Why Advanced Nuclear

X-energy’s Reactors + TRISO fuel


A fundamental shift to where and how we use nuclear energy

X-energy is developing high temperature gas-cooled (HTGR) pebble bed modular reactors as well as the complementary line of TRISO-based fuel. Our reactors build upon an extensive heritage of worldwide HTGR development efforts.

X-energy’s reactors are a disruption to the global power generating market. They produce zero emissions, provide for size flexibility, serve nontraditional markets, provide power to remote and underserved markets, and are economically attractive.

An adaptable nuclear solution built on an innovative business case

The X-energy Reactor is a time-tested nuclear reactor concept. Pebble-bed high temperature gas-cooled reactors were first proposed in 1944, and the X-energy Reactor builds upon an extensive heritage of worldwide development and operation.

Meltdown Proof

Traditional reactors generate a lot of heat in a small volume known as the core. This high concentration of heat means that even when the reactor is shutdown the decay heat needs to be removed by pumping water over the core to prevent it from melting. The X-energy Reactor has a low power density (i.e. about 30 times lower than traditional reactors). This has the advantage that the reactor can be designed so that the heat generated during a loss of coolant event can be removed passively through conduction, thermal radiation and natural convection. These natural mechanisms are always present and therefore the X-energy Reactor does not have to rely on electricity to drive pumps or safety systems to prevent a core melt.

Online Refueling

Our reactor is designed for on-line refueling. Each day 175 fresh fuel pebbles are added and an equal removed. This removes the need to shut the reactor down on a regular basis to load fresh fuel and therefore also reduces operational risks.

Helium Cooling

Helium is a safer coolant than water, due to its transparency to neutrons, chemical inertness, low heat capacity, and high thermal conductivity. Helium also does not change phases during the cooling process.

Proliferation Resistant

A spent fuel cask can hold 10,000 spent fuel pebbles sealed with inert gas and stored in a below grade spent area. It has no need for conditioning or interim active cooling of the spent fuel. With a high burn up of pebble fuel so it cannot be weaponized.

Waste Management

Pebble fuel is neatly packaged in a graphite sphere and self-contained for the life of the facility. Spent fuel is discharged directly from the reactor into the spent-fuel casks, with no conditioning or interim cooling of the spent fuel required. Each spent-fuel cask can hold approximately 10,000 spent-fuel pebbles (two full-power months). The casks are sealed with inert gas and stored on site in the spent fuel area that is cooled through natural convection. Storage capacity is provided to accommodate the total inventory of spent fuel over the lifetime of the reactor.

Wide Range of Siting Options

Helium cooling reduces the reactor’s reliance on proximity to large bodies of water. Inherent safety features outlined above reduce the required emergency planning zones, allowing siting closer to population centers.

Load Following

Unlike today’s nuclear power plants, the X-energy Reactor has a variable output capability that allows for power output to be as low as 40% of nameplate capacity and can replace and supplement other fuel sources (coal, wind, solar) to leverage existing transmission and distribution infrastructure. The X-energy Reactor has the ability to perform rapid load following in real time within the power range 100-40-100%.


X-energy has identified three market segments with requirements that are aligned with the X-energy Reactor’s unique benefits: utilities, industrial/commercial and government.


Up to eight 75MWe reactor units can be bunched into a single plant and share common controls and utilities. Reactor unit will be priced accordingly for small-scale power output.


Capable of operating using advanced fuel cycles


No power needed for safety


Low security risk profile


13-acre plant footprint

Nuclear Energy. Reimagined.