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January 28, 2010

On the package of measures undertaken to improve the safety of the hydro-engineering facilities at the Sayano-Shushenskaya HPP during the winter period

For the purpose of ensuring the safety and reliability of the hydro-engineering facilities s and units at the Sayano-Shushenskaya HPP during the winter period, a whole range of measures is being carried out.

Control indicators of the «dam-foundation» system both in December 2009 and January this year have been changing in accordance with external loads and impacts and complied with the required safety criteria. Control over the state of the dam at the Sayano-Shushenskaya HPP has been a continuous process virtually since the power plant was first built. Specialists of the service for monitoring the hydro-engineering facilities at the Sayano-Shushenskaya HPP exercise constant visual, filtration, geodetic, telemetric and seismological control over the of the Sayano-Shushenskaya hydro-engineering facilities. Automated telemetric, geodetic and seismological control systems have been set up on the dam and there are over 6,000 sensors within the body of the dam itself. With their help, the «behaviour» of the hydro-engineering facility is under constant observation. On the whole, there are over 11,000 measurement points on the power station’s structures and the adjacent territory, where indicators of the state of the structure and its foundations are monitored. According to the readings of the control and measurement equipment, the blocks securing the bottom of the hydraulic jump basin are in satisfactory condition, too.

A natural salt, bischofite, is being used within the scope of the programme to reduce snowing- and icing-up of the surface. Bischofite (MgCl26H2O) has been thoroughly testes by a number of institutes, such as MADI, VNIITMASH and GiprodorNII, with respect to its use against snow and effect on equipment and the environment. The studies have confirmed that it causes far less metal corrosion than calcium chloride and sodium chloride. Bischofite prevents ice formation at a considerably lower temperature than the other anti-icing agents (down to − 35°Ñ) and acts quickly — in 15 minutes, it melts twice as much ice as sodium chloride. The main thing, however, is that bischofite, according to the A. N. Kostyakov Hydro-engineering and Reclamation Scientific Research Institute, does not change the properties of plants and is environmentally safe. No other anti-icing agent used today has such characteristics.

The problem of icing up of the roof of the turbine room has been resolved by heating the area beneath the roof with 70 specially acquired heaters with a total capacity of 1.5 MW and treating the roof surface with anti-icing agent. Maintenance of positive temperature of the roof prevents a build-up of ice and facilitates the mechanical removal of any ice.

The tent installed over the crest of the abutment, after it had been cleared of snow that built up there during the November freeze, and periodical treatment of its surface with an anti-icing agent have made it possible to prevent a second freezing up of the watershed abutment during the period of low outside air temperatures during January 2010.

The snow and ice cover forms as a result of the air and water particle cloud produced by the service spillway. The formation of the snow and ice cover is taken into account, as it cannot be completely eliminated, but it can be substantially reduced. Previously, the water passed through the power plant section along turbine water pipes to the hydro-units, but nowadays, the spillway part of the dam is used to let the water through. At the same time, the service spillway of the power plant has been shifted to basic, fixed regime, with all the spillway valves set at an intermediate degree of opening, thus ensuring that the reservoir operates in accordance with the set timetable. Introduction of design changes into the structure of the service spillway valves and their transfer to an intermediate degree of opening makes it possible to distribute the water release set by the timetable evenly over all 11 spillways. As a result, there is a substantial drop in the load carried by the spillway basin structures and in the formation of water particles. Calculations made by the general designer Lengidroproekt confirm the structure’s stability given such a water release pattern.

On 25 January 2010, the water release amounts to 985 cubic metres a second and the inflow into the reservoir is 500 cubic metres a second. The race levels comply with the water release pattern recommended by the Angara-Yenisei Basin Water Board: the level of the upper race is 523.59 metres (the normal water level of the Sayano-Shushenskaya HPP being 539 metres), and that of the lower race — 323.77 metres.

At outside air temperature below −15°Ñ, evaporation or water particle cloud rises to a height of 100 — 200 metres above the spillway basin and falls in the form of snow on to the crest and platform of the water-spill dyke. At the 430 − 340 metres level, a snow and ice wall about 2 metres thick has grown up on the conjoined support piers of the spillway, thus reducing the water flow. If the frozen snow joins above the water races at their middle height levels, this does not reduce the through capacity of the spillway in connection with the release of warm water from the lower levels of the reservoir and high flow speed, but it does reduce the intensity of evaporation. In the lower part of the spillway, joining together is not possible since, at the joining point of the tail race water, the flow spend is about 50 metres a second. In addition, snow and ice formations above the spillway apertures are not solid and, at a temperature above −10°Ñ, the water races begin to clear themselves and above −5°Ñ — pieces of ice detach themselves from the spillway support piers. Snow-clearing work is carried out round-the-clock using snow-clearing equipment.

Snow and ice also builds up on the crane trestle. The ice builds up unevenly, at different heights and widths, from one to another span of the trestle. The crane trestle has 11 sections (spans) of 12.3 metres and it is about 135 metres long. The snow and ice has now built up along the entire length and depth of no more than half the width of the whole trestle. If the build-up of snow and ice were to stretch along the whole width of the trestle and reached a height of 22 metres, calculations predict that the load would be 250 metric tonnes per metre in length. The load at the moment is about 100 metric tonnes per metre in length, given a permissible load of 400 metric tonnes a metre. In addition, the snow and ice that has built up on the crane trestle have lose structure and is subject to constant natural washing away by the flow of water through the service spillway. In fact, these lose build-ups, shaped like pyramids, are being washed away from beneath by the water flow, pose no danger to the crane trestle or other hydro-engineering structures.

On the morning of 25 January, according to the Cheryomushki weather station, the temperature was minus 15.4 °Ñ, the relative humidity − 71%, the air pressure − 736.7 mm, with no precipitation.




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