Editor's Note: X-energy is one of seven private companies Inc. identified that are driving development within seven key pathways to net zero--eliminating one ton of greenhouse gases for every ton emitted.

HOW CAN A company that produces nuclear-fission reactors be on any list of greentech startups in the year 2022? Because X-energy is reinventing nuclear power, with fuel and reactors designed to neutralize both the risks and the traditional arguments against its use--giving nuclear energy, the generation of which emits no carbon dioxide, a chance to contribute far more to the nation's grid. Today, nuclear power supplies less than 20 percent of America's electricity, from typically old and hugely expensive plants.

Fission starts when a radioactive trigger emits a neutron that strikes and splits a uranium atom, releasing three things. The first is energy, which the reactor harnesses. Second, fission products like barium or krypton, which make up the reactor's waste. And finally, more neutrons, which go on to split more uranium, kicking off the chain reaction.

The standard design for housing this process hasn't changed much in more than 40 years and carries the dreaded (though highly unlikely) risk of meltdown, which happens when the cooling system, for whatever reason, can't contain the energy unleashed by the chain reaction. Traditional nuclear power companies incur huge costs hedging against this scenario. They locate plants away from major cities and near sources of water, and install backup pumps and their telltale containment domes.

X-energy's advances may sweep away those concerns--and costs. The company is commercializing next-gen nuclear. It makes fuel by wrapping specks of uranium in layers of carbon and ceram­ic, and then encasing those bits in graphite balls, which flow through its Xe-100 reactor like gumballs through a dispenser. When a neutron hits the uranium inside a fuel pebble, the shell keeps the neutron from moving too quickly, which makes for a safe chain reaction. The fuel ball never gets hot enough to melt, and it contains the fission products. All of the nuclear waste from X-energy reactions ends up encased in the graphite orbs.

"It is walkaway safe," says X-energy CEO J. Clay Sell, former deputy secretary of energy under George W. Bush. You can turn off an X-energy reactor like you would the lights in your house, and be confident the system will shut down without incident. For many Americans who grew up during the Cold War, nuclear power carried all kinds of negative associations­--Three Mile Island, Chernobyl, Homer Simpson. That baggage seems lighter today. "People in my generation talk about why we can't solve the nuclear waste problem," says Sell, 55. "People under 35 realize nuclear power is the only way we solve the real waste problem--emissions coming out of tailpipes and the stacks of coal plants."

Indeed, a rare bipartisan consensus exists among politicians for supporting the industry. In 2020, X-energy and Bill Gates's Terra­Power were the two companies chosen by the DOE to get next-gen funding for the demonstration of their advanced reactors. Last year's infrastructure law resulted in an additional $1.1 billion for the project, and X-energy is now building its Xe-100 reactors, modular units that utilities can essentially plop down anywhere. It plans to pack four of them into a demonstration facility near Richland, Washington, that will generate 320 megawatts--enough to power about 250,000 homes. It sees 30 months of construction ahead, another 48 to earn regulatory approval. "This," says Sell, "is not your daddy's nuclear company."