A proposed mechanism for internal cladding corrosion in LMFBR mixed oxide fuel pins

A model is proposed which describes a possible chronological sequence of events during inner cladding corrosion in mixed oxide fuel pins. The corrosion reaction is visualized as being primarily chemical in character, involving the cladding steel, the fuel and the more aggressive fission products, notably caesium in the presence of oxygen. The model attempts to explain how corrosion starts, how it depends on the oxygen potential, why ir occurs non-uniformly; also covered are phase changes within the cladding steel and morphological features such as the inter-granular form of attack and the distribution of corrosion products in the fuel/cladding gap. (Auth.)