Of four reactor projects identified by the Energy Department in 2009 as the most likely candidates for federal loan guarantees, only two are moving forward. At a third, in Calvert Cliffs, Md., there has been no public sign of progress since the lead partner withdrew in October and the other partner said it would seek a replacement.

And at the fourth, in Texas, a would-be builder has been driven to try something never done before in nuclear construction: finding a buyer for the electricity before the concrete is even poured. Customers are not rushing forward, given that the market is awash in generating capacity and an alternative fuel, natural gas, is currently cheap.

“The short answer is, there has to be a market for the power,” said John Reed, an investment banker who specializes in nuclear projects. “That’s the most immediate hurdle these projects have to get over.”