Ministry spokesman Georgy Kaurov said Vladimir Turusin, deputy director in charge of personnel at the Mayak plant in the closed Urals city of Ozersk, was found in the street with a crushed skull last Friday and later died in hospital.
Kaurov said it was not yet clear whether Turusin had been murdered.
Ozersk, formerly known as Chelyabinsk-65, is home to many nuclear enterprises. It fell under suspicion earlier this year when police seized several batches of weapons-grade nuclear material in various parts of Germany.
Western experts said the material could well have come from the Mayak plant, a claim Russia firmly rejected.
In late August a small fire broke out at Mayak -- one of the few Russian plants capable of producing weapons-grade plutonium -- and triggered a radioactive leak which authorities said was insignificant.
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