Are they new stations, or new reactors in existing stations?
All these stations are in operation and will remain so for another 50 or so years. Because of the design of the Westinghouse AP-1000, these will effectively be new stations at existing sites, since adding any kind of building to any existing building would require about a billion dollars (no exaggeration) in engineering evaluations.
All the nuclear plants in the United States are custom built. There are 4 general designs (Westinghouse, General Electric, Combustion Engineering, and Babcox & Wilcox), but each reactor had to have every detail of design approved by the NRC. With the AP-1000, and the General Electric ABWR, the design has already been approved by the NRC, and the utilities will only have to prove to the NRC they’ve built the plants according to design. If they try to add to existing buildings, that would be a change in design, so you’d lose the economic advantages. At Harris, the plan is to locate the new reactors across one finger of the cooling lake from the existing plant. I’m pretty sure the others will be doing similar things.