Norway has discovered that a Soviet-era submarine that sank in the Norwegian Sea 30 years ago is leaking radiation at levels up to 800,000 times higher than what is normal.

Using a remote controlled vehicle to probe the wreck, researchers found extensive damage to the Komsomolets sub, which lies more than 5,500-feet down on the seafloor. Their investigation revealed the exceptionally high radiation level in the area around a ventilation duct at the wreck, according to the Norwegian Radiation and Nuclear Safety Authority.

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.

“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 Reuters.

Two nuclear warheads and a nuclear reactor remain on board the 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.

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.

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

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 men 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.