For more than a half century, nuclear power has been focused on one kind of plant: a huge, complicated, expensive facility, with armed guards, located away from cities and next to a river.
Now, a new generation of nuclear engineers focused on climate change is designing plants that are smaller and cheaper, and could be located closer to where people live. Companies say the plants are also safer, but to help their business models succeed they need changes to regulations that were designed for the larger existing plants.
One of the start-ups getting attention is Oklo, whose proposed nuclear power plant looks more like a stylish ski chalet than an industrial facility.
"We're not using water. We're not large. We're not using the same type of fuel. We're able to recycle waste and used fuel," says Caroline Cochran, Oklo chief operating officer and co-founder.
Cochran says her company's plants are more like the small research reactors found on college campuses. Each would generate enough electricity to power hundreds of homes. Initially the plan is to use them in remote areas such as rural Alaska, where they could replace more-polluting diesel generators.
NuScale Power has designed a larger nuclear power plant that is still very different from existing generators. Instead of one big reactor, each NuScale facility would have up to 12 smaller reactors that sit underground in a huge pool of water that absorbs heat.
NuScale co-founder José Reyes told NPR last year that there are no pumps or generators that could fail. That's what happened in the Fukishima accident that led to melt-downs.
Reyes says if there's a problem and radiation is released, the danger to people would be limited to the plant site. That means his plants could be located closer to homes, say at old coal power plant sites.
"They would love to re-purpose those sites for clean energy like nuclear power," said Reyes. "Our design would fit perfectly with those plans."
But first the Nuclear Regulatory Commission would have to change its rules.
Taking safety claims "with a big grain of salt"
The NRC is considering whether to shrink emergency planning and evacuation zones around these newer reactors — from a 10-mile radius to, in some cases, the boundary of the plant site.
Nuclear energy critics say that would be a mistake.
"When you're talking about a reactor that's never been built or operated, you have to take with a big grain of salt the claims that it's actually safer or more secure," says Edwin Lyman at Union of Concerned Scientists.
He says the industry also wants to use weaker reactor containment shells, and in some cases they don't want to have to keep an operator at the site.
Lyman thinks companies should build plants under current rules first. "You have to work out the kinks of these new plants," he says. "And then over time you might be able to adjust your requirements accordingly. But you don't do that at the get-go."
A National Nuclear Security Administration (NNSA) official recently echoed some of Lyman's concerns in comments sent to the NRC. The NNSA is a semi-autonomous agency within the Department of Energy.
Deputy Under Secretary Jay Tilden called the proposed rule a major departure from "the successful 42-year-old practice of using a 10-mile plume exposure emergency planning zone." That existing regulation, he wrote, provides "the last layer of a defense-in-depth for low-probability, high-consequence accidents."
But a day later, U.S. Department of Energy Spokesperson Jessica Szymanski said the comments "do not represent the official position of DOE or NNSA." She said both agencies support the proposed rulemaking.
That's in line with nuclear industry arguments that these plants are simpler and safer, and so deserve different and less stringent regulations.
"As technology evolves, the regulations should evolve to match the new state of technology," says Marcus Nichol, senior director of new reactors at the Nuclear Energy Institute.
Nichol says there's a lot of knowledge about how these new reactor designs work, and years of testing behind the components.
Previous accidents — including Three Mile Island in 1979 — stopped the nuclear industry's growth. Nichol says companies and regulators are committed to making sure these new plants are safe.
"We recognize that if we were to do anything that's not safe, that is the end of our industry as we know it," he says.
The NRC has extended a comment period on the proposed rule to September 25th. A final rule on whether to shrink evacuation zones around plants is expected next year.
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