Six more workers remain missing and are being presumed to also have been killed by the explosion on 17 August, which would take the total number of workers killed in Russia’s largest hydro power scheme to 75.

Plant owner RusHydro said the reconstruction and repair work at the facilities could take approximately three years to complete, reported the Emergency Situations Ministry.

No explanation has yet been given for the cause of the explosion except that it was hydraulic-related and terrorism has been ruled out.

The 6.4GW plant is the largest owned by RusHydro and is located in the Republic of Khakassia, part of the Russian Federation and located in south central Siberia. The facility has 10 turbines, which were installed over 1978-1985. The project was completed in the late 1980s.

At the time of the accident there were nine units available for operations and one unit (No 6) was undergoing the last stage of a refurbishment programme underway since January. The total active power at the plant was 4.4GW on the day of the accident.

The Ministry said the explosion was centred on generating unit No 2, resulting in the collapse of the walls and roof at the location.

RusHydro said a loud bang was heard in the area of unit No 2 and a column of water shot up. Emergency systems acted to shut down the plant’s output but structural and other damage by then was happening, and dozens were killed.

Water inflow to the powerhouse was manually stopped by closing the emergency repair gates at the 1070m long crest of the 242m high concrete arch gravity dam about an hour after the explosion. The surface powerhouse is at the foot of the dam, which is 110m wide at the base.

With high inflows to the reservoir, water was then spilled from the dam with the help of a diesel generator at a gantry crane on the dam. There were 11 gates partially opened to spill the water.

RusHydro has noted that both units No 7 and No 9 were destroyed by the accident, there was serious damage to units No 1 and No 3, slight damage to units No4, No 5, No 8 and No 10. The idle unit, No 6, is in satisfactory condition, it added. Some of the damage to the other units was due to partial collapse of the powerhouse building.

The 156 tonnes radial-axial turbines have rotors of 6.77m diameter and 16 blades, are designed to operate over a head range of 175m-220m and have rated output of 640MW. The design flow and rotation speed are 358.5m3/sec and 142.8rpm, respectively.

The guide vane has 20 blades with servo-motors for each. The regulation of the unit is designed to handle pressures of 63MPa.

RusHydro despatched about 400 staff, consultant and contractor personnel to assist the Ministry’s emergency services’ workers in the disaster recovery work.

The utility has also launched a fund for charitable donations to the families of the workers killed in the accident.

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