Ternary UMoX alloys as alternative fuels for research reactors

Uranium-molybdenum (UMo) alloys with 7-10 wt.% Mo are promising candidates for high-density fuels in research reactors. However, their application is limited by the formation of an interdiffusion layer (IDL) at the interface between UMo and aluminum (Al), which reduces thermal performance and fission gas retention and contributes to fuel swelling and overall performance degradation. Conventional mitigation strategies rely on additional diffusion barrier layers (IDBs), while ternary alloying provides an alloy-intrinsic approach. This study investigates five ternary UMoX alloys (X = Zr, Pt, Nb, Ti, W) with respect to solubility, IDL growth, and γ -phase stability under thermal annealing up to 803 K and under heavy-ion irradiation (80 MeV Xe) to simulate selected in-pile effects. Compositional analyses by energy-dispersive X-ray spectroscopy (EDS), particle-induced X-ray emission (PIXE), and Rutherford backscattering spectrometry (RBS) revealed full or near-complete solubility for Pt, Zr, and Nb in UMo, whereas Ti and W exhibited limited solubility. Compared to binary UMo, all ternary alloys showed reduced IDL growth with Al. Under thermal annealing, UMoZr and UMoNb exhibited a pronounced mitigation of interdiffusion, while UMoPt showed the highest γ -phase stability. Under ion irradiation, interdiffusion was limited in all alloys. The most pronounced reduction in IDL growth was observed for UMoPt, while γ -phase stability was maintained across all compositions. Overall, UMoPt, UMoNb, and UMoZr emerge as promising candidates for high-density fuels, potentially enabling IDL mitigation without relying on additional IDBs.