US lab begins TRISO fuel irradiation test

TRISO-X is a specialised version of TRISO (tri-structural isotropic) fuel, fabricated into billiard ball-sized spheres - or 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 made consist of a uranium, carbon and oxygen fuel kernel encapsulated by three layers of carbon- and ceramic-based materials that prevent the release of radioactive fission products. This novel structure means that the fuel cannot melt in a commercial high-temperature reactor and can withstand extreme radiation and temperatures that are well 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 - dubbed XPeRT - will see the fuel undergo irradiation testing in INL's Advanced Test Reactor (ATR), a pressurised water reactor which produces neutrons, rather than heat, to evaluate how TRISO-X fuel performs under various power levels, temperatures, and burnup conditions relevant to the Xe-100 SMR design. Post-irradiation examination at INL and Oak Ridge National Laboratory will measure the fuel's fission product retention and structural stability under the full range of expected commercial operating conditions.

Dan Wachs, the National Technical Director for DOE's Advanced Fuels Campaign, said the experiment 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," he said.

_{Loading the TRISO-X experiment into the ATR (Image: INL)}

TRISO-X has operated a pilot nuclear fuel fabrication facility at Oak Ridge National Laboratory since 2016. It is planning to build two further facilities at Oak Ridge to manufacture its proprietary fuel for commercial deployment of the Xe-100, which is one of two advanced reactor demonstration projects receiving support through the DOE's Advanced Reactor Demonstration Program. The first of those facilities, TX-1, is already under construction. TRISO-X is also participating in the DOE's Fuel Line Pilot Program, established earlier this year to establish a domestic nuclear fuel supply chain for testing new reactors.

"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," X-energy CEO Clay Sell said. "TRISO-X embodies decades of US innovation in fuel design and this testing programme 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 Dow’s Seadrift site on the Texas Gulf Coast, to supply both power and high-temperature heat to industrial-scale operations. X-energy and Amazon have also committed to the goal of more than 5 GW of new nuclear by 2039, starting with a joint plan with Washington state utility Energy Northwest to build up to 12 SMRs near Energy Northwest's Columbia Generating Station.