990s.

The activity of plutonium isotopes in bottom sediments at the site corresponds to background levels for the Arctic. This indicates that the submarine’s hull is currently effectively containing hazardous materials. The findings were published recently in the journal Marine Pollution Bulletin.

Previous joint Norwegian Russian studies have detected releases of radionuclides from the reactor via a ventilation pipe, but the two plutonium warheads are believed to remain intact. This is despite significant damage to the submarine’s forward section, including both the outer hull and the inner pressure hull, particularly around the torpedo compartment. The warheads are mounted on torpedoes.

A recent Norwegian study, published based on earlier expeditions to the Komsomolets, reached a similar conclusion: No evidence was found of plutonium in the surrounding environment near the damaged forward section of the submarine originating from the nuclear warheads.

Leakage of caesium-137 and strontium-90 from the nuclear reactor has been confirmed, but there is no evidence that these isotopes are accumulating in the marine environment.

The highest levels recorded were around 800 becquerels per liter of seawater inside the wreck’s pipe systems. By comparison, typical levels in the Norwegian Sea today are around 0.001 becquerels per liter indicating that measured samples were approximately 800,000 times higher than normal.

Despite more than 30 years of releases from the reactor, there is little evidence of any build-up of radionuclides in the surrounding environment, as they appear to be rapidly diluted in seawater. These findings have previously been reported by the Barents Observer.

The Komsomolets was on a training mission to the waters where the shallow Barents Sea meets the deeper Norwegian Sea when it sank after a fire on April 7, 1989. The submarine had Zapadnaya Litsa on the Kola Peninsula as home port.

The Russian expedition to the wreck site formed part of an extensive study of plutonium contamination on the Arctic seabed. In total, sediment samples from 22 sites across the Norwegian and Barents Seas were collected and analyzed.

The highest plutonium levels were found north of Novaya Zemlya in the Russian Arctic, originating from global fallout from nuclear testing in the 1950s and 1960s.

The highest 239+240Pu activity concentrations were identified north of Novaya Zemlya archipelago and reached 2314 ± 178 mBq·kg−1. Although three to four times higher than normal background, the results pose no risk to marine life or humans.

Novaya Zemlya served as the Soviet Union’s primary testing ground for thermonuclear weapons. Between 1954 and 1990, a total of 224 tests were carried out across the archipelago, 88 of which were detonated in the atmosphere. The most powerful of these was the so-called Tsar Bomba, detonated on 30 October 1961, with a yield of 58 megatons which was about 4,000 times more powerful than the bomb dropped on Hiroshima.

The Barents Observer has previously reported that radioactive material from this testing program is now leaking into the marine environment. As the Arctic warms, glaciers on the northern island of Novaya Zemlya are melting, releasing fallout that had long been trapped in the ice.

Another potential source of plutonium in sediments north of Novaya Zemlya is the release from the Mayak plant, located north of Chelyabinsk in the southern Urals.

Significant discharges of radionuclides occurred between 1949 and 1951, when cooling water from the Soviet Union’s first plutonium production reactor was released into the Techa River. From there, it flowed into the Irtysh River and continued northwards via the Ob River, eventually reaching the Kara and Barents Seas.

Soviet scientists detected plutonium in sediments in the Ob Bay, east of the Yamal Peninsula, as early as 1951.