Energy

First officially approved Gen IV nuclear reactor in the US breaks ground

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A Kairos test bed for the molten salt cooling system
Kairos Power
A Kairos test bed for the molten salt cooling system
Kairos Power
Diagram of the Hermes reactor
Kairos Power
Schematic of the Hermes reactor layout
Kairos Power
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Kairos Power has broken ground at Oak Ridge on the first officially approved Generation IV reactor ever in the US and the first non-light-water reactor in 50 years. It is being constructed alongside a non-nuclear demonstration unit that will help inform the design of the new reactor facility.

Despite being one of the pioneering nations in the field of civilian nuclear power, the United States has fallen far behind even what were once non-players like China and India. There are a number of reasons for this, some political and some economic, but the drive to cut carbon emissions while sustaining a modern industrial society is causing nuclear reactors to make a comeback in more advanced forms.

On July 17, 2024, Kairos Power began construction at Oak Ridge, Tennessee on its Hernes low-power demonstration reactor. It won't be generating electricity for the grid. Instead, its function will be to develop Kairos's molten fluoride salt-cooled pebble-bed reactor, which is an inherently safe design that is capable of shutting itself down and keeping the reactor core safely cool in the event of an accident.

In addition, the company is building a second plant at Oak Ridge, called ETU 3.0, that is essentially a non-nuclear version of Hermes. This test bed will allow engineers to study the machinery in operation without worrying about radiation and let them find ways to make the construction and operation of such a nuclear station more economical. This is extremely important because the major cost of nuclear power isn't the reactor but the civil engineering needed to house and service it.

According to the company, construction at Oak Ridge is only half the project. The reactor itself is of a modular design. These modules will be built and tested at a factory in Albuquerque, New Mexico before shipping to Tennessee.

Hermes is a pebble-bed reactor, where the nuclear fuel is encased in spherical pellets made of layers of enriched uranium, carbon, and ceramics. These TRi-structural ISOtropic (TRISO) particles are about the size of a poppyseed and act as tiny nuclear pressure vessels. These are formed into large, round pebbles about the size of a cobblestone. The pebbles are placed inside a reactor core that's more like a hopper in design. Fresh fuel goes in the top, the pebbles crowded together start and sustain the reaction, and spent fuel is collected at the bottom of the vessel.

Diagram of the Hermes reactor
Kairos Power

Where similar reactors are cooled by helium gas, Hermes is cooled by molten fluoride salts circulating through the reactor. The salts maintain the reactor core at 1,085 °F (585 °C) as they carry off the heat to a heat exchanger. This secondary salt loop is connected to a steam generator that, in turn, runs a turbine.

Should the power to the reactor fail for whatever reason, the fuel pebbles automatically regulate the nuclear reaction by the laws of physics. As the reactor heats, fewer neutrons are available to sustain the reaction and it dies down. Within hours, the reactor reaches a point of stability. Meanwhile, molten salt flows through natural circulation, cooling the core. Even if the reactor temperature should spike, the fuel pebbles are extremely robust and won't degrade in any projected scenario.

All of this occurs at ordinary sea-level pressure, so no special containment structure or pressure vessel is required. The reactor is also made out of 316 stainless steel, which is highly resistant to salt corrosion.

Schematic of the Hermes reactor layout
Kairos Power

Being developed with the help of a US$303-million Department of Energy grant, Hermes is expected to be completed by 2027. Though Bill Gates is working on his own reactor project in Wyoming, he is still waiting on government approval before he can build the nuclear plant itself – approval that Kairos already has.

"Hermes is a pivotal step toward deploying advanced reactor technology with the potential to transform our energy landscape," said Mike Laufer, Kairos Power CEO and co-founder. "The lessons we take away from the construction and operation of this reactor will be invaluable to enable continued innovation in our testing program and accelerate Kairos Power’s progress toward delivering true cost certainty to our customers."

Source: Kairos Power

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11 comments
Robt
‘…the major cost of nuclear power isn't the reactor but the civil engineering needed to house and service it’
I’m not so sure about that.
It certainly is ‘a’ major cost, but alongside that is the lunatic regulatory environment that any nuclear powerplant has to navigate for years, before a single gram of cement or other building material is laid down.
cookiethecat
The aspect that was not addressed is 'recycling' - currently a very high percentage can be recovered from spent fuel rods - 90%+, the novel packaging proposed in this case appears to trade of a well known concept of intrinsically safe fuel encapsulation - which has two disadvantages, the first being limited yield and the second being reprocessing and increased waste material handling and storage overheads.
matthew4506
The Major cost is dealing with the waste and decommissioning the plants after their usable lifetime which remain dangerous for hundreds of millennia. Fission is still and has always been a very short sighted solution, kind of like the monumental stupidity of using plastics for food packaging, makes sense when you’re thirsty but will remain a problem for longer your entire lifetime. So stupid.
Jose Gros-Aymerich
Kairós does not mean 'Good times', is another name the Greek gave to Chronos, called 'master of time', as It can move up and down on time.
When they thought Chronos, Saturn, Sachi, Moloch, Remfam, Quevvam was favorable to them, they called it 'Kairos'
No way of having devils, all murderers, origin of lie, in favor of anyone.
Beware of Dog!
Jag Levak
The Kairos fuel balls will be more like golf-ball sized. They are slightly buoyant in molten salt, so the fuel will be fed in at the bottom and be extracted at the top. It is true that today's conventional spent fuel would be much easier to reprocess than Triso, but that's because the zircalloy coatings are much flimsier. That's not a feature. That's a leakage hazard--the main reason we worry about spent fuel. Combined with Deep Isolation sequesters, we could have fuel grains inside triple-coatings, inside carbide-cased balls, embedded in synroc, inside cannisters, inside clay packing, inside steel casing in wellbores into very deep stable geologic formations.
Karmudjun
Until we have feasible fusion electrical production we should continue developing more efficient processes for fission reactors. Just like PV cell and Lithium recycling, the issues with a recycling process for decommissioned nuclear reactors are ripe for disruptive innovation. Certainly the benefit of Fusion reactors is the ability to utilize spent fission reactor fuel products, but we don't have functioning proof of concept on a commercial scale under our belts. At least we will continue to have safety protocols and regulatory oversight to minimize risks to workers, infrastructure, and our environment! Good article David, Thanks for the article and video. OMG - is the sky really falling?
jerryd
Too complicated when gas cooled is 25% more efficient due to much higher temps/delta T.

The waste, reactor is barely radioactive and easily stored in the open. The fuel is just diluted becomes little more than very hard sand, not radioactive unless large amounts are brought together.

But nuke can't compete with solar, wind, hydro, geo, CSP, CHP, so really only for niche apps like large/ military ships, far northern towns as a CHP source, certain factories, ... .
Catweazle
Difficult to believe now, the UK's civil nuclear power programme having been signed off in 1952, construction of Calder Hall, the World’s first grid scale nuclear power station, commenced in 1953, was carried out by Taylor Woodrow Construction and was officially opened on 17 October 1956, all done using 1950s technology and construction techniques.
The station was closed on 31 March 2003, the first reactor having been in use for nearly 47 years.
pete-y
In the UK we are dependent on nuclear.
Today it is providing 25% of our energy (15, UK & 11 France) and it is sunny and with a gentle wind.
The only dependable supply in no sun/wind is nuclear or gas.
So improving this technology is crucial for the foreseeable future.
PeakSpecies
The above article failed to provide any critical assessments which is typical for promotional pieces. The fact that the U.S. still doesn't have a final spent nuclear fuel repository wasn't mentioned. A past report indicated that small nuclear reactors are not likely to be competitive. The 2027 date, for this experimental reactor's first operation, demonstrates that the following warning has been ignored.

UN chief: World has less than 2 years to avoid 'runaway climate change' (TheHill)
* This statement was made 5.5 years ago.