Critics are calling a floating nuclear power plant bound for a Russian town in the Arctic Circle “Chernobyl on ice.” While there isn’t really enough information to make a specific risk assessment, a floating nuclear reactor in and of itself isn’t necessarily a cause for alarm: nuclear reactors have been powering submarines for over 60 years.

The floating power station, called the Akademik Lomonosov, has been under construction since 2009. Russian state-run nuclear power company Rosatom launched it on its first voyage on Saturday. Right now, the Akademik Lomonosov is slowly being towed from St. Petersburg, Russia, to the town of Murmansk, where its two nuclear reactors will be fueled up this fall.

The plan is for the barge to leave for the town of Pevek sometime in summer 2019, where it’s supposed to provide enough electricity for 100,000 people, according to a Rosatom press release. The two nuclear reactors on the barge can produce up to 70 megawatts of electricity, Rosatom says. That’s about 7 percent of what a large commercial reactor in the US typically puts out, according to John Kotek, vice president of policy development and public affairs for the Nuclear Energy Institute.

Greenpeace, which coined the phrase “Chernobyl on Ice,” worries that the reactors will endanger the environment and that there isn’t enough oversight of the plant. We’ve certainly seen devastating accidents before, like in 1986, when a nuclear reactor in Chernobyl, Ukraine, exploded, spewing out so much radiation that children still aren’t allowed to live within an 18-mile radius of the plant. In Fukushima, Japan, the massive 2011 earthquake and tsunami caused a nuclear accident that forced more than 100,000 people to evacuate — and many still haven’t returned.

But we’ve also seen nuclear reactors going to sea since 1955 when the submarine USS Nautilus took its first voyage. In fact, the US Navy has more than 80 nuclear-powered warships, including aircraft carriers and submarines, according to a 2015 report by an independent task force with the Federation of American Scientists. Russia also has a nuclear-powered fleet that includes icebreakers, which are designed to plow through ice with nuclear reactors on board.

The idea of using floating nuclear reactors to power an electrical grid on land isn’t that out there, either. The US Navy suggested running Kauai’s grid off of a nuclear submarine after a hurricane wiped out the Hawaiian island’s power system in 1982. Megan Geuss at Ars Technica discovered that a ship from World War II became a floating nuclear power station in Gatun Lake in Panama until 1976.

Still, designing a nuclear reactor that functions safely on open waters isn’t easy, says Dale Klein, who was the former head of the Nuclear Regulatory Commission under President George W. Bush and is now associate vice chancellor for research for the University of Texas system. In land-based nuclear power plants, for example, the nuclear core is usually contained in a dome made out of reinforced concrete that’s about four feet thick, Klein says. “So if you have a massive pipe break, all that material would be contained within that vessel, within that containment building,” he says.

That would be pretty heavy for a mobile nuclear power plant, which is something the designers would have to consider, he says: “What sort of scenarios are you planning for? What kinds of pipes might break, and how would you make sure the reactor shuts down and is cooled safely?”

The Verge spoke with Klein about safety, security, and scare tactics for floating nuclear power plants.

The following interview has been edited for clarity and brevity.

In general, nuclear power works by using the heat from a nuclear reaction to generate steam, which drives a turbine to generate electricity. How do you have to adapt a nuclear reactor so that it can function at sea?

So on a land-based system, you know all the time where gravity is. Typically, when you’re heating something, hot water will rise and your steam will be generated in a manner that’s very predictable.

When you have a reactor that will not always be in the same vertical orientation [like on a submarine or aircraft carrier], then your fluid flow characteristics will be a little bit different. And you’ll just have to analyze that to make sure your systems are designed to handle the removal of the heat so that it’s always with margins of safety.

What are some of the challenges to making a nuclear reactor that can be mobile — especially at sea?

The real challenge, from my perspective, is how much containment do you have on that reactor core. [Stationary] reactors that we have in the US have huge containments so that the radiation will be contained in the unlikely event of an accident. Like in the case of Three Mile Island, very little radiation escaped because of that massive containment structure.

So, when you have a containment structure, that typically means that’s going to be heavy. And so for the Russian reactor — I have not seen their designs, so I don’t know if it’s a single wall or a double wall — if you just think about it, it’s going to be very heavy. So that means you’ll probably have to have a very big ship. The alternative is if you have a not-very-robust containment, then it would certainly be lighter. I don’t know the design, but that’s going to be one of the challenges.

The other challenge is unusual events — if you have any kind of massive wave motion, any kind of hurricanes, adverse weather — you’ll have to analyze how you keep the ship stable, and how you keep all the components running when the ship might be bouncing. The other big issue would be security. How can you secure a situation where you have a fairly large target but you have people who could access it out of the water and you might not see it coming?

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I’ve been seeing people calling it a “floating Chernobyl.” Is that name reasonable?

No, not at all. It’s just a scare tactic. It’s just to make people think about an accident of some kind. So it has no basis in science, and it’s really just meant to scare people when you use those kinds of statements.

What does the science say about the risks here?

Just like on aircraft carriers and submarines, you do a very detailed analysis so that the reactor core is always covered [with water], you have margins of safety in all the systems, you have backup pumps, you have backup systems, you have well-trained operators, and then you’re able to operate our aircraft carriers and our submarines in a mode where the reactor is not always vertical, because the ships will go up and down and side to side. So when you do all of your analyses, you just have to say how far is it likely that the ship will rock, and how much will it go up and down as you’re going across waves.

If you were running this barge, what sort of safety and security operations would you want to have in place?

A lot of backup systems — so that you just have a lot of options, basically. If a piece of equipment fails, you have another one ready to start up. For pumps, batteries, your own electrical supplies, water, cooling, thermal capacity — all of those things that typically tend to go into a safety analysis study.

Security is going to be a challenge because if you look at, say, for your aircraft carriers and your submarines, when they come into dock, they’re usually in highly secure facilities. There’s a lot of military security, and a lot of other kinds of detection systems so you can know if anybody is trying to do mischief. So if you go into just a normal civilian area, then how do you prevent a terrorist, for example, trying to come in to do damage to that facility? So the security would be a challenge, as well as how do you handle storms and hurricanes and typhoons and that sort of thing?

If there were a radioactive spill in the ocean, would it get diluted? How much of a problem would it be?

If there were a problem out in the middle of the ocean, you would probably never see it on land. Or, you might be able to measure it, but it would be such a minimal impact [on land] because the ocean is so big. But if you have this barge that’s anchored providing electricity 24 hours, seven days a week, and you had a spill, then it could get into the environment locally onshore. And so you’d have to make sure that that never happens.

Update August 28 2:05PM ET: This article was originally published on May 2, 2018 and has been updated to include video.