US-based X-energy Reactor Company has signed an agreement with the US Department of Defense (DOD) Defense Innovation Unit (DIU) and the US Department of the Air Force (DAF) to advance the development of its Xenith microreactor. The agreement supports continued design and development for the Xenith microreactor under the Advanced Nuclear Power for Installations (ANPI) programme, an initiative led by DIU in partnership with DAF. X-energy was among eight microreactor suppliers selected by DOD in April as eligible to seek funding through the ANPI programme.
ANPI is designed to accelerate the deployment of next-generation microreactor technologies to provide resilient, secure power at military installations, and enables governmental sponsors such as DAF to engage with X-energy under a flexible contracting mechanism that allows for faster development and deployment of commercial nuclear systems.
“We’re seeing the full force of federal partnership mobilised to bring advanced nuclear to market, and the leadership of the Trump Administration has been phenomenal,” said X-energy CEO J Clay Sell. The agreement aligns with President Trump’s Executive Order on Deploying Advanced Nuclear Reactor Technologies for National Security, issued in May, which directs DOD to deploy an advanced reactor at a military installation before the end of the decade. As part of this effort, X-energy was selected to demonstrate commercial microreactors that can power critical defence infrastructure and remote microgrids.
Xenith is a high-temperature gas-cooled microreactor first developed for DOD’s Project Pele, a mobile microreactor initiative led by the Strategic Capabilities Office. The design refined with support from DOD’s Operational Energy Capability Improvement Fund (OECIF) and the Department of Energy Office of Nuclear Energy’s Industry Funding Opportunity Announcement (IFOA) project. It was selected to continue into an enhanced engineering phase, focused on achieving preliminary design maturity and initiating pre-licensing engagement with NRC for both military and commercial applications.
X-energy is also advancing the deployment of its Xe-100 high-temperature gas-cooled reactor as a grid-scale energy solution for utilities, industrial customers, and hyperscalers. It is constructing a nuclear fuel fabrication facility to manufacture its proprietary TRISO-X fuel.
The Xenith conceptual design has been docketed with NRC. X-energy is engaged in ongoing pre-application activities, including multiple submitted topical reports and a comprehensive Concept of Operations, to ensure compliance with all applicable NRC requirements.
X-energy says the Xenith microreactor solution combines proven nuclear technology with innovative engineering. Using advanced TRISO-X fuel and High Temperature Gas-cooled Reactor (HTGR) technology, it operates continuously for 20 years, delivering 3-10 MWe of electricity with minimal maintenance requirements. It is scalable to multiple units for higher power output and enhanced redundancy.
Each Xenith microreactor installation consists of four integrated components designed for optimal performance:
- Nuclear reactor system with advanced safety features powered by TRISO-X fuel technology;
- Heat transfer system using helium as the primary coolant for safety and efficiency;
- Power conversion system featuring open-air Brayton cycle with industrial gas turbine;
- Nuclear island building housing components and providing easy access for operations and maintenance.
The system can be configured for both electricity generation and industrial process heating, maximising versatility for diverse applications. Its modular design supports: factory assembly and testing; transportability (to remote locations); alternate power conversion systems and upgrades; reactor replacement; stand-alone operation or as backbone of a microgrid. Configurable radiation shielding enables collocation of site operations personnel and no residual radioactive material left at the site.
Earlier in August, California-based Radiant also signed an agreement with the DIU and DAF- the first-ever deal designed to deliver a mass-manufactured nuclear microreactor to a US military base. The company is developing the 1 MWe Kaleidos high-temperature gas-cooled portable microreactor. Radiant says it plans to test its first reactor in 2026, with initial customer deployments beginning in 2028.
