Thermal Analysis of Natural Uranium Oxide Fuel

Predicting fuel temperature during residence in a reactor is paramount for ensuring safe operations. This chapter delves into models that facilitate the evaluation of fuel parameters, aiding in informed decision-making regarding fuel-related operational aspects, ultimately reducing the reliance on expensive experiments. Fuel temperature plays a critical role in influencing fission cross-sections and maintaining fuel integrity, which in turn affects operational safety and decisions related to the retention of fuel bundles post-power transients. Our primary focus lies on the impact of fission product noble gases (FPNGs), particularly Xenon and Krypton, on the thermal behavior of natural uranium oxide fuel. We introduce a novel model, FCCAL, designed to estimate fuel temperatures with improved accuracy. Simulations utilizing the FCCAL framework indicate significant risks of fuel failure within the core, as high concentrations of Xenon can markedly degrade thermal conductivity, resulting in elevated centerline temperatures, even in heavily irradiated low-power fuel. This study underscores the critical nature of modeling FPNG accumulation in the pellet-sheath gap, exploring its overall implications for fuel performance. Additionally, we address the role of reactivity devices in incidents of fuel failure, prompting a reexamination of overlooked aspects of fuel operations. The insights provided herein aim to inspire further investigation and improvement in nuclear fuel management practices.