Recently, however, there have been murmurs of a new nuclear age. Many environmental groups remain opposed to nuclear energy. But as the realities of climate change — and the fast-growing demand for energy worldwide — become more apparent, a handful of environmental activists and politicians are mentioning nuclear power alongside other carbon-free options.

“Given the urgency and the scale of the challenge, we have to keep all low- and zero-carbon technologies on the table,” Gov. Jay Inslee told New York magazine in a profile of his presidential campaign, which centers on climate change..

This is where TerraPower steps in. Founded 11 years ago by Bill Gates, the Bellevue company has been pursuing more perfect nuclear power, as it works to create a new type of reactor that requires refueling just once every 20 to 60 years.

That means 80% less waste to treat and dispose of. If successful, this approach would cut back on the biggest environmental threat from reactors.

In a Dec. 29, 2018, entry in his blog, Gates wrote that global emissions of greenhouse gases went up in 2018, reinforcing the need for clean energy. While solar and wind power solve part of the carbon-emissions problem, these are also intermittent sources of energy, he noted. “Nuclear is ideal for dealing with climate change, because it is the only carbon-free, scalable energy source that’s available 24 hours a day,” he wrote. “The problems with today’s reactors, such as the risk of accidents, can be solved through innovation."

Yet Gates' vision has been stalled itself by unintended consequences of the Trump administration's trade war with China. Now, the future of nuclear technology is relying on a Plan B.

TerraPower was formally founded in 2008 after two years of discussions about developing a so-called breed-and-burn reactor. “They felt nuclear power was an important area to focus on,” said TerraPower Chief Financial Officer Marcia Burkey.

While the idea of a breed-and-burn reactor has existed on paper since the 1950s, no one has yet built one. In oversimplified terms, fuel in a reactor holds a small portion — much less than 10 percent — of enriched uranium 235. This is the stuff that “burns” in the reactor. When the uranium 235 is gone — usually in one or two years — the fuel has to be replaced. In a breed-and-burn reactor, the depleted uranium that makes up the overwhelming majority of the fuel is also burned, dramatically expanding the lifespan of a fuel assembly.

“Think of it as a log … that burns for 60 years,” Gates said in a 2010 TED Talk about TerraPower. “There is a lot less waste under this approach.”

The concept is simple. The nuclear physics aspect is cutting edge. The nuts-and-bolts engineering is extremely difficult.