Management failures and technical shortcomings were this week blamed for a hydropower plant disaster in Russia in August in which 75 people died.
A turbine at the Sayano-Shushenskaya plant − the largest power-plant in Russia and the sixth-largest hydro station in the world − was ripped from its seating at 8.13am on 17 August.
Within seconds, a deluge of water began flooding the facility’s turbine hall and engine rooms, causing a transformer explosion and short circuiting, crippling the plant’s electrical systems as well as causing devastating structural damage. Fortunately the hydroplant’s 245.5m tall arch gravity dam was not breached.
Russian investigators have now concluded that the turbine failed due to excessive vibration and the failure of holding-down bolts which kept the unit in position.
“Massive short circuits were caused, soon leaving the entire plant without power.”
Nikolai Kutin, Rostekhnadzor
They said the unit was overstressed due to poor maintenance and technical deficiencies. The disaster report was published at the weekend by Rostekhnadzor, Russia’s industrial and technical standards safety watchdog.
It makes stinging criticism of management at the plant, which is owned and run by RusHydro, a stock-market listed company in which the Russian state has a 60% shareholding.
Rostekhnadzor director Nikolai Kutin who headed the investigation said that fire in another hydropower facility in Bratsk, several hundred kilometres away, began the chain of events which lead to tragedy.
Fire damage at the Bratsk plant and loss of generating capacity forced an idle turbine generator at Sayano to be pressed into service to provide more power for the electricity network.
One of 10 Russian-made 640MW turbines at the facility, Kutin said the unit was overstressed. He said that the turbinegenerator had been vibrating abnormally in the weeks before the accident, but had begun to shudder even more dangerously in the hours preceding the disaster.
Eventually the massive 1,500t unit broke free and was hurled 14m into the air by the huge pressure from water flowing through the penstock into the turbine from the dam behind.
Kutin said that the restraining bolts holding the turbine in place had been badly worn before the disaster.
After the unit was blown out of position and the control rooms and turbine hall began flooding rapidly, two other turbine generating units continued to run while under water for more than a minute causing short circuits. “Massive short circuits were caused, soon leaving the entire plant without power,” said Kutin. The loss of power meant safety systems failed, increasing the scale of the catastrophe.
Those who died were staff working in the control area − the nerve-centre of the plant − which was rapidly flooded while massive structural damage was caused both by the surging water and electrical explosions.
The 140-page report identifies a number of key managers and staff described as “conducive” to the tragedy (see box). Kutin said the purpose of his investigation was not to attribute guilt, as that was the function of the judicial system. A criminal inquiry is underway.
The plant opened in 1978 after 10 years of construction. It was privatised in 1993 after the break up of the Soviet Union. The arch-gravity dam in the Yenisei River, near Sayanogorsk is 245.5m high with a crest length of 1066m, with the crest with of 25m widening to a base width of 105.7m.
Among those identified by Kutin’s investigation is Anatoly Chubais, who signed off papers commissioning the plant in 2000 − even though it had been running for many years. Chubais was head of the post-Soviet power authority United Energy Systems.
Chubais is detested by the Russian public for his role in spearheading Boris Yeltsin’s privatisation drive which enriched a golden circle of oligarchs while selling state-owned concerns for peppercorn prices.
He said he accepted his role as described by the report. But he added that he had no option but to sign the papers because the plant was vital for Siberia and the Russian economy and had been already running.
“Effective and timely compensatory measures were not worked out or carried out to ensure safe operation of the Sayano-Shushenskaya plant.”
Almost three-quarters of the plant’s output goes to fuelling four massive aluminium smelting plants in Siberia, as well as providing power over a wide area. Its average annual production was around 23.5TWh. The report accuses him of signing-off but failing “to give a proper assessment of the actual condition of the plant.”
“Furthermore, effective and timely compensatory measures were not worked out or carried out to ensure safe operation of the Sayano-Shushenskaya plant,” the report says.
The report accuses Chubais − an engineer by training − and a number of other senior managers, including Russian deputy energy minister and chairman of the federal hydro-generating board Vyacheslav Sinyugin, of a range of breaches leading to the tragedy. These include failing to ensure that “repair and maintenance contracts include a provision on regular technical monitoring of core production equipment.”
Senior management failed to “create conditions for assessing the actual state of the plant and take effective measures to work out, finance and carry out compensatory steps towards ensuring its safe operation.”
Managers are also accused of failing to replace rotor wheels in the power units.
Engineering recommendations to complete the construction of an additional discharge sluice at the plant were also ignored, the report says.
Various accidents have occurred at the plant since it began operation, and in 1998 the Russian Emergency Situations Ministry reported concerns about the dam wall from increased spring floods, which had led to two previous flooding accidents.
Structural improvements were made, including resin treatment to the concrete, and soil grouting to limit water seepage around and under the structure.
The Russian Accounts Chamber − Russia’s auditing watchdog − revealed in September that the plant had been audited in 2007, with inspectors concluding that 85% of all technical equipment needed to be replaced. The government and prosecution authorities were notified.
However owner RusHydro said that all concerns had been dealt with and that the authorities had been notified. The company has also said that the dam is safe.
Repairs are expected to cost around £500M and Russia’s energy minister Sergey Shmatko said that foreign help may be needed after the disaster.
“I believe it would be most useful to involve foreign companies using such large dams or equipment producers to find the most objective cause of what happened,” he said.
Russia’s prime minister Vladmir Putin has ordered a complete inspection of Russia’s other power plants in the wake of the Sayano disaster. This is expected to be completed next month.