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Snow and ice build-up has been removed from the left-bank dividing wall at the Sayano-Shushenskaya HPP

Snow and ice build-up has been removed from the left-bank dividing wall at the Sayano-Shushenskaya HPP. Steps to chip off the ice were undertaken by specialists of the Siberian regional search and rescue unit of the Russian Ministry for Emergency Situations (EMERCOM).

Eight EMERCOM specialists, 6 of them from Krasnoyarsk and 2 from Khakassia, together with industrial climbers, have destroyed the main part of the build-up on the dividing wall. During the ice removal operation, no damage was caused to the plant's structures. As predicted, the collapse of the snow and ice build-up did not harm the spillway basin in any way either.

The snow and ice cover appeared as a result of a cloud of water and air spray forming from the working service spillway and was exacerbated by the low temperatures in the region at the end of January. The appearance of snow and ice masses on the HPP's structures was forecast by the plant's engineers immediately after the accident, when it became clear that the spillway part of the dam would be used to release the water during the winter period (in normal years, this is carried out through the plant part of the dam, with the water passing along the power conduits to the hydro units).

During the autumn and winter period of 2009 - 2010, the service spillway at the Sayano-Shushenskaya HPP was transferred to operating in basic stationary mode, with all the spillway valves set at an intermediate degree of opening, this ensuring that the reservoir operates in accordance with the set timetable and guaranteeing sanitary releases into the tail race. Calculations made by the general designer (JSC Lengidroproyekt) confirm the safety of the facility's operation given such a water release scheme. In addition, the snow and ice build-up has a crumbly structure and is subject to constant natural washing away by the flow of water through the service spillway. Their mass is considerably below the permissible level calculated by the specialists. All the structures of the scoring sluice and the crane trestle, where most of the snow and ice is concentrated, are capable of withstanding a much greater load.

The operation to destroy the snow and ice build-up was preceded by a complex of preparatory measures. Detailed inspection of the state of the icing, with which the EMERCOM team started, showed that the ice build-up was split by a diagonal crack in the lower frontal part. Beginning from 24 January, the specialists used pneumatic jacks to widen the existing cracks and thus to bring down the ice overhangs. To speed up the work, specialists from the Fire Safety Research Institute were also brought in. They used a nozzle with a water-heating system to wash more of the ice away at the base of the mass. The rescue teams worked 18 hours a day and, by the evening of 28 January, had managed to remove 30% of the ice build-up, after which the main part of it was also removed. The ice has now been removed from the passageway between the dividing wall and the engine room.

The management of the Sayano-Shushenskaya HPP has decided that the Emergency Ministry rescue team has completed its work and fulfilled the tasks set for it. The parties have signed a certificate of completion, acknowledging that the rescue team has fulfilled its terms of reference in full without any violations of the safety rules or damage to the structures or equipment. The administration of the hydropower plant has thanked the team for their outstanding work and given them souvenirs.

For the purpose of ensuring the safety and reliability of the hydraulic structures and units at the Sayano-Shushenskaya HPP, a whole complex of work is carried out at the plant during the winter period. Within the scope of the programme to reduce the snow and ice cover, active use is made of bischofite, a natural ice-melting salt, the high effectiveness and safety of which has been confirmed by a number of institutions (MADI, VNIITMASH and GiprodorNII). Bischofite prevents ice forming at a considerably lower temperature than the other anti-icing agents (down to -35╟С) and acts quickly - in 15 minutes, it melts twice as much ice as sodium chloride.

The Sayano-Shushenskaya HPP services have resolved the problem of icing up of the roof of the engine room by heating the area beneath the roof with 70 heaters with a total capacity of 1.5 MW acquired for this purpose and by treating the roof surface with an anti-icing agent. Maintenance of a 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 the 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 another freezing up of the watershed abutment during the period of low outside air temperatures in January.

On the power plant's structures and the adjacent territory, there are a total of over 11 000 measurement points to monitor the state of the facility and its foundations, and 6000 embedded detectors are installed within the body of the dam itself. Both the automated systems and specialists of the service for monitoring the plant comprehensively analyse the state of the HPP's structures. Control indicators of the "dam-foundation" system changed in both December and January in accordance with external loads and impacts: they complied fully with the required safety criteria. The blocks securing the bottom of the hydraulic jump basin are also, according to the control and measurement instrument readings, in a satisfactory condition.

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