The military garrison near Nyonoksa in Arkhangelsk Region, Russia, on Oct. 7, 2018. (Stringer/Reuters)

RUSSIA HAS SUFFERED a string of military accidents this summer. In early July, a fire aboard a secret deep-water submersible killed 14 people. On Aug. 5, an ammunition depot in the Krasnoyarsk region exploded, creating a massive fireball. The most concerning, however, came Aug. 8 in an explosion during a missile engine test on a platform in the White Sea at the Nyonoksa test facility in the Arkhangelsk region, in Russia’s far northwest.

Initially, Russia’s defense ministry said two people died in the explosion, three were injured and there was no radiation release. Then officials in Severodvinsk, a larger city some 19 miles away, posted on its website a statement that sensors recorded a short-term spike in radiation, without saying how much. The report was subsequently taken down. Residents rushed to stockpile iodine against possible radiation exposure. Ambulances carrying the injured appeared to be sealed by some kind of plastic film, and personnel were wearing hazmat suits. On Aug. 10, the Russian state nuclear agency, Rosatom, said five of its employees had died in the accident, bringing the total to seven. Moreover, Rosatom said the blast resulted from the test of a jet engine “propulsion system involving isotopes,” or nuclear materials. On Aug. 13, residents of the small village of Nyonoksa were told they would be evacuated temporarily.

If this slow dribble of facts sounds familiar, it is — the same parade of misdirection happened during the Chernobyl nuclear disaster in 1986. This accident is nothing like Chernobyl in scale, but the government response looks familiar, including a lack of transparency about radiation release. As the recent television series “Chernobyl” vividly illustrated, that accident, the worst in the nuclear age, was characterized by lies and deception. At the very least, Russia should immediately clear up what occurred at Nyonoksa.

The accident has also offered a hint about a mysterious Russian missile project. In an address to the Federal Assembly in 2018, President Vladimir Putin claimed Russia was developing a new cruise missile that could carry a nuclear warhead with almost unlimited range around the globe. The cruise missile would be propelled by nuclear fission, with an engine that is essentially a reactor, what Mr. Putin called a “small-scale heavy-duty nuclear energy unit.” The missile, designated the 9M730 Burevestnik by Russia, or the SSC-X-9 Skyfall by NATO, apparently used a ramjet in which the nuclear reactor heats incoming air to provide thrust. The United States once toyed with the idea in the 1960s, but it is extremely difficult, and Mr. Putin’s announcement seemed more a fanciful political boast than an operational missile.

If the Nyonoksa blast was a test of the Burevestnik engine, Russia may be further along than previously thought. Mr. Putin has taken pains to brag that Russian can develop weapons with an asymmetric threat to the United States. Test failures are to be expected. But at a time when nuclear arms control is falling apart, this test raises a question: If successful, what kind of new nuclear threat will Russia possess?