Four years ago, it seemed one of Bill Gates’ globe-changing moonshots had taken a significant step forward. Reports were saying that Gates had struck a deal with Chinese officials to help build a new type of nuclear reactor with TerraPower, the Bellevue-based company Gates bankrolled.

Those early reports were premature, though — Gates had only begun discussions with China to partner with TerraPower in building the company’s traveling wave reactor. But after four years of talks, Gates announced Tuesday, during China President Xi Jinping’s visit, that TerraPower would collaborate with the state-owned China National Nuclear Corporation to develop the reactor.

“We recognized from the beginning that we needed a key partnership to take this design and make it a reality,” Gates told the audience at a Tuesday seminar. “We are very excited that CNNC has been talking with us and working with us about a very important partnership. The MOU we signed today was a milestone with our relationship with them.”

TerraPower's traveling wave reactor. Courtesy TerraPower.

TerraPower’s traveling wave reactor. Courtesy TerraPower.

The memorandum of understanding signed by TerraPower and the CNNC is important in a couple of respects. One, as Gates alluded to yesterday, the traveling wave reactor must clear technical hurdles before it can be deployed in a large-scale fashion. Once the reactor’s ready to be built, TerraPower needs a host nation, and China just stepped to the front of that line.

Meanwhile, plenty of implementations await. “We’re still working on the preliminary design,” said Roger Reynolds, TerraPower’s senior technology adviser. “We’ve already done a lot of materials testing to develop the new materials that we need. We’re about to engage in fuels testing in a fast reactor in Russia.”

The key feature of TerraPower’s reactor is its ability to sustain fission without using enriched uranium. In its natural state, uranium is composed of about 0.7 percent U235, the isotope necessary to sustain a fission reaction, so it is enriched to contain 5 percent of that isotope. It’s this enrichment process that can lead to foreign conflicts such as the current one with Iran; a country can say it is enriching fuel-grade uranium, but if unabated, uranium can be enriched to the U235 concentration necessary for atomic weapons.

In TerraPower’s reactor, the conversion of spent or natural uranium to a fissile material occurs in the reactor itself, thus eliminating the need for external enrichment. Furthermore, spent fuel rods from light-water reactors popular today can power fission in the traveling wave reactor.

“(Light-water reactors) can only run so long” — about six years — “on the fuel before the other fission products prevent the reaction from taking place,” Rogers said. “In our reactor, we never really get to that point because we’re always breeding fuel. … The thing that gets us to the end of our cycle is plant issues.”

Developing this reactor, of course, is a capital- and research-intensive process, and the CNNC’s involvement adds more nuclear expertise and money to the cause. But once a design is settled on, TerraPower needs a place to build a prototype reactor. The company doesn’t expect to be to that stage for about another decade, but once ready, its new partnership with the CNNC means China will likely be the test location for the next-generation nuclear reactor. While TerraPower can test the reactor’s components in multiple nations, it needs a single host to try out the first traveling wave reactor. The company had discussed a prototype with China, India, Russia, and France.

Starting the process in China is in line with the company’s commercialization goals. While TerraPower hopes to eventually provide carbon-free baseload power for nations of all sizes, its first customers will likely be fast-growing countries that are either looking for new electricity sources or are transitioning from fossil fuels. China’s economic growth, though slowing, is still among the speediest in the world, and the country is far more open to new nuclear installations than the United States.

Coal is the fuel of choice for baseload power in most developing nations, China included. But that economic slowdown has triggered a corresponding decrease in Chinese coal production, which could provide an opportunity for new energy technologies like TerraPower’s to begin establishing a foothold. If the model works in China, other industrialized nations could follow suit.

TerraPower maintains its reactor likely won’t hit the market until about 2030. As the prevalence of wind and solar energy systems increases, and as costs fall, some argue nuclear’s attractiveness will sunset by the time TerraPower is ready to roll out its reactor. But Kevan Weaver, the company’s director of technology integration, says nuclear’s success doesn’t depend on it winning out over other renewable sources. Nineteen percent of U.S. electricity was generated by nuclear power in 2014, and 13 percent came from renewables such as hydropower (6 percent), wind (4.4 percent), and solar (0.4 percent).

“The problem is that, while we are technology neutral for sure, from a numbers standpoint, trying to get the other non-carbon-emitting sources to make up that difference is pretty tough because most of them bar backed up by fossil (fuels),” Weaver said.

Most renewable energy is intermittent — rivers dwindle, clouds block the sun, the wind slows. When those sources decrease output, baseload sources pick up the slack, and most baseload energy sources are coal or natural gas, the fossil fuels that produced two-thirds of America’s electricity last year. Weaver sees TerraPower acting as the baseload in a more diverse energy mix than what exists today. With the agreement formalized yesterday, China might be the first clean-energy laboratory TerraPower calls on.