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Exposure to high temperatures and irradiation results in interaction and interdiffusion between fuel and cladding constituents that can lead to formation of undesirable brittle or low-melting point phases. A diffusion couple study has been conducted to understand fuel-cladding interaction occurring between U-22Pu-4Zr (in wt%) fuel and pure Fe at elevated temperatures. The phases formed within fuel cladding chemical interaction (FCCI) layer have been characterized in the transmission electron microscope (TEM). The phases formed within FCCI layer have been identified as Fe 2 U (Fd-3m), FeU 6 (I4/mcm), Fe 2 Zr (Fd-3m), FeZr 2 (I4/mcm), Fe 2 Pu (Fd-3m), UZr 2 (P6/mmm), β-Zr (Im-3m), and ZrO 2 (Fm-3m).

Transmutation of minor actinides such as Np, Am, and Cm in spent nuclear fuel is of international interest because of its potential for reducing the long-term health and safety hazards caused by the radioactivity of the spent fuel. One important approach to transmutation (currently being pursued by the DOE Fuel Cycle Research & Development Advanced Fuels Campaign) involves incorporating the minor actinides into U-Pu-Zr alloys, which can be used as fuel in fast reactors. It is, therefore, important to understand the properties of U-Pu-Zr alloys, both with and without minor actinide additions.

This work investigates fuel-cladding chemical interaction (FCCI) between U-25Pu-14Zr (in wt pct) fuel and pure Fe at elevated temperatures, understanding of which is critical for evaluation of the fuel performance. Phases and microstructure formed in the quaternary uranium-plutonium-zirconium-iron (U-Pu-Zr-Fe) system were characterized using the transmission electron microscopy technique. Phases formed within the FCCI layer were identified using selective area electron diffraction (SAED) analysis as Fe 2 U (Fd-m), Fe 2 Zr (Fd-3m), a-U (Cmcm), Fe 2 Pu (Fd-3m), b-Pu (C12/m1), and b-Zr (Im-3m).

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