What are people's views on Deep Fission's idea?
https://interestingengineering.com/ener ... reactor-ca
US startup moves one-mile underground reactor closer to reality with key prototype.
California-based advanced nuclear energy company Deep Fission has delivered the prototype reactor canister for its underground small modular reactor system to its test site in Parsons, Kansas, marking a key step toward validating its unconventional nuclear power concept.
The factory-built canister will be used in the company’s Proof-of-Concept Well program, a nearly full-scale demonstration designed to test installation methods, infrastructure readiness, and operating procedures before any nuclear fuel is introduced.
Unlike conventional small modular reactors, Deep Fission’s design places a pressurized water reactor inside a borehole about one mile underground. The company says the approach could simplify construction while using the surrounding water column to help maintain operating pressure and cooling.
The prototype has completed fabrication, hydrostatic testing, and delivery, allowing the company to move into the next phase of non-nuclear testing as it prepares for large-diameter drilling at the Kansas site.
Underground reactor design
“The arrival of our prototype reactor canister at the Kansas site is a clear step forward in moving from design to deployed infrastructure,” said Mark Pérès, Chief Nuclear Officer of Deep Fission. “Successfully manufacturing, testing, and delivering this hardware demonstrates performance of our design and supply chain capabilities.”
The Proof-of-Concept Well is intended to validate the complete deployment sequence using commercial-grade, non-nuclear equipment. The company plans to test how the canister is assembled, lowered into the borehole, installed, and integrated with supporting infrastructure under real-world conditions.
The demonstration is designed to verify engineering assumptions before construction of the company’s first nuclear demonstration well, reducing technical risk ahead of commercial deployment.
Deep Fission’s Gravity Nuclear Reactor uses established pressurized water reactor technology but deploys it in a vertical borehole approximately one mile deep. Instead of relying solely on conventional reactor vessels and containment structures, the design uses the pressure generated by a mile-long water column surrounding the reactor to support reactor operating pressure while also providing cooling.
Heat generated by the reactor is transferred through a closed-loop system to a heat exchanger before traveling back to the surface through a secondary loop, where it can be converted into electricity using equipment similar to conventional geothermal power plants.
Testing before fuel
Following delivery, the prototype canister will undergo additional testing while the company advances permitting for its non-nuclear borehole with the Kansas Department of Health and Environment. The borehole is expected to become the next major milestone in demonstrating the technology.
“This milestone reflects disciplined execution across fabrication, testing, and delivery, and strengthens the foundation for scaled deployment of our Gravity Nuclear Reactor™ system,” said Mike Brasel, Chief Operating Officer of Deep Fission.
Alongside the proof-of-concept program, the company is continuing work on a full-scale nuclear demonstration borehole and the design of its primary heat exchanger. These efforts are intended to validate the unique aspects of its underground deployment strategy before commercial operation.
Deep Fission is also participating in the U.S. Department of Energy’s Reactor Pilot Program, which was authorized under Executive Order 14301 to accelerate reactor testing and commercialization of advanced nuclear technologies.
Deep Fission - Mile Deep Nuclear ractor
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Paul Nuttall
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Nightwatch2
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Re: Deep Fission - Mile Deep Nuclear ractor
Interesting concept and design.
If the cooling doesn’t work and the reactor melts down then it is essentially a man made geothermal site…
If the cooling doesn’t work and the reactor melts down then it is essentially a man made geothermal site…
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jemhouston
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Re: Deep Fission - Mile Deep Nuclear ractor
Hopefully there isn't vital aquafer nearby.
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Paul Nuttall
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Re: Deep Fission - Mile Deep Nuclear ractor
That was my first thought but this proposal is many many months old now and i've not seen any questioning of it.
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warshipadmin
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Re: Deep Fission - Mile Deep Nuclear ractor
So that's 2400 psi of head if they fill it to the top. 350deg C boiling point.
Re: Deep Fission - Mile Deep Nuclear ractor
sooo, what happens when a 25 cent component needs replacement
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Kunkmiester
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Re: Deep Fission - Mile Deep Nuclear ractor
What are the thermal losses on piping the heat exchange fluid up? I can't imagine it's small no matter how well you insulate.
Though if you can drop a reactor down, I'm sure a turbine would fit too.
Though if you can drop a reactor down, I'm sure a turbine would fit too.
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Demon Lord Razgriz
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Re: Deep Fission - Mile Deep Nuclear ractor
No more than Geothermal plants, I'd imagine.Kunkmiester wrote: ↑Sun Jul 19, 2026 2:35 am What are the thermal losses on piping the heat exchange fluid up? I can't imagine it's small no matter how well you insulate.
Though if you can drop a reactor down, I'm sure a turbine would fit too.
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Paul Nuttall
- Posts: 853
- Joined: Thu Nov 17, 2022 5:19 pm
Re: Deep Fission - Mile Deep Nuclear ractor
They seem to be moving forward with this.
https://interestingengineering.com/ener ... e=hs_email
Deep Fission has successfully lowered a 20-foot reactor canister 100 feet underground and retrieved it using commercial drilling equipment, testing a key part of its plan to bury small nuclear reactors a mile below the surface.
The demonstration took place on September 3, when a commercial drilling and rigging crew lowered the full-size canister into a 34-inch-wide borehole. The crew aligned the canister at depth before bringing it back to the surface.
The test focused on whether the large reactor canister can be handled underground using equipment already available to drilling contractors. Deep Fission said the demonstration did not require equipment invented, custom-built, or adapted for nuclear service.
The canister was a full-size, non-nuclear replica of the vessel designed to house the company’s Gravity reactor core. It contained no nuclear fuel, so the test was aimed at validating the physical deployment and retrieval process rather than reactor operation.
“The most important thing about this demonstration is what we did not have to do,” said Liz Muller, CEO and Co-Founder of Deep Fission. “We did not have to develop new technology. We used a rig and rigging that is commercially available in the field today, and our reactor uses pressurized water technology that has been operating in the nuclear industry for decades.”
Deep Fission’s reactor concept combines established pressurized water reactor technology with an underground deployment system. The Gravity reactor would use standard low-enriched uranium fuel, while the company’s main change is to place the reactor deep underground.
The proposed reactor would sit in a water-filled borehole approximately one mile below the surface. Deep Fission says the water column and surrounding rock could provide containment, operating pressure, heat transfer, and emergency cooling.
That configuration could reduce the surface infrastructure normally associated with nuclear plants. Instead of constructing a large reactor facility above ground, the company’s model would shift much of the system underground.
The company believes this could simplify construction, reduce costs, and shorten deployment schedules while providing additional safety margins.
The latest test does not demonstrate that a commercial reactor can operate underground. Deep Fission still has to validate the broader system, including drilling, reactor integration, regulatory requirements, and eventual commercial operation.
The company recently received approval from the US Department of Energy for its Nuclear Safety Design Agreement for the Gravity reactor. It is advancing the project under the DOE Reactor Pilot Program and is developing its first reactor project in Parsons, Kansas.
The underground approach is also intended to support deployment closer to customers that need reliable electricity. Deep Fission is targeting utilities, industrial customers, and data centers seeking low-carbon baseload power.
“Our innovation is in how we put proven pieces together, not in inventing something that has never been built. That is the difference between a science project and something you can deploy,” Muller said.
The company now needs to move from a mechanical demonstration to the much harder task of proving that its underground reactor design can meet engineering, safety, licensing, and commercial requirements.
https://interestingengineering.com/ener ... e=hs_email
Deep Fission has successfully lowered a 20-foot reactor canister 100 feet underground and retrieved it using commercial drilling equipment, testing a key part of its plan to bury small nuclear reactors a mile below the surface.
The demonstration took place on September 3, when a commercial drilling and rigging crew lowered the full-size canister into a 34-inch-wide borehole. The crew aligned the canister at depth before bringing it back to the surface.
The test focused on whether the large reactor canister can be handled underground using equipment already available to drilling contractors. Deep Fission said the demonstration did not require equipment invented, custom-built, or adapted for nuclear service.
The canister was a full-size, non-nuclear replica of the vessel designed to house the company’s Gravity reactor core. It contained no nuclear fuel, so the test was aimed at validating the physical deployment and retrieval process rather than reactor operation.
“The most important thing about this demonstration is what we did not have to do,” said Liz Muller, CEO and Co-Founder of Deep Fission. “We did not have to develop new technology. We used a rig and rigging that is commercially available in the field today, and our reactor uses pressurized water technology that has been operating in the nuclear industry for decades.”
Deep Fission’s reactor concept combines established pressurized water reactor technology with an underground deployment system. The Gravity reactor would use standard low-enriched uranium fuel, while the company’s main change is to place the reactor deep underground.
The proposed reactor would sit in a water-filled borehole approximately one mile below the surface. Deep Fission says the water column and surrounding rock could provide containment, operating pressure, heat transfer, and emergency cooling.
That configuration could reduce the surface infrastructure normally associated with nuclear plants. Instead of constructing a large reactor facility above ground, the company’s model would shift much of the system underground.
The company believes this could simplify construction, reduce costs, and shorten deployment schedules while providing additional safety margins.
The latest test does not demonstrate that a commercial reactor can operate underground. Deep Fission still has to validate the broader system, including drilling, reactor integration, regulatory requirements, and eventual commercial operation.
The company recently received approval from the US Department of Energy for its Nuclear Safety Design Agreement for the Gravity reactor. It is advancing the project under the DOE Reactor Pilot Program and is developing its first reactor project in Parsons, Kansas.
The underground approach is also intended to support deployment closer to customers that need reliable electricity. Deep Fission is targeting utilities, industrial customers, and data centers seeking low-carbon baseload power.
“Our innovation is in how we put proven pieces together, not in inventing something that has never been built. That is the difference between a science project and something you can deploy,” Muller said.
The company now needs to move from a mechanical demonstration to the much harder task of proving that its underground reactor design can meet engineering, safety, licensing, and commercial requirements.