Energy Department graphic

A sphere of TRISO fuel, with cross-section showing the individual fuel pellets inside.

PENTAGON: From torpedoed oil tankers in World War II to ambushed fuel convoys in Afghanistan, meeting the military’s need for energy has long been costly in both money and human lives. But while aircraft carriers went to nuclear power decades ago, the Defense Department has not seen reactors as a viable alternative for its energy-hungry outposts on land — until now.

But what about the much-publicized risks of nuclear power? Better technology and a much smaller size should make the new mini-reactors dramatically safer than any existing nuclear power plant, the program director told me.

courtesy Jeff Waksman

Jeff Waksman

Earlier this month, the Defense Department announced it had awarded contracts to three companies – BWX, Westinghouse, and X-Energy – to develop competing designs for a mobile miniature nuclear reactor. It’s part of a program named Project Pele, after the Hawaiian goddess of creation and fire.

The program manager, Jeff Waksman – a PhD physicist who worked for IBM, NASA, and Congress – had been scheduled to speak at the AUSA Global Force conference in Huntsville last month, on a panel I was supposed to moderate. With the cancellation of Global Force due to the COVID-19 coronavirus, I sat down with Waksman in the Pentagon to bring our readers his perspective in writing instead.

[Click here for more surrogate AUSA stories]

“We want to build one prototype,” Waksman told me. “But there’s no guarantee we’re going to build a prototype. It’s going to depend on how well the designs come in. It’s going to depend on what our funding profile is. All we’ve locked in right now is three companies for one year.”

Whatever the Pentagon does build, he continued, will be safer than any existing reactor. “We now have the capability to build completely, inherently safe reactors,” he told me.

Energy Department photo

A TRISO fuel pellet — less than a millimeter across — cut open to reveal the three protective layers around the uranium core.

That’s thanks to a revolutionary new technology called TRISO, which replaces large uranium cores with millions of tiny pellets, each of them sufficiently hardened to lock radioactivity inside that they can remain intact at temperatures that would melt steel. That means you can design a TRISO reactor so it physically can’t melt down. That’s because a meltdown happens when the reactor core melts and burns through the concrete and steel around it; a TRISO core would remain intact even as the steel around it melts.

Even if an enemy missile hit a TRISO reactor – and the Pentagon doesn’t plan to put these anywhere near a war zone – the blast would mainly scatter pellets across the landscape, with only a few breaking open to emit tiny amounts of radioactive material. The goal is to design the TRISO reactor so that a conventional warhead powerful enough to crack the reactor open would actually do more damage to the surrounding environment by the sheer force of its explosive blast than any radiation released.

But why does the Defense Department want this technology in the first place? The answer begins in a very low-tech place: the bloody, dusty roads of Iraq and Afghanistan, where thousands of US troops were killed or wounded convoying fossil fuel to power forward bases.

Energy Department graphic

Alternative forms of TRISO nuclear fuel.

Here’s Waksman in his own words (edited for clarity and brevity from a long and technical interview):

Q: Where did the idea for this project come from?

A: Jeff Waksman, Project Pele program manager, Strategic Capabilities Office:

This started because there’s this growing need for energy. It was a big problem in Iraq and Afghanistan, where 52 percent of all casualties happened on land convoy missions. Those land convoys take primarily fuel and water: That’s over 80 percent.

Congress had asked the Defense Science Board to look into this, and in 2018, the Defense Science Board put out a report arguing that the energy logistics chain is more at risk than it’s ever been before. A key weakness in the American way of war –moving fuel far across the ocean to support deployed U.S. forces is very, very difficult.

They felt that nuclear power is a potential game changer because the technology now is very different from where it was in the ’60s and ’70s. We now have the capability to build completely, inherently safe reactors. We have the ability to build reactors that, even in worst case scenarios, have very minor radiological imprints. It’s not that they’re no risk, but it is just a different era.

That led Congress to say, “We think the DOD and the DOE should explore this. We’d like to see a plan of how you’re going to achieve a prototype.”

Undersecretary of Defense Mike Griffin asked SCO to take this project on. That was when I was hired as program manager, in September of 2018.

The big game changer that we’ve seized on is what’s called TRISO fuel technology: TRi-structural ISOtropic. This is not something that DOD invented. The Department of Energy decided in 2002 to develop a new advanced fuel that would be able to produce inherently safe reactors.

One of the big benefits of this fuel is that it’s been tested to be able to stand 1800 degrees Celsius [over 3,200 Fahrenheit]. That is hotter than the melting temperature of steel. Steel will melt, and the fuel will hold. Even in your worst-case scenario where all your redundancy systems fail, it never gets close to 1800 degrees, so the meltdown of fuel is highly improbable.

Submarine reactors and commercial reactors operate at temperatures way, way lower than that. For commercial reactors, you’re talking about a few hundred degrees. When you have a situation like Three Mile Island, they have a failure where it starts to heat up, and you get to the melting point of the fuel.

So, if you look at Three Mile Island or any traditional reactor design, they have to make these colossal containment vessels that can withstand even melted uranium. The reason why no one was harmed by Three Mile Island is that even after the uranium melted, you had these super-thick steel vessels that held the melted fuel inside. It never breached, but that’s colossally expensive, colossal amount of maintenance.

The premise for TRISO is you can now drop these huge elaborate steel containment vessels, these huge reinforced concrete domes, because now the fuel can withstand higher temperatures and pressures than your containment vessel can. It’s just a complete paradigm shift for nuclear safety.

Q: What if an enemy attacks the reactor?

A: We do not visualize, in short term, these reactors being in a tactical zone. That is not our intention here.

Our main focus is the strategic support area, thousands of miles away from the front. How do we keep the ports open? How do we keep the railways open? How do we keep key radars or computers or drone controllers operating?

For the first operational use of this reactor I’d be looking at, for example, early warning radar sites in Alaska. Those tend to be in very remote places, very difficult to get fuel to, and they are very power hungry.

Another application that’s very useful is humanitarian assistance and disaster relief missions. A place like Puerto Rico gets hammered by a hurricane, the whole electrical grid goes down. You could generate one to three megawatts for, say, a refugee center or hospitals.

That said, anything in the world is a target. You absolutely can hit this thing with something big enough that it’s going to break. We recognize that. We understand that the Army is never going to employ these if you’ve got 10-mile exclusion zones after thing gets hit.

But most people don’t understand that raw uranium is not radioactive. What’s radioactive are all the fission products that come out. It’s all these nasty gasses like xenon and cesium. In a traditional reactor, if you breach the core, those gases get out, and that’s what harms everybody.

The premise of the TRISO is that all those gases are divvied up among a million little pellets. If you only breach one pellet, only one millionth of the gas gets out. We believe that the area that would be impacted by radiation should be comparable to the area that would be destroyed by the explosive.

The pellets are really small. They’re less than a millimeter in diameter. If you look at the different layers inside, it looks like jawbreakers:

  • The center part is where your uranium is.
  • It’s then surrounded by a spongy carbon material: This is what absorbs all the fission gases.
  • Then that’s surrounded by the silicon carbide. That’s what provides the toughness and the ability to withstand very high temperatures.
  • Those are the TRISO, the three layers: uranium, carbon, silicon carbide.
  • Then outside that, you then have an outer carbon layer that glues everything together.

What you actually fuel the real reactors, you smoosh the pellets into cylinders or spheres, called compacts, about 25 millimeters [in their longest dimension]: There are about 3,000 little pellets in that. That’s what you actually load your reactor with.

There’s different ways you can assemble them, but basically think of these as your fuel rods. In a traditional reactor, you’ve got to have fuel rods to generate heat. You’ve got to have moderators to transfer the heat out. Similarly, we’re going to have a core that’s going to have fuel and a moderator so it can transfer heat out.

For a moderator, a traditional nuclear reactor is going to be hooked up to a large body of water. They’re almost always on rivers or near seas because you need colossal amounts of water to go through those famous cooling towers. That does not make for mobile reactor.

Historically the reason why all reactors are made with water is because all the reactors that we have today in the commercial world are descendants of Rickover’s original Naval Reactor. It turns when you’re have a submarine or a carrier, it’s very easy to just churn water in and out. That’s why they’re all water-based. Since we’re not doing these on the sea, we have to look for another alternative.

There’s different designs for different moderators. What those choices are is definitely proprietary. One of the things we’re doing is doing a trade-off study to understand the benefits and risks of different moderators: helium, carbon dioxide, sodium – there’s lots of different things you could use.

We’ve awarded three companies to do a design competition and we fund those three companies for one year. At that point we will evaluate: If everything is going well, we have the option of going for a second year, which would take us to a final engineering design. At that point we’ll make a decision whether we want to go build a prototype. If we do, the goal will be to be in construction by the end of 2023.

It’s hard for us to guess cost at this stage, but certainly this is not intended to be a multi-billion dollar program. We understand that these need to be cost competitive with the existing real sources out there.

Our plan to initially operate this reactor is to go to a Department of Energy site and do initial testing indoors, inside a containment building. Once we’re confident that we’ve proven that it’s safe, we will then take it outside, drive around a little bit on the DOE site, plop it down somewhere and produce power. That’s when we’ve demonstrated a mobile reactor. At that point it becomes a Department of Defense decision on what they want to do next.

Q: What do you do when it’s time to dispose of the used-up pellets and all the radioactive material inside them?

A: Disposition of radiological material is a national issue. In that large debate, we are a very tiny fraction. On average the Navy produces and disposes of two and a half reactor cores a year. Those are much, much larger than ours. If you compare the amount of fissile material in our reactor versus, say, a carrier reactor, it’s about 1000:1.

But all the nuclear waste that gets created in the whole country in a year, fits on a football field. It’s really very little waste. For now, we can just deal with it by keeping it on these nuclear sites, but that’s a question for Congress to resolve.