A technical overview of Clean Core Thorium Energy's thorium-HALEU ANEEL fuel

Pressurized heavy water reactors (PHWRs) fueled with natural uranium (NU) are constrained by low discharge burnup (∼7500 MWd/MTHM), high spent fuel volumes, and a positive coolant void reactivity (CVR) that poses a safety challenge under loss-of-coolant accident (LOCA) conditions. Clean Core Thorium Energy, Inc. (CCTE) is developing Advanced Nuclear Energy for Enriched Life (ANEEL), a thoria-urania (ThO₂-UO₂) mixed oxide fuel using high-assay low-enriched uranium (HALEU) and a burnable neutron absorber, designed as a “plug and play” replacement for existing PHWR NU fuel bundles. This paper presents physics, thermal-hydraulic, and fuel performance analyses supporting the technical feasibility of ANEEL fuel in a CANDU-6 reactor. Fuel composition optimization using DRAGON/DONJON yielded a design achieving an average discharge burnup of over 44,000 MWd/MTHM — approximately six times that of NU fuel — while reducing the full-core CVR from 16.4 mk to below 13.3 mk for an equilibrium core. Core-follow simulations confirm that maximum channel and bundle powers remain within licensing limits throughout the fresh-to-equilibrium transition. Independent MCNP calculations confirm that reactivity device worths deviate by no more than 16% from NU values and that the fuel and moderator temperature coefficients are more negative for ANEEL compared to NU fuel. CATHENA LOCA simulations show peak sheath and centerline temperatures for ANEEL are lower than for NU fuel. PEGASUS finite element analysis confirms structural integrity throughout irradiation, with fission gas pressure remaining below coolant pressure and end-of-life cladding strain of much less than 1%. These results demonstrate that ANEEL fuel achieves substantially higher burnup with improved safety margins relative to NU fuel, with manageable impacts on existing PHWR core design and control systems.