The Soviets only built one nuclear-powered attack sub like Komsomolets (K-278). Its inner and outer hulls were both forged from a titanium alloy capable of carrying its crew deeper than any other vessel of its era. Today, however, over 30 years later, Komsomolets lies trapped down there permanently—5,511 feet (1,680 meters) below the Norwegian Sea—with two nuclear weapons and a leaking nuclear reactor.

That said, the situation is actually remarkably under control, according to researchers with Norway’s Radiation and Nuclear Safety Authority and its Institute of Marine Research. Their new study integrates sonar and video survey data alongside seawater, sediment, and biological samples, all collected near the K-278 wreck in July 2019. Their main takeaway: Russian leaders pulled off a surprisingly solid environmental remediation plan, even after the Berlin Wall fell.

“It was an incredible effort, especially given the state in which the country was in the early 1990s,” noted Svetlana Savranskaya, director of Russia programs for George Washington University‘s National Security Archive, who reviewed the new study for Gizmodo.

“The study that’s coming out from Norway confirms what I saw in multiple Soviet and Russian documents,” said Savranskaya, who has extensively probed similar cases of Soviet submarine crises. “They saw it as one of their top priorities to make sure that it was secured, that it was cleaned up, that it was transparent, and that they could be trusted by other international actors.”

Fire down below

K-278’s fate was sealed on April 7th, 1989 when a manageable fire in its rear compartment erupted into a blow torch, fueled by compressed air from a cracked ballast tank pipe literally fanning the flames. Only 27 members of its 69-person crew survived.

Between 1989 and 2007, Soviet and Russian expeditions plunged manned Mir submersibles to assess and continue monitoring the damage. In 1994, with evidence that the two nukes were exposed to the open ocean, torpedo tubes were sealed with titanium plugs, and other exposed areas were plated over with titanium.

“Apart from the very obvious damage to the forward section and in particular the torpedo compartment, the submarine looks like it sank the same day (as we were looking at it) rather than 30 years ago,” study coauthor Justin Gwynn, a senior scientist specializing in marine radioecology for the Norwegian government, told Gizmodo via email. “It’s just sitting upright on the seafloor.”

Norway has taken over monitoring duties on the Komsomolets sunken nuclear mausoleum in recent decades. Gwynn and his colleagues’ new analysis focused on data collected in 2019 via remotely operated submersibles sent to survey the wreck, armed with (among other tools) sonar, video, and large 11-gallon (40-liter) water sampling containers used to test for radioactive isotopes. Their most concerning find was an active leak of radioactive material from a ventilation pipe and nearby metal grill, a leak occasionally powerful enough to be visible on video.

“We were very surprised to actually see something coming out of the ventilation pipe where previous Russian investigations had detected releases from the reactor,” Gwynn told Gizmodo, adding that the visual coincided with “elevated levels of radionuclides being released.”

To better verify what these measurements might actually mean, the researchers had to turn to known ratios of plutonium and uranium isotopes used by the old Soviet fleet of nuclear-powered subs, as well as to ratios found in global fallout and emissions by nearby nuclear facilities. The quantities of certain isotopes and the ratio of plutonium-240 to plutonium-239 “provide clear evidence that releases of these radionuclides are occurring from the reactor in Komsomolets and that the nuclear fuel in the reactor is corroding,” as they wrote in the study, published today in Proceedings of the National Academy of Sciences.

Fortunately, the team found no indication that these leakages were impacting marine life or the environment locally, thanks to the material’s rapid dilution in seawater.

Even better, sediment and seawater samples taken close to K-278’s torpedo compartment found “no evidence of any plutonium from the warheads in the torpedo compartment,” confirming that Russia’s early ‘90s titanium patches have held strong decades later.

Learning ‘lessons from Chernobyl’

“Gorbachev and Yeltsin wanted to be seen as responsible international actors,” according to Savranskaya at the National Security Archive. “They did learn lessons from Chernobyl—that secrecy is, really, not helpful in these situations.”

That transparency included the Russians’ own monitoring data as well as other technical specs on K-278 needed to help the Norwegians better help interpret it, which Russia kept supplying even as its economy “goes into a complete tailspin” during the Yeltsin years, she noted.

But, not everything was likely shared. “I’m sure there are secrets that they kept because the boat itself was one-of-a-kind,” Savranskaya told Gizmodo, “technology that, at the time, was not available yet. But they did provide information—and they kept providing information throughout the 1990s.”

Back then, Russian authorities assessed that it would be too costly and too risky to simply fully remove K-278 for a more thorough disposal somewhere on land. Gwynn told Gizmodo that this was his and his colleagues’ opinion as well.

“Any potential release to the atmosphere during any salvage operation could result in contamination deposited on land that would likely have far greater and longer-term impact,” Gwynn said.

But, he added, his team would like to send more remotely operated or even manned submersibles back down to Komsomolets to better understand the leak. “We certainly would like to understand the cause of the visual release,” he wrote, “but also to understand more as to why the releases seem to vary over time.”