The U.S. Department of Energy (DOE) awarded nearly $3.5 million to X-energy to further the development of its pebble bed, high-temperature gas-cooled nuclear reactor.

The project will focus on cutting costs through underground construction, the use of pooled off-site resources and simplified passive safety systems that don’t rely on large local water sources or pumps to prevent fuel damage. DOE is funding $3,468,323 of the $7,127,814 cost-shared project.

A TRISO fuel pebble. Source: X-energyThe Xe-100 would be a modular reactor with each unit designed to produce around 76 megawatts of electric power. Its reactor core would be made of graphite and filled with 15.5% enriched fuel pebbles. Each pebble (roughly the size of a billiard ball) would contain thousands of coated Tristructural Isotropic (TRISO) uranium fuel particles.

The coating is intended to create a seal around a kernel of uranium fuel. The company said this helps retain fission products and gases that are produced during operations and could allow reactors to be built close to urban areas.

In operation, fresh pebbles would be loaded into the reactor like a gumball machine. Helium would be pumped through the pebble bed to extract heat that would be directed to a steam generator to spin a turbine to produce electricity.

Each pebble would remain in the core for roughly three years and could circulate through the core up to six times to achieve full burn-up. Spent fuel would be placed into dry casks and stored on-site.

Letter of intent

In November, the Kingdom of Jordan signed a letter of intent with X-energy to evaluate possible use of the pebble bed reactor technology. X-energy has been in discussions with Jordanian energy officials since 2017 and had previously signed a Memorandum of Understanding that provided for a technology feasibility and deployment readiness evaluation of the Xe-100 in Jordan.

The company said that traditional reactors generate heat in a small volume known as the reactor core. This high concentration of heat means that even when the reactor is shut down, so-called decay heat needs to be removed by pumping water over the core to prevent it from melting.

The company said that its reactor is designed to have a low power density, meaning that heat generated during a loss of coolant event can be removed through passive means such as conduction, thermal radiation and natural convection. As a result, the reactor does not have to rely on electricity to drive pumps or safety systems to prevent a core melt.

Potential applications

The Xe-100 is designed to be used in energy-intensive processes such as hydrogen production and petroleum refining. This reactor concept could also be designed to incorporate passive cooling through natural conduction, thermal radiation and convection in the case of a loss of helium coolant. Those design features mean it would not have to rely on large local water sources, pumps or safety systems to prevent fuel damage.

X-energy is expected to complete its Xe-100 conceptual design by the end of 2019 and has fabricated its first fuel pebbles using natural uranium at the Oak Ridge National Laboratory.

The company also plans to submit a Nuclear Regulatory Commission license application for the facility by mid-2021.

X-energy was founded in 2009 by Dr. Kam Ghaffarian who founded Stinger Ghaffarian Technologies Inc. in 1994, a government services company focusing on IT, Engineering, Science Applications and Mission Operations. He is a member of the Nuclear Energy Institute’s Board of Directors, and holds a B.S. in Computer Science, a B.S. in Electronics Engineering, an M.Sc. in Information Management and a Ph.D. in Management Information Systems.