Q: How many nuclear plants are under construction in the U.S.?

A: Three. Two nuclear reactors are being built at Plant Vogtle in eastern Georgia. Two more reactors are under construction at Plant Summer in central South Carolina. A fifth reactor mothballed in 1985 is being finished at Plant Watts Bar in Tennessee.

Q: How often are nuclear plants built?

A: The last nuclear plant built in the United States was the existing reactor finished at Watts Bar in 1996.

Q: How much does a nuclear plant cost?

A: Billions of dollars. Nuclear plants are among the most complicated and expensive infrastructure projects in the world. The plants require incredible amounts of design and engineering work and must be built to exacting safety standards. Federal inspectors can require that parts of the plant be ripped out and replaced if they don't meet muster. The plants require huge amounts of metal, concrete, cables and wires. Building two Westinghouse Electric Co. AP1000 reactors at Plant Vogtle is supposed to cost roughly $14 billion, though the final expenses could be more.

Q: How does that compare with building coal- or gas-powered plants?

A: Nuclear plants are far pricier to build than are gas- or coal-fired power plants. The Tennessee Valley Authority, for instance, spent $790 million to build a gas-fired plant that opened last month in northeast Tennessee. Analysts and energy companies say nuclear plants can be cheaper to operate in the long run.

Q: Why do building costs matter to customers?

A: Because customers ultimately pay for the construction costs as part of their monthly power bills. The more a plant costs, the more customers will pay.

Q: Are any projects over budget right now?

A: Yes. The TVA originally approved a $2.5 billion budget to complete a partially built reactor at its Watts Bar plant. It recently approved an additional $1.5 billion to $2 billion in spending to finish the project. Plant Vogtle will likely exceed its $14 billion budget, judging by the latest financial disclosures from the utilities involved. The companies building the plant want utility owners to pay more than $800 million for unexpected expenses related to delays in getting federal approval. A monitor hired by Georgia regulators said the project cannot be built on budget.

Q: What about Plant Summer in South Carolina?

A: Plant owners SCANA and Santee Cooper have experienced a nearly $670 million increase in construction and ownership costs. But in the most recent estimates, the overall project cost has actually decreased because the owners expect to spend less money on other expenses.