A new generation of nuclear power plants is on the drawing boards in the U.S., but the projected cost is causing some sticker shock: $5 billion to $12 billion a plant, double to quadruple earlier rough estimates.

Nuclear power is regaining favor as an alternative to other sources of power generation, such as coal-fired plants, which have fallen out of favor because they are major polluters. But the high cost could lead to sharply higher electricity bills for consumers and inevitably reignite debate about the nuclear industry's suitability to meet growing energy needs.

Nuclear plants haven't been built in meaningful numbers in the U.S. since the 1980s. Part of the cost escalation is bad luck. Plants are being proposed in a period of skyrocketing costs for commodities such as cement, steel and copper; amid a growing shortage of skilled labor; and against the backdrop of a shrunken supplier network for the industry.

The price escalation is sobering because the industry and regulators have worked hard to make development more efficient, in hopes of eliminating problems that in the past produced harrowing cost overruns. The Nuclear Regulatory Commission, for example, has created a streamlined licensing process to make timelier, more comprehensive decisions about proposals. Nuclear vendors have developed standardized designs for plants to reduce construction and operating costs. And utility executives, with years of operating experience behind them, are more astute buyers.

Now, 104 nuclear reactors are operating in the U.S. Most are highly profitable but that was not the case until fairly recently. For the 75 units built between 1966 and 1986, the average cost was $3 billion or triple early estimates, according to the Congressional Budget Office. Many plants operate profitably now because they were sold to current operators for less than their actual cost.