Monday's accident during repairs at the massive Sayano-Shushenskaya plant in southern Siberia drowned or crushed at least 12 workers and shut down electrical supplies to a wide region. Two workers were found alive Monday in niches inside the flooded structure, RusHydro acting chief Vasily Zubakin was quoted as saying by the ITAR-Tass news agency.
Federal investigators said an explosion destroyed walls and the ceiling in an engine room where turbines are located and caused the room to flood. One of the plant's 10 turbines was destroyed, two were partly destroyed while three others were damaged, officials said.
The plant's dam, a towering structure that stretches a kilometer (more than half a mile) across the Yenisei River, was not damaged and towns downstream were not in danger, Emergency Situations Minister Sergei Shoigu said.
Regional Gov. Viktor Zimin refuted allegations that rescue teams had heard knocking sounds from inside the plant's structure as if workers trapped inside were calling for help. He said the dam's thick concrete walls would muffle any sounds from inside, Russian news reports said.
Former plant director Alexander Toloshinov, however, said some workers trapped in the flooded control room could have survived by finding a corner with some air left.
Three groups of divers were searching for the missing workers both inside the flooded rooms and in the Yenisei river outside, Shoigu said in televised comments, adding that the workers are now believed to have drowned or been crushed by the debris.
The accident shut down the power plant, located 2,050 miles (3,300 kilometers) east of Moscow, and left several towns and major factories without electricity on Monday. Supplies from other power plants were being rerouted Tuesday to help cover the shortfall.
It still was unclear how long other power plants would be able to continue making up for the energy shortage. The plant satisfies 10 percent of Siberia's energy needs, according to Russian media reports.
The accident also produced an oil slick that by Tuesday stretched over 50 miles (80 kilometers) downriver. Crews were struggling to stop it but so far had not.
RusHydro said a faulty turbine at the plant, which began operating in 1978, was likely to blame. Investigators believe the accident occurred after a defective lid of one of the plant's 10 turbines got torn off during repair work, Vishnyakova, the RusHydro spokeswoman, told the AP.
Shoigu, however, said later that was merely one of several theories why the accident occurred, Russian news agencies reported.
RusHydro said replacing the damaged equipment at the plant may take up to two years but the undamaged turbines could be put back into operation in as soon as a month.
Shoigu said the repairs would be difficult.
"We're probably talking about years rather than months to restore three of the 10 turbines," he said on state-run television.
More than 70 percent of all energy from the Sayano-Shushenskaya goes to four Siberian smelters of Rusal, the world's largest aluminum producer. Rusal reported Monday that it was operating as usual with smelters being powered from other plants.
Analysts said the lack of energy from the Sayano-Shushenskaya did not pose immediate risks for Rusal, but could seriously impede its development if the metals market picks up next year.
Aging infrastructure has long been regarded as a key obstacle to Russia's development.
Analysts have warned that Russia needs to boost its power production significantly to meet the growing demand of industrial producers or it would face regular power shortages in the next several years. Monday's accident put these plans in jeopardy.
RusHydro said each bereaved family would receive 1 million rubles ($31,300) in compensation for their loss. The 12 dead workers are to be buried on Wednesday and Thursday.
Trading in RusHydro's shares at two Russian stock exchanges remained halted on Tuesday although the company said it could resume on Wednesday.