US-based X-energy and Germany-based SGL Carbon have signed a binding agreement to double the manufacturing capacity of NBG-18 medium-grain isotropic graphite. This specialised material is central for X-energy’s planned Xe-100 high-temperature gas-cooled reactor (HTGR) fleet.
While the corporate headquarters of SGL Carbon are in Wiesbaden, Germany, the company operates as a global manufacturer with a vast international footprint including 29 manufacturing facilities distributed worldwide – 17 in Europe, eight in North America, and four in Asia. NBG-18 is a nuclear-grade graphite central to the Xe-100 design, functioning as a neutron moderator and a structural component of the pebble-bed core.
The Xe-100 is an 80 MWe helium-cooled HTGR that can be deployed in modular 4-unit or 12-unit configurations. The design simultaneously generates grid electricity and high-temperature heat/steam. This makes it ideal for heavy industrial decarbonisation. It uses X-energy’s TRISO-X Tri-structural Isotropic particle fuel pebbles.
X-energy has a potential commercial pipeline for the Xe-100 of more than 11 GWe based on projects in the US and UK. Because each individual Xe-100 unit generates 80 MWe of power, this pipeline represents a global deployment of around 144 advanced reactors. The agreements underpinning X-energy’s major commercial projects were signed between 2023 and 2025.
In March 2023, Dow and X-energy finalised a Joint Development Agreement (JDA) to deploy a four-unit reactor plant at an industrial facility in Seadrift, Texas. In October 2024, Amazon Web Services (AWS) anchored an approximate $500m Series C-1 financing round for X-energy and signed a formal partnership to fund and deploy over 5 GWe of SMR capacity to power its data centres. Centrica signed a Joint Development Agreement with X-energy in September 2025 to establish a UK-based development firm and pursue a 6 GWe fleet.
Under the agreement with SGL Carbon, X-energy will invest up to $8m in milestone-based payments to support new facilities and equipment upgrades at SGL’s site in Chedde, France. This will enable the facility to produce graphite billets for up to eight new Xe-100 reactors a year. SGL has concurrently agreed to expand US capacity for machining of billets into graphite blocks, helping to ensure greater supply chain continuity for a safety-critical material, doubling European manufacturing capacity for NBG-18 by 2030.
The expansion builds on a 10-year Supplier Framework Agreement established in January, which included an initial three-year award valued at over $100m for X-energy’s first commercial projects. The first NBG-18 billets produced in France under this award have since been shipped to SGL facilities in the US for machining into components. They are intended for the Dow project. This follows a prototyping campaign which began earlier this year, consisting of non-nuclear testing and validation at X-energy’s Technology Advancement Center (XTAC) in Frederick, Maryland in advance of final production.
“Commercialising new nuclear at scale rests first and foremost on our ability to significantly expand the nuclear supply chain, a challenge that extends beyond any one company, supplier, or nation,” said X-energy CEO J Clay Sell. “We look forward to driving this work forward with SGL, and to engaging with potential partners who share our bold vision for a robust, resilient, US and allied nuclear supply chain.”
Andreas Klein, CEO of SGL Carbon, noted: “By jointly expanding our production capacity for nuclear-grade graphite, we are reinforcing the importance of our partnership and ensuring reliable supply to X-energy. For SGL Carbon, this agreement is a strategically important step that strengthens our position in the highly specialized growth market for nuclear-grade graphite, underscores the importance of our graphite expertise for safety-critical applications, and opens up attractive opportunities for further growth.”
NBG-18 was first developed for South Africa’s Pebble Bed Modular Reactor programme, and later for DOE’s Next Generation Nuclear Plant project, two direct predecessors of the Xe-100. Through these and X-energy’s own initiatives, NBG-18 has undergone extensive qualification work for commercial nuclear operation, gathering operational data that helps to validate the material’s performance over decades of high-temperature operation.
