It was not just to rescue fish from the suction tube that the platform below the U07 turbine was set up. While the environmental crew buckled down to descend the 18 meters inside the tube, a technical team looked up, focusing on the “teeth” of the turbine wheel.
The comparison is apropos: maintenance on a turbine wheel is not that different from the inspection performed by a dentist. However, far from looking for cavities, technicians from the Generator Units Mechanical Maintenance Division (SMMU.DT, in Portuguese) search for small erosions in the turbine wheel material.
The technical term is “cavitation”, explains expert SMMU.DT technician Cláudio Urbano de Mattos, in charge of the turbine. According to Cláudio, as water flows through the turbine, it exercises pressure that causes small air bubbles. These bubbles collapse and over time rip the metallic material away from the wheel.
Mapping takes place every four years but occasional fillings via soldering are required only once every decade. “After the area is repaired via soldering, it is filed down and the turbine wheel is good as new again”, said Cláudio. For new units 9A and 18A this type of maintenance will be even more sporadic as the entire wheel is built in stainless steel.
Inspections are also performed on the top section of the wheel, at the outlet of the scroll case. There, between the turbine blades, staff from the Civil Maintenance Division (SMMC.DT, in Portuguese) set up small wooden platforms to enable maintenance services.
To work on the scroll case, the water was entirely drained and the SMMU.DT team hit the ground cleaning. Other maintenance services on the scroll case take part in its outer section, at the inlet hatch. But will talk about that in coming articles.