what a mess.
The report states that the accident was primarily caused by the turbine vibrations which led to the fatigue damage of the mountings of the turbine 2, including the cover of the turbine.
It was also found that at the moment of accident at least six nuts were missing from the bolts securing the turbine cover. After the accident 49 recovered bolts were investigated from which 41 had fatigue cracks. On 8 bolts, the fatigue damaged area exceeded 90% of the total cross-sectional area.
According to this report, on 17 August 2009 at 1:20AM (local time) there was a fire at the hydroelectric power station of Bratsk which broke both communications and the automatic driving systems of other power plants in the region, including Sayano-Shushenskaya. The situation was recovered on 17 August 2009 at 15:03. At 8:12AM local time, turbine 2's output power was reduced by the turbine regulator and it entered into the non-recommended powerband II.
Shortly after this, the bolts keeping the turbine cover in place were broken, and under water pressure of about 20 bars (2,000 kPa), the spinning turbine with its cover, rotor, and upper parts started to move up, destroying machinery hall installations. At the same time, pressurized water flooded the rooms and continued damaging plant constructions.
According to Rostekhnadzor, the automatic shutdown system of the water intake pipes' gates failed after failure of the turbine 2.This accusation was dismissed by Rakurs, the company which designed the automated safety system for the plant.
According to the newspaper Izvestia, the increased vibration of turbine 2 was going on for some 10 years and was well-known to the plant personnel.
According to the former director of Irkutskenergo, Viktor Bobrovski, the accident could have been caused by an incorrect start-up process of the turbine which resulted in an hydraulic pressure surge, or the excess load of the turbine caused by the peak consumption of electricity.
According to Bobrovski, it is common practice in the region to compensate for peak load by overloading hydroelectric power plants, and the energy system of the region is near collapse, as the main goal of its owners is to take out as much profit as possible cutting down on maintenance, investment, safety, and educational costs. Since the load for other turbines ceased after the collapse of the turbine 2, they probably started to spin without load at increasing speed until they smashed.
He said that former director of Sayano–Shushenskaya hydroelectric power station, Valentin Bryzgalov, had alerted that it is dangerous to operate the plant at its maximum loads when the turbines are starting to vibrate in the axial direction.
He said that the accident probably would not have had such catastrophic results if the safety systems had worked and the safety rules had been followed.
The former general director of the plant, Alexander Toloshinov, has said that the accident was most likely due to a "manufacturing defect" in a turbine.
According to Toloshinov, the construction of the turbine blades of this type of turbine is not very reliable and cracks are known to develop in them under some working conditions.
On 11 September 2009, RusHydro refuted allegations that the dam overwhelmed the machinery hall leading to the destruction of turbine 2. According to RusHydro, displacements of the dam are seasonal and have been reduced in recent years. The maximum displacement (141.5 millimetres / 5.57 inches) was recorded in 2006, which was below the allowed maximum of 145.5 mm (5.73 in). According to RusHydro, the scope of displacement between the anchor legs and the machinery hall does not exceed 2.3 mm (0.091 in), which is less than the width between them (50 mm/2.0 in), and therefore the dam cannot overwhelm the machinery hall
