OXIDE THICKNESS MEASUREMENTS AND CHARACTERIZATION OF TWO Zr-2.5Nb PRESSURE TUBES OF EMBALSE NUCLEAR POWER PLANT

Embalse Nuclear Power Plant (CNE) is a PHWR (Pressurized Heavy Water Reactor), CANDU 600, with Pressure Tubes (PT) of Zr-2.5Nb. Two PTs were removed from this plant after 9.9 effective full power years (EFPY), one of the central zone and the other of the peripheric one of the core. Samples cut out from these PTs allowed the oxide film characterization from the inside (internal side) and outside (external side) surfaces of the PTs and to measure also the oxide thickness. The inside oxide thickness varies between 6 to 12 mu m along the peripheric pressure tube, and between 7 to 15 mu m along the central tube. The maximum average corrosion rate was 1.2 mu m/EFPY and 1.5 mu m/EFPY at the outlet end of the peripheric and central tubes respectively, that are within the range of the values reported for PTs removed in other CANDU reactors. The outside oxide thickness varies between 2 to 5 mu m and 2 to 3.5 mu m for the peripheric and central tubes respectively.