Pebbles of X-energy’s TRISO-X fuel have begun thirteen months of irradiation testing at the Idaho National Laboratory (INL) to evaluate fuel performance across operating scenarios and qualify them for commercial use.

TRISO-X is a specialized version of TRISO (tri-structural isotropic) nuclear fuel, fabricated into billiard ball-sized spheres also called pebbles that will be used to power high temperature gas-cooled reactors, such as X-energy’s Xe-100 small modular reactor (SMR). The TRISO particles from which the pebbles are created from uranium, carbon and oxygen fuel kernel encapsulated in three layers of carbon- and ceramic-based materials that prevent the release of radioactive fission products. This structure means that the fuel cannot melt in a commercial high-temperature reactor and can withstand extreme radiation and temperatures that are way beyond the threshold of the nuclear fuels that are in use today, according to the US Department of Energy (DoE).

The X-energy Pebble Reactor Test has been named XPeRT. The fuel will undergo irradiation testing in INL’s Advanced Test Reactor (ATR), a pressurized water reactor which produces neutrons, rather than heat, to evaluate how TRISO-X fuel performs under various power levels, temperatures, and burnup conditions related to the Xe-100 SMR design. Post-irradiation examination at INL and Oak Ridge National Laboratory (ORNL) will analyze the fuel’s fission product retention and structural stability under the full range of expected commercial operating conditions.

Dan Wachs is the National Technical Director for DoE’s Advanced Fuels Campaign. He said that the experimental cycle at ATR is “a huge one” for advanced nuclear. “The test marks INL’s first irradiations of TRISO fuel for advanced reactors since 2020 and the first use a new lead-out test capability at ATR that makes these advanced fuel tests possible.”

TRISO-X has operated a pilot nuclear fuel fabrication facility at ORNL since 2016. It is planning to construct two further facilities at ORNL to manufacture its proprietary fuel for commercial deployment of the Xe-100, which is one of two advanced reactor demonstration projects receiving support from the DoE’s Advanced Reactor Demonstration Program. The first of those facilities, TX-1, is already being built. TRISO-X is also participating in the DoE’s Fuel Line Pilot Program, established earlier this year to support the develolpment a domestic nuclear fuel supply chain for testing new reactors.

Clay Sell is the CEO of X-energy. He said, “What began in Oak Ridge as a pioneering effort to advance TRISO manufacturing is now leading the way in qualifying the fuel that will power the next generation of reactors. TRISO-X embodies decades of US innovation in fuel design and this testing program brings us one step closer to redefining the standard for safety and reliability in nuclear energy.”

The first deployment of the Xe-100 is planned for the Dow’s Seadrift site on the Texas Gulf Coast. It will supply both power and high-temperature heat to industrial-scale operations. X-energy and Amazon have also agreed to the goal of more than five gigawatt of new nuclear by 2039, beginning with a joint plan with Washington state utility Energy Northwest to build up to twelve SMRs near Energy Northwest’s Columbia Generating Station.

X-energy