US nuclear fuel developer Lightbridge Corporation has completed work in collaboration with Pacific Northwest National Laboratory (PNNL) to support the development of Lightbridge Fuel. The work was carried out under the US Department of Energy’s (DOE’s) Gateway for Accelerated Innovation in Nuclear (GAIN) voucher programme.

Lightbridge is developing a new fuel design that incorporates an extruded metallic bar composed of a zirconium-uranium matrix within a zirconium alloy cladding. Lightbridge says this will: significantly increase fuel thermal conductivity (compared with ceramics) promoting lower operating temperatures; offer complete retention of fission products avoiding release of those products upon cladding failure; and support higher power and longer fuel cycles.

The fuel is designed to work in both new and existing reactors. Lightbridge also claims that its fuel increases power output and extends the length of the fuel cycle and offers nuclear plants a better solution for load-follow operations on a grid with renewables.

Working in collaboration with PNNL, the project scope was to demonstrate Lightbridge’s nuclear fuel casting process using depleted uranium, a key step in fuel manufacturing. Several castings were performed throughout the project, and the cast ingots were analysed. The casting methodology was gradually modified based on the characterisation results

Lightbridge has long enjoyed support from DOE and various US national laboratories. In 2018, Lightbridge and France’s Framatome launched Enfission, a 50-50 joint venture (JV) company to develop, license and sell nuclear fuel assemblies. The previous year Lightbridge and Framatome (then Areva) had signed an agreement to set up a JV to develop, manufacture and commercialise Lightbridge’s advanced metallic fuel.

In May 2019, Lightbridge Corporation announced that Framatome had received a voucher from the DOE GAIN programme to support development of Lightbridge fuel in collaboration with Idaho National Laboratory (INL). This was Framatome’s third GAIN voucher and its first supporting the Lightbridge Fuel design conducted by the Enfission JV. Framatome said the voucher would enable it to apply focused attention on key licensing steps to commercialise Lightbridge Fuel.

In 2020, Lightbridge entered into a cooperative research and development agreement with Battelle Energy Alliance (BEA), the operator of INL, to design an experiment for irradiation of metallic fuel material in the Advanced Test Reactor (ATR) DOE funded three-quarters of this through the GAIN programme. Lightbridge and INL were to establish the test plan for measuring key thermo-physical properties of Lightbridge Fuel material both before and after irradiation in the ATR.

Lightbridge and Framatome terminated the Enfission joint venture in 2021 and Lightbridge announced a Cooperative Research & Development Agreement (CRADA) with the Battelle Memorial Institute, Pacific Northwest Division, the operating contractor of PNNL. This agreement sought to advance a critical stage in the manufacturing process of Lightbridge Fuel by demonstrating a casting process using depleted uranium-zirconium material. Three-quarters of this was funded by DOE.

In June 2022, Lightbridge announced that the Massachusetts Institute of Technology (MIT) had received an support under DOE’s Nuclear Energy University Program R&D Awards to study the deployment of Accident Tolerant Fuels (ATF) in Small Modular Reactors (SMRs). The project, funded entirely by DOE, would include simulation of the fuel and safety performance of Lightbridge Fuel inside a SMR designed by NuScale Power.

In December 2022 Lightbridge signed further agreements with INL, in collaboration with DOE. The framework agreements comprised an “umbrella” Strategic Partnership Project Agreement (SPP) and an “umbrella” CRADA, each with BEA, with an initial duration of seven years. The initial phase of work under the two agreements is expected to culminate in irradiation testing in the ATR of fuel samples using enriched uranium supplied by DOE. The initial phase of work aims to generate irradiation performance data for Lightbridge’s delta-phase uranium-zirconium alloy relating to various thermophysical properties. The data will support fuel performance modelling and regulatory licensing efforts for the commercial deployment of Lightbridge Fuel.

The results of this work with PNNL will help Lightbridge determine a final process suitable to produce fuel material coupons for the upcoming irradiation tests in the ATR. Ali Zbib, PNNL nuclear industry programme manager, commented, “One of our missions at PNNL is to support US nuclear industry partners in advancing their technology. Working on this GAIN-funded project was an excellent opportunity to use national laboratory resources and expertise on these fuel development efforts for light water reactors.”

Seth Grae, President and CEO of Lightbridge, commented, “Our successful collaboration with the GAIN Office at the US Department of Energy and access to US national laboratories’ teams of experts and world-class facilities has enabled Lightbridge to make meaningful progress in our fuel development programme.”

Image: Cross-section of the new fuel assembly from Lightbridge (courtesy of Lightbridge Fuel)