Mass-produced floating nuclear reactors use super-safe molten salt fuel

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The Copenhagen startup Seaborg Technologies has raised an eight-digit euro amount to start building a fascinating new type of cheap, portable, flexible and super-safe nuclear reactor. The size of a shipping container, these compact molten salt reactors are rapidly mass-produced in their thousands and then placed on floating barges for global use – on schedules that will break the paradigms of the energy industry.

Like other molten salt reactors that have been around since the 1950s, they are designed to minimize the impact of accidents on investment.

First, they use nuclear fuel mixed in fluoride salts. The combination is liquid above 500 ° C (932 ° F) and can flow through the reactor, which operates at near atmospheric pressure. This liquid salt serves as a coolant for the nuclear fuel and replaces the high-pressure water cooling in older reactor concepts. But when this fuel is exposed to the air instead of escaping explosively as vapor, it acts like lava and solidifies into rock.

Yes, the rock is radioactive and you shouldn’t picnic on it, but it’s not a cloud of radioactive gas that can blow over the continent; it is solid rock that security teams can clean with Geiger counters. It also has very low solubility in water, making it comparatively safe even if it falls into the sea.

The Seaborg molten salt reactor design is incredibly compact and has several passive safety features

Seaborg technologies

Second, if the temperature gets out of control for any reason, the first thing to do is to melt a plug of “frozen salt” at the bottom of the reactor and this will immediately drain the reactor core into a series of chilled drainage tanks below.

This pair of simple measures, says Troels Schönefeldt, co-founder and CEO of Seaborg Technologies, is radically reorienting the issue of nuclear safety, away from total accident prevention with four levels of redundancy at every point of failure, towards a much simpler impact mitigation. They have a huge impact on the cost of nuclear power.

“We’re taking a different approach,” he told Radio Spectrum in an interview. “We’re not reducing the accident probability to zero, there will be accidents. We should avoid them as much as possible, but there will be accidents. Hopefully there will be many accidents because we will have many.” of these reactors. Instead of reducing the likelihood, what we are doing is reducing the consequences of even the worst disasters. Or even acts of war where you actually bomb the reactor. The result is that this fluoride salt will flow out of the reactor, or you will explode out of the reactor and lie down on the field. It will solidify. And now you shouldn’t go into that field. They should actually be 3 or 20 feet apart. But you can go there and clean up with a Geiger counter. It’s insanely expensive, but you can do it. And that changes the basic security profile of the technology. And with that we are changing the costs, which in turn changes the business model. “

The reactors themselves are built in Denmark and then sent to shipyards in South Korea to be installed on floating barges and taken to their final location
The reactors themselves are built in Denmark and then sent to shipyards in South Korea to be installed on floating barges and taken to their final location

Seaborg technologies

But perhaps the most powerful change to the business model is Seaborg’s proposal to install these reactors on barges and take them offshore, rather than buying up land for the development of nuclear power plants. There are several advantages here. First of all, you can make them in bulk on a single plant. Seaborg is looking at Korean shipyards that are already tightly and efficiently linked to supply chains with enormous production capacities. “If you want us to build not one reactor but a thousand, we could start building a thousand,” Schoenefeldt told Radio Spectrum. “It’s going to take about three or four years at these shipyards. So it’s basically not considered how quickly you can scale it.”

These barges can be moved almost anywhere on the planet, either moored offshore or on large or small rivers, depending on the size of the reactor. Virtually no site preparation is required; It is completely self-sufficient and very easy to connect to a power grid. Seaborg estimates that in this way it can supply 95 percent of the world’s population and basically does not require any land for a base load or load-following power plant of up to a healthy 600 MW that could supply nearly 100,000 households.

Each module the size of a shipping container generates up to 200 MW, and mounting them on floating barges could make these power plants incredibly quick to build and deploy worldwide
Each module the size of a shipping container generates up to 200 MW, and mounting them on floating barges could make these power plants incredibly quick to build and deploy worldwide

Seaborg technologies

The challenge here, as with all molten salt reactors, is corrosion. Hot molten salt itself is highly corrosive and this will be a serious challenge for any component that comes into contact with the fuel salt. Float the reactors on barges in salty sea water and you expose the entire exterior to a strong corrosive agent as well; Cargo ships are typically designed to last 25 years due to the effects of life in salt water.

And it doesn’t stop at Seaborg. Other molten salt reactors use graphite as a moderator, which slows down the neutrons generated in each fission reaction in order to keep the chain reaction going. However, graphite tends to crack and weaken when exposed to intense radiation with repeated heating and cooling, eventually leading to what Seaborg co-founder and CTO Eirik Eide Pettersen Thomas Thor Associates calls “unacceptable hotspots”.

Seaborg’s solution is to use another molten salt – sodium hydroxide – as a liquid moderator. So the core design places the fuel salt tube in a larger tube filled with sodium hydroxide, creating a unique all-liquid reactor that is remarkably compact. But caustic soda itself is a highly caustic base that is often used as an oven cleaner or drain cleaner; Seaborg’s design also has to deal with this additional corrosive agent.

In addition, there is the wacky phenomenon of “grain boundary corrosion”, caused by the presence of tellurium as a by-product of the fission in the fuel salt stream. Tellurium atoms can happily penetrate metals and swap positions with other elements, which leads to the embrittlement of the metals at their weakest points.

The company is aware of its central challenges here. “Seaborg’s core IP is based on the corrosion protection in the moderator salt and the application of knowledge gained since the 1950s,” says Pettersen. “But it’s not just a question of corrosion, it’s also how easy it is to put these things together. Practical experience is important. They have to be welded, tested, inspected, serviced. We are working on it, maybe 20 or 30 test loops in Copenhagen where the experiments were designed, set up and carried out. The conception is already finished, we are now working on the basic design and are working towards a true-to-scale prototype. “

Seaborg commissioned regulatory authorities in the nuclear industry at a very early stage to enable mass production and global rollout in a very short time
Seaborg commissioned regulatory authorities in the nuclear industry at a very early stage to enable mass production and global rollout in a very short time

Seaborg technologies

This full-size prototype is currently slated to go online in 2025 and then likely sent to work from an island in Southeast Asia. After raising some sizable capital, Seaborg is hiring like crazy to work towards that goal. It hopes to receive regulatory type approval for its design by 2026, and commercial series production could follow as early as 2027.

Those schedules are “almost insane” in the energy market, Schönefeldt told the Switch 2020 audience in a presentation earlier this year and a validation of the mass production strategy and approaches for floating barge. Investors from the energy industry who are used to dealing with extremely long planning and construction phases as well as decades of return-on-investment times can now invest their money in something that is online incredibly quickly and pays for itself within 6-10 years .

The Seaborg reactor is small enough to fit in a shipping container, making it remarkably easy to move, even with ground installations. It will run for about 12 years without refueling. Its fuel cannot be used in nuclear weapons. It can run on refined, recycled nuclear waste from older reactors – although there will be some regulatory hurdles there, says Schönefeldt. You can pull heat directly from the reactor even more efficiently than electricity, so it will be useful in other ways than just being a power plant.

Next-generation advanced nuclear power is a hot topic right now. As the global commitment to the goal of zero carbon emissions by 2050 solidifies, coal and gas fired power plants are rapidly being decommissioned. Renewable resources like solar and wind will provide most of the energy we will need in the future, but nuclear power offers a reliable, inexpensive, and environmentally friendly way to increase the base load and fill in gaps when renewables are not generating.

Despite some extremely high-profile catastrophes, nuclear power is already by far the safest method of generating electricity, with a 330 times smaller “death track” than coal-fired electricity. The new generation of advanced nuclear reactors promise to be even safer, and molten salt structures like Seaborg’s can also dramatically reduce the consequences of these vanishingly rare incidents. If this company can solve corrosion problems as effectively as its investors believe, it could be a huge game changer.

Source: Seaborg Technologies via IEEE Spectrum, Thomas Thor Associates and Switch 2020



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