Chromium-coated accident tolerant fuel : characterisation and modelling of its oxidation

Abstract

As a critical aspect for nuclear reactors design, ensuring safety is a critical, particularly if a Severe Accident were to occur, where core degradation can lead to dangerous consequences. These include hydrogen generation (potentially causing explosions within the containment building) and loss of containment integrity (which may result in the release of fission products into the environment). Accident Tolerant Fuels have emerged as a promising solution to improve fuel performance and mitigate accident progression. This thesis aims to research on the thermodynamic behaviour, oxidation kinetics, and failure mechanisms of chromium-coated zirconium-based cladding- a leading ATF candidate for replacing conventional nuclear fuels in a near future.

For the current work, the cr_igb model was developed to simulate the oxidation behaviour of Cr-coated ATF fuel rods under high-temperature steam conditions. The model was developed and implemented using experimental data to quantify oxidation kinetics, eutectic mixture formation, and associated hydrogen and heat production rates. The results demonstrate that chromium coatings effectively reduce oxidation rates, delay heat generation, and enhance cladding structural integrity. However, at temperatures exceeding 1313ºC, Cr-Zr interdiffusion leads to the formation of brittle intermetallic phase, which may compromise mechanical integrity of the cladding.

The results and conclusions of this thesis contribute to ongoing research on ATF technologies by providing a model for assessing the behaviour of Cr-coated Zr-based cladding.