Technology

Magnetic confinement

Holding a hot plasma away from material walls using magnetic fields, sustained for seconds to steady-state rather than the nanosecond pulses of inertial confinement. The open problem shared by every configuration below is exhausting the plasma's heat and helium ash without eroding the wall that must survive it for years, not seconds.

26 companies · 127 devices · 0 reactor designs

• Tokamak

  Doughnut-shaped magnetic confinement using a strong toroidal field plus a current driven through the plasma itself. The most-studied configuration, and the one ITER uses. Its main open problem is heat exhaust at the divertor, where the plasma edge concentrates power onto a small area, together with the risk of disruptions: sudden, uncontrolled losses of the plasma current.

  9 companies · 83 devices · 0 reactor designs

  • Spherical tokamak

    A tokamak squeezed towards a cored-apple shape. The tighter aspect ratio holds plasma pressure with less magnetic field, which is efficient, but leaves very little room at the centre for the central column.

    3 companies · 29 devices · 0 reactor designs

• Stellarator

  Confinement produced by external coils twisted into complex three-dimensional shapes, so no net current has to be driven through the plasma. That removes the disruptions a tokamak's plasma current can cause and allows continuous operation, at the price of coils that are far harder to design and build.

  7 companies · 16 devices · 0 reactor designs

• Magnetic mirror

  Plasma trapped between two regions of strong magnetic field that reflect particles back. Simple and linear, but historically leaky at the ends.

  4 companies · 9 devices · 0 reactor designs

• Field-reversed configuration

  A self-organised plasma ring that generates its own confining field, with no central coil. Compact and high-beta, but stability over long timescales is the open question.

  4 companies · 8 devices · 0 reactor designs

• Levitated dipole

  Confinement around a single magnetically levitated superconducting ring, modelled on how planetary magnetospheres hold plasma. No levitated-dipole device has run at reactor-relevant scale; the main open problem is engineering a superconducting ring that can be levitated, cooled and shielded from neutrons without any physical support.

  1 company · 1 device · 0 reactor designs

• Reversed-field pinch

  A toroidal configuration where the field reverses direction at the plasma edge, allowing confinement at much lower external field than a tokamak. That has come at the cost of confinement quality: RFPs have not matched tokamak performance, and closing that gap without the stronger field is the configuration's main open problem.

  0 companies · 5 devices · 0 reactor designs

Inertial confinement

Compressing fuel so fast that its own inertia holds it together long enough to burn: nanoseconds, not seconds. Every ICF approach shares the same open problem beyond ignition itself: repeating a shot several times a second at low enough cost per shot to run a power plant, which no driver has yet demonstrated.

12 companies · 9 devices · 0 reactor designs

• Laser ICF, indirect drive

  Laser energy is converted to X-rays inside a small gold or uranium can (a hohlraum), and the X-rays drive the capsule. The NIF configuration. Only about a tenth of the laser energy ends up absorbed by the capsule, most of the rest heating the hohlraum wall, which is the main efficiency cost indirect drive carries relative to direct drive.

  2 companies · 1 device · 0 reactor designs

• Laser ICF, direct drive

  Laser beams strike the fuel capsule directly. More efficient than indirect drive in principle, but far more sensitive to how evenly the beams are applied.

  7 companies · 1 device · 0 reactor designs

• Heavy-ion ICF

  Heavy ion beams rather than lasers deliver the compression energy. Accelerators are efficient and repeat readily, which lasers of this scale do not. No facility has been built at fusion-relevant scale; the main open problem is focusing multiple intense ion beams onto a millimetre-scale target simultaneously.

  0 companies · 0 devices · 0 reactor designs

• Projectile-driven

  A physical projectile accelerated to extreme velocity compresses the fuel on impact. The main open problem is achieving symmetric compression from one, or a few, points of impact, where laser and heavy-ion approaches can spread the drive over many beams.

  1 company · 1 device · 0 reactor designs

Magneto-inertial

Compression of a magnetised plasma; sits between MCF and ICF in density and timescale.

8 companies · 7 devices · 0 reactor designs

• Z-pinch

  A current driven straight through a plasma column, whose own magnetic field squeezes it inward. Long set aside as unstable; sheared-flow stabilisation, studied at the University of Washington and pursued commercially by Zap Energy, renewed work on it.

  2 companies · 5 devices · 0 reactor designs

• Magnetized target

  A magnetised plasma target compressed mechanically or by an imploding liner. Sits between magnetic and inertial confinement in density and timescale. The main open problem is compressing the liner onto the plasma symmetrically and fast enough to reach fusion conditions before the plasma cools or the liner breaks up.

  2 companies · 2 devices · 0 reactor designs

• Pulsed magnetic compression

  Repeated compression of a plasma by pulsed magnetic fields, recovering energy directly from the expansion rather than through a steam cycle. The main open problem is hardware lifetime: the compression coil and switching electronics must survive millions of repeated pulses for a power plant to be economic.

  1 company · 0 devices · 0 reactor designs

Electrostatic confinement

Confinement by electric rather than magnetic fields.

3 companies · 1 device · 0 reactor designs

• Inertial electrostatic confinement

  Electric fields rather than magnetic ones confine the ions. Simple to build and well proven as a neutron source; net energy is a different matter.

  2 companies · 1 device · 0 reactor designs

Other fusion approaches

• Beam-target

  A beam of fast ions fired into a fuel target that is not itself a hot plasma, such as a gas cell or a solid loaded with deuterium or tritium. As each beam ion ploughs through the target it loses its energy to the target's electrons far faster than it is likely to fuse, so only a tiny fraction of the ions fuse before they stop. The fusion energy returned is a small fraction of the energy spent accelerating the beam, so the approach cannot reach net energy gain however the beam or target is arranged. It is commercially useful anyway, as a compact and reliable source of neutrons for imaging and medical isotope production.

  2 companies · 0 devices · 0 reactor designs

• Muon-catalysed fusion

  A negative muon temporarily replaces an electron in a D-T (or D-D) molecule, pulling the nuclei roughly 200 times closer together than an electron would, so fusion happens at room temperature without confining a hot plasma at all. Added as its own branch of the fusion tree rather than filed under magnetic or inertial confinement, because it confines nothing: the muon does the work electromagnetically at the molecular scale. No net-energy device has been built: a muon typically catalyses only 100-150 fusions before it is captured by a helium nucleus and lost, and the main open problem is extending that cycle count, or cutting the cost of producing muons, enough to get more energy out than went into making them.

  1 company · 0 devices · 0 reactor designs

Water-cooled

Reactors cooled by ordinary or heavy water, which in most designs is also the neutron moderator.

38 companies · 125 reactors · 26 reactor designs

• Pressurised water reactor

  Ordinary (light) water kept under high pressure so it heats without boiling, transferring heat to a separate steam loop; the water is both coolant and moderator. Fuel is low-enriched uranium oxide pellets in zirconium-alloy rods. The most common reactor type in service worldwide.

  26 companies · 5 reactors · 21 reactor designs

• Boiling water reactor

  Light water boils directly in the core and the steam drives the turbine: one loop instead of two, simpler but with an activated steam circuit. Water is again both coolant and moderator, and fuel is low-enriched uranium oxide, as in a PWR.

  4 companies · 3 reactors · 3 reactor designs

• Pressurised heavy-water reactor

  Heavy water (deuterium oxide) kept under pressure as both coolant and moderator, which absorbs far fewer neutrons than ordinary water and so lets the reactor run on natural, unenriched uranium. That is the CANDU design's defining trade: heavy water is expensive to produce, but the fuel needs no enrichment plant. Fuel is natural or slightly enriched uranium oxide, usually in horizontal pressure tubes, refuelled online without shutting the reactor down.

  7 companies · 0 reactors · 1 reactor design

Salt-based

Reactors using molten salt as fuel carrier, coolant, or both.

11 companies · 4 reactors · 9 reactor designs

• Molten salt reactor

  Fuel DISSOLVED in the salt, which in most designs is fuel carrier and coolant at once. Distinct from a salt-cooled reactor with solid fuel; the two are often confused. Moderator, where one is used at all, is a separate design choice from the salt: thermal-spectrum MSRs are typically graphite-moderated, fast-spectrum MSRs carry no moderator.

  10 companies · 2 reactors · 8 reactor designs

• Fluoride salt-cooled high-temperature reactor

  Molten salt COOLANT with solid fuel, typically TRISO, and a separate solid moderator, usually graphite. Kairos Power's KP-FHR is the reference example.

  1 company · 2 reactors · 1 reactor design

Gas-cooled

Reactors cooled by gas, usually helium or carbon dioxide, allowing higher outlet temperatures than water.

11 companies · 4 reactors · 14 reactor designs

• High-temperature gas-cooled reactor

  Helium-cooled and graphite-moderated, running far hotter than a water reactor. Fuel is TRISO particles, typically formed into pebbles or prismatic blocks, at LEU or HALEU enrichment depending on the design. The high outlet temperature suits industrial process heat as well as electricity.

  10 companies · 4 reactors · 11 reactor designs

Liquid-metal cooled

Reactors cooled by molten metal at near-atmospheric pressure. Most designs use no moderator, so the neutrons stay fast. A few do slow their neutrons: Aalo Atomics describes its sodium-cooled Aalo-1 as a thermal reactor, and the IAEA lists Idaho National Laboratory's MARVEL microreactor as liquid-metal-cooled with a thermal spectrum.

13 companies · 9 reactors · 9 reactor designs

• Sodium fast reactor

  Liquid sodium coolant with a fast, unmoderated neutron spectrum. Sodium carries heat superbly at atmospheric pressure, but burns in air and reacts violently with water. Large sodium-cooled cores can have a positive sodium void effect that the core design must offset. Fuel is typically metal alloy or mixed-oxide.

  8 companies · 7 reactors · 3 reactor designs

• Lead fast reactor

  Molten lead or lead-bismuth coolant, fast and unmoderated. Does not burn in air or react violently with water, unlike sodium, at the cost of weight and corrosion engineering. Fuel is typically nitride or mixed-oxide.

  3 companies · 2 reactors · 3 reactor designs

Heat-pipe microreactor

Heat moved by sealed heat pipes rather than pumped coolant or forced convection. No primary pumps and no coolant loop, which suits very small transportable reactors. Heat-pipe describes how heat is moved, not the neutron spectrum. Moderator and fuel vary by design: some designs are fast and unmoderated, others use a graphite or beryllium oxide moderator, with TRISO or metal fuel, usually HALEU.

4 companies · 0 reactors · 3 reactor designs