The failed missile test that ended in an explosion killing five scientists last week on Russia's White Sea involved a small nuclear reactor, according to a top official at the institute where they worked.
The institute is working on small-scale power sources that use "radioactive materials, including fissile and radioisotope materials" for the Defense Ministry and civilian uses, Vyacheslav Soloviev, scientific director of the institute, said in a video.
The men were national heroes and the "elite of the Russian Federal Nuclear Center," Director Valentin Kostyukov said in the video, which was also posted on an official website in Sarov, a high-security city devoted to nuclear research less than 250 miles east of Moscow.
The blast occurred Aug. 8 during a test of a missile that used "isotope power sources" on an offshore platform in the Arkhangelsk region, close to the Arctic Circle, Russia's state nuclear company Rosatom said. The Defense Ministry initially reported two were killed in the accident, which it said involved testing of a liquid-fueled missile engine.
The incident caused a brief spike in radiation in the port city of Severodvinsk, said a statement on the local administration's website that was removed. The military said radiation levels were normal but disclosed few details.
News of the explosion set off a run on iodine, which is believed to help prevent the absorption of radiation.
Norway said it had stepped up radiation monitoring after the incident but hadn't detected anything abnormal.
Southerly winds and the distance between the border and the explosion make it unlikely that Finland will detect any radiation, said Pia Vesterbacka, director at Finland's Radiation and Nuclear Safety Authority.
Rosatom declined to comment on the incident Monday.
Russian media have speculated that the weapon being tested was the SSC-X-9 Skyfall, known in Russia as the Burevestnik, a nuclear-powered cruise missile that President Vladimir Putin introduced to the world in a brief animated segment during his state-of-the-nation address last year.
The incident comes after a series of massive explosions earlier last week at a Siberian military depot killed one and injured 13, and forced the evacuation of 16,500 people from their homes.
Russia's navy has suffered numerous high-profile accidents over the years, including a July fire aboard a nuclear-powered submarine in the Barents Sea that killed 14 sailors. A top naval official later said the men gave their lives preventing a "planetary catastrophe."
