According to the official, the accident did not affect the operation of the power plant and the radiation levels in the area remained normal at about 16 micro-roentgen per hour.
Earlier, Rosenergoatom, the nuclear industry's management body, reported that the explosion happened on the grounds of Ecomet-S, Russia's first private company working with radiation technologies.
The NPP official said Ecomet-S "has its own fence, security and it is located one kilometer from the power plant."
Meanwhile, Ecomet-S confirmed the accident at its facilities at about 3:20 a.m. Moscow time (00:20 a.m. GMT) on December 15. Hot metal spilled out from the smelter and seriously burnt three workers.
The private company has been recycling low-radioactive metals since 1994. According to Bellona.com, the Ecomet-S facility was built without a mandatory environmental impact assessment. Other accidents occurred at the company in 2002 and 2003, the site said.