The Rosenergoatom agency said radiation levels remained normal as the reactor inside the Leningrad nuclear plant was being repaired. Rosenergoatom initially called Thursday's incident an explosion in a press statement, then hours later changed course and called it a "splash."
A plant spokesman said the accident was caused by violations of technical and production rules.
The mishap occurred at the plant in the closed nuclear town of Sosnovy Bor, 50 miles west of the northern city of St. Petersburg. The smelter is operated by Ekomet-S, a company reprocessing scrap metal.
Thursday's accident shone a spotlight on what environmentalists called uncontrolled operations at Russian nuclear sites.
"The enterprise ... functions illegally because there was no mandatory (state) environmental impact assessment on its construction," Dmitry Artamonov, head of the St. Petersburg branch of Greenpeace, told The Associated Press.
He said Greenpeace had complained against Ekomet-S to the Sosnovy Bor prosecutors' office, but the office took no action.
The nuclear plant has four units, or reactors, in all. Rosenergoatom said the smelter was on the grounds of the plant's second unit, and plant spokesman Sergei Averyanov said it was about a half-mile from the reactor.
Oleg Bodrov, a physicist who heads the Green World ecological group in Sosnovy Bor, said the reactor was only 700 yards from the smelter, which is about 50 yards from a covered liquid radioactive waste pond.
A 33-year-old worker died of his injuries Friday morning, and two others were injured, Yuri Lameko, chief doctor of the Sosnovy Bor hospital, told the AP.
"There were no violations of safety levels and operating conditions of the energy units of the Leningrad nuclear plant," Rosenergoatom said in a statement.
The second unit had been shut down for planned major repairs in July, it said.
Averyanov said molten metal spurt out of the smelter. Besides scrap metal from the plant, Ekomet-S reprocesses metal from Russian nuclear submarines and disassembled oil and gas pipelines from the Russian Far North, Bodrov said.
Averyanov said the metal reprocessed Thursday was clear of radiation, and he blamed the accident on violations of technical and production rules.
Bodrov said Ekomet-S workers told him more than 2 tons of molten metal were in the smelter at the time of the accident, and several hundred pounds splashed out for unknown reasons.
He said Ekomet-S began operating two years ago and was in violation of the law because it had not undergone a state environmental impact assessment. When the firm was founded, the only environmental monitoring laboratory in the town of 65,000 was shut down for lack of funding, he said.
"There is no independent environmental monitoring in the nuclear city of Sosnovy Bor," Bodrov said.
Sosnovy Bor prosecutor Stanislav Rumyantsev said he opened a criminal investigation into charges of violations of safety regulations.
Bodrov visited Ekomet-S on Friday afternoon, taking along his own radiation monitor. He said radiation levels were normal.
He said this was the second accident at Ekomet-S, with the first happening in summer 2003 and injuring two workers.
In March 1992, an accident at the Sosnovy Bor plant caused radioactive gases and iodine to be leaked into the air, according to nuclear watchdog groups.
One of the reactors at the 30-year-old plant is of the same type as the one at the Chernobyl nuclear power plant that exploded in Soviet Ukraine in 1986 in the world's worst nuclear accident.
The station is the main supplier of electricity to St. Petersburg, and there are plans to transport some of its power to Finland.
Sosnovy Bor, a center of nuclear technology, was founded 25 years ago and has 60,000 people. The town also is home to a regional radioactive waste reservoir and an experimental laboratory and training center for nuclear submarine reactors.
Almost everyone in Sosnovy Bor, which means Pine Forest, is connected with nuclear technology, and most are not native to the region.
In an unrelated development, Chechen prosecutors said they have opened a criminal investigation into the improper storage of radioactive waste by a state-owned company.
Prosecutors said a "catastrophic radioactivity situation" had developed at the Grozny Chemical Factory in the breakaway province in southern Russia. Grozny is Chechnya's capital.
Radiation levels at one storage center at the plant are 58,000 times higher than normal, the Russian Prosecutor General's office said Friday.
"It's a threat to the population because the leadership of the plant is taking no steps whatsoever to remove the radioactive material or isolate access to the plant," Chechen Prosecutor Valery Kuznetsov said.