US-based Lightbridge Corporation has secured access to the Advanced Test Reactor (ATR) loop testing facility at the Idaho National Laboratory (INL) to irradiate its proprietary clad fuel rodlets under prototypic commercial reactor conditions.
This represents the next critical phase in moving Lightbridge’s advanced nuclear fuel technology from materials research toward full commercial fuel qualification. Lightbridge signed Project Task Statement (PTS) No 2 under an existing Cooperative Research & Development Agreement (CRADA) with Battelle Energy Alliance, LLC (BEA), the operating contractor for INL.
The experiment will test fuel rodlets fabricated from an enriched uranium-zirconium alloy with cladding. Testing will evaluate both cylindrical and multi-lobe fuel geometries. Data gathered from this loop test will be used to benchmark fuel performance models and confirm the real-world durability of the fuel design and materials.
“Getting into a loop at the ATR is the access that matters,” explained Lightbridge Chairman & CEO Seth Grae. “There are a limited number of positions in the world where a fuel rod can be irradiated under the conditions it will actually see inside a commercial reactor, and our fuel now has one of them. Every conversation we are having with utilities eventually arrives at the same question: show us the irradiation data. This is how we answer it.”
Lightbridge Senior Vice President & Chief Technology Officer Dr Scott Holcombe noted: “This is the experiment the fabrication work has been building toward. The data collected from this irradiation test will be used to confirm the performance of our fuel rod design and materials and will be used to benchmark our models. Samples from this irradiation are later intended to be subject to further irradiation testing in INL’s Transient Reactor Test Facility (TREAT) under transient conditions.”
The Lightbridge Fuel design features a distinct multi-lobe, helically twisted metallic structure engineered to replace conventional cylindrical ceramic oxide pellets. By combining this geometric design with updated infrastructure plans, Lightbridge has established an accelerated timeline for commercial reactor deployment.
The high thermal conductivity of this design prevents fission gases from releasing during design-basis accidents. In a Large-Break Loss-of-Coolant Accident (LOCA), the fuel cladding stays below the 850–900°C threshold. This completely prevents the steam-zirconium reaction that creates explosive hydrogen gas. It enables existing light water reactors (LWRs) to achieve a 10-17% power increase (with extended 24-month fuel cycles) and up to a 30% power increase for new-build reactors.
This new agreement follows a highly active period for the company, including its selection for the Department of Energy’s (DOE’s) Launch Pad INL programme and the successful initial removal of its unclad fuel material samples from the ATR earlier in the year.
Initial unclad fuel coupons began loop irradiation in the ATR in late 2025, and the initial batch, discharged in May will begin post-irradiation examination (PIE) later this year to measure vital thermophysical properties (swelling, thermal degradation) for the Nuclear Regulatory Commission (NRC) qualification package.
Leveraging its selection into the Launch Pad INL programme, Lightbridge has bypassed the traditional timeline by establishing a dedicated pilot facility at INL. The Special HALEU Extrusion Demonstration (SHED) will house full-scale manufacturing equipment to build the company’s first lead test assemblies (LTAs).
The LTAs will be inserted into operating commercial power reactors under DOE authorisation. In parallel with LTA testing, Lightbridge is partnering with an unnamed major engineering, procurement & construction (EPC) firm to finalise the design of the Lightbridge Expandable Fuel Facility (LEFF), which will be licensed directly by NRC. LEFF is designed to scale output from a few initial batch reloads up to high-volume commercial production for the global utility market. The company is also exploring co-located manufacturing setups with advanced reactor developers.
