From our collaborating partner “Living on Earth,” public radio’s environmental news magazine, an interview by Host Steve Curwood with Jacopo Buongiorno, a professor of nuclear science and engineering at the Massachusetts Institute of Technology.

Half of the zero-emission electricity generated for the grid in the U.S. comes from nuclear reactors, and the Biden-Harris administration is aiming to triple nuclear power generation by 2050. The Inflation Reduction Act and other federal funds are providing billions of dollars in loan guarantees to help existing nuclear power plants upgrade to stay in business. 

Billions more are being deployed to support advanced nuclear reactor designs, from small ones that can use breeder-type reactions and theoretically never run out of fuel, to large ones that use liquid metals like sodium as coolants to boost efficiency and flexibility. The administration’s nuclear power program also promotes using locations where coal-fired plants have retired. 

TerraPower, founded by Bill Gates, is using such a site in Kemmerer, Wyoming, where it aims to build its sodium-based reactor. 

Jacopo Buongiorno is a professor of nuclear science and engineering at MIT, and joins us to discuss these developments. This interview has been edited for length and clarity. 

STEVE CURWOOD: In the face of the climate emergency, we have to reduce our reliance on fossil fuels as quickly as possible. To what extent can nuclear energy play a role in our urgent race to decarbonize?

JACOPO BUONGIORNO: Nuclear can play a big role—already plays a role. Roughly half of our low carbon or clean electricity at the moment in the United States comes from nuclear, so it already is a big part of our clean energy infrastructure. It can play even a bigger role, and not just on the grid. 

CURWOOD: Can we have a bit of context? Compared to the nuclear power plants online in the United States right now, what’s new or revolutionary about TerraPower’s Wyoming plant?

BUONGIORNO: That’s a great question. The reactor itself is really a different design from the 90-plus plants that are in operation at the moment in the United States. Those plants use water, perhaps the simplest fluid that we can think of as the coolant inside the reactor, whereas the new TerraPower plant will use liquid sodium, a liquid metal, as the coolant. 

It’s not an entirely new concept. As a matter of fact, it has been proven, tested in the United States many decades ago, in France, in Russia. But it never caught up commercially. Now it’s coming back, thanks to Bill Gates’s TerraPower.

CURWOOD: Sodium is used to cool the reaction, but I gather it’s used for a lot more?

BUONGIORNO: A nuclear reactor is a heat source. The nuclear reaction that takes place within what we call the core is called nuclear fission. The product of that nuclear fission is heat. 

The first order of business in a nuclear reactor is to take that heat from the reactor core to another section of the plant where that heat is typically converted to electricity, because that’s what you sell to the grid. Sodium is used as the circulating fluid within the reactor core to do just that, to move the heat from the core somewhere else within the plant. It happens to be very efficient, more efficient at that job than water. 

Because of its thermodynamic properties, sodium can operate at a higher temperature, so it allows you to actually store the heat more efficiently on site, and to modulate the electric power output so that when the grid demands more power, you can sell more power. When the grid demands less power, you can basically keep storing the heat on site and selling that power later. It’s the ability of swinging up and down in power output that is allowed with this particular reactor design that would be more difficult with the traditional designs.

CURWOOD: What’s the advantage?

BUONGIORNO: This particular feature is important because there is a lot of variability on the grid for two reasons. First, because the demand for electricity on the grid is not constant, since people switch on their appliances in the morning and then in the afternoon; there are peaks and valleys created by demand.

But there is also quite a bit of variability on the grid because of the penetration of intermittent renewables like solar and wind. The sun doesn’t always shine, the wind doesn’t always blow. So you have ups and downs in what electricity is generated on the grid. This reactor, which is able to vary its power output, is particularly useful in that context.

CURWOOD: So you have a thermal battery with this design so that you can store extra heat and use that to make electricity when you want to. And meanwhile, the reactor itself is creating a whole bunch of heat.

BUONGIORNO: That’s a great way to put it. And in principle, you could change the amount of heat that is generated from the reactor itself. But that’s not economically very attractive because a nuclear reactor, a nuclear power plant is essentially an expensive machine that burns cheap fuel. 

What that means is that it takes a lot of money to build the plant, but it doesn’t take a lot of money to operate it. The implication of this is that once the plant is built, you want to always run it at 100 percent output. 

The location matters. This particular plant in southwestern Wyoming is located on a major transmission line that connects that site to California. California is obviously a very big power market to begin with, but also has a lot of variability because of their reliance on solar and wind. The plan for this nuclear power plant in Wyoming is to sell a significant amount of its electric output to California via transmission line.

CURWOOD: This plant is being built where a coal-fired plant once was; I guess that puts it at a good connection for the grid. What other advantages are there to being where a coal-fired power plant was?

BUONGIORNO: Many advantages, starting with the fact that communities that were relying on the economic footprint of those coal-fired plants now find themselves in a position to benefit from the new plant, right? So it’s jobs, it’s tax revenues, it’s overall economic impact. 

But strictly speaking from the point of view of the plant itself, you can reuse transmission lines, which we’ve already mentioned. You can also reuse cooling infrastructure, as well as access roads, administrative buildings. And lastly, the workforce has to be retrained because a coal plant is not the same as a nuclear plant. But in fact, a nuclear plant, everything else being the same, typically employs more people than a coal-fired plant. So there are several advantages there.

CURWOOD: What public health advantages are there from this approach?

BUONGIORNO: That’s another good side of the story. Coal plants have been keeping the lights on for decades, but they’re now going out of business because of their environmental impact. They emit a lot of CO2, and it’s a greenhouse gas, so it’s associated with climate change. A reduction of those emissions is very, very important. 

Number two, if you look cold-blooded at the number of casualties per unit of electricity generated, even if you calculate the number of people that have been harmed by radiation in accidents—which is a very, very small number—there is no comparison. Coal plants unfortunately kill scores of people. In addition to CO2, they spew out into the atmosphere a lot of particulates and a lot of pollutants that cause respiratory problems. So as coal plants go out of business and are replaced by nuclear power plants, which don’t have any such emissions, the quality of the air locally should also improve.

CURWOOD: Now, there’s a lot of talk that this plant’s reactor has a safer design than the current light water reactors. Your response?

BUONGIORNO: My response is, current light water reactors are extremely safe. They have a very good record. I wouldn’t characterize these as safer; I would say it has a different safety approach. A vast majority of the reactors that we have been operating for the past few decades rely on what we call “active safety philosophy.” 

What that means is that if there is a failure or a malfunction, there are a number of engineer systems, powered by external energy sources, things like diesel generators or batteries, to ensure that those engineer safety systems operate properly. That approach works, and it realizes a very, very safe system, but it’s fairly
complicated because it requires operator action; it requires to maintain those engineer safety systems in good shape. So there is cost and there is complexity associated with it. 

All the new reactor designs that are being contemplated now, including TerraPower, use a different safety philosophy or a safety approach, which we call “passive safety.” They don’t rely on external energy sources to drive the safety systems. They rely on things like thermal siphoning—natural circulation, gravity, pressure differences—so physical phenomena that don’t require an external input of energy from diesel generators, batteries, pumps or things of that type. 

What that means is that if there is a malfunction or a failure of components within the plant, even in case of a major disaster, like an earthquake, tsunami, fire or terrorist attack, the human operator does not have to intervene, does not have to launch the engineer safety systems. The safety systems would be able to run on their own. 

The expectation is that this overall is going to make for a more reliable, more robust, more human-error-tolerant system. So, safe in both cases, just different approaches.

CURWOOD: When one talks with people about nuclear power, inevitably they say, what about the waste? So what do you say?

BUONGIORNO: Yeah, waste has been a tough issue for nuclear all along. It still is, at least in the United States, simply because we don’t have what people call the ultimate solution—the ultimate disposal site. 

First of all, what we call waste is really the spent fuel that comes out of the reactor, which has sort of run out of juice, run out of its energy content, and it’s become highly radioactive. 

What’s done at the moment in the United States is we keep it very safely stored at the site, first in spent-fuel pools for several years. Radioactivity naturally decays, so its radioactive levels go from very high to significantly lower within a couple of years. 

Then they are moved from these pools into what people call dry casks. These are canisters made of steel and concrete, highly engineered and well shielded. At the moment, we have this material at the individual nuclear power plant sites. It is safe, it’s relatively cheap to manage, we can continue to do this for decades.

But eventually, all that material’s got to go somewhere; it’s got to be consolidated. The consensus is that it has to go underground. It’s what people call a geological repository.

The issue we have in the U.S. is that we’ve been unable to find a site anywhere in our big country that will host that final repository. I keep saying “in the U.S.” because other countries have solved the problem. The first country that is going to open a geological repository is Finland, that should happen either next year or the year after, between now and 2026. They have a different political process, and the general public has a higher level of trust in their government. It’s all about that. It’s not a technical problem. It’s never been really a technical problem, it’s always been an issue with how you manage the process that leads to the selection, authorization, construction, and finally, operation of a geological repository. 

CURWOOD: What’s the volume of so-called nuclear waste right now in America? How big a space would it occupy if it were consolidated? 

BUONGIORNO: That’s actually one of the positive attributes about nuclear. It doesn’t produce a lot of waste. And that’s because the energy content of uranium is extraordinarily high. That’s always been the attractive feature of nuclear is that it doesn’t require a lot of fuel to generate a lot of energy. The implication of this is that you also don’t generate a lot of waste. 

If a person like me or you were to use only nuclear energy for all our lives, the amount of spent fuel that we would produce would
basically fit within a cup of coffee. Now, there are a lot of us. So if we all use nuclear energy, the cups of coffee add up. 

But to give you another example, all the spent fuel, all the waste that we have produced now in the United States over the past
60 years of operation of 100 reactors generating roughly 20 percent of our electricity, if consolidated, would basically fit on something that looks like a football field. So the volumes are not large, but we’ve got to put it somewhere. And that’s been the challenge.

CURWOOD: What about all the atomic weapons that people would like to see decommissioned? To what extent might that help the fuel situation for nuclear power reactors?

BUONGIORNO: Well, it did. There was a program that I think ended just a few years back, it was called megatons to megawatts. Under that program, a lot of the idea of rich uranium that was producing nuclear weapons was converted to lower enriched uranium and used in reactors around the world, in particular in the United States. So a lot of the warheads that were decommissioned under treaties between the U.S. and the former Soviet Union, and then Russia, that material has made its way into the commercial domain and is being used that way. 

So if the great nuclear powers—the U.S., Russia and China—decide that they want to reduce their arsenals, this scheme can be implemented again.

But I don’t need to tell you that it’s not looking particularly good on the international scene. The geopolitics are such that, if anything, I think we might see an increase in nuclear weapons, unfortunately.

CURWOOD: What’s the current public opinion about nuclear power? How do people feel about its safety and viability?

BUONGIORNO: At least in the United States, the support for nuclear has always been pretty high. And when I say always, I mean, over the past 20 years, including just following the Fukushima accident. At the moment, it’s at an all-time high.

I’ve been in this community for 27 years, and I’ve never seen sort of numbers as they are now, I think low 70s. That’s generic support by the public in the United States. I’m always sort of hesitant to translate that to, how can I say, solid support, either for nuclear or anything else? 

There is a difference between generically supporting something and then supporting it when that something becomes a project in
your town. There is the NIMBY “not in my backyard” syndrome. But this applies to all technologies. 

If you look at the support for solar and wind, it’s off the charts. Everybody likes solar and wind. But then you look at the realization of big solar, wind and transmission line projects in the United States. And they keep running into serious issues of authorization and opposition from locals. 

I would expect that if there was a push for a widespread increase of nuclear power plants around the United States, especially in new sites, sites that don’t already have nuclear power plants, we might see a little bit of the same NIMBY response. But in general, it seems to be doing OK. And of course, it’s also geographically dependent. Some states are more supportive than others.

CURWOOD: To what extent do you think that this TerraPower plant will spark a new era for nuclear energy? How’s it going to deal with the present obstacles facing the nuclear energy power market here in the U.S. today?

BUONGIORNO: Well, I don’t think it’s one size fits all. In other words, while I like that project, I don’t think it’s just going to be that project that will propel nuclear forward, so to speak. 

It is an important part of it. It does address the question of increasing the economic attractiveness of nuclear on the grid, and again with the idea that you can vary your power output while maintaining that full utilization of your reactor. That’s a smart approach. That’s new. And if that’s proven successful, I think that model might be followed. 

But there are other projects that are ongoing. They’re all, in many ways, equally important because they address different applications, different sectors of the economy. It’s going to be a combination of these projects that will determine if nuclear is going to be successful or not in the U.S.