Image 1: Assembly of the capsules for the ATOMIC-GFR experiment
The Accelerated Testing of Materials in Capsules (ATOMIC) project is a multi-focused irradiation campaign designed to provide irradiation data on innovative fuel designs and materials for use in generation IV reactors within Second Framework for Irradiation Experiments (FIDES-II) joint project. With the reaching of target burnup for medium burnup SiC cladded UO2 fuel pellets, ATOMIC has now completed its first irradiation.
ATOMIC uses scaled geometries and increased enrichments to irradiate fuel and cladding materials to high burnup conditions faster than conventional irradiation tests. This utilises the principals of the Fission Accelerated Steady-state Testing (FAST) method which scales the fuel system to smaller diameters with increased power density to reduce the time to reach burnup by factors of four or more. The ATOMIC project is irradiating SiC-SiCf cladded UO2 for gas fast reactors (ATOMIC-GFR), next generation TRISO fuel with UN kernels (ATOMIC-TRISO), innovative microstructure mixed oxide fuels for SFRs (ATOMIC-MOX), and metallic fuel designs for SFRs (ATOMIC-METAL).
Image 2: SiC-SiCf cladded rodlets used in the ATOMIC-GFR irradiation test
The ATOMIC-GFR rodlets, shown in Image 2, are SiC cladded UO2 fuel pellets with varying fuel-cladding gaps. The SiC cladding, provided by General Atomics, is an advanced composite cladding designed to withstand significant temperatures and stresses that conventional alloy cladding cannot. The fuel rodlets were fabricated at both prototypic diameters and reduced diameters for accelerated irradiation testing. The experiment is targeting both moderate and high burnup conditions along with two different fuel-pellet gaps. The different fuel-cladding gaps are intended to challenge the fuel-cladding mechanical interaction limits and the hermiticity of the cladding at high burnups and high stress.
Image 3: Completed test capsules for the ATOMIC-GFR experiment, ready for insertion into ATR
The test capsules, shown in images 1 and 3, utilise concentric capsules to produce the thermal conditions that are representative of a gas-cooled reactors. The capsules were inserted into the Advanced Test Reactor (ATR) at Idaho National Laboratory in May 2025. The irradiation tests will go for three cycles for the moderate burnup rodlets (>45 MWd/kgU) and up to six cycles for high burnup targets (>90 MWd/kgU). The moderate burnup rodlets completed their three cycles in January 2026, the high burnup rodlets will complete their six cycles in July 2026 and all four rodlets will be prepared for shipment from ATR to the Hot Fuels Examination Facility (HFEF) in late 2026. Once at HFEF, the rodlets will undergo post-irradiation examination (PIE) that includes neutron radiography imaging, cladding profilometry, fission gas analysis, and optical metallography. Advanced microscopy PIE will continue at the Irradiated Materials Characterisation Laboratory (IMCL). IMCL hosts an array of shielded electron microscopes, a thermal properties hot cell, micro-mechanical testing, and other techniques.
Image 4: GE-100 shipping container used to transport the capsules from ATR to HFEF
