Transmutex develops technology for an accelerator-driven nuclear reactor that can transmute long-lived transuranic elements and problematic fission products from the traditional uranium fuel cycle. This includes transuranic nuclides such as plutonium, neptunium, americium, and curium, as well as transmuting long-lived fission products like iodine-129, technetium-99, and selenium-79. Studies in Switzerland and Germany show that this approach can reduce nuclear waste volumes by factors of 6.2 and 8.8, and lower the lifetime of high-activity waste to well below 1,000 years.
The reactor design also supports breeding U-233 from thorium, which can be used in both PHWRs (pressurized heavy-water reactor) and LWRs (light water reactors). Thorium-based fuel is particularly advantageous in PHWRs, while in LWRs, reprocessed or depleted uranium can be used as a base. Both transmutation and breeding require metallic fuel pellets, which offer high fissile density, are easier to fabricate and reprocess, and have high thermal conductivity for better safety.
Metallic fuels, however, have challenges such as low melting points with high transuranic content, possible chemical interactions with cladding, dimensional changes during irradiation, and issues with fission gas release. To address these, Transmutex is developing fuel pellets with a macroscopic amorphous structure and about 26% interconnected porosity, which helps manage swelling and allows fission gases to escape.
At PSI hotlab, the Transmutex team aim to prepare porous metal fuel pellets by sintering thorium metal powder. Staff are being trained in glove box operations, and surrogate materials like solder tin and bronze powders are used to refine the process. The procedure, carried out under nitrogen and eventually under argon for Thorium, has already produced porous pellets of good quality and adjustable porosity, and can be applied to thorium. Thorium metal powder has been ordered from the US, with import approved by BFE and delivery expected soon. Once received, the powder will be tested for purity and grain size, and then used to produce thorium pellets, including variants with 1% natural uranium as a proliferation barrier. These pellets will be analyzed for structure, porosity, mechanical and thermal stability, density, and thermal conductivity, supporting future industrial-scale production.
