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X Energy, LLC
TypePrivately held
IndustryNuclear power
Greenbelt, MD
Key people
Clay Sell
Dr. Kam Ghaffarian

X-energy is an American private nuclear reactor and fuel design engineering company. It is developing a Generation IV high-temperature gas-cooled nuclear reactor design. In January 2016 X-energy was awarded a five-year $53M United States Department of Energy Advanced Reactor Concept Cooperative Agreement award to advance elements of their reactor development.[1][2][3] In 2019, X-energy received funding from the United States Department of Defense to develop small military reactors for use at forward bases.[4]

In October 2020, the company was chosen by the United States Department of Energy as a recipient of a matching grant totalling between $400 million and $4 billion over the next 5 to 7 years for the cost of building a demonstration reactor of their Xe-100, helium cooled pebble-bed reactor design.[5]

Reactor design[edit]

The Xe-100 is a pebble bed high-temperature gas-cooled nuclear reactor design that is planned to be smaller, simpler and safer when compared to conventional nuclear designs. Pebble bed high temperature gas-cooled reactors were first proposed in 1944. Each reactor is planned to generate 200 MWt and approximately 76 MWe. The fuel for the Xe-100 is a spherical fuel element, or pebble, that utilizes the tristructural-isotropic (TRISO) particle nuclear fuel design, with Uranium enriched to 20%, to allow for longer periods between refueling.[5]


The company was founded in 2009 by Kam Ghaffarian.[6]

X-energy's CEO is Clay Sell, previously Deputy Secretary of Energy of the United States Department of Energy.


  1. ^ Fountain, Henry (January 19, 2016). "U.S. Acts to Spur Development of High-Tech Reactors". The New York Times. ISSN 0362-4331. Retrieved April 2, 2017.
  2. ^ Fehrenbacher, Katie (February 16, 2016). "Meet a Startup Making a New Kind of Safer, Smaller Nuclear Reactor". Fortune. Retrieved November 9, 2017.
  3. ^ Conca, James (March 27, 2017). "X-Energy Steps Into The Ring With Its Advanced Pebble Bed Modular Nuclear Reactor". Forbes. Retrieved November 9, 2017.
  4. ^ Harper, John (April 27, 2020). "Safety Concerns Could Stymie Nuclear Reactor Plans". National Defense.
  5. ^ a b Cho, Adrian (October 16, 2020). "Department of Energy picks two advanced nuclear reactors for demonstration projects". Science. Retrieved October 20, 2020. DOE will split the total cost of building each plant with private industry. Each project receives $80 million this year and could receive a total of between $400 million and $4 billion in funding over the next 5 to 7 years. ... In contrast, the Xe-100 design from X-Energy would use pressurized helium gas to cool its uranium-based fuel. That fuel would be packaged not in the conventional metal-clad rods, but in “pebbles”—spheres of graphite infused with countless ceramic kernels that contain the uranium. Like a giant gumball machine, the reactor would hold 220,000 pebbles, which would slowly descend through the core and, as their fuel was spent, would exit from a port at the bottom. Heated to 750°C, the helium would generate steam in a secondary circuit to produce electricity. In principle, the pebbles can’t melt, eliminating the risk of a meltdown. ... The Natrium and Xe-100 reactors would use fuel enriched to 20%, which would enable them to run longer on a batch of fuel and extract more energy from it.
  6. ^ "Profile | Kam Ghaffarian, President and Chief Executive, Stinger Ghaffarian Technologies - SpaceNews.com". SpaceNews.com. February 18, 2013. Retrieved April 2, 2017.