SiCf/SiC cladding for LWR: Assessment of flow accelerated corrosion
Résumé
To improve the tolerance of the fuel towards accidental scenarios of light water reactors (LWR), an extensive R&D is performed by the French Alternative Energies and Atomic Energy Commission (CEA) in the framework of the French Nuclear Institute with FRAMATOME and EDF. In particular, fuel cladding constituted of silicon carbide continuous fiber ceramic matrix composite materials (SiCf/SiC) is considered as a long-term option besides evolutionary designs (e.g. Cr-coated cladding).
The outstanding mechanical behaviour of SiCf/SiC cladding tubes at high temperature and their low oxidation rate, resulting in reduction in hydrogen generation, has been previously reported both in LWR operating conditions and in high temperature steam conditions. However, after exposure in autoclaves, some recession of the SiC was detected. Even if it remains limited, this raises the question of the cladding dissolution, the resulting pollution of the primary loop by silicium-base species and the effect of the water flow on these phenomena.
The present work reports the preliminary result obtained in a corrosion loop especially developed at CEA to address the flow accelerated corrosion of SiCf/SiC cladding tubes. The device FACETT (Flow Accelerated Corrosion Experiments for Tube Testing) allows to investigate four 50-mm-long tubes in primary loop conditions (350°C, appropriate chemistry) and with water flow of 4 m.s-1. Sampling of the media can be performed to follow the chemistry change. The results will include weight loss measurements, surface examination and chemical analyses after a 5-month-exposure of CEA-made SiCf/SiC cladding tubes. A comparison with the results obtained in static media will be done.