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 Central Intelligence Agency. report. 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 Komsomolets was a nuclear-powered attack submarine, built in the early 1980s.
Several samples taken in and around a ventilation duct on the wreck of the submarine contained far higher levels of radioactive cesium than you would normally find in the Norwegian Sea, the institute said in a statement.
'The levels we detected were clearly above what is normal in the oceans, but they weren't alarmingly high'.
Ms Heldal said that the radiation levels were not dangerously high, referring to the permitted limit for radioactive caesium in food.
Norwegian authorities have carried out regular expeditions to the sunken submarine, sometimes in coordination with their Russian counterparts, to monitor radiation levels in the sea, but this year's inspection was the first time a remotely operated vehicle - called Aegir 6000 - was used to film the wreckage and take samples which will be analyzed.
"What we have found during has very little impact on Norwegian fish and seafood", she added.
The joint Norwegian-Russian expedition set off Saturday from Tromsoe, northern Norway, to study the wreck site.
The Norwegian research vessel GO Sars arrived on location Sunday and sent down a remote-controlled submersible, which made the measurements that will be analysed further at a later stage, the institute said.
Russian Federation has suffered a number of high-profile submarine disasters. The fire itself killed only a handful of sailors - but dozens of others died from the cold as they awaited rescue.
In addition to Heldal's description of the need to reassure Norwegian fishermen the local food chain has not been contaminated by radiation, the other obvious reason for intense interest in the latest survey of the Komsomolets is that Norway just assisted Russian Federation with a disturbingly similar accident, a fire that killed 14 sailors aboard a mysterious submarine Moscow has depicted as a deep-sea research vessel.
Russian Defense Minister Sergei Shoigu said the sub, believed to be the Losharik, was on a research mission to measure sea depths in the Barents Sea.
Some others survived, although there has been no confirmation of how many.
Officials didn't name the nuclear-powered vessel, but Russian media reported that it was Russia's most secret submersible, the Losharik.