The Corrosion Behaviour of Coated Fuel Particles. Dragon Project Report

An attempt has teen made to assess the corrosion behaviour of a number of experimental batches of coated fuel particles, by subjecting them to oxidation in an atmosphere of argon containing carefully controlled amounts of water vapour at 1000°C. The extent of the damage to the particles has been noted using a low powered stereomicroscope. In some instances metallographic examination has also been carried out. By these means it has been possible to compare the behaviour of the various batches qualitatively, and to some extent quantitatively. It has been found that, in general, the particles were remarkably resistant to oxidation at this temperature. Eventually the PyC coating did succumb to attack and penetration by the water vapour, resulting in either, the destruction of the particle from within - by rupture of the kernel, or progressive destruction of the outer coating - shown by roughening and finally deep pitting of the PyC surface. In the case of particles having a SiC layer in the coating, no internal damage to the kernel was observed even after the most prolonged exposure to severe oxidising conditions (more than 300 x 10⁴ microatmosphere hours water vapour*), and the SiC appeared to be a most effective barrier to the water vapour. An attempt has also been made to correlate corrosion behaviour with a specific, mechanical, physical or chemical property of the coating. Unfortunately it has not proved possible to identify the relevant parameter, and it is considered that a much more detailed study of the deposited PyC structure is necessary. (author)