US-based startup Radiant has received its first tranche of nuclear fuel delivered to the National Reactor Innovation Center’s (NRIC’s) Demonstration of Microreactor Experiments (DOME) facility located at Idaho National Laboratory (INL). The TRI-structural ISOtropic (TRISO)-fuel was fabricated by Standard Nuclear in Oak Ridge, Tennessee, to Radiant’s specifications earlier this year.
The fuel will be used to power Radiant’s 1 MWe/3.5 MWt Kaleidos microreactor for its upcoming full-power, full-temperature testing programme. This will initiate months of rigorous testing and validation, to support manufacturing and customer delivery by 2028.
Radiant Industries is an El Segundo, California-based clean energy startup founded in 2020 by former SpaceX engineers with the goal of eliminating global reliance on diesel generators. Led by CEO Doug Bernauer, the company designs mass-producible, containerised nuclear microreactors capable of delivering rapid, zero-emission grid power to remote communities, military installations, and disaster relief zones.
The company operates on a “test-first” engineering ethos expects to begin operational testing at INL in 2026, aiming for commercial deployment by 2028. Kaleidos, a high temperature helium-cooled reactor, is designed as a factory-assembled “reactor-in-a-box” that fits entirely within a single standard shipping container. It is rapidly transportable by standard cargo aircraft, semi-trucks, or ships without requiring heavy specialised infrastructure.
Kaleidos operates continuously for five years between refuellings, with a total asset lifespan of 20 years. It uses a highly compact zirconium hydride moderator embedded within prismatic graphite blocks to safely slow down neutrons and maximise fuel efficiency. It eliminates the need for local body water by using integrated cooling fans to shed residual energy.
Radiant is the only developer conducting testing at the DOME facility. The company is embarking on a five-phase reactor development testing programme designed to collect critical reactor and fuel performance data, which will help accelerate the commercial licensing process with the Nuclear Regulatory Commission (NRC).
With fuel now on site, Radiant is poised to bring Kaleidos online – progressing through zero-power criticality, 1 MW thermal, full power, and full heat, before operating for a minimum of 150 hours at full power without operator intervention, a crucial milestone in proving commercial readiness.
“We are de-risking a commercial product that will be manufactured and delivered within 18 months,” said Dr Rita Baranwal, Chief Nuclear Officer at Radiant. “Receipt of our freshly fabricated, modern-pedigree, custom-made fuel is a key milestone toward that goal. Radiant has been very disciplined with our testing programme at the DOME; we are testing our prototypic fuel, coolant, and power levels to validate our product and ensure success for our customer deployment by 2028.”
The data collected will also support Radiant’s Part 70 licence application for its R-50 manufacturing facility in Tennessee, which is in accelerated review by NRC. Once approved, the licence will enable Radiant to handle and load fuel for its Kaleidos reactors before shipping them to customers across the US.
DOE has provided extensive funding, regulatory, and logistical support to commercialise the Kaleidos microreactor coordinated through NRIC. In October 2023, the DOE selected Radiant as one of three developers to share $3.9m in total funding to engineer microreactor test configurations. Radiant completed the DOE’s Front-End Engineering and Experiment Design (FEEED) programme in November 2024 enabling transition into the Detailed Engineering and Experiment Planning (DEEP) phase to prepare for live testing at DOME.
Radiant received two Gateway for Accelerated Innovation in Nuclear (GAIN) vouchers to leverage federal laboratory expertise. The first voucher (December 2022) enabled Radiant to partner with Argonne National Laboratory (ANL) to construct a multiphysics coupling framework simulating control drum failures.
Subsequent voucher support (mid-2025-2026) saw Radiant collaborate with both ANL and INL to develop advanced computational design analysis tools for the Kaleidos reactor. This granted direct access to specialised DOE laboratory equipment and expert computational modelling.
In April 2025, DOE selected Radiant as part of the first round of the HALEU (high-assay low-enriched uranium) Availability Programme alongside four other advanced reactor developers. In January 2026, Standard Nuclear physically received the DOE-allotted HALEU feedstock at its Oak Ridge facility to begin fabricating Radiant’s custom TRISO fuel compacts.
DOE, on 1 July 2025, announced the selection of Radiant for the inaugural test phase at DOME. alongside Westinghouse’s eVinci reactor. When the DOME test bed officially opened for business in April, DOE confirmed that Radiant would go first.
As to regulatory support, in June 2024 DOE formally approved the Safety Design Strategy for the Kaleidos reactor. This established the baseline safety metrics required to proceed toward live operations. In February 2026, DOE approved the DOE Authorization Request for Kaleidos (DARK), approving the project’s Preliminary Documented Safety Analysis (PDSA), satisfying the second of three major safety requirements. The final step requires the submittal and approval of a Documented Safety Analysis (DSA) to secure full startup operational clearance.
