Conceptual design stage · Simulation-driven · COREX · ONYX · CAIRN
Nuclear power from the edge of the grid to the grid itself.
Two reactor lines on one simulation-first platform. COREX heat-pipe microreactors, 100 kWe to 1.2 MWe, for remote sites. CAIRN helium-cooled pebble-bed modules, 20 to 80 MWe each, fueled by ONYX, our denser and tougher coated-particle fuel.
All figures are design targets for the conceptual COREX family, derived from modeling and simulation. No COREX unit has yet been built or tested.
Mission
The most expensive electricity on Earth is diesel at the end of a supply chain.
Every remote mine, arctic village, island grid, radar station, and forward operating base pays it — in dollars, in emissions, and sometimes in lives.
Remote Alaskan communities pay $0.50 to over $1.00 per kWh for diesel power. Fully accounted off-grid diesel — fuel, transport, and maintenance — commonly runs $0.80–$1.00/kWh. For the military, the fully burdened cost of fuel delivered to a contested theater has been estimated at hundreds of dollars per gallon, and U.S. Army data from Iraq and Afghanistan attributed roughly one casualty to every 24 fuel resupply convoys.
Our mission is to replace that lifeline with sealed, solid-state nuclear units that arrive on one truck, run for years on a single core, and leave nothing behind when they're done.
Technology · Solid-state core
A reactor with no moving parts at its heart.
A COREX core is a solid metal monolith threaded with fuel channels and hundreds of sealed sodium heat pipes. Fission heat leaves the core the way heat leaves a spacecraft — passively, silently, with nothing to pump, pressurize, or break.
No pumps. No valves. No LOCA.
The core is solid — there is no circulating primary coolant to lose, so the loss-of-coolant accident class that dominates conventional reactor safety is designed out entirely. The system is designed to operate near atmospheric pressure.
Walk-away safe by design
The core is designed with a strong negative temperature coefficient so that it throttles itself: as temperature rises, reactivity falls. Decay heat is designed to be removed passively by conduction, natural convection, and radiation — no operator action, no AC power, no water.
TRISO — each particle its own containment
Poppy-seed-sized HALEU fuel particles (enriched below 20%) wrapped in ceramic layers engineered to retain fission products beyond 1,600 °C — a fuel form backed by decades of DOE testing and reactor operating experience going back to the 1960s.
Drums out, rods in
Reactivity is managed by rotating control drums around the core — absorber on one face, reflector on the other — with independent shutdown rods that stay locked in throughout transport.
Stirling to Brayton, by scale
Free-piston Stirling engines at the 100 kWe class; compact supercritical-CO₂ Brayton from the 400 kWe class up. Air-cooled heat rejection — zero site water, from the Arctic to the equator.
Built on proven physics
NASA and NNSA's KRUSTY test (2018) ran a sodium-heat-pipe reactor at full power — riding through simulated heat-pipe and engine failures on physics alone. COREX builds on that demonstrated physics — an architecture now being actively pursued across the industry.
Anatomy of a COREX unit
Select a system to explore the architecture.
A solid block threaded with TRISO fuel channels and heat-pipe bores. No coolant flows through it — heat conducts to the pipes, and the block's thermal mass buffers transients.
The COREX family
One architecture. Sized to your site.
Every COREX shares the same solid-state heat-pipe core — scaled, configured, and shielded around your load profile. Three baseline classes, plus a bespoke design service for everything from 50 kWe to 5 MWe.
COREX-100
- ≈350 kWt thermal output
- Free-piston Stirling conversion
- Single 20-ft ISO envelope
- 5-year sealed-core life target
EXPLORATION CAMPS · TELECOM & RADAR SITES · DISASTER RESPONSE
COREX-400
- ≈1.3 MWt thermal output
- sCO₂ Brayton conversion
- 40-ft ISO envelope
- 6-year sealed-core life target
MINE CAMPS · ISLAND MICROGRIDS · OFF-GRID INDUSTRY
COREX-1200
- ≈3.5 MWt with cogeneration heat
- sCO₂ Brayton conversion
- 40-ft envelope + support module
- 8-year sealed-core life target
PRODUCING MINES · DEFENSE INSTALLATIONS · LARGE ISLAND GRIDS · DISTRICT HEAT
COREX-C
- Your load profile becomes a reactor
- Parametric digital-core sizing
- Site-matched shielding & transport
- Heat, power, or both
CUSTOM ENVELOPE · COGENERATION · DESALINATION · HYBRID MICROGRIDS
| Parameter | COREX-100 | COREX-400 | COREX-1200 |
|---|---|---|---|
| Electric output | 100 kWe | 400 kWe | 1.2 MWe |
| Thermal output | ≈350 kWt | ≈1.3 MWt | ≈3.5 MWt |
| Core cooling | Sodium heat pipes — solid-state, passive, redundant | ||
| Fuel | TRISO particles, HALEU <20% enrichment, factory-sealed core | ||
| Power conversion | Stirling array | sCO₂ Brayton | sCO₂ Brayton |
| Core life target | 5 yr | 6 yr | 8 yr |
| Refueling model | Sealed core returns to factory — no on-site fuel handling, no waste left on site | ||
| Site water | None — air-cooled heat rejection | ||
| Transport | 20-ft ISO | 40-ft ISO | 40-ft + support module |
| Transport mode | Truck, rail, or barge — shutdown rods locked in, passive decay-heat rejection in transit | ||
| Turndown | Designed for load-following operation across remote microgrid profiles | ||
Design targets, not measured performance. The COREX family is in the conceptual design stage; figures derive from our simulation campaigns and from published reference designs in the 100 kWe–5 MWe heat-pipe class, and will be refined through preliminary design and testing.
ONYX fuel · Coated-particle pebble fuel
ONYX. A denser, tougher coated-particle fuel.
Every ONYX pebble holds about 17,500 independent ceramic pressure vessels, each sealing its own speck of fuel. ONYX gives each one a denser uranium-nitride kernel and two carbide shells, and wraps the whole pebble in silicon-carbide armour.
- Kernel · UN, 99.5% N-15425 µm · 12.8 g U/cm³
Uranium nitride packs 12.8 g of uranium into each cubic centimetre, among the densest ceramic fuels. Nitrogen-15 is required: natural nitrogen absorbs neutrons and breeds carbon-14.
- Buffer · porous carbon100 µm
Holds fission gas and absorbs kernel swelling and fission-fragment recoil.
- Inner pyrocarbon40 µm
Seals the kernel and gives the ceramic layers a smooth substrate.
- Zirconium carbide · new barrier20 µm
A second carbide shell that resists palladium attack and keeps its strength far above SiC limits. It sits inside the SiC, protected from air.
- Silicon carbide35 µm
The proven pressure vessel and fission-product barrier of coated-particle fuel.
- Outer pyrocarbon40 µm
Protects the SiC and bonds the particle into the graphite matrix.
More uranium per particle
The nitride kernel lets one pebble carry 9.0 g of uranium in 17,499 particles. Each pebble delivers about 2.00 MWd of heat before it is retired.
Two carbide shells
ZrC inside SiC gives each particle a second ceramic pressure boundary and a second fission-product barrier. If one shell has a defect, the other still holds.
SiC-armoured surface
A 0.5 mm silicon-carbide skin on the 60 mm pebble is designed to slow graphite oxidation if air or steam ever enters the core, and to cut graphite dust from pebble-on-pebble wear.
| Parameter | ONYX | Basis |
|---|---|---|
| Kernel | UN, 99.5% N-15, Ø 425 µm, 12.8 g U/cm³ | Design |
| Enrichment | 19.75 wt% U-235 (HALEU) | Design |
| Uranium per pebble | 9.0 g (1.78 g U-235) | OpenMC model bookkeeping |
| Particles per pebble | 17,499 · Ø 895 µm | OpenMC model bookkeeping |
| Ceramic barriers per particle | 2 (ZrC + SiC) plus 3 carbon layers | Design |
| Pebble surface | 0.5 mm SiC armour | Design |
| Infinite-lattice k, fresh | 1.4763 ± 105 pcm | OpenMC, explicit particles |
| Discharge burnup | ≈220 MWd/kg uranium | OpenMC depletion + CAIRN-80 leakage |
| Heat delivered per pebble | 2.00 MWd | Burnup × uranium |
| Spent pebbles per year, CAIRN-80 | 32,844 | 200 MWt, 90% capacity factor |
| Fuel temperature coefficient | +2.89 ± 0.24 pcm/K | OpenMC, 900→1,200 K |
| Natural-nitrogen penalty | −887 pcm | Why N-15 is required |
ONYX is a COREXTION design concept. It has not yet been fabricated or irradiated; the figures above come from our simulations.
What ONYX still has to prove
- Nitrogen-15 at 99.5% purity costs far more than natural nitrogen today. Recycling it from spent kernels is part of the plan.
- Uranium nitride reacts with hot steam if a particle fails. The two carbide shells and the armoured pebble exist to keep that from happening.
- Zirconium carbide has a much thinner irradiation record than SiC. ONYX needs an AGR-style irradiation and heating campaign.
- A SiC skin on graphite must survive thermal-expansion mismatch over years of cycling. That is a materials test before it is a design claim.
CAIRN series · Pebble-bed modules
CAIRN. Pebble-bed power, sized to the load.
A cairn is a pile of stones that marks the way. A CAIRN module is a helium-cooled bed of ONYX pebbles that keeps itself cool after shutdown with no pumps, no water and no operator action. Three module sizes cover 20 to 80 MWe each, and units combine into plants for larger demand.
CAIRN-20
- 50 MWt · helium 750 °C
- Bed Ø 2.2 m × 3.3 m
- ≈68,000 ONYX pebbles
- ≤1,278 °C peak fuel, no cooling
MINES · ISLANDS · DATA CENTRES · DISTRICT HEAT
CAIRN-50
- 125 MWt · helium 750 °C
- Bed Ø 2.6 m × 6.0 m
- ≈172,000 ONYX pebbles
- ≤1,483 °C peak fuel, no cooling
PROCESS STEAM · DESALINATION · REGIONAL GRIDS
CAIRN-80
- 200 MWt · helium 750 °C
- Bed Ø 2.8 m × 9.5 m
- ≈316,000 ONYX pebbles
- ≤1,490 °C peak fuel, no cooling
COAL-PLANT REPLACEMENT · 4-PACK = 320 MWe
| Parameter | CAIRN-20 | CAIRN-50 | CAIRN-80 |
|---|---|---|---|
| Thermal power | 50 MWt | 125 MWt | 200 MWt |
| Electric output (≈40%) | 20 MWe | 50 MWe | 80 MWe |
| Pebble bed | Ø 2.2 m × 3.3 m | Ø 2.6 m × 6.0 m | Ø 2.8 m × 9.5 m |
| Core power density | 4.0 MW/m³ | 3.9 MW/m³ | 3.4 MW/m³ |
| Pebbles in core | 67,659 | 171,817 | 315,506 |
| Uranium in core | 0.61 t | 1.55 t | 2.84 t |
| k-eff, fresh core, rods out (OpenMC) | 1.3036 ± 81 pcm | 1.3522 ± 90 pcm | 1.3706 ± 84 pcm |
| Side-reflector rod bank worth (OpenMC) | 9,383 pcm | 7,489 pcm | 6,703 pcm |
| Peak fuel in DLOFC | 1,113 °C (OpenMC shape) · 1,278 °C (top-peaked) | 1,315 °C (OpenMC shape) · 1,483 °C (top-peaked) | 1,337 °C (OpenMC shape) · 1,490 °C (top-peaked) |
| Spent ONYX pebbles per year | 8,211 | 20,527 | 32,844 |
| Coolant | Helium, 6 MPa, 260 °C in / 750 °C out | ||
| Fuel | ONYX pebbles, 60 mm, 9.0 g uranium at 19.75% U-235, multi-pass online refueling | ||
| Power conversion | 565 °C steam Rankine cycle (≈40% net, ASSUMED) or process heat and steam | ||
| Shutdown | Control rods in the side reflector plus a reserve shutdown system; strong negative temperature feedback | ||
| Decay-heat removal | Passive: conduction and radiation through bed, reflector and vessel to an air- or water-cooled cavity panel | ||
Fresh-core states. In operation a CAIRN module runs near k = 1 with continuous online refueling, so only about 1,000 pcm of excess reactivity is held by the rods. A fresh core is started with a mix of fuel and graphite pebbles. Cold-shutdown margin and the reserve shutdown system are next-phase work.
Plant sizer
How many CAIRN units does your load need?
Picks the fewest identical modules that cover the demand at ≈40% net efficiency and 90% capacity factor. Fuel figures use the OpenMC discharge burnup of ONYX shown below. Directional planning numbers, not a quote.
Simulation evidence · ONYX & CAIRN
The numbers behind the claims.
Every ONYX and CAIRN figure on this page comes from our own calculations: continuous-energy Monte Carlo transport in OpenMC with ENDF/B-VIII.0 data, depletion with the ENDF/B-VIII.0 decay chain, and a 2-D transient heat-transfer model for the loss-of-cooling accident.
| Case | Description | k∞ | ±1σ (pcm) | Histories |
|---|---|---|---|---|
| ONYX | ONYX UN(N-15), 19.75%, 9.0 g U/pebble, 900 K | 1.47634 | 105 | 0.60 M |
| ONYX_natN | ONYX with natural nitrogen (0.37% N-15) | 1.45726 | 109 | 0.60 M |
| ONYX_Tf1200 | ONYX with fuel kernels at 1,200 K | 1.45769 | 113 | 0.60 M |
| Module | Power | Bed (D × H) | Power density | Peak fuel, OpenMC power shape | Peak fuel, top-peaked shape | Time of peak | Peak vessel |
|---|---|---|---|---|---|---|---|
| CAIRN-20 | 50 MWt | Ø 2.2 × 3.3 m | 4.0 MW/m³ | 1,113 °C | 1,278 °C | 13 h | 323 °C |
| CAIRN-50 | 125 MWt | Ø 2.6 × 6.0 m | 3.9 MW/m³ | 1,315 °C | 1,483 °C | 20 h | 384 °C |
| CAIRN-80 | 200 MWt | Ø 2.8 × 9.5 m | 3.4 MW/m³ | 1,337 °C | 1,490 °C | 25 h | 392 °C |
| HTR-PM-like check | 250 MWt | Ø 3.0 × 11.0 m | 3.2 MW/m³ | 1,524 °C | 1,524 °C | 28 h | 371 °C |
Method and assumptions
- Neutronics. OpenMC 0.16.0, ENDF/B-VIII.0, explicit coated particles placed by random sequential packing inside each 50 mm fuel zone, pebbles on a body-centred cubic lattice at 61% packing. Bound thermal scattering for graphite, SiC, UN and UO₂; ZrC uses free-gas scattering because no bound table exists.
- Depletion. CE/CM predictor-corrector in the explicit-particle pebble lattice at 885 W per pebble, 228-nuclide CASL decay chain, direct reaction-rate tallies for the actinides, xenon, samarium and nitrogen. Discharge burnup uses the linear-reactivity model of a multi-pass bed, with leakage taken from the full-core CAIRN-80 model and a 1,000 pcm control margin. The reduced chain makes this estimate slightly optimistic.
- Full core. Explicit pebbles and particles in a cylindrical bed with graphite reflectors and B4C rods in side-reflector channels; vacuum outside the reflector, which overstates leakage. Fresh-core states; the fission-power shape from these runs drives the accident model.
- Accident heat transfer. 2-D r-z conduction and radiation, Zehner-Schlünder bed conductivity with Breitbach-Barthels radiation, Way-Wigner decay heat with a 10% margin, no convection credit. The same model gives 1,524 °C for an HTR-PM-like 250 MWt module, against published analyses near 1,500 °C.
- Limits of this work. Conceptual-design calculations. No fuel-performance code, no coupled thermal-hydraulics, no fabrication or irradiation data for ONYX. They size the design and rank options; they do not replace testing or licensing analysis.
Digital core · Simulation
Every COREX is born as a digital twin.
Before we cut metal, a COREX exists as a complete multi-physics model — neutronics, heat-pipe transients, thermo-mechanics, and CFD, cross-verified and benchmarked against published experimental data. Simulation is how we de-risk the design. Testing is how we'll prove it.
Coupled thermal solution — conjugate heat transfer across monolith, fuel channels, and heat-pipe bores. Illustrative animation; production CFD renders will replace this panel.
Neutronics — continuous-energy Monte Carlo over the full core geometry, ENDF/B-VIII.0 nuclear data. Illustrative animation · histories: 0
Heat-pipe performance — every COREX pipe is sized with margin against capillary, sonic, entrainment, and boiling limits across its full mission profile. Illustrative chart.
The toolchain
Neutronics in OpenMC and Serpent 2, cross-verified against MCNP with ENDF/B-VIII.0 data. Coupled core multi-physics in the DOE MOOSE ecosystem — Griffin for reactor physics, BISON for fuel performance, and Sockeye for heat-pipe transient behavior. Thermal-structural and CFD analysis in ANSYS and STAR-CCM+. Benchmarked against published data from the KRUSTY heat-pipe reactor test — the field's canonical validation experiment.
Simulation results characterize the conceptual design; they are a de-risking tool, not a substitute for hardware testing. Our roadmap takes the digital core to metal.
Deployment
Designed to arrive like cargo. Run like infrastructure.
Factory-fueled & sealed
Each COREX is designed to leave the factory fueled, tested, and sealed — no fuel handling ever happens at your site.
One move
Truck, rail, or barge in an ISO-class envelope. Shutdown rods locked in; decay heat rejected passively — designed to meet transport surface-temperature limits with no active cooling.
Set on a pad
Designed for placement on a prepared gravel pad — minimal excavation, no cooling water intake, no switchyard-scale footprint.
Power in days
Designed to reach full power within days of arrival — then run for years, load-following your site, with the sealed core returning to the factory at end of life.
Markets
Built for the places the grid forgot.
Remote mining
Power is up to a third of a remote mine's operating cost, hauled in as diesel over ice roads and barge seasons. A COREX is designed to power a full camp or concentrator for years per core — plus process heat.
INDEPENDENT STUDIES PROJECT NUCLEAR CUTTING REMOTE-MINE POWER COSTS BY DOUBLE-DIGIT PERCENTAGES VS DIESEL
Arctic & northern communities
Hundreds of northern communities run on diesel at the end of a thousand-kilometer supply line — among the highest electricity prices on Earth, plus heating oil on top. COREX cogeneration is designed to serve both.
REMOTE ALASKA DIESEL POWER: $0.50–$1.00+/kWh
Islands
Island grids import nearly every kilowatt-hour as fuel, exposed to price swings and storm-broken supply chains. One COREX-1200 is designed to anchor an island microgrid — with desalination heat as a by-product.
FUEL-IMPORT DEPENDENCE ≈100% ON MOST NON-INTERCONNECTED ISLANDS
Defense installations
Energy resilience is now a mission requirement. A sealed microreactor is designed to keep a base's critical loads independent of vulnerable fuel logistics and fragile local grids.
FULLY BURDENED FUEL COST IN THEATER: UP TO HUNDREDS OF $/GALLON · ≈1 CASUALTY PER 24 FUEL RESUPPLY CONVOYS (U.S. ARMY DATA)
Disaster response
After a hurricane or earthquake, generators queue for fuel that isn't coming. A transportable reactor is designed to restore hospital-scale power in days and hold it for years of rebuild — the least contested, most human use case in nuclear.
DESIGNED FOR: HOSPITAL LOADS · WATER TREATMENT · EMERGENCY SHELTER MICROGRIDS
Off-grid industry
Pipelines, telecom backbones, hydrogen pilots, remote data and research stations — steady loads in hard places, where COREX's zero-water, zero-logistics profile is designed to fit.
HEAT + POWER COGENERATION UP TO ≈600 °C-CLASS PROCESS TEMPERATURES
Diesel reality check
What is diesel really costing your site?
Directional estimate only. Assumes ≈3.5 kWh per liter genset yield; excludes generator O&M, logistics, and capital on the diesel side, and reflects third-party (NEI) cost estimates — not a COREXTION price quote — on the microreactor side.
| Attribute | Diesel gensets | Gas-cooled microreactor | COREX heat-pipe |
|---|---|---|---|
| Fuel resupply | Continuous convoys / barges | Years per core | Years per core (5–8 yr targets) |
| Primary coolant loop | — | Pressurized gas + circulators | None — solid-state core |
| Moving parts in heat removal | Many, service-intensive | Blowers & circulators | Zero |
| Single-point cooling failures | Radiator / pump failures | Circulator class | 100s of independent pipes — graceful degradation |
| Site water | None | None | None |
| CO₂ at site | ≈2.7 kg per liter burned | Zero | Zero |
| Noise & exhaust | Constant | Minimal | Minimal — no combustion, few rotating parts |
COREX columns state design intent for the conceptual COREX family. "Gas-cooled microreactor" describes the technology class generally, not any specific competitor product.
Roadmap · Where we are
From digital core to first power. In the open.
We publish our stage honestly — dated milestones behind us as fact, everything ahead of us as a target.
COREXTION LLC founded. COREX family conceptual design established. ONYX fuel and the CAIRN pebble-bed series defined, with OpenMC neutronics, depletion and passive-cooling studies published on this page.
ONYX surrogate-particle coating trials (ZrC and SiC chemical vapor deposition) and SiC-armoured pebble oxidation tests with university and national-laboratory partners. COREX-100 preliminary design freeze. Non-nuclear heat-pipe test rig — first hardware validation of the digital core. Targeting initiation of NRC pre-application engagement (Regulatory Engagement Plan).
Electrically heated integrated prototype — full-scale core simulator validating thermal, control, and power-conversion behavior without nuclear fuel. Applications to DOE test-bed and demonstration programs.
Fueled demonstration at a national-laboratory test bed. Pilot deployments with launch partners in mining, island, and disaster-response markets.
Forward-looking targets, not commitments. Development, licensing outcomes, and timing are subject to significant uncertainty; there can be no assurance these milestones will be achieved as described or on these dates.
About COREXTION
Engineering in the open.
COREXTION LLC is a U.S. company founded in 2026 to design the COREX family of solid-state heat-pipe microreactors. We are simulation natives: our craft is taking a site's load profile and turning it into a compact, transportable reactor — rigorously, transparently, and fast.
Our transparency pledge
- Every performance number on this site is labeled for what it is — a design target from modeling and simulation.
- We name our codes, our data libraries, and our benchmarks, and we'll publish our methodology as we go.
- Renders are labeled as concepts. When we have hardware, you'll see photographs.
- Our roadmap shows targets, not promises — and we'll report the misses along with the milestones.
Contact
Tell us about your site.
Mine operator, island utility, defense energy office, relief agency, investor, or future teammate — if your problem is power in a hard place, we want the details: location, load, current fuel cost, and constraints.
Direct line: contact@corextion.com
We answer every serious inquiry. Early conversations shape the COREX-C bespoke program — the earlier you talk to us, the better the reactor fits your site.