Fuel-Cladding Chemical Interaction in U-Pu-Zr Metallic Fuels: A Critical Review

Fuel-cladding chemical interaction (FCCI) is a phenomenon that occurs at the fuel-cladding interface during the irradiation of U-Zr and U-Pu-Zr metallic nuclear fuel and stainless steel cladding. The inter-diffusion zone that develops places both the fuel and cladding at risk through the reduction in cladding strength and the formation of a (U,Pu)/Fe eutectic in the fuel. Due to the impact FCCI has on limiting fuel pin burnup, there is a need for better understanding of the governing FCCI mechanisms in order to make accurate predictions using fuel-performance codes. By performing a critical review of previous work, the physics of FCCI can be separated into individual phenomena so that targeted models can be developed for each. Through examination of experiments conducted both in- and out-of-reactor, the behavior of lanthanides provides a natural separation of models by tracking their behavior through (1) production and transport in the fuel to the clad, (2) interaction with macroscopic changes in fuel topography including cracking and swelling, and finally (3) inter-diffusion at the fuel-cladding interface. Informed by past experience, phenomenological models can be built for each separate effect and subsequently combined in an integral fuel-performance simulation. Prototypical simulation approaches at each level have been included, as well as suggestions for several experiments to help bolster the understanding of irradiated fuel. A robust and predictive FCCI model will provide fuel-performance codes with the ability to predict clad failure and/or fuel eutectic melting. Armed with this information, advanced concepts such as palladium doped fuel, ODS steels, or mitigating reactor designs may be able to reduce FCCI enough to extend fuel burnup beyond its current limits, potentially boosting safety margins and reducing cost through higher fuel utilization.