The U.S. nuclear-power industry just can’t seem to catch a break lately. While the Tennessee Valley Authority’s Watts Bar Unit 2 plant made history last October as the first new U.S. nuclear generating station to come online in 20 years, four other reactors under construction in Georgia and South Carolina remain behind schedule and over budget, and a fifth planned unit was canceled by its utility in March. On top of all that, the developer of all five projects, Westinghouse, filed for bankruptcy in late March.

In addition to new plants, rapidly changing economics are forcing owners to reconsider the fortunes of existing stations that otherwise could be kicking out electrons for another two decades or longer. Fear of losing such significant providers of greenhouse-gas-free electricity is forcing some states to promote incentives for plant owners as planners struggle to maintain supplies without a concurrent rise in carbon dioxide (CO2).

The four reactors under construction—two units each at Georgia Power’s existing Plant Vogtle station and South Carolina’s Summer station—are all expected to be completed, though perhaps not by the 2020 date on the books. However, the design and construction challenges faced by the plants’ developers and owners have caused a number of other plans to be mothballed.

All four units were being developed according to the new AP1000 design from Toshiba’s Westinghouse subsidiary. This approach incorporates a gravity-powered cooling system that can operate without external electric or diesel power. Its modular design allows individual components to be manufactured elsewhere, shipped to the job site and craned into place. In theory, this is a less expensive process than the on-site, in-place fabrication used in all previous U.S. plants.

Unfortunately, manufacturers’ efforts fell short of the needs of this ambitious effort. The demands of four reactors gearing up at once, after decades of inactivity, overwhelmed the capacities of the companies tasked with manufacturing and assembling the plants’ infrastructure and modular components.

“We haven’t finished nuclear power plants in the United States in 30 years,” said Edward Kee, CEO of Nuclear Economics Consulting Group, emphasizing the skill deficit created by three decades of inactivity. “There were people who’d never built a nuclear plant before.”

The resulting overruns and delays have devastated Westinghouse and its parent company, Toshiba, which purchased the nuclear-technology leader in 2006, when nuclear energy’s fortunes appeared to be on the way up. In an attempt to gain control over the construction process, Westinghouse bought out its engineering partner Stone & Webster in 2015. However, that move might have been too little, too late, and Toshiba has been forced to sell several of its more profitable businesses—including, possibly, its highly profitable memory-chip business. The company is reportedly trying to sell the Westinghouse unit, as well, though the looming bankruptcy will make any sale difficult.

The four plants under construction are being paid for by electric utilities in states with regulated electricity markets, so their costs are incorporated into the utilities customers’ monthly bills. In deregulated states, however, merchant nuclear plants are facing different challenges, as their profits are threatened by less expensive electricity from wind farms and natural gas generators.

“It’s a bleak situation for a merchant nuclear plant,” Kee said. “Gas is cheap, wind is getting incentives, and the market doesn’t pay for reliability and zero emissions.”

Regulators and legislators in Illinois and New York are hoping to help plant owners benefit from the advantages of reliable, CO2-free operations in an effort to stem a growing threat of plant closures. Both states recently passed some form of zero emissions credit (ZEC) program to subsidize owners through ratepayer charges. Ohio is looking into a similar program for its nuclear operators.

In addition to the loss of significant electricity supplies, shuttering a plant also puts hundreds of employees out of work and eliminates millions of dollars in payments to local government coffers. The Pilgrim Nuclear Power Station in Plymouth, Mass., which is scheduled to cease operations in 2019, employs 600 full-time workers and up to an additional 900 temporary staff during refueling operations. It also pays almost $10 million annually in town property taxes.

“Zero emissions credits on paper were about CO2 emissions, but were really about jobs,” Kee said. “The negative economic impact of closing the nuclear plants would be more than the cost of ZEC payments.”

For now, states are only applying ZEC incentives to existing plants, meaning utilities and merchant-power providers have little motivation to pursue new nuclear construction, at least at the scale of the plants now underway in South Carolina and Georgia.

“There are no more new nuclear plants moving forward with an investment decision,” Kee said. “These two plants will be the last ones built in the U.S. for a decade or more.”