It’s been almost three weeks since a nuclear accident took place near the secret military city of Sarov, and Russia has only now begun to acknowledge it. Yesterday, the country’s weather service reported the elevated presence of four isotopes in the environment while still claiming that no particular danger exists:

Russia’s state weather and environment monitoring agency on Monday released new details about a brief spike in radioactivity following a mysterious explosion at the navy’s testing range that has been surrounded by secrecy and fueled fears of increased radiation levels.

The Aug. 8 incident at the Russian navy’s range in Nyonoksa on the White Sea killed two servicemen and five nuclear engineers and injured six others. The authorities reported a rise in radiation levels in nearby Severodvinsk, but insisted it didn’t pose any danger.

Russia’s state weather and environmental monitoring agency Rosgidromet said Monday the brief rise in radiation levels was caused by a cloud of radioactive gases containing isotopes of barium, strontium and lanthanum that drifted across the area. The agency said its monitoring has found no trace of radiation in air or ground samples since Aug. 8.

Russia has finally — if indirectly — acknowledged that the accident involved their new nuclear-powered cruise missile, which NATO calls Skyfall:

Russian officials have not conceded that the explosion involved the missile called the Skyfall. But on Monday, a Russian diplomat for the first time spoke of the accident in terms of the purpose for such a missile.

The diplomat, Aleksei Karpov, Russia’s envoy to international organizations in Vienna, blamed the United States for setting Russia on the path to developing a new device by withdrawing from an antiballistic missile treaty over 15 years ago.

Just how bad was this explosion? The types of isotopes in the leading edge of the cloud makes it clear that this was a reactor explosion, as was Chernobyl in 1986, if not on the same scale. It also leads observers to conclude that the radiation risk is likely worse in the region than Russia’s weather service admits:

“These are fission products,” Joshua Pollack, a leading expert on nuclear and missile proliferation, told Insider. “If anyone still doubts that a nuclear reactor was involved in this incident, this report should go a long way toward resolving that.”

Alexander Uvarov, the editor of the independent news site AtomInfo.ru, told the news agency RIA Novosti that these isotopes were products of nuclear fission involving uranium, Agence France-Presse reported Monday. This collection of radioisotopes could be released by a reaction involving uranium-235.

Nils Bohmer, a Norwegian nuclear-safety expert, told The Barents Observer that “the presence of decay products like barium and strontium is coming from a nuclear chain reaction,” adding that it was evidence that it “was a nuclear reactor that exploded.”

The Russians have acted as though the danger was higher than they were willing to admit on camera. In their zeal to protect themselves from criticism over the accident, Russian authorities left residents in the dark about the risks, including the first responders:

The Defense Ministry denied any radiation leak even as the local administration in Severodvinsk reported a hike in radiation levels and told residents to stay indoors — a move that prompted frightened residents to buy iodine, which can help reduce risks from exposure to radiation.

Russian media reported that the victims of the explosion received high doses of radiation. They said that medical workers at the Arkhangelsk city hospital that treated three of those injured said they hadn’t been warned that they would treat people exposed to radiation and lacked elementary protective gear.

The Moscow Times on Monday cited Igor Semin, a cardiovascular surgeon at the hospital, who scathingly criticized the authorities in a social network post for failing to warn the hospital workers about the deadly risks. “They were abandoned and left to fend for themselves,” the newspaper quoted Semin as saying.

Anyone who has studied the Chernobyl accident will find frightening parallels in this new accident. For years, the Soviets denied the true scope of the accident, and in the first few hours denied an accident had taken place at all. When Western nations began detecting high levels of radiation on the winds, the Soviets admitted that an accident had taken place but denied the scope of the problem. They delayed evacuations so as not to embarrass the political leadership, lied to the first responders, and only admitted to the true nature of the accident after the Soviet system had collapsed — bad engineering combined with incompetent operation.

This accident may not be anywhere near as bad as Chernobyl, but given the Russian government’s desire to follow the Chernobyl playbook, it must be pretty bad on its own. They’re only admitting to what cannot be denied — the dispersal of radioactive elements — while still denying any other implications of what seems clearly to be a reactor explosion, which would be a highly contaminative event. The need for secrecy suggests something closer to the worst-case scenario rather than the best-case scenario.

Perhaps this will convince Russia and others to dispense with the idea of nuclear propulsion on missiles. Don’t count on that, though; Chernobyl should have forced the Soviets to shut down all of its RBMK-type reactors, but they continued to operate — and in fact ten still operate in Russia. Some lessons never quite get learned when accountability is non-existent.