A traveling wave reactor is a type of Generation IV nuclear reactor that much of the nuclear industry anticipates can convert fertile material into nuclear fuel via nuclear transmutation in tandem with the burnup of fissile material. This particular design is very different from other kinds of fast-neutron and breeder reactors in their ability to utilize fuel efficiently without costly and impractical enrichment or reprocessing of uranium. TWRs instead directly use depleted uranium, natural (unenriched) uranium, thorium, spent fuel removed from light water reactors, or potentially a combination of these materials. 

The “traveling wave” name refers to the fact that fission will not occur throughout the entire core, but remains confined to a boundary zone that slowly advances through the core over time. Theoretically, TWRs could run self-sustained for decades without having to remove and replace spent fuel from the reactor. 

Some have criticized this implementation of the fast breeder reactor design as particularly difficult, especially given the fact that typical fast breeder reactors are already hard to build. Many have lauded the goal of addressing the global energy poverty with TWRs but have pointed out that its overall cost of construction is competitive with conventional nuclear power, and that isn’t as low as fossil fuels. Bill Gates has invested deeply into the development of TWRs not, as he stated in an interview, because he “expects to make a ton of money on it,” but because this Generation IV design is “very attractive from an economic point of view.”

Image: Conceptual design of the TWR.

GIF: A numeric simulation of a TWR. Red: Uranium-238. Light Green: Plutonium-239. Black: Fission products. The intensity of the blue color between the tiles indicates neutron density.

TerraPower—with the backing of Bill Gates—has a radical vision for the reactors of tomorrow

Bill Gates reshaped the computer industry by pumping out new versions of Microsoft Windows software every few years, fixing and fine tuning it as he went along.

He’s now betting that he can reshape the energy industry with a project akin to shipping Windows once and having it work, bug-free, for 50 years.

Thanks to his role funding and guiding a start-up called TerraPower LLC, where he serves as chairman, Mr. Gates has become a player in a field of inventors whose goal is to make nuclear reactors smaller, cheaper and safer than today’s nuclear energy sources. The 30-person company recently completed a basic design for a reactor that theoretically could run untouched for decades on spent nuclear fuel. Now the company is seeking a partner to help build the experimental reactor, and a country willing to host it.

Bill Gates AFP/Getty Images

It’s a long-term, risky endeavor for Mr. Gates and his fellow investors. The idea will require years to test, billions of dollars (not all from him) and changes in U.S. nuclear regulations if the reactor is to be built here. Current U.S. rules don’t even cover the type of technology TerraPower hopes to use.

“A cheaper reactor design that can burn waste and doesn’t run into fuel limitations would be a big thing,” Mr. Gates says. He adds that in general “capitalism underinvests in innovation,” particularly in areas with “long time horizons and where government regulations are unclear.”

TerraPower is one of a host of inventors, reactor makers and electric utilities trying to kick-start innovation in a field that hasn’t seen a big technological advance in decades. President Barack Obama wants to help, too, designating $853 million for nuclear research, including small-scale reactors, in his proposed 2012 budget.

The type of reactor TerraPower is working on, a traveling-wave reactor, could reduce the need for enrichment and reprocessing of uranium. Executives at the Bellevue, Wash., company say their reactor could even be buried in the ground, where it could run for 100 years.

Green Wood

I am absolutely in favor of pursuing nuclear power, but it is a totally unforgiving technology. One minor ‘oops’ and large areas can become uninhabitable for thousands of years. When the experiment is over, you can’t just turn your reactor off and walk away from it – decommissioning it may cost more than building it in the first place.Yes, we need to do this. No, we cannot afford to just jump in and start building reactors.

—Bill Brown

To understand how a traveling-wave reactor works, think of a wood-burning stove. Today’s reactors use dried wood—enriched uranium-235—that burns hot and quickly. A traveling-wave reactor would start with a little bit of dried wood to get a hot flame going, but most of the fuel would be green, or wet, wood—depleted uranium-238. The wet logs wouldn’t burn as hot as the dried ones, but they would continue to burn long after the hot flame goes out.

Burning the enriched uranium would shoot neutrons into the depleted uranium making up roughly 90% of the fuel. That process would produce plutonium, which would create energy as it continued to get hit by even more neutrons. It’s a slow, controlled reaction that could continue over many years without need of human intervention. And in TerraPower’s design, the core of the reactor, where fission takes place, would be small: a cylinder about 10 feet wide and 13 feet long.

Enlarge Image

View the parts of TerraPower’s traveling-wave reactor.

Another plus: Large supplies of depleted uranium are available as a byproduct of today’s water-cooled reactors. Removing it from those reactors and reprocessing it for reuse is a costly procedure, and a source of worry that radioactive material might fall into the wrong hands. Reducing the need for reprocessing could save money and reduce the risk of nuclear proliferation.

The idea for traveling-wave reactors has been around for decades but was mothballed amid waning U.S. interest in nuclear power. Then came a boost in the 1990s from a research paper by scientists at Lawrence Livermore National Laboratory, including Edward Teller, the father of the hydrogen bomb and the brain behind Ronald Reagan’s Star Wars missile-defense initiative; and an acolyte of Mr. Teller’s named Lowell Wood.

Mr. Wood recently found a receptive ear in Nathan Myrhvold, a former Microsoft executive and head of Intellectual Ventures, a patent and invention firm in Bellevue. Mr. Myrhvold is a close friend of Mr. Gates, who is also an investor in Intellectual Ventures. In recent years the three men have done a lot of brainstorming about future technologies, including the traveling-wave reactor.

The reactor idea intrigued Mr. Gates, who was studying energy and climate change at the time. Among the reactor’s other potential advantages, Mr. Gates says he was interested in its potential for producing cheap, zero-carbon energy and its ability to turn “what is a waste product into fuel.”

Mr. Gates got the project rolling with seed money in the tens of millions of dollars. Venture-capital firms Charles River Ventures and Khosla Ventures invested $35 million last year. Nuclear-industry veteran John Gilleland is TerraPower’s chief executive; a network of part-time researchers and scientists around the country offer input.

Looking for a Home

The traveling-wave reactor is still virtual, existing only in software on computers at TerraPower headquarters. Mr. Myrhvold says there is a basic design, not a full blueprint. But it’s enough for the next step: building a test version of the reactor. TerraPower is looking for a customer, such as an electric utility, and a country that is willing to house an experimental reactor.

The company has made pitches in France and Japan, Mr. Myrhvold says; both have big nuclear-power industries. He’s also made the rounds in Russia, China and India, he says. So far, there have been no takers.

One country he is certain won’t be a customer anytime soon is the U.S., which doesn’t yet have a certification process for reactors like TerraPower’s. It would likely be a decade or more before the reactor could be tested on U.S. soil. “I don’t think the U.S. has the willpower or desire to build new kinds of nuclear reactors,” Mr. Myrhvold says. “Right now there’s a long, drawn-out process.”

Policy experts say that’s with good cause. “Our regulatory process, while burdensome, is there for a reason, and it does represent the gold standard around the world for nuclear safety,” says Paul Genoa, director of policy development at the Nuclear Energy Institute in Washington.

Mr. Myrhvold says he hopes the process will speed up and spark innovation to meet the world’s growing energy demand. “Let’s try 20 ideas,” he says. “Maybe five of them work. That’s the only way to invent our way out of the pickle we’re in.”

Mr. Guth is the Los Angeles bureau chief for The Wall Street Journal. 

TerraPower, a start-up led by Bill Gates, is at work on a new kind of reactor that would be fueled by today’s nuclear waste.

If you were a TerraPower executive, would you develop a nuclear energy demonstration plant of the future in China or the United States?

In a drab one-story building here, set between an indoor tennis club and a home appliance showroom, dozens of engineers, physicists and nuclear experts are chasing a radical dream of Bill Gates.

The quest is for a new kind of nuclear reactor that would be fueled by today’s nuclear waste, supply all the electricity in the United States for the next 800 years and, possibly, cut the risk of nuclear weapons proliferation around the world.

The people developing the reactor work for a start-up, TerraPower, led by Mr. Gates and a fellow Microsoft billionaire, Nathan Myhrvold. So far, it has raised tens of millions of dollars for the project, but building a prototype reactor could cost $5 billion — a reason Mr. Gates is looking for a home for the demonstration plant in rich and energy-hungry China.

(Mr. Gates, of course, has plenty of money of his own. This year Forbes listed him as the world’s second-richest person, with a net worth of $67 billion.)

“The hope is that we’ll find a country, with China being the most likely, that would be able to build the demo plant,” Mr. Gates said last year in a conversation with the energy expert Daniel Yergin. “If that happens, then the economics of this are quite a bit better than the plants we have today.”

Perhaps one of the most intriguing arguments supporters make about Mr. Gates’s reactor is that it could eliminate several routes to weapons proliferation. Iran, for example, says its nuclear program is for peaceful purposes, but it is enriching far more uranium than it needs for power generation. The United States has long said that Iran’s enrichment could lead to a nuclear bomb.

Today’s nuclear reactors run on concentrations of 3 to 5 percent uranium 235, an enriched fuel that leaves behind a pure, mostly natural waste, uranium 238. (A uranium bomb runs on more than 90 percent uranium 235.) In today’s reactors, some uranium 238 is converted to plutonium that is used as a small, supplemental fuel, but most of the plutonium is left behind as waste.

In contrast, the TerraPower reactor makes more plutonium from the uranium 238 for use as fuel, and so would run almost entirely on uranium 238. It would need only a small amount of uranium 235, which would function like lighter fluid getting a charcoal barbecue started.

The result, TerraPower’s supporters hope, is that countries would not need to enrich uranium in the quantities they do now, undercutting arguments that they have to have vast stores on hand for a civilian program. TerraPower’s concept would also blunt the logic behind a second route to a bomb: recovering plutonium from spent reactor fuel, which is how most nuclear weapons are built. Since so much uranium 238 is available, there would be no reason to use that plutonium, TerraPower says.

Countries that do not have nuclear weapons will still need lots of electricity, said John Gilleland, chief executive of TerraPower, and “we would like to see them build something that allows us to sleep at night.”

But no one disputes that this is a very long-term bet. Even optimists say it would take until at least 2030 to commercialize the technology. What the competition would look like then — wind, solar, natural gas or some other technology — is not clear. If the idea can be commercialized, it is not even clear that TerraPower could do it first.

The engineers working for Mr. Gates acknowledge the enormous challenges but say they are convinced that he, and they, are chasing the solution not only to energy and weapons proliferation but also to climate change and poverty.

“If you could pick just one thing to lower the price of — to reduce poverty — by far you would pick energy,” Mr. Gates said as he introduced the reactor idea in a speech in 2010. “Energy and climate are extremely important to these people, in fact, more important to them than anyone else on the planet,” he added, referring to killer floods, droughts and crop failures driven by carbon dioxide given off in energy production. He illustrated his talk with a photo of schoolchildren doing their homework under street lamps.

Doug Adkisson, TerraPower’s senior vice president for operations, said Mr. Gates had “a very humanitarian but very cold assessment” about nuclear power and what it could do. What drives him to nuclear power, he said, are the questions “What have you got, and what can you do to raise the living standard of a whole lot of people?”

Despite its difficulties, some outside experts applaud Mr. Gates for trying.

“If you’ve got a huge amount of money, for whatever reasons, you are willing to make a long-term bet, which is not typical of what venture capitalists do,” said Burton Richter, a Nobel laureate in physics. “It’s hard to get a 20-year thing from the standard venture capital world,” he said, adding that financing projects like TerraPower’s is more typical of governments or sovereign wealth funds.

One-hour meetings with Mr. Gates about TerraPower sometimes turn into five-hour meetings, associates say.

In Bellevue, TerraPower is a spinoff of Intellectual Ventures, a company co-founded by Mr. Myhrvold that focuses on inventing new products and techniques, among them improved seeds for subsistence farmers and methods for keeping vaccines cold for weeks in places where there is no electricity. But its critics call it a patent troll because it buys large portfolios of technology patents and uses them, they say, to sue software designers, smartphone makers and others.

TerraPower employees work in a building that also houses Intellectual Ventures, which includes a chamber for raising mosquitoes, a test kitchen for developing new ways to prepare and preserve food, and hand-built, high-precision instruments for measuring tiny details of prototype nuclear fuel.

Some of its equipment has more than one use: the nuclear effort shares a supercomputer, one of the 500 fastest in the world, with the vaccine and disease vector section, and a tool that cuts steel with a jet of water propelled to three times the speed of sound is used for various programs.

One of the biggest challenges TerraPower faces is that neutrons — the particles released when a uranium atom is split in a reactor — damage a reactor’s metal parts. In today’s reactors, the problem is manageable because the fuel stays in place for no more than six years and can stand the bombardment. But the TerraPower fuel is supposed to stay in place for 30 years.

“The biggest problem is swelling,” said Kevan Weaver, a physicist and TerraPower’s director of technology development. “The neutrons knock an atom out of the lattice, and leaves a hole, and then the holes coalesce and form voids, and the part swells.”

So TerraPower’s engineers are experimenting with different types of metals, at different temperatures. In December they will put thousands of samples into a Russian reactor that will irradiate them for six years, with neutrons of the same energy that TerraPower’s reactor would have. At the end of this decade, they will see how the metals’ strength was changed, and predict if the metal will survive for 30 years.

Another problem is that when uranium is split, some of the fragments are gases. This is tolerable in current fuels, but no fuel could hold a 30-year accumulation.

Simply designing the core of the reactor is an additional problem. TerraPower engineers call it a “traveling wave reactor,” because the area in which the uranium 238 has been converted to plutonium and can be fissioned travels through the core like a wave.

But every time the designers change the thickness or type of metal they are using, the flow of neutrons will change, too, and the 30-year life of the core is so long that the inventory of fission products, some of which absorb neutrons, will also change, as some unstable materials give off radiation and transmute themselves into something else.

To allow the neutrons to travel at a speed that is best for converting waste uranium into plutonium fuel, the reactor uses sodium, not water, to moderate the neutrons’ speed and carry off the usable heat. But hot sodium burns on contact with air.

TerraPower is not alone in pursuing a reactor that will turn waste uranium into energy, and if such a concept can be commercialized, Mr. Gates might not be the first to do it. General Atomics, which has decades of experience in nuclear power, but is probably best known for producing the Predator drone, is pursuing what it calls an “energy multiplier” reactor module on the same general principal. General Atomics, which is based in San Diego, would use helium, not sodium, however, potentially simplifying some problems.

“You just set it up, let it burn, and it goes,” said John Parmentola, the company’s senior vice president.

Like TerraPower, General Atomics is courting the Chinese.


“Their new technology is still in development, but boasts the ability to turn nuclear waste (depleted uranium) into vast sources of power.  TerraPower projects their traveling wave reactor (TWR) to turn an 8-metric-ton canister of depleted uranium into 25 million megawatt-hours. That is enough power for 2.5 million households for an entire year.”

Yes please. Let’s use the vast amount of nuclear waste to our benefit instead of just handwaving nuclear power away with a “cleaner than coal!"