The highest measurement researchers recorded stood at 800 becquerel per liter; radiation levels in that body of water typically remain around 0.001 Bq per liter, the authority said.

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“This is, of course, a higher level than we would usually measure out at sea, but the levels we have found now are not alarming,” said expedition leader Hilde Elise Heldal of the Norwegian Institute of Marine Research, according to the Reuters news agency.

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Two nuclear warheads and a nuclear reactor remain on board the defunct 400-foot-long submarine. Norwegian and Russian authorities have periodically examined the wreck to monitor radiation levels and assess the pollution risks. Russian investigators had previously found small radiation leaks there in the 1990s and in 2007, the Norwegian Radiation and Nuclear Safety Authority said.

Heldal said team members “weren’t surprised” to discover elevated radiation levels this time around, the BBC reported.

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The discovery should not cause alarm, she added. Radioactive cesium is easily diluted in the depths of the Norwegian Sea, and few fish live in the area surrounding the wreck.

"What we have found … has very little impact on Norwegian fish and seafood,” Heldal said, according to the Associated Press. “In general, cesium levels in the Norwegian Sea are very low, and as the wreck is so deep, the pollution from Komsomolets is quickly diluted.”

The Komsomolets — which translates to “member of the Young Communist League” — was a Russian nuclear attack submarine launched in May 1983 from Severodvinsk, a city on the Barents Sea. Sixty-nine crew members manned the vessel — the world’s deepest diving submarine at the time — according to a U.S. Central Intelligence Agency publication on the Komsomolets disaster. It had the capacity to launch both nuclear and conventional weapons.

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The Komsomolets had been patrolling the waters for 39 days when a fire broke out in one compartment and quickly spread through the submarine on April 7, 1989, according to the CIA report. Forty-two crew died either in the fire or while awaiting rescue, and the sub sank to the bottom of the sea.

The joint Norwegian-Russian expedition to the site this month was the first in which researchers used a remotely operated vehicle to examine and film the remains of the submarine. The team released an eerie video of the wreckage this week, showing intact torpedoes lying amid the destruction fire and time wrought on the titanium-hulled sub.