MOSCOW — When a container of radioactive waste exploded at the Mayak factory 60 years ago, in one of the worst accidents of the nuclear age, the episode was so shrouded in secrecy that even residents of nearby towns had little clue of the danger.

That secrecy proved deadly.

Among the estimated 272,000 people who were exposed was a newborn girl who withered and died from radiation sickness. Taisia A. Fomina, a friend of the family’s, recalled that the girl’s father, ignorant of the danger, welded a bed frame from irradiated metal recycled from the nuclear plant. The child was poisoned as she slept.

Residents learned of the radiation risk only a year after the accident, said Ms. Fomina, now 84. “Some rumors went around town that something blew up at the factory, but we didn’t know what,” she added. “Of course, they didn’t tell us.”

Now, another possible accident at Mayak, a plant at the heart of Russia’s nuclear program, and the paucity of information coming out about it, is again raising alarms.