Engineers from Energie Ouest Suisse are examining the Cleuson-Dixence hydroelectric plant in Switzerland to attempt to determine the source of a 9m rupture in the penstock. The rupture, which took place on 13 December, was in the penstock on the newest power house at Bieudron, and resulted in flooding and landslips in the local area.
On 15 December engineers had not yet been inside the penstock to examine the damaged area in detail and speculation as to the cause was wide ranging. A faulty weld was an immediate possibility, which may have been caused by inadequacies during the original construction or by corrosion in the two years since the hydro plant started up. Rumours also blamed an earthquake said to have taken place on the day of the accident.
Whatever the cause, the effects were both dramatic and hazardous. Eyewitnesses described a mass of water being driven out of a crevice in the rock near to the foot of the tunnel at Nendez. The water was said to have damaged several buildings and some people had to be evacuated from the area. Landslips caused by the water blocked a local road and more flooding was caused when material from the landslip landed in the Rhone river. The situation is now said to be stable.
The Bieudron power house went into operation in 1998, drawing water from the Cleuson dam through a tunnel that falls some 1800m from the reservoir. The water pressure in the tunnel varies from 26.5 bar at the top to some 210 bar at the bottom, and the tunnel was completely steel lined. The original construction of the penstocks was completed by a consortium of Giovanola of Italy (consortium leader), Sulzer Hydro and the then GEC Alsthom Neyrpic. In the fabrication 6m and 9m lengths were assembled at site into sections 12m long, before being lowered into the shaft. Members of the consortium assembled different parts of the penstocks, using several different welding methods and automatic, semi automatic or manual techniques as appropriate.