What have the foreigners heard on the causes of the tragedy at Sayan-Sushensk Hydro-Power Plant?

Perhaps the most complete version of the causes of the accident at the Sayan-Shushenskaya Hydro-Power Plant was presented by Rostekhnadzor (Russian Technical Supervisory Body) at the VIII International Forum on Industrial Safety, which has brought together experts from 16 countries worldwide. Surprisingly, the report "RusHydro" was removed due to "objective reasons" just a couple of days before the commencement of event.

Vladimir Pimenov, Member of the State Commission for Technical investigations into the causes of the accident at the Sayan-Shushensk Hydro Power Plant, Head of The State Supervisory Body for the Safety of Hydraulic Structures of the North-West Division of the Federal Service for Ecological, Technological and Nuclear Supervision, reported that the Sayan-Shushensk HPP "tortured" with intensive exploitation, moreover, in regimes that was contraindicated. This has imposed on other problems that led to the catastrophe on 17 August, 2009.

Problems began in 1979

According to Vladimir Pimenov the problems in the Sayan-Shushensk HPP began even during the construction. In 1979 a disastrous flood occurred on  the Yenisei River, and the water has flowed through the unfinished dam. At that time unit No.1 was flooded. Unit No.1 was already installed and was operational (although running only in half capacity) in order to provide power to the very construction itself. This has revealed the first problem: during the melting of the ice, the spillway was not functioning, as it was blocked by ice. To eliminate it, it was decided way back then to build an additional shore spillway. But the work is getting completed only now.

Intense flooding caused problems in 1985 and 1988. In these years, by the mass water fall the energy dissipating well was destroyed. From the very beginning there were problems of filtration of water through a number of cracks appeared on the body of the dam. Loss of strength of the  dam foundation was noted. All these were the consequences of certain violations during the  construction. Efforts were made to repair the cracks by injecting concrete solution; sought the help of the French experts. With their help the filtration could be stopped.

Not everything was in order with the turbines as well. Their efficiency was very high - 96%! However, each time when the turbine unit is switched on or switched off for some time it had to pass through a mode, in which there were stresses and vibrations, exceeding the maximum permissible level. That is, every switching off of the turbine and its subsequent switching on accompanied the risk of further deterioration and even destruction.

In 2009, on the Yenisei River there was very high level of water, and that created strong pressure on the turbine blades. A few months prior to the accident an increase in vibration of the units was observed. Moreover, the vibration exceeded the maximum permissible level. Operational Department of the Plant knew about it, but no measures were taken. In the units of the Sayan-Shushensk HPP there was no Automation System, which could have stopped the turbine, if the indices of the vibration exceeded the maximum permissible limit. Well, it could not have had it; otherwise the system would have turned off the units every time one tries to start them (when the turbine passed through the prohibited mode).

The station generally worked at the extreme load, generating at that time more electricity than planned while constructing it. Immediately before the accident the situation became more complicated. At the Bratsk hydro power station a fire occurred, and to compensate the loss of power capacity, the Siberian Supervisory Authority turned to Sayan-Shushensk HPP in order to maintain the power capacity along the entire grid, i.e., it was on the peak regime operation. This demanded frequent restarts of the units, most of those starts and stops were contraindicated to the turbines of the Sayan-Shushensk HPP.

As a result, on August 17 at 8:13 on the unit No.2, which at that time was to unload (ie, in the zone of dangerous regime), the pressure of the water tore off the turbine cover. Depressurization occurred and the water poured into the machine room, flooding the remaining units. Automatic lowering system of shutter of the upper pool failed to function, and in a matter of seconds the power supply system (transformers, located next to the units) was flooded and the station was left without electricity. Water continued to flow in to the Plant. The shutters were lowered manually. As a result, the flooding has stopped only after one and half hours.

Are the eyes fastened with nuts?

Why precisely the second unit could not withstand it? According to Vladimir Pimenov, during the investigation the commission found out that the turbine cover was fixed poorly. On 6 of the 80 clinch studs there were no nuts at all. As for the rest, it can not be excluded, that some of them must have broken during the repair of the unit in 2000.

The GCE experts in their report noted: the accident could have happened partly due to such "trifles" as a failure to observe the instructions or even their unavailability. Experts have presumed that the work of mounting the turbine covers must have been performed just by "eye sight" without the use of proper tools. Precisely, that is why the wear of some of them reached up to 90%, while some of the studs, as seen in the survey, happened to be in completely "healthy" state.

Units flooded unevenly. At the fifth unit the automatic system of the shutters of the upper pool triggered and within 15 seconds water flow was blocked, and therefore the unit has been affected the least.

The sixth unit at that moment was no in operational regime, so it also remained virtually intact. It was put under operation in February this year, and the fifth unit - in March. Besides the second, the most affected were seventh, ninth and tenth units: they can not be restored. Units No.3 and No.4 are planned to be put into operation by the end of this year.

It was feared that the dam of the Sayan-Shushensk hydro-power plant will not survive this winter. Previously, the spillway did not function in winter. It was decided to unveil it a bit and leave it in that position for the winter. In winter, a strong freezing of the dam was observed, which, of course, was not present in the running station. Through out the winter the staff had to contend with ice: amounted to 100 tons of ice which was an unbearable load. Fortunately, nothing happened. Now the shore spillway construction is about to be completed. These will be two lines with a flow capacity of 4 thousand cubic meters of water per second. The first one is to be commissioned in June.

Lessons learned from the accident

As a result, according to the assessment of Vladimir Pimenov, the accident at SS HPP occurred due to many causes which are related to design, technology and operation. They all occured together, and brought such a tragic outcome.
According to the expert, a decision was taken to conduct a survey on all facilities and equipment of hydropower stations of Russia with the participation of leading specialists and to conduct diagnostic survey on all major structures and machinery components. The entire HPP should be provided with appropriate means for protection and safety of the personnel. They intend to install additional system of protection and blocking. "Black boxes" are to be installed for constant monitoring of the technological systems. Vibration control will have to be conducted constantly and not half-yearly as it used to be till now.

Part of the sites and equipment, including power supplies, must now be shifted to nonfloodable areas.

Alexander Moskalenko, the president of GCE Group, specialists of which have been involved in the work of establishing the causes of the accident, noted that the main problem in many of the industrial sites is as follows: "We continue to build, making one and the same mistake. We dislocate in one confined space all vital technological systems of the enterprise. Failure of one element leads to a chain reaction on the others. Should learn from the experience of the army personnel: the principle of sectional construction of ships. The flooding of one compartment, usually does not lead to the sinking of the ship.

Based on the results of the VIII International Forum on Industrial Safety
www.conference.gce.ru

Department of Public Relations,
GCE Group: (812) 325-0621, 331-8353
www.gce.ru


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