I'm assuming it's a power plant related querry. At high pressures, contaminant copper can carry over in the steam and deposit itself of turbine blades, leading to a decrease in cycle efficiency.
And as Metal guy said, it can increase the corrosion rate of steel (boiler tubes), usually via an underdeposit corrosion or galvanic mechanism.
Heavy deposition is usually a result of feed water heater corrosion, that is if the feed waters are made from a copper alloy. Feed water heaters on the power plants I've seen are either of the carbons steel or stainless variety.
Good feed water chemistry control can mitigate the problem somewhat. pH in particular is important to control - the optimum feed water pH depends whether your system contains FW heaters or not.
Can't tell you about how things work in the nuclear power industry... don't have any nuclear power stations in Australia!