Behaviour of Copper in Generator Stator Cooling-Water Systems

Summary of copper release rates in function of oxygen level and pH. Operating areas of various chemistry regimes [2] Figure 4: Oxides from oxidation of a fresh copper surface in laboratory loop: at pH=8 (left) and pH=7 (center). Pile of oxide flakes found in a generator stator (right). Scale: the horizontal width of each picture corresponds to 5 μm. With long-term generator operation, the picture becomes more complex. Deposits can be of either predominantly crystallized growth, Figure 1, or an agglomeration of broken-off particles, or a combination of both, Figures 4 and 5. Figure 5: Oxide deposit in a used hollow conductor taken from a generator. Flow is from right to left. The oxides from a generator stator are always a mixture between Cu 2 O and CuO, with Cu 2 O dominating in low-oxygen systems, and CuO dominating in high-oxygen systems. There is evidence that an accumulation of deposit growth occurs preferentially in areas of increased turbulence, that is: at the inlets, outlets of hollow conductors and inside its length also on bends and Roebel transpositions. Very often, the first step of excessive deposition is ripple-like growth, Figure 5. An explanation of this dependence on hydrodynamics could be the increased mass transport from the bulk liquid to the copper surface, enhancing crystallographic growth. As the water velocity in hollow conductors is moderate (usually 0.5 - 2 m/s), Flow Accelerated 2