Integrity of protective coatings of irradiated and as-received nuclear fuel cladding under accident conditions – EFFICAC

The safety and reliability of nuclear reactors hinge critically on the performance of nuclear fuel under both normal operation and accident conditions. Traditional fuel cladding materials, while effective under normal conditions, pose significant safety risks during accidents (e.g. Loss-of-Coolant-Accident, LOCA).
In response to Fukushima Daiichi accident and increasing regulatory and public demand for improved reactor safety, the nuclear industry and research community have developed Accident Tolerant Fuels (ATFs), consisting in fuel and cladding systems that can better withstand accident conditions. Among the various ATF concepts under investigation, chromium-coated zirconium-based claddings have emerged as one of the most promising near-term solutions. The application of a thin Cr layer on conventional zirconium alloy claddings significantly enhances their high-temperature oxidation resistance, mechanical robustness, and wettability, all while retaining the favorable neutronic properties of zirconium. These improvements directly address key failure mechanisms observed during nuclear accidents. While some investigations had been conducted on the non-irradiated material and its behaviour under normal and accident conditions, the long-term in-reactor behavior of Cr-coated cladding, particularly under irradiation, is an active area of investigation.
Irradiation can induce microstructural changes, phase transformations, swelling, and embrittlement, potentially affecting the integrity of the coating and its adhesion to the substrate. Moreover, the formation of fissures or cracks—whether through thermal cycling, mechanical loading, or radiation-induced damage—poses a critical threat to the protective function of the Cr layer. Understanding and characterizing the fissuration behaviour of Cr-coated cladding under both irradiated and unirradiated conditions is therefore essential for validating its long-term performance and for supporting its licensing and deployment in commercial nuclear reactors.
The main goal of the project is to better understand and thus qualify the effect of irradiation on the behaviour of Cr-coated ATFs under transient conditions by comparative experimental and analytical study. The obtained results will feed the development of codes and methods to be used in support of the safety of the nuclear power plants.
The proposed project will provide a solid reference comparison between irradiated and non-irradiated Cr-coated ATFs under transient conditions. It will also directly impact the accuracy of irradiated material models, thus improving the margins of safety studies by reducing the uncertainties characterizing the in-reactor behavior of the fuel during an accidental scenario.