What is a microreactor?

The short answer

A microreactor is a small nuclear power plant. It makes up to about 20 megawatts of electricity, or about 50 megawatts of heat. A factory builds the reactor as one module. A truck, a train, or a ship delivers it to the site.

The size changes how nuclear power gets built. A large plant takes a decade and a city-sized construction site. A microreactor arrives nearly complete, and the site work takes months. The plant can then sit next to the load it serves: a data center, a mine, a remote town, a military base, or a factory that needs heat.

Most designs run for years without refueling. Many use high-assay low-enriched uranium, called HALEU, which holds between 5 and 20 percent uranium-235. The small core and the long fuel life let one or two operators oversee the plant, with a remote center watching too.

How the plant in the 3D model works

The model shows a representative sodium-cooled, pool-type microreactor of about 10 megawatts electric and 30 megawatts thermal. Sixty-one hexagonal fuel assemblies sit in a compact core about 1.2 meters across. A reflector ring around the core bounces neutrons back in, so a small core can sustain the chain reaction.

Twelve control drums sit inside the reflector. Each drum has a neutron-absorbing face. Turned toward the core, the drum lowers power. Turned away, it raises power. Three shutdown rods hang above the core on electromagnets. If the magnets lose power, the rods drop by gravity and stop the reaction in under two seconds.

Liquid sodium fills the reactor vessel. It enters the core at about 400 °C and leaves at about 550 °C. Sodium boils at 883 °C, so the vessel runs at near atmospheric pressure. Two electromagnetic pumps move the sodium with magnetic fields and no moving parts. If they stop, natural circulation keeps the sodium moving.

Two intermediate heat exchangers pass the heat to a clean intermediate loop. That loop leaves the reactor vault and feeds the power conversion unit. A supercritical carbon dioxide turbine spins a generator and makes about 10 megawatts. Fans blow air across finned tubes to reject the waste heat. The plant uses no cooling water.

The whole reactor module ships on one steel skid. A heavy-haul trailer brings it from the factory. A bridge crane lifts it into a concrete shield silo inside the reactor building. The silo gives radiation shielding, seismic protection, and a final barrier for sodium.

Reactor core →Primary system →Power conversion →

How it stays safe

The design relies on physics rather than on pumps, valves, or operators. The sodium pool is large, so it absorbs heat slowly. After shutdown, the fuel still makes a few percent of full power. Air ducts around the guard vessel let natural convection carry that heat up a chimney. This system has no pumps and no power supply, and it is always on.

A second steel vessel, the guard vessel, surrounds the reactor vessel with a small argon-filled gap. If the inner vessel leaks, the guard vessel catches the sodium and keeps the core covered. Thick concrete and borated steel around the vessel absorb neutrons and gamma rays, so workers can approach the building while the reactor runs.

Sodium reacts with water and air, so it stays inside sealed steel systems under an argon cover gas. The intermediate loop keeps radioactive sodium inside the reactor vault. Only clean fluid reaches the turbine hall.

How it powers a data center

A short 69 kV line on steel poles carries the plant output to a campus substation. Two transformers step the voltage down to 13.8 kV and feed the data hall through an underground duct bank. The hall holds about 320 racks and draws about 8 megawatts of IT load, plus cooling and losses.

The reactor runs flat out all the time. Battery containers absorb or supply the difference as the load moves, and they can black-start the campus. UPS units ride through short dips. Two standby diesel generators cover the hall if the reactor or the line is out. With the reactor as prime power, they run only for tests.

Rooftop dry coolers reject the heat the servers make. Like the reactor, the data center uses no cooling water.

Other kinds of microreactors

Not every microreactor uses liquid sodium in a pool. The demonstration park down the road shows three other designs at a basic level. A heat-pipe reactor has no pumps and no coolant loop at all. Sealed sodium heat pipes carry heat out of a solid core block. A gas-cooled reactor circulates helium through TRISO fuel, and this one stores heat in molten salt tanks like a thermal battery. A molten-salt reactor dissolves the fuel in the coolant itself and drains it to a safe tank if power fails.

Each design trades one set of engineering problems for another. The reactor types page compares them side by side.

Compare the four reactor types →

About this model

The 3D plant is a representative design for education. It does not describe a specific company or product. The values are typical of a 10 MWe class pool-type sodium-cooled microreactor and of a data center of about 8 MW. Regulators review every real design before it can operate, and real plants will differ in detail.

You can cut the model open, explode it, search every part, run the start-up sequence, change the physics live, and walk the site on foot. The written guide lists every labeled component with its role and typical specifications.