Inspection of the Cleuson-Dixence penstock

The 1200 MW Bieudron power station generates some two billion kWh a year. Commencing a few months ago and continuing until 2026, this facility is undergoing a complete refurbishment. The project is being preceded by a wide-ranging inspection of areas that are usually under water.

The Bieudron scheme involves a tunnel more than 15 km long carrying the water from the Grande Dixence dam to the head valve at Tracouet, below the Dent de Nendaz. From there, the water continues on to the power station through a high-pressure penstock 2.85 m in diameter and more than four kilometres long.

For a facility of this magnitude, the inspection is prepared before the system is emptied. A preliminary study defined the logistics that needed to be put in place.

Civil engineering and mechanical survey

The tunnel and surge tank consist of concrete-lined and reinforced sections. HYDRO’s civil engineering and mechanical teams worked in shifts for two weeks to draw up a list of the various defects. The area needing inspection was such that many kilometres had to be walked, rope descents made and even a drone used to cover the entire facility.

The penstock, on the other hand, required heavier logistics. A winch fitted with a trolley specially designed for the purpose had to be installed via four access hatches. It took over three weeks to inspect the entire penstock.

HYDRO worked with several companies to carry out this inspection without delaying the return to water. The next one is due in some ten years’ time.