To some observers, the plan’s collapse also raises questions about the feasibility of other planned advanced reactors, meant to provide clean energy with fewer drawbacks than existing reactors. NuScale’s was the most conventional of the designs, and the closest to construction. “There’s plenty of reasons to think [the other projects] are going to be even more difficult and expensive,” says Edwin Lyman, a physicist and director of nuclear power safety at the Union of Concerned Scientists. //

Jacopo Buongiorno, a nuclear engineer at the Massachusetts Institute of Technology, says the NuScale design has an Achilles’ heel. Each reactor’s core resides within a double-walled steel cylinder, with a vacuum between the walls to keep heat from leaking out. The reactor modules sit in a big pool of water, which in an emergency can flood into the vacuum space around a reactor to prevent it overheating. Compared with a conventional reactor’s building, the pool requires more reinforced concrete, the price of which has soared, Buongiorno says. “In terms of tons of reinforced concrete per megawatt of power, NuScale’s design is off the chart.” //

Buongiorno says he wouldn’t read NuScale’s failure as a verdict on all advanced reactor designs. “I would steer clear of broad-stroke comments in terms of cost,” he says. Baker says he has no doubt that the country needs new nuclear plants to supplement the fluctuating supply of power from wind and solar. “To achieve the nation’s decarbonization goals, it’s got to happen.”